PO89ZB, an inline DC filter for SMPS wall warts. Preamps, HPA, Korg NuTube, etc
- By Mark Johnson
- Analog Line Level
- 1185 Replies
Attachments
For Sale Audio Precision System One SYS-322A Audio Analyzer + Burst Option + APIB USB Adapter
- Swap Meet
- 2 Replies
Attachments
Hello, I just burnt some resistors and some More!
- By HHhelpneeded
- Instruments and Amps
- 23 Replies
Attachments
SAE Mark IIICM defective resistors
- By Mark'51
- Solid State
- 36 Replies
I have been in the process of resurrecting my old SAE 3CM amplifier. It's been more problematic than I expected. It hadn't been fired up for 30+ years so I bought a re-cap kit and swapped out all the electrolytics before I punched the "on" switch. The re-cap job went OK, although I first had to un-do some "improvements" the previous owner had done. Like remodeling old houses, you never know what you're going to find once the studs have been exposed.
Initial testing after the re-cap job looked OK -- the driver board's idle-current measurements were good and the output voltage offsets were reasonable and could be adjusted to a few mV.
But longer-term operation revealed a problem in one of the channels. The output would limit on the negative portion of a test waveform (1KHz sine). And I also observed that the bias voltage went down, from the normal ~2.1V to about 1.85V. I suspected a problem in the Darlington VASes so started my troubleshooting by measuring the emitter resistors on the Darlington emitters (R24 & R25, see below). The 3CM uses symmetrical NPN/PNP LTPs that drive two Darlington pairs, one for the + side and one for the - side. So there were two emitter resistors to measure: and BOTH measured quite high. The schematic indicates that the resistors should be 62 ohms. The one on the + side measured over TWICE that, and the one on the - side measured about 90 ohms! That is far beyond the 5% tolerance the SM specifies for those guys.....
For a sanity check I also measured the 10 ohm resistors that are used to isolate the driver board's supply busses from the output board supplies. They were spot on.
I also measured the emitter resistors in the "good" channel and they also measured high, although not as bad as the failing side. The SM indicates that the R's are carbon film types. Visual examination didn't reveal any indication that the resistors were subjected to excessive current, and I didn't see any obvious mechanical damage.
In normal operation those 62 ohm resistors should be dissipating far less than 1/2 watt. I think they are that size so they will survive if/when a short circuit condition occurs & Q11 or Q12 turn on.
I'm puzzled why the resistor on the plus side is the worst, but the output waveform clips on the negative side. That channel initially works -- more or less -- but then starts clipping after it's warmed up. So there may be a thermal intermittent situation. My next test will be to monitor the resistances while I heat them with a hot-air gun.
The main point of this post, however, is to ask folks if they have seen a similar problem with old carbon film resistors spontaneously failing like this. If not, there's a good chance something else is going on that is over-stressing those resistors. The other thing is: if those went bad simply due to their age, it doesn't bode well for the other CF resistors in there. And there are a lot of them. Replacing all of them is not my idea of a fun time.....
Mark
PS driver board schematic below:
Initial testing after the re-cap job looked OK -- the driver board's idle-current measurements were good and the output voltage offsets were reasonable and could be adjusted to a few mV.
But longer-term operation revealed a problem in one of the channels. The output would limit on the negative portion of a test waveform (1KHz sine). And I also observed that the bias voltage went down, from the normal ~2.1V to about 1.85V. I suspected a problem in the Darlington VASes so started my troubleshooting by measuring the emitter resistors on the Darlington emitters (R24 & R25, see below). The 3CM uses symmetrical NPN/PNP LTPs that drive two Darlington pairs, one for the + side and one for the - side. So there were two emitter resistors to measure: and BOTH measured quite high. The schematic indicates that the resistors should be 62 ohms. The one on the + side measured over TWICE that, and the one on the - side measured about 90 ohms! That is far beyond the 5% tolerance the SM specifies for those guys.....
For a sanity check I also measured the 10 ohm resistors that are used to isolate the driver board's supply busses from the output board supplies. They were spot on.
I also measured the emitter resistors in the "good" channel and they also measured high, although not as bad as the failing side. The SM indicates that the R's are carbon film types. Visual examination didn't reveal any indication that the resistors were subjected to excessive current, and I didn't see any obvious mechanical damage.
In normal operation those 62 ohm resistors should be dissipating far less than 1/2 watt. I think they are that size so they will survive if/when a short circuit condition occurs & Q11 or Q12 turn on.
I'm puzzled why the resistor on the plus side is the worst, but the output waveform clips on the negative side. That channel initially works -- more or less -- but then starts clipping after it's warmed up. So there may be a thermal intermittent situation. My next test will be to monitor the resistances while I heat them with a hot-air gun.
The main point of this post, however, is to ask folks if they have seen a similar problem with old carbon film resistors spontaneously failing like this. If not, there's a good chance something else is going on that is over-stressing those resistors. The other thing is: if those went bad simply due to their age, it doesn't bode well for the other CF resistors in there. And there are a lot of them. Replacing all of them is not my idea of a fun time.....
Mark
PS driver board schematic below:
Versatile Hybrid Preamp w. Power-Amp Option
- Solid State
- 0 Replies
Experimental Hybrid Preamp Design
By Kurtus Richter
Here is a collection of diagrams for a very versatile hybrid guitar preamp, meaning a preamp involving both solid-state and tube-type circuits in one project. The reasons for hybridization are as follows. (1) With purely analog circuitry, tube-amps sound better than solid-state amps, and which also applies to preamps. (2) Hybrid preamps allow for the mixing of a nearly pure input signal from the solid-state circuitry with a distorted signal from a tube circuit in which the tubes are deliberately overdriven. (3) Tubes have a slower slew-rate than solid-state devices; by orders of magnitude. In fact, a guitarist who plays very fast scales can exceed the slew rate of the tubes in a tube-type amp, resulting in indistinct attacks of individually picked notes, heard as a muddy sound, but solid-state devises have slew rates that cannot be exceeded. Consequently, for analog circuits (i.e., no digital processing involving modern sampling technology), one remedy is to use two kinds of amps, or two preamps; one solid-state for attack definition, and one tube-type for the tone. Hence my design for a hybrid preamp.
The block diagram above illustrates how different circuits in my Hybrid Preamp can be connected together, though other arrangements are possible. I have deliberately placed input and output jacks on each of the solid-state subcircuits, and recommend they be retained, in order to maximize versatility. This gives the user the ability to connect the different circuits as desired and insert external devices, such as stomp-boxes, between any two such circuits, though the tube circuit is self-contained, since it is a distortion circuit inspired by the Garnet Herzog unit made famous in the ‘60s and ‘70s by guitarist Randy Bachman, who used it on hits American Woman and Takin’ Care of Business.
But first I show the input preamp, which has highly user-adjustable parameters, and can also be considered a distribution amp, where one output can be a direct signal sent to the Mixer, another can go to the solid-state 5-Band Tone Control or the Booster, or both in series, and the third to the Tubes.
The table in the diagram lists the low corner frequency that can be set by switches S1 and S2, according to the user’s personal taste. For instance, for deep lows, use the 20 Hz setting, but for no lows at all use the 240 Hz or even the 400 Hz setting. The gain of the preamp can also be adjusted from 2 to 200, depending on the setting of switch S3 and the position of the Gain control. High gain, in conjunction with a sufficient setting of the input Level control allows for enough signal voltage to be sent to all three preamp outputs so there should be no trouble adequately driving subsequent circuits. Below is a 5-band active tone-control circuit, which is of my own design.
Ordinarily, 3-band tone controls work fine for the electric guitar. Yet, I designed the above 5-band control for users who want greater adjustment of the sound of the solid-state circuitry. There is also volume control on the output of the Tone Control circuit, and a Booster circuit has been provided, with its own simply tone-control, to help the signal from the 5-Band Tone Control compete with the signal from the Tube Circuit.
The 5-Band Tone Control’s frequency bands divide the audio spectrum by 5, labeled here as Bass, Lo Mid, Mid, HI Mid, and Treble. The approximate frequencies are:
Bass < 250 Hz, Lo-Mid 250 – 500 Hz, Mid 500 Hz – 2.5 kHz, Hi-Mid 2.5 kHz – 10 kHz, and Treble > 10 kHz.
But, of course, the user must set the positions of pots by ear to compensate for personal taste and how the human ear hears different frequencies.
Next up is the Booster circuit.
The booster has four controls; Input Level, Tone, Gain, and Volume. The Input Level control is needed to keep the Booster from being overdriven if it is to be used cleanly, but will also allow it to be overdriven if desired. The Tone control here only affects the highs, the Gain control adjusts the amount of boost, and the Volume control sets the circuit’s output voltage. And here are some active filters; one low-pass with a high cutoff, and one high-pass with a low cutoff. In series they form a 2-stage audio band-pass filter, to mitigate unwanted subsonics and ultrasonics generated in the other circuits. They can be used separately or in series in any order.
And we have a 4-input mixer, to mix-down as many as four different signals. And while the project is designed to provide three channels, one direct, one amplified, and one for the tube circuits, there is a fourth input to the mixer in case it’s needed.
The added mixer input is provided in the event an external splitter is used for some reason between any two stages and the user has an extra signal to be mixed with all the others. Below I show the power-supply and the pinout diagrams for the ICs used in the solid-state circuits. This supply is only for the ICs. The tubes have their own supply.
Note: A builder of this project may wish to make two or three of these supplies, each providing voltage to only two or three ICs, to keep from overtaxing a lone supply.
As said, the Tube Circuit is my version of a Herzog distortion unit. It is in fact a single-ended low-wattage guitar-amp in which the output tube is used as a preamp tube, for the purpose of overdriving it to get its distortion sound. The tube-type sub-circuits are given as follows. They must be treated collectively as one channel.
For a power-amp build to go with this preamp, consider the following resources.
A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier - Circuit Basics
Audio Amplifier Boards & Modules Amp Kits | Mojotone Amp Maker: Guitar amp kits
Amazon.com: 1 pc LM3886 Amplifier Board Power Amplifier Audio Amplifier OPA445 high
Voltage Version : Electronics
As an example, however, I copied a power-amp design below, or the builder can keep the power-amp separate from the preamp, according to personal preference.
Should anyone build this project, know that I have not built it in order to test it, so it must be considered EXPERIMENTAL CIRCUITRY all the way. Also, the builder must assume all responsibility for the outcome. I cannot be responsible for someone else building this project.
Comments welcome here, and/or send me an email. hkurtrichter@gmail.com
By Kurtus Richter
Here is a collection of diagrams for a very versatile hybrid guitar preamp, meaning a preamp involving both solid-state and tube-type circuits in one project. The reasons for hybridization are as follows. (1) With purely analog circuitry, tube-amps sound better than solid-state amps, and which also applies to preamps. (2) Hybrid preamps allow for the mixing of a nearly pure input signal from the solid-state circuitry with a distorted signal from a tube circuit in which the tubes are deliberately overdriven. (3) Tubes have a slower slew-rate than solid-state devices; by orders of magnitude. In fact, a guitarist who plays very fast scales can exceed the slew rate of the tubes in a tube-type amp, resulting in indistinct attacks of individually picked notes, heard as a muddy sound, but solid-state devises have slew rates that cannot be exceeded. Consequently, for analog circuits (i.e., no digital processing involving modern sampling technology), one remedy is to use two kinds of amps, or two preamps; one solid-state for attack definition, and one tube-type for the tone. Hence my design for a hybrid preamp.
The block diagram above illustrates how different circuits in my Hybrid Preamp can be connected together, though other arrangements are possible. I have deliberately placed input and output jacks on each of the solid-state subcircuits, and recommend they be retained, in order to maximize versatility. This gives the user the ability to connect the different circuits as desired and insert external devices, such as stomp-boxes, between any two such circuits, though the tube circuit is self-contained, since it is a distortion circuit inspired by the Garnet Herzog unit made famous in the ‘60s and ‘70s by guitarist Randy Bachman, who used it on hits American Woman and Takin’ Care of Business.
But first I show the input preamp, which has highly user-adjustable parameters, and can also be considered a distribution amp, where one output can be a direct signal sent to the Mixer, another can go to the solid-state 5-Band Tone Control or the Booster, or both in series, and the third to the Tubes.
The table in the diagram lists the low corner frequency that can be set by switches S1 and S2, according to the user’s personal taste. For instance, for deep lows, use the 20 Hz setting, but for no lows at all use the 240 Hz or even the 400 Hz setting. The gain of the preamp can also be adjusted from 2 to 200, depending on the setting of switch S3 and the position of the Gain control. High gain, in conjunction with a sufficient setting of the input Level control allows for enough signal voltage to be sent to all three preamp outputs so there should be no trouble adequately driving subsequent circuits. Below is a 5-band active tone-control circuit, which is of my own design.
Ordinarily, 3-band tone controls work fine for the electric guitar. Yet, I designed the above 5-band control for users who want greater adjustment of the sound of the solid-state circuitry. There is also volume control on the output of the Tone Control circuit, and a Booster circuit has been provided, with its own simply tone-control, to help the signal from the 5-Band Tone Control compete with the signal from the Tube Circuit.
The 5-Band Tone Control’s frequency bands divide the audio spectrum by 5, labeled here as Bass, Lo Mid, Mid, HI Mid, and Treble. The approximate frequencies are:
Bass < 250 Hz, Lo-Mid 250 – 500 Hz, Mid 500 Hz – 2.5 kHz, Hi-Mid 2.5 kHz – 10 kHz, and Treble > 10 kHz.
But, of course, the user must set the positions of pots by ear to compensate for personal taste and how the human ear hears different frequencies.
Next up is the Booster circuit.
The booster has four controls; Input Level, Tone, Gain, and Volume. The Input Level control is needed to keep the Booster from being overdriven if it is to be used cleanly, but will also allow it to be overdriven if desired. The Tone control here only affects the highs, the Gain control adjusts the amount of boost, and the Volume control sets the circuit’s output voltage. And here are some active filters; one low-pass with a high cutoff, and one high-pass with a low cutoff. In series they form a 2-stage audio band-pass filter, to mitigate unwanted subsonics and ultrasonics generated in the other circuits. They can be used separately or in series in any order.
And we have a 4-input mixer, to mix-down as many as four different signals. And while the project is designed to provide three channels, one direct, one amplified, and one for the tube circuits, there is a fourth input to the mixer in case it’s needed.
The added mixer input is provided in the event an external splitter is used for some reason between any two stages and the user has an extra signal to be mixed with all the others. Below I show the power-supply and the pinout diagrams for the ICs used in the solid-state circuits. This supply is only for the ICs. The tubes have their own supply.
Note: A builder of this project may wish to make two or three of these supplies, each providing voltage to only two or three ICs, to keep from overtaxing a lone supply.
As said, the Tube Circuit is my version of a Herzog distortion unit. It is in fact a single-ended low-wattage guitar-amp in which the output tube is used as a preamp tube, for the purpose of overdriving it to get its distortion sound. The tube-type sub-circuits are given as follows. They must be treated collectively as one channel.
For a power-amp build to go with this preamp, consider the following resources.
A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier - Circuit Basics
Audio Amplifier Boards & Modules Amp Kits | Mojotone Amp Maker: Guitar amp kits
Amazon.com: 1 pc LM3886 Amplifier Board Power Amplifier Audio Amplifier OPA445 high
Voltage Version : Electronics
As an example, however, I copied a power-amp design below, or the builder can keep the power-amp separate from the preamp, according to personal preference.
Should anyone build this project, know that I have not built it in order to test it, so it must be considered EXPERIMENTAL CIRCUITRY all the way. Also, the builder must assume all responsibility for the outcome. I cannot be responsible for someone else building this project.
Comments welcome here, and/or send me an email. hkurtrichter@gmail.com
Getting accurate measurements in the worst measurement space
- Equipment & Tools
- 1 Replies
This past weekend I did a talk on how to get good measurements when you don't have somewhere good to do it.
I designed and build a small sealed reference speaker in the UK using a B&C 12NDL88
I got some measurements outside fully calibrated in half space:
I then measured it at 8.49v to account for the 3m and 1w at 8 ohm
This got me this result:
I wish I had done more sweeps and a bit slower to get it a little smoother but I was in a bit of a rush getting prepared to come over to Berlin for the Hackathon.
I also measured a duel 12" reflex box outside in half space to compare it to.
On the following graph there is one very uncalibrated measurement of the duel 12" reflex which is the purple at the top, one measurement that is the half space measurement of the duel 12 reflex (half space so +6db) then the final lower purple measurement is the corrected measurement from above with the reference box.
As you can see from the graph above it gets you very close using the reference speaker to calibrate but the space I measured it in wasn't too bad.
When I got to berlin I borrowed a 12NDL88 and rebuilt the reference box.
In the workshop I used possibly the worst space I could find to do a measurement to see what results I could get using a 12" tapped horn:
These were the uncalibrated results:
As you can see there isn't much you could do with these measurements as the room was tiny and there was a lot of reflections.
After processing the results using my outdoor half space measurement:
As you can see the measurement has been cleaned up to the point of being extremely usable, it would be possible to EQ this flat and time align it to other speakers measured in the same place.
I think after testing this with the other measurement it is very important to get the measurement environment as similar as possible, measuring indoors without the background noise and other things changing seems to work really well.
Another factor is I found a sub to measure with a similar baffle size whereas that could add some distortion to the measurement, the duel 12 reflex was cleaned up reasonably well just off by a few DB, which I think was from me rushing and not measuring it properly. I thought I had calibrated it all but in my rush it was a good 15db too high haha.
Over the next few days I will release my outdoor measurement for this box and the dimensions of the sealed box for anyone else to build. This should allow anyone to get really good measurements without needing to find a massive space outdoors.
You can do this in your living room and get to within +-1db
Also using this subtractive method will allow you to in theory use any microphone and not calibrate anything and as long as you keep it all the same between tests it will calibrate it to my measurement
Another note is I had been messing around with REW before this and forgot to reapply my mic calibration, it doesn't adjust it too much but I will try and get a better measurement of my reference box, it won't change it too much though as it is already pretty flat.
All the presented measurements have no smoothing or windowing.
Another note would be that the 12ndl88 isn't the best for this but it was a driver that I owned and someone I knew in berlin owned so we could test this.
I was given this Idea by Kyle from Neuron AV but I couldn't find his profile on here to tag
I designed and build a small sealed reference speaker in the UK using a B&C 12NDL88
I got some measurements outside fully calibrated in half space:
I then measured it at 8.49v to account for the 3m and 1w at 8 ohm
This got me this result:
I wish I had done more sweeps and a bit slower to get it a little smoother but I was in a bit of a rush getting prepared to come over to Berlin for the Hackathon.
I also measured a duel 12" reflex box outside in half space to compare it to.
On the following graph there is one very uncalibrated measurement of the duel 12" reflex which is the purple at the top, one measurement that is the half space measurement of the duel 12 reflex (half space so +6db) then the final lower purple measurement is the corrected measurement from above with the reference box.
As you can see from the graph above it gets you very close using the reference speaker to calibrate but the space I measured it in wasn't too bad.
When I got to berlin I borrowed a 12NDL88 and rebuilt the reference box.
In the workshop I used possibly the worst space I could find to do a measurement to see what results I could get using a 12" tapped horn:
These were the uncalibrated results:
As you can see there isn't much you could do with these measurements as the room was tiny and there was a lot of reflections.
After processing the results using my outdoor half space measurement:
As you can see the measurement has been cleaned up to the point of being extremely usable, it would be possible to EQ this flat and time align it to other speakers measured in the same place.
I think after testing this with the other measurement it is very important to get the measurement environment as similar as possible, measuring indoors without the background noise and other things changing seems to work really well.
Another factor is I found a sub to measure with a similar baffle size whereas that could add some distortion to the measurement, the duel 12 reflex was cleaned up reasonably well just off by a few DB, which I think was from me rushing and not measuring it properly. I thought I had calibrated it all but in my rush it was a good 15db too high haha.
Over the next few days I will release my outdoor measurement for this box and the dimensions of the sealed box for anyone else to build. This should allow anyone to get really good measurements without needing to find a massive space outdoors.
You can do this in your living room and get to within +-1db
Also using this subtractive method will allow you to in theory use any microphone and not calibrate anything and as long as you keep it all the same between tests it will calibrate it to my measurement
Another note is I had been messing around with REW before this and forgot to reapply my mic calibration, it doesn't adjust it too much but I will try and get a better measurement of my reference box, it won't change it too much though as it is already pretty flat.
All the presented measurements have no smoothing or windowing.
Another note would be that the 12ndl88 isn't the best for this but it was a driver that I owned and someone I knew in berlin owned so we could test this.
I was given this Idea by Kyle from Neuron AV but I couldn't find his profile on here to tag
Yet another Adcom GFA-555 cry for help
- By wiz1
- Solid State
- 157 Replies
So, my Adcom 555 journey started in 2015. I picked up an early rackmount version of a GFA-555 for 300.00. I had never seen one like this one, the speaker connections on the back are not the the red/black variety, but a reddish brown for both the positive and negative.
Upon receiving it, I took it to Jim Williams (Pro audio upgrades), who did his thing on the driver board, and the main PSU caps tested as good.
I hadn't used it much, but late last year, I started to use it more with some JBL 6332's. One day one side went out. I opened it up and I saw there were 4 fuses, which I carefully ordered the same type and replaced them. All was good until one day, one side would make a pop sound and then volume on that side would get really low, and then come back intermittently.
I found a local guy that took a look around, checked some values on some caps, and said he repaired "30 things" and tested another 250 things. He charged me 150.00.
I got the amp home and it sounded great! i was playing it at relatively high volume and then, POP again, signal gets low. Out of anger, and smacked the front of the amp around the power switch, and loud static, and it came back to life. Something is loose.
I have built some studio style mic preamps and a compressor back in the day, so I am not an expert, but can get around a bit. I called the guy back to see what his input was on this symptom, and I wasn't that keen on taking it back to him, and he did lift a trace while he was working and I now have an extra wire on the bottom of the board....He advised me to get a piece of wood and poke different parts of the unit to try and isolate where the loose connection is. I used a 6 inch long wooden q-tip and started poking around while audio was passing through. When i hit one of the fuse holders on one of the output boards, POP! I found the issue!
I disconnected the amp and re-flowed the solder on all four fuse holders, as well as rough them up a bit for solid connection. I also re-flowed some joints on the outputs. Felling like I really accomplished something, I decided to check the bias before I closed it up. As I was too impatient to wait for clip leads to arrive, I tried it with regular leads and while on one of the emitter resistors, it slipped and sparked, shorting to i believe either the orange or white wire pad right near the 2nd emitter resisitor. After this and before I turned it off, the driver board started to smoke just a little bit, so I immediately shut it off.
I did call another local guy, but his wait time was 6 weeks. After looking at may ADCOM troubleshooting/check out vids on you tube, and reading every thread here on Adcom 555, I have decided to tackle it myself!
When powered on the left distortion LED on the front panel stays on. I powered it down and used the multimeter to check for resistance on the output board ( not sure if it's the pos or neg side, but its the one with the green transistor at the top. There is no resistance on the Toshiba TO3's so I know that at least one of them is bad. I plan on taking this board out and removing all of the TO3's to test. One of the things bugging me on this is that the board does not have the silk screening, and the layout is close, but doesn't match the one that I have downloaded, and I have looked high and low for this board layout and cannot locate. The only one I couldn't get to was hifiengine, as they are closed for new registrations.
I would also like to address if possible the resistor that the guy moved to the bottom of the board and the wire trace.
Side note, while I was beating myself out for shorting the unit, i started to look around for another 555 locally, and found one 3 exits from me for only 280.00. I went to see and hear it, it his guy was the original owner! Unit is super clean, and is also an early version but with the red black horizontal terminals on the back. I opened this one when i got home, and it is pure untouched! so at least I have a back up if something goes south, but my hopes are to get the non functioning unit back on it's feet, and then may replace the electrolytics on the driver board, the one safety transistor that is a known possible failure point, and the filter caps on the bottom as Jim Williams did to my 1st unit.
This is a great community and I'm kind of glad I found it, as I'm starting to get the electronic bug again! Thanks to all in advance!
Upon receiving it, I took it to Jim Williams (Pro audio upgrades), who did his thing on the driver board, and the main PSU caps tested as good.
I hadn't used it much, but late last year, I started to use it more with some JBL 6332's. One day one side went out. I opened it up and I saw there were 4 fuses, which I carefully ordered the same type and replaced them. All was good until one day, one side would make a pop sound and then volume on that side would get really low, and then come back intermittently.
I found a local guy that took a look around, checked some values on some caps, and said he repaired "30 things" and tested another 250 things. He charged me 150.00.
I got the amp home and it sounded great! i was playing it at relatively high volume and then, POP again, signal gets low. Out of anger, and smacked the front of the amp around the power switch, and loud static, and it came back to life. Something is loose.
I have built some studio style mic preamps and a compressor back in the day, so I am not an expert, but can get around a bit. I called the guy back to see what his input was on this symptom, and I wasn't that keen on taking it back to him, and he did lift a trace while he was working and I now have an extra wire on the bottom of the board....He advised me to get a piece of wood and poke different parts of the unit to try and isolate where the loose connection is. I used a 6 inch long wooden q-tip and started poking around while audio was passing through. When i hit one of the fuse holders on one of the output boards, POP! I found the issue!
I disconnected the amp and re-flowed the solder on all four fuse holders, as well as rough them up a bit for solid connection. I also re-flowed some joints on the outputs. Felling like I really accomplished something, I decided to check the bias before I closed it up. As I was too impatient to wait for clip leads to arrive, I tried it with regular leads and while on one of the emitter resistors, it slipped and sparked, shorting to i believe either the orange or white wire pad right near the 2nd emitter resisitor. After this and before I turned it off, the driver board started to smoke just a little bit, so I immediately shut it off.
I did call another local guy, but his wait time was 6 weeks. After looking at may ADCOM troubleshooting/check out vids on you tube, and reading every thread here on Adcom 555, I have decided to tackle it myself!
When powered on the left distortion LED on the front panel stays on. I powered it down and used the multimeter to check for resistance on the output board ( not sure if it's the pos or neg side, but its the one with the green transistor at the top. There is no resistance on the Toshiba TO3's so I know that at least one of them is bad. I plan on taking this board out and removing all of the TO3's to test. One of the things bugging me on this is that the board does not have the silk screening, and the layout is close, but doesn't match the one that I have downloaded, and I have looked high and low for this board layout and cannot locate. The only one I couldn't get to was hifiengine, as they are closed for new registrations.
I would also like to address if possible the resistor that the guy moved to the bottom of the board and the wire trace.
Side note, while I was beating myself out for shorting the unit, i started to look around for another 555 locally, and found one 3 exits from me for only 280.00. I went to see and hear it, it his guy was the original owner! Unit is super clean, and is also an early version but with the red black horizontal terminals on the back. I opened this one when i got home, and it is pure untouched! so at least I have a back up if something goes south, but my hopes are to get the non functioning unit back on it's feet, and then may replace the electrolytics on the driver board, the one safety transistor that is a known possible failure point, and the filter caps on the bottom as Jim Williams did to my 1st unit.
This is a great community and I'm kind of glad I found it, as I'm starting to get the electronic bug again! Thanks to all in advance!
For Sale unfinished project: mini tube amp with DC-DC step up converter
Hey! I'm selling off projects that, due to situation, I can't finish. 20 EUR + shipping from Lithuania
I have: a sturdy metal case with two sockets for 9-pin tubes, a ready-made boost converter board, a jack, and a potentiometer.
I planned to build a low-power amplifier running on low voltage (12V). I can recommend a circuit, or you can choose one yourself.
I have: a sturdy metal case with two sockets for 9-pin tubes, a ready-made boost converter board, a jack, and a potentiometer.
I planned to build a low-power amplifier running on low voltage (12V). I can recommend a circuit, or you can choose one yourself.
Another KT88 PP
- By MagicBus
- Tubes / Valves
- 5 Replies
I had questions about my amp(s) -a pair of monos- but I can tell only what I know. It is my first ever tube project and it has been "evolving" for more than 15 years. Most of what I know about tubes -together with what I don't- came out of this. If anything, I post it here as evidence of what a laboratory mouse can do provided with time and resources. 🙂
It all started from the schematic bellow which seemed very attractive for an amateur equipped only with a DMM. Still, not informative about that 6,3V going where. Go figure!
First implementation shown bellow. Very heavy, kitchen oven wiring, integrated stereo with all kind of inputs and twelve region graphic equalizer per channel. Custom made transformers by a local manufacturer.
Soon it was split in two halves with solid state omitted and these served as "guinea pig" platforms for whatever I found on the internet before I came across to diyaudio.com. In fact, I became a follower of this forum searching for solutions for this amp.
From the above to its current state, all steps were taken one by one. The picture bellow shows what stayed on. Many other things have been tried.
The final schematic is following. Admittedly, not what an engineer would do out of parts ready to deliver 35W in class AB or even 50W in class B. This is just 16W in class A.
I know exactly the difference each new part made to the sound but I'm going to keep it brief. There are some obvious modifications for reliability, like the power section negative bias circuit and the heaters DC elevation. Then the NFB was removed together with the equalization network at the original EF86 input tube. Also, for this the coupling caps to the output stage had to be increased. Sparkling gain was addressed by wiring input and output tubes in triode mode -and moving from EL34 to KT88. One of the most important changes was to replace the ECC82 with the 6N6P with tail CCS. The soundstage got its third dimension after that. The particular CCS has to deal with 140V/34mA and you can see the flimsy heatsink on the top of the pic showing the inner parts. It is floating at 140V and I've found that shunting it with a cap to ground reduced third harmonic by about 5dB.
The power supply is something one will never find in an "orthodox" schematic. Definitely, it's not going to work inside a feedback loop let alone class AB. The idea was to decouple all three stages taking advantage of the steady current consumption. For this, the input stage moved to differential double triode with tail CCS, with ECC40 chosen because it's electrically similar to the EF86 and was fitting to the same hole. Otherwise it should be 6SN7. Accordingly, the output stage was converted to class A by means of two power resistors to take B+ from 500V down to 375V. Originally meant to be a temporary test but it stayed.
PSUDII was extensively used for simulations. I was looking for low ripple and fast clean transition on load transients -if any.
Finally, tube operating points and basic measurements.
ECC40
6N6P
KT88
Distortion @1W
I ended up with a relatively colorless amp... Whenever I want the tuby sound I have to connect some solid state! 😛
It all started from the schematic bellow which seemed very attractive for an amateur equipped only with a DMM. Still, not informative about that 6,3V going where. Go figure!
Soon it was split in two halves with solid state omitted and these served as "guinea pig" platforms for whatever I found on the internet before I came across to diyaudio.com. In fact, I became a follower of this forum searching for solutions for this amp.
From the above to its current state, all steps were taken one by one. The picture bellow shows what stayed on. Many other things have been tried.
The final schematic is following. Admittedly, not what an engineer would do out of parts ready to deliver 35W in class AB or even 50W in class B. This is just 16W in class A.
The power supply is something one will never find in an "orthodox" schematic. Definitely, it's not going to work inside a feedback loop let alone class AB. The idea was to decouple all three stages taking advantage of the steady current consumption. For this, the input stage moved to differential double triode with tail CCS, with ECC40 chosen because it's electrically similar to the EF86 and was fitting to the same hole. Otherwise it should be 6SN7. Accordingly, the output stage was converted to class A by means of two power resistors to take B+ from 500V down to 375V. Originally meant to be a temporary test but it stayed.
PSUDII was extensively used for simulations. I was looking for low ripple and fast clean transition on load transients -if any.
Finally, tube operating points and basic measurements.
ECC40
6N6P
KT88
Distortion @1W
I ended up with a relatively colorless amp... Whenever I want the tuby sound I have to connect some solid state! 😛
Simplest OpAmp opto-compressor
- By NovaPA
- Electronic Design
- 0 Replies
A little preface: back in 2017 (8 years ago, hard to believe!), I designed this circuit. Well—"designed" might be a stretch, as it was based on the well-known and popular "optical compressor" structure using an op-amp and a photoresistor.
Recently, I saw someone publish a very similar circuit (most likely based on the same source), and it inspired me to finally refine my own design.
And so, after 8 years, I finally built and tested it—and it worked right away...
The circuit is very simple. It uses a dual operational amplifier, which can be a TL072, NE5532, or any other op-amp with the same pinout. Power - bilopar +-15V
The first op-amp acts as a controlled amplifier. A photoresistor (VR1) is placed in its feedback loop—its resistance decreases as the light shining on it becomes brighter. In series with it is a potentiometer (R7), which will be mounted on the front panel and will determine the "compression" level: at high resistance, the op-amp's gain will be at its maximum. When R7 is set to 0 resistance, the gain will be entirely dependent on the signal amplitude.
The trimmer resistor (R5) is optional (that's why it's marked in blue), but if installed, it can be used to limit the maximum gain.
Additionally, you can see the input diodes marked in blue—they are also optional and primarily serve a protective function against excessive signal overload.
The second operational amplifier further amplifies the signal for the LED. After it, there is a buffer on a complementary transistor pair—this is necessary to allow the use of an ultra-bright LED. Following that, there is a diode bridge.
You may have noticed that the transistors are connected without biasing, meaning they operate in pure Class B. This is intentional. Unlike an amplifier output stage, where such a configuration would cause distortion at low amplitudes, here it establishes a threshold. In other words, until the signal reaches a certain amplitude (0.6V voltage drop across the transistor's PN junction + 0.6V drop across the diode bridge, totaling 1.2V), the compressor will not "intervene" in the signal.
After the diode bridge, there is a single smoothing capacitor (1µF). There is no dedicated soft release time control, but an additional 10µF capacitor can be connected if needed.
A few words about the optocoupler construction. It’s quite simple: take a piece of heat shrink tubing, insert an ultra-bright LED on one side and a photoresistor on the other. Then, fill it with glue—and that’s it!
The PCB has a designated spot for this component.
The tubing is essential; otherwise, ambient light will interfere with the operation!
If anyone is interested in replicating the design, I’ll prepare and share the Gerber files a bit later. Original CAD files on GitHub.
Thread on the GroupDIY forum
And of course, if you like it, we can refine and improve it in the future!
An audio compressor is a device that reduces the difference between loud and quiet sounds by automatically lowering the signal level when it exceeds a set threshold. This helps balance the sound, making it more even and controlled. It's called a compressor because it "compresses" the dynamic range of the audio signal.
Essentially, what I developed back then was a variation featuring a transistor buffer and an ultra-bright LED to exert more "influence" on the photoresistor.Recently, I saw someone publish a very similar circuit (most likely based on the same source), and it inspired me to finally refine my own design.
And so, after 8 years, I finally built and tested it—and it worked right away...
The circuit is very simple. It uses a dual operational amplifier, which can be a TL072, NE5532, or any other op-amp with the same pinout. Power - bilopar +-15V
The first op-amp acts as a controlled amplifier. A photoresistor (VR1) is placed in its feedback loop—its resistance decreases as the light shining on it becomes brighter. In series with it is a potentiometer (R7), which will be mounted on the front panel and will determine the "compression" level: at high resistance, the op-amp's gain will be at its maximum. When R7 is set to 0 resistance, the gain will be entirely dependent on the signal amplitude.
The trimmer resistor (R5) is optional (that's why it's marked in blue), but if installed, it can be used to limit the maximum gain.
Additionally, you can see the input diodes marked in blue—they are also optional and primarily serve a protective function against excessive signal overload.
The second operational amplifier further amplifies the signal for the LED. After it, there is a buffer on a complementary transistor pair—this is necessary to allow the use of an ultra-bright LED. Following that, there is a diode bridge.
You may have noticed that the transistors are connected without biasing, meaning they operate in pure Class B. This is intentional. Unlike an amplifier output stage, where such a configuration would cause distortion at low amplitudes, here it establishes a threshold. In other words, until the signal reaches a certain amplitude (0.6V voltage drop across the transistor's PN junction + 0.6V drop across the diode bridge, totaling 1.2V), the compressor will not "intervene" in the signal.
After the diode bridge, there is a single smoothing capacitor (1µF). There is no dedicated soft release time control, but an additional 10µF capacitor can be connected if needed.
A few words about the optocoupler construction. It’s quite simple: take a piece of heat shrink tubing, insert an ultra-bright LED on one side and a photoresistor on the other. Then, fill it with glue—and that’s it!
The PCB has a designated spot for this component.
The tubing is essential; otherwise, ambient light will interfere with the operation!
If anyone is interested in replicating the design, I’ll prepare and share the Gerber files a bit later. Original CAD files on GitHub.
Thread on the GroupDIY forum
And of course, if you like it, we can refine and improve it in the future!
Low voltage tube line preamp
- By NovaPA
- Tubes / Valves
- 49 Replies
I want to introduce you one interesting circuit. There is absolutely nothing innovational, circuit is hyper simple. But, I hope, my experience of construction building will be helpful for novices.
Tubes, used in this circuit may be 6AS6 or Russian 6Ж1П.
This tubes can work with LOW anode voltage!
In the circuit I suggest power is 12-20V DC
To use single supply, I put LM7806 voltage regulator to convert input DC to 6V for heat.
Original Article on my blog
This is very convenient because you don't need to build special power supply, you may use standard adapter (better is switching).
This was the first try. After testings, when I heared sound is really well (testing gear: Soundtech Series A mixing desc and Quested S6 monitors, signal sourse - audio interface e-mu tracker) I assembled the second version - with factory-made panels and whole better look.
Also, if anybody wants - there is video of testing.
And - certanly - inside mount.
or
Tubes, used in this circuit may be 6AS6 or Russian 6Ж1П.
This tubes can work with LOW anode voltage!
In the circuit I suggest power is 12-20V DC
To use single supply, I put LM7806 voltage regulator to convert input DC to 6V for heat.
Original Article on my blog
This is very convenient because you don't need to build special power supply, you may use standard adapter (better is switching).
This was the first try. After testings, when I heared sound is really well (testing gear: Soundtech Series A mixing desc and Quested S6 monitors, signal sourse - audio interface e-mu tracker) I assembled the second version - with factory-made panels and whole better look.
Also, if anybody wants - there is video of testing.
And - certanly - inside mount.
or
My Balanced Line Receiver
- By alexcp
- Analog Line Level
- 65 Replies
My balanced line receiver is a small PCB that adds a true balanced input to any amplifier, thus helping to avoid certain problems inherent in single ended (e.g. RCA) connections. Compared to integrated receivers such as THAT1200 series, the board offers an order of magnitude lower distortion (depending on the choice of opamps) and built-in DC removal, which makes a downstream DC blocking capacitor unnecessary.
This project is based on my prior series of volume control boards, which itself was based on Bruno Putzeys' a demo project that illustrated his article "The G-word, or how to get your audio off the Ground", first published in Linear Audio Vol.5. While the focus of those previous projects was volume control, I realized that the combination of a low-distortion balanced input and a ground sensing output is useful by itself, for example, in a monoblock or even a stereo power amplifier.
There was some interest in this receiver in the discussion of our Omicron headphone amplifier earlier this year, so in the coming days I will publish the schematic (post #6 below), measurements and other info on this little board that may be useful.
GB Group Buy Salas UltraFSP RIAA
- By Tea-Bag
- Group Buys
- 256 Replies
After significant amounts of design and testing, we are announcing a group buy for a revised Salas Folded Simple Phono preamplifier.
The power supply has been updated for the UltraBIB type, 1.3S. The S being for Special application in supporting only higher voltages. It keeps the voltage very steady at 28-36volts, depending on gain needs.
Also, additional switch banks are provided to making gain changes much easier. This can allow with a few switch settings and voltage adjustments to change the gain signature and use a different cartridge.
The signal portion remains otherwise the same as the legacy FSP. Schematics for UltraFSP
The BOM is provided here.
UFSP BOM
There is significant cost associated with the boards, the transistors and parts for the kit. If you are a previous owner of the previous Salas FSP, you can reuse your signal transistors as needed as well as signal caps.
However, I will be offering kits as well. I realize that we are in the midst of ... supply chain problems, postal delays, lost wages and more. Please be mindful I will do my best to provide boards and parts as best as I possibly can, but substitions and other matters may come up, which I will try to communicate.
To the meat of it.
UFSP Board cost 58.00 a pair.
RAW power supply, 15.00 (shown with optional parts kit)
Minikit costs, include MSRP of mouser parts, + packing and paypal fees. 55.00
Includes matched C1 and C2, plus C2Y trimmer caps. Matched Q3 and Q7.
See BOM link above.
Big Parts Kit, including minikit - 185.00.
Big Parts kit does not include below
Full Parts Kit for RAW PS - 44.00
2SK369BL matched Pair, for high gain settings, all except low MC - 12.00 R1 included for IDSS.
2SK369BL matched Quad, for LOMC Gain settings - 26.00 R1-R2 included for IDSS. (See BOM Spreadsheet TAB for 2SK369BL)
2SK170BL - triple Pairs for Q4-Q6. Includes resistors R8 and R11 based on IDSS of Q4, Q5. 36.00
Above Jfets, one set per pair of boards sold
max.
https://docs.google.com/document/d/1ip_eB3CbCMnZqCa7Nrlpsx4D9TfRMBJnN2GqJsKhqFE/edit
The power supply has been updated for the UltraBIB type, 1.3S. The S being for Special application in supporting only higher voltages. It keeps the voltage very steady at 28-36volts, depending on gain needs.
Also, additional switch banks are provided to making gain changes much easier. This can allow with a few switch settings and voltage adjustments to change the gain signature and use a different cartridge.
The signal portion remains otherwise the same as the legacy FSP. Schematics for UltraFSP
The BOM is provided here.
UFSP BOM
There is significant cost associated with the boards, the transistors and parts for the kit. If you are a previous owner of the previous Salas FSP, you can reuse your signal transistors as needed as well as signal caps.
However, I will be offering kits as well. I realize that we are in the midst of ... supply chain problems, postal delays, lost wages and more. Please be mindful I will do my best to provide boards and parts as best as I possibly can, but substitions and other matters may come up, which I will try to communicate.
To the meat of it.
UFSP Board cost 58.00 a pair.
RAW power supply, 15.00 (shown with optional parts kit)
Minikit costs, include MSRP of mouser parts, + packing and paypal fees. 55.00
Includes matched C1 and C2, plus C2Y trimmer caps. Matched Q3 and Q7.
See BOM link above.
Big Parts Kit, including minikit - 185.00.
Big Parts kit does not include below
Full Parts Kit for RAW PS - 44.00
2SK369BL matched Pair, for high gain settings, all except low MC - 12.00 R1 included for IDSS.
2SK369BL matched Quad, for LOMC Gain settings - 26.00 R1-R2 included for IDSS. (See BOM Spreadsheet TAB for 2SK369BL)
2SK170BL - triple Pairs for Q4-Q6. Includes resistors R8 and R11 based on IDSS of Q4, Q5. 36.00
Above Jfets, one set per pair of boards sold
max.
https://docs.google.com/document/d/1ip_eB3CbCMnZqCa7Nrlpsx4D9TfRMBJnN2GqJsKhqFE/edit
Maplin MosFET Amplifier GA28F construction thread
- By jamesfeline
- Solid State
- 387 Replies
Attachments
Ath generated CD 2-way
After looking at these fancy CD waveguides for about 10 years, i finally found some time to wrap my head around mabat´s ath waveguide generator and made my own. Thank´s to sheer endluss information on this forum, i feel pretty confident that i am on the "right" track so far. After simulating probably 100s of iterations between christmas and newyears, i think i found a compromise that i am going to build.
Below you can see the current state CAD design and ABEC SPL response with enclosure. It´s supposed to be mated to an 8" fullrange, used as a Midwoofer up until 1,5kHz in this case, in a 60l BR enclosure. I want to use basotect on the inside walls to reduce mid reflections. Main design goal is to get rid of room reflections and keep as much midrange dynamics as possible. If general frequency response is within a reasonable target its a welcome bonus.
As much as i´d love to just get myself a Hypex FA (you can see it semitransparent in my drawing), i am not quite confident enough to sell my beautiful NS1000s to be able to afford those.
As of now i plan on building said enclosures, measure both drivers and use VituixCAD to design a simple crossover and take care of frequency response with DSP. I could go forward and spent another 2 weeks to setup a working Akabak simulation, but i am not sure it´ll be precise enough to get me in the ballpark, working with a CD horn in this case.
I´ve been looking into a Le Cléac`h crossover to compensate for HF driver position and increased center to center distance.
https://www.melaudia.net/zdoc/jml_crossovers_etf04.pdf
Honestly i have no idea how it is going to work out, but i might need some directions for crossover design.
Looks like i need to use a 10kHz first order lowpass to get somewhere close to a linear frequence response and attenuate efficiency to match with my woofers 90db? Is it possible to combine a first order lowpass with a 3rd order butterworth for a Le Cléac`h crossover concept? I might get some strange tweeter response below my crossover frequency i guess...
I will document further development here. As somebody building his first proper pair of diy speakers, i might need input at some point. 🙂
Below you can see the current state CAD design and ABEC SPL response with enclosure. It´s supposed to be mated to an 8" fullrange, used as a Midwoofer up until 1,5kHz in this case, in a 60l BR enclosure. I want to use basotect on the inside walls to reduce mid reflections. Main design goal is to get rid of room reflections and keep as much midrange dynamics as possible. If general frequency response is within a reasonable target its a welcome bonus.
As much as i´d love to just get myself a Hypex FA (you can see it semitransparent in my drawing), i am not quite confident enough to sell my beautiful NS1000s to be able to afford those.
As of now i plan on building said enclosures, measure both drivers and use VituixCAD to design a simple crossover and take care of frequency response with DSP. I could go forward and spent another 2 weeks to setup a working Akabak simulation, but i am not sure it´ll be precise enough to get me in the ballpark, working with a CD horn in this case.
I´ve been looking into a Le Cléac`h crossover to compensate for HF driver position and increased center to center distance.
https://www.melaudia.net/zdoc/jml_crossovers_etf04.pdf
Honestly i have no idea how it is going to work out, but i might need some directions for crossover design.
Looks like i need to use a 10kHz first order lowpass to get somewhere close to a linear frequence response and attenuate efficiency to match with my woofers 90db? Is it possible to combine a first order lowpass with a 3rd order butterworth for a Le Cléac`h crossover concept? I might get some strange tweeter response below my crossover frequency i guess...
I will document further development here. As somebody building his first proper pair of diy speakers, i might need input at some point. 🙂
LS 3/5a garage
- By jeffrowland
- Multi-Way
- 1 Replies
ideas and project started two years earlier, but in April 2023 the first prototype of LS 3/5a box.
immediately after the summer the second box, the veneer with true Walnut thickness 1.4mm over 15 years old.
the prototype was born with a few millimeters more in depth than the standard BBC / Rogers specifications.
I then made others with different features, exact measurements and different aesthetic finishes.
here you go:
---
immediately after the summer the second box, the veneer with true Walnut thickness 1.4mm over 15 years old.
the prototype was born with a few millimeters more in depth than the standard BBC / Rogers specifications.
I then made others with different features, exact measurements and different aesthetic finishes.
here you go:
---
Poweramp 10 Watt IRFP240/9240 Symmetric Class A
- By lineup
- Solid State
- 7 Replies
Simple Symmetric Class A with IRFP240/9240 MOSFET.
Moderate THD.
Power supply 30V single.
Moderate THD.
Power supply 30V single.
For Sale Biamp front ends similar to Diy FE 2022
- By schultzsch
- Swap Meet
- 5 Replies
Hello,
I have for sale some nice and shiny stuff.
This time I have a few pairs of modules that can be used as a low thd line preamp or as an low thd amplifier front end, you know to drive a follower os.
These have balanced inputs, single ended outputs and a voltage gain of ~10x which can easily be changed on each side by replacing 2 smd resistors.
You can power them with up to +/-29vdc and they draw 30ma/entire module.
Each of the two big pcbs hosts 2 preamp channels.
These channels are connected in such a way that you can use them only for biamping so half pcb amplifies the lows and half the highs or whatever being same channel, for a stereo setup 2 pcbs will be needed.
Here is how the thd looks at 2.85vrms or close to 1w/8r
And here at close to 17vrms or close to 36w/8r
Now probably you wonder what are those small pcbs, right?
Well the preamp produces a turn on thump and the small module is a relay that keeps the output shorted to gnd for a few seconds so it silences the thump.
The offer includes 2 preamp modules(4 channels) and 2 thump silencer modules.
Sold
I have for sale some nice and shiny stuff.
This time I have a few pairs of modules that can be used as a low thd line preamp or as an low thd amplifier front end, you know to drive a follower os.
These have balanced inputs, single ended outputs and a voltage gain of ~10x which can easily be changed on each side by replacing 2 smd resistors.
You can power them with up to +/-29vdc and they draw 30ma/entire module.
Each of the two big pcbs hosts 2 preamp channels.
These channels are connected in such a way that you can use them only for biamping so half pcb amplifies the lows and half the highs or whatever being same channel, for a stereo setup 2 pcbs will be needed.
Here is how the thd looks at 2.85vrms or close to 1w/8r
And here at close to 17vrms or close to 36w/8r
Now probably you wonder what are those small pcbs, right?
Well the preamp produces a turn on thump and the small module is a relay that keeps the output shorted to gnd for a few seconds so it silences the thump.
The offer includes 2 preamp modules(4 channels) and 2 thump silencer modules.
Sold
Adcom GFA5802 pcbs and IRF244
- By schultzsch
- Swap Meet
- 10 Replies
I have for sale the amplifier pcbs from a GFA5802. One has a few burned tracks and components(resistors and a to92bjt) meanwhile the other one was working first of disassembling everything.
Both pcbs suffered numerous repairs by how they look and how the vgs of the mosfets measure. This is not my amp and I don`t know much about its past.
The pcbs are sold as they are.
This is the one with the burned components and tracks and is the left channel.
And here is the “good” one that will come exactly like the above one, without the aluminium bracket and power mosfets.
I measured the vgs of all mosfets(at 30Vds and 0.9A Id) to see if they still are ok and got the following list
3.863
3.864
3.897
3.898
3.905
3.923
3.926
3.936
3.937
3.940
3.945
3.968
3.978
3.992
4.002
4.004
4.029
4.035
4.037
4.060
4.063
4.084
4.090
4.138
4.144
4.177
4.184
4.324
4.342
4.378
The mosfets look like this
Adding also the brackets where the mosfets are mounted
Adding also the input modules
Price for everything 150€
Or trade with sits, k170/j74 jfets or j313/k2013 mosfets.
Both pcbs suffered numerous repairs by how they look and how the vgs of the mosfets measure. This is not my amp and I don`t know much about its past.
The pcbs are sold as they are.
This is the one with the burned components and tracks and is the left channel.
And here is the “good” one that will come exactly like the above one, without the aluminium bracket and power mosfets.
I measured the vgs of all mosfets(at 30Vds and 0.9A Id) to see if they still are ok and got the following list
3.863
3.864
3.897
3.898
3.905
3.923
3.926
3.936
3.937
3.940
3.945
3.968
3.978
3.992
4.002
4.004
4.029
4.035
4.037
4.060
4.063
4.084
4.090
4.138
4.144
4.177
4.184
4.324
4.342
4.378
The mosfets look like this
Adding also the brackets where the mosfets are mounted
Adding also the input modules
Price for everything 150€
Or trade with sits, k170/j74 jfets or j313/k2013 mosfets.
15W Poweramp Folded Cascode and Laterals
- By lineup
- Solid State
- 15 Replies
What is unique is the use of folded cascode.
Simulation shows THD 0.00032% but what the real value is we can not know.
Let us say the distortion should be low.
Folded cascode makes the input pair drive the output.
Because EXICON Laterals are easy to drive, it works.
Simulation shows THD 0.00032% but what the real value is we can not know.
Let us say the distortion should be low.
Folded cascode makes the input pair drive the output.
Because EXICON Laterals are easy to drive, it works.
New Stasis front end
- By Nelson Pass
- Pass Labs
- 1499 Replies
Not too long ago I received a request for some help from an owner of
an old Threshold Stasis amp, whose amp was broken and where some
previous work had left some issues with the circuit board.
As many of you will know, I have lots of time on my hands 😉 and a
sentimental desire to revise old product in light of the wisdom I have
acquired in 50 years.
So.
I revised the circuit, making it more simple, and laying out a circuit board
which should be usable for all known versions with minor adaptation.
Attached are various schematics and graphics and also the gerber files
for the circuit board, which was made my pcbway.com, who will ask
what dimensions are, which is 5.5" x 3.5"
This thread will also serve as the location for asking additional questions
and so on.
EDIT --
Gerbers and info for Nelson's front end that fits the old Stasis chassis and has mounting holes (post #281) - https://www.diyaudio.com/community/threads/new-stasis-front-end.363701/page-15#post-6447824
@Zen Mod made PCB for this project, information and gerbers can be found here :
Front End (post #282) - https://www.diyaudio.com/community/threads/new-stasis-front-end.363701/page-15#post-6447826
6-deep output stage (post #283) - https://www.diyaudio.com/community/threads/new-stasis-front-end.363701/page-15#post-6447831
8-deep output stage (post #284) - https://www.diyaudio.com/community/threads/new-stasis-front-end.363701/page-15#post-6447835
--
an old Threshold Stasis amp, whose amp was broken and where some
previous work had left some issues with the circuit board.
As many of you will know, I have lots of time on my hands 😉 and a
sentimental desire to revise old product in light of the wisdom I have
acquired in 50 years.
So.
I revised the circuit, making it more simple, and laying out a circuit board
which should be usable for all known versions with minor adaptation.
Attached are various schematics and graphics and also the gerber files
for the circuit board, which was made my pcbway.com, who will ask
what dimensions are, which is 5.5" x 3.5"
This thread will also serve as the location for asking additional questions
and so on.
EDIT --
Gerbers and info for Nelson's front end that fits the old Stasis chassis and has mounting holes (post #281) - https://www.diyaudio.com/community/threads/new-stasis-front-end.363701/page-15#post-6447824
@Zen Mod made PCB for this project, information and gerbers can be found here :
Front End (post #282) - https://www.diyaudio.com/community/threads/new-stasis-front-end.363701/page-15#post-6447826
6-deep output stage (post #283) - https://www.diyaudio.com/community/threads/new-stasis-front-end.363701/page-15#post-6447831
8-deep output stage (post #284) - https://www.diyaudio.com/community/threads/new-stasis-front-end.363701/page-15#post-6447835
--
Attachments
May he rest in peace, its a great loss Bernt/Bandsei
- By WrineX
- In Memoriam
- 10 Replies
I just heard from a friend of my mine Bernt passed away due to cancer, and this might not be the right place for it, but it is the place he spend most of his times with incredible builds/posts/topics in AMT's and other planar magnetic drivers. and i always loved the way he worked and helped you out if you had any questions.
i still have some builds from him and will cling on to them! my heart goes out to his family and may he rest in peace !
https://www.facebook.com/bernt.lassen.1
i still have some builds from him and will cling on to them! my heart goes out to his family and may he rest in peace !
https://www.facebook.com/bernt.lassen.1
Finally building my MkIIIs, a pictorial thread
- By kb2wyl
- Tubes / Valves
- 63 Replies
Of all the Amps I've had over the years, I never had a pair of Mkiii's. And not to say anything for, or against them, for some reason I've always been curious of how they'd sound. Refurbished not as if money, or original design, were no barriers, but with respect to them. A very similar topology, well implemented. So, this is how I found them. Gotta love the single ccs phase splitter driver stage, led biased even!, 12bx7, feeding the 6550s directly 🤦♂️ Aside from that, and the added "heater voltage doubler" for -15v (now that ccs is working perfectly, I'm sure...) both of the amps are identical with stock iron. Couple weeks apart in '64 says the serials, so probably came from a store is what I'm thinking, as a set? I do know parts are starting to arrive, so it's time to do something with these dilapidated classics.
Yuck, what a mess under here. At least I won't have to worry about trimming the OPT secondary leads, they barely reach. Lot of extra wires for that heater based DC- supply too. If you look close, you can see that whoever made these "driver" boards was recycling them from some other board design. At least they were trying, I tell myself...
Alright now we're talking. Reduced to everything we're keeping on this one. Well, ok, maybe not Dynaco's venerable c-354. Does lamination lacquer come out of carpets if it drips? But seriously, they'll certainly find use elsewhere. And forever thank me for stopping the beating....Ok on to prep..
Ahh there we go. Every surface, every angle and hole. Used a single stage 220grit, which is more than sufficient for chassis like these, without any serious pitting problems. I don't know if you can see in first pic, but they had the chokes screwed in through the tube vent slats! This made one of them be shaped like they now all are. What a pain in the butt hand filing, but I'm glad they look as if they're supposed to be that way now 😅. Besides more ventilation is welcome on a 1.75" chassis with bottom plate (Hmm....more on that later..). I'm thinking close to stock for the transformers, and then a kind of aqua blue for the chassis.
I'll be using the Tubes4HiFi octal driver boards in these. Probably do the mod for the current source. The driver stage is going to have a fairly serious choke, but not decided yet on how much effort vs. gain with one beforehand for B+ as well, other than a beefier 1.5H. Definitely more C than stock, probably top can and underside. And, I'm going to play around with feedback to the cathodes from the OPT secondary. Another nice feature this thing came with 😅 I'll do bias meters (and t.p.?), be going with standard spacing and a switch for 4/8 and maybe 16ohm for the binding posts, and power tubes will be KT88 or 120, we'll see..
Any input is more than welcome, and I love seeing others' examples. I'll post more pics in the coming days as these take shape.
Loren
Attachments
Cheap Germanium transistor amplifiers and FREE service literature for fun and learning . . .
- By wparks
- Electronic Design
- 1 Replies
I don't see a lot of posts on Germanium transistor amplifiers, and wanted to throw a shout out to a really cheap, fun, area ready for learning and experimentation-
I have been tinkering lately with the 12V germanium amplifiers found in extremely affordable 8-track automotive decks from the late 60's and early 70's that can be found at yard sales or on ebay for under $30 including shipping. While 8-track tape is a dismal source, don't let that turn you off- the amplifiers present a great opportunity to study vintage designs that use these early transistors. Easily restored and modified, the result can sound unique, amazing, different, whatever you are in the mood for. These really are hidden gems- because they include all of the impossible to find parts (the interstage transformers, thermistors, and matching sets of germanium pre and power transistors) all in one functional package, usually working fine even if the tape deck is dead.
These amplifiers are typically designed and built in Japan, so are often fairly high quality in a compact package- Generally stripped down to the most basic elements to save cost and area, but using high quality components. They are, however, pretty low power- With only 12-14V car battery voltage to work with, a class AB can only generate about 4-5 Watts per channel even into 4 Ohm speakers. This is not enough for full-room listening, but it is perfect for near-field listening on a desk top or bookshelf, headphone amplifier, or a little test amp.
I reworked one of these as a learning exercise into a small stand-alone amplifier that I detailed in my "Germanium Bake King" project.
You can find FREE service literature for many such auto radio designs at the World Radio History website. Just search for "SAMS" at the main site, (or see the SAMS listings directly here ) and you will find a great many volumes of the SAM's "Auto Radio Series" included there among the SAMS bookshelf. The Auto Radio Series was a long series of periodic books, each volume of which included service literature for a dozen or so various recent models. These books alone are a treasure trove of design examples worthy of study.
You can look up your desired make and model using the free SAMS Annual Index Volume 1, which covers all SAMS models from 1946 through 2001. If the SAMS number starts with "AR-", it is in one of these Auto Radio Series books and =MAY= be there for free at the World Radio History library.
Here is the eBay search string I usually use to find good cheap automotive 8-track players, ranked lowest cost first. Generally you will want to look for a deck that is 8-track only, usually an earlier looking design, the more chrome the better. 😀 It should be from the late 60's or early 70's, with a boxy rectangular "under the dash" design (Not the two-shaft through the dash design). You should see only volume, tone, and maybe balance, with no radio. Once you get into the late 70's with AM or AM/FM designs they have moved on to silicon transistors or integrated circuits- also fun, but not my focus here. If you want to be really sure, find the ones where you can see the power transistors mounted on the outside of the rear panel:
You might even be able to see a transistor number and look it up. Even if you can't see the transistors on the outside, if it's 8-track only, you stand a good chance.
Anyway, happy hunting, and please share you results or thoughts.
I have been tinkering lately with the 12V germanium amplifiers found in extremely affordable 8-track automotive decks from the late 60's and early 70's that can be found at yard sales or on ebay for under $30 including shipping. While 8-track tape is a dismal source, don't let that turn you off- the amplifiers present a great opportunity to study vintage designs that use these early transistors. Easily restored and modified, the result can sound unique, amazing, different, whatever you are in the mood for. These really are hidden gems- because they include all of the impossible to find parts (the interstage transformers, thermistors, and matching sets of germanium pre and power transistors) all in one functional package, usually working fine even if the tape deck is dead.
These amplifiers are typically designed and built in Japan, so are often fairly high quality in a compact package- Generally stripped down to the most basic elements to save cost and area, but using high quality components. They are, however, pretty low power- With only 12-14V car battery voltage to work with, a class AB can only generate about 4-5 Watts per channel even into 4 Ohm speakers. This is not enough for full-room listening, but it is perfect for near-field listening on a desk top or bookshelf, headphone amplifier, or a little test amp.
I reworked one of these as a learning exercise into a small stand-alone amplifier that I detailed in my "Germanium Bake King" project.
You can find FREE service literature for many such auto radio designs at the World Radio History website. Just search for "SAMS" at the main site, (or see the SAMS listings directly here ) and you will find a great many volumes of the SAM's "Auto Radio Series" included there among the SAMS bookshelf. The Auto Radio Series was a long series of periodic books, each volume of which included service literature for a dozen or so various recent models. These books alone are a treasure trove of design examples worthy of study.
You can look up your desired make and model using the free SAMS Annual Index Volume 1, which covers all SAMS models from 1946 through 2001. If the SAMS number starts with "AR-", it is in one of these Auto Radio Series books and =MAY= be there for free at the World Radio History library.
Here is the eBay search string I usually use to find good cheap automotive 8-track players, ranked lowest cost first. Generally you will want to look for a deck that is 8-track only, usually an earlier looking design, the more chrome the better. 😀 It should be from the late 60's or early 70's, with a boxy rectangular "under the dash" design (Not the two-shaft through the dash design). You should see only volume, tone, and maybe balance, with no radio. Once you get into the late 70's with AM or AM/FM designs they have moved on to silicon transistors or integrated circuits- also fun, but not my focus here. If you want to be really sure, find the ones where you can see the power transistors mounted on the outside of the rear panel:
You might even be able to see a transistor number and look it up. Even if you can't see the transistors on the outside, if it's 8-track only, you stand a good chance.
Anyway, happy hunting, and please share you results or thoughts.
My first attemp (Dynaudio D260 + Scanspeak 15W/4531G00)
First time tried to diy speakers, and with the help of Vituix and REW, it was a lot easier. Referring to DYNAUDIO SIRIUS and use first-order crossover, sounds pretty good so far. The actual measured impedance curve seems to be okay. Sharing here seeking for more advice!
Choctaw - 10 Watt Amplifier, 1 Opamp + 2 MOSFET
- By lineup
- Solid State
- 398 Replies
Here I will present my new 10 Watt amplifier.
All you need to play music.
The supply is one transformer 2x12VAC.
Just you wait until I start posting the amplifier.
Here is the idea, simplified.
The opamp controls the amp.
The MOSFETs are biased to about 250mA.
The compensation of the opamp rolls off bandwidth at 200kHz.
Gain is set to 11.
The max output is like 10 Watt RMS.
All you need to play music.
The supply is one transformer 2x12VAC.
Just you wait until I start posting the amplifier.
Here is the idea, simplified.
The opamp controls the amp.
The MOSFETs are biased to about 250mA.
The compensation of the opamp rolls off bandwidth at 200kHz.
Gain is set to 11.
The max output is like 10 Watt RMS.
Attachments
Speaker build
- By Tube Radio
- Multi-Way
- 1 Replies
Was given what looked like a cheap more modern Phillips stereo with two two way speakers awhile back and with my recent success with open baffle speakers decided to test these drivers to see if they would sound good.
Here's the woofer. Looks like it will be fine for open baffle
Here's the tweeter.
I had the parts I needed to connect up a two way 6dB/octave crossover and the speaker seems to sound pretty good. Bass response seems decent for the driver size.
Here's the crossover schematic
Here's the temporary mounting for the drivers.
Now these paired with a 10-20 watt stereo amp will make a nice pair of computer speakers.
The only thing I don't like is that the cone tweeter doesn't really output anything above about 12.5kHz.
I do have 90% of a box of 200 Onkyo dome tweeters I bought for $10 over 10 years ago from Parts Express which were meant for certain models of GM vehicles and they are close enough to the measured impedance of the cone tweeter to where I can connect it up to the temporary crossover to see if it's output needs to be padded down any with an l-pad and how good it sounds.
Normally I'd use the cone tweeter then cross the dome over at 12-13 kHz, however I want this to be a smaller build so I'll leave off the cone tweeter.
It may not be easy to do given how close the speaker mounting holes are to one part of the speaker, but I'll try to front mount the woofers. I could then find some grills to put over the woofers if so desired.
I'll then need to find a decently small reasonably priced solid state amplifier.
Ok so it looks like I'm either going to buy a dome tweeter that plays down to 3.2kHz or I will need to take the cheaper route and use the stock tweeters and cross in a dome at 12kHz. Doing a brief test by using the cone tweeter and using a 2.5uF cap in series with the dome definitely shows some improvement.
C1 is 1.39uF and the tweeter zobel is 1.4uF. Can get a 1uF and .33uF cap. The 5% tolerance will be enough to compensate.
I honestly think some of the all in one type systems with detachable speakers like the Phillips I got these drivers from may often have decent drivers with the problem being that the implementation of said drivers leaves a lot to be desired.
The phillips speaker has a rear round port and a front port. It has a woofer and cone tweeter. It also has what looks to be like two piezo elements attached to the plastic beside the tweeter. Have no clue what those are for as they don't seem to make any sound that I can hear. Oh it also has a plastic piece on top with two fake dome tweeters in it. They were oh so close with the piezo elements. Just about 4" higher and they could have placed them where the domes are so that they could at least add to the sound.
Here's the drivers in their original box. Absolutely horrible and it sounds about as bad as the graph looks.
Here's the woofer. Looks like it will be fine for open baffle
Here's the tweeter.
I had the parts I needed to connect up a two way 6dB/octave crossover and the speaker seems to sound pretty good. Bass response seems decent for the driver size.
Here's the crossover schematic
Here's the temporary mounting for the drivers.
Now these paired with a 10-20 watt stereo amp will make a nice pair of computer speakers.
The only thing I don't like is that the cone tweeter doesn't really output anything above about 12.5kHz.
I do have 90% of a box of 200 Onkyo dome tweeters I bought for $10 over 10 years ago from Parts Express which were meant for certain models of GM vehicles and they are close enough to the measured impedance of the cone tweeter to where I can connect it up to the temporary crossover to see if it's output needs to be padded down any with an l-pad and how good it sounds.
Normally I'd use the cone tweeter then cross the dome over at 12-13 kHz, however I want this to be a smaller build so I'll leave off the cone tweeter.
It may not be easy to do given how close the speaker mounting holes are to one part of the speaker, but I'll try to front mount the woofers. I could then find some grills to put over the woofers if so desired.
I'll then need to find a decently small reasonably priced solid state amplifier.
Ok so it looks like I'm either going to buy a dome tweeter that plays down to 3.2kHz or I will need to take the cheaper route and use the stock tweeters and cross in a dome at 12kHz. Doing a brief test by using the cone tweeter and using a 2.5uF cap in series with the dome definitely shows some improvement.
C1 is 1.39uF and the tweeter zobel is 1.4uF. Can get a 1uF and .33uF cap. The 5% tolerance will be enough to compensate.
I honestly think some of the all in one type systems with detachable speakers like the Phillips I got these drivers from may often have decent drivers with the problem being that the implementation of said drivers leaves a lot to be desired.
The phillips speaker has a rear round port and a front port. It has a woofer and cone tweeter. It also has what looks to be like two piezo elements attached to the plastic beside the tweeter. Have no clue what those are for as they don't seem to make any sound that I can hear. Oh it also has a plastic piece on top with two fake dome tweeters in it. They were oh so close with the piezo elements. Just about 4" higher and they could have placed them where the domes are so that they could at least add to the sound.
Here's the drivers in their original box. Absolutely horrible and it sounds about as bad as the graph looks.
New DynaKitParts ST-35 Build
- Tubes / Valves
- 284 Replies
Over the next few months, I'll be building the DynakitParts ST-35 with their bias control upgrade and choke. I also will be doing some other simple and inexpensive upgrades, whether "necessary" or not. I have opted not to use "enhanced fixed bias" circuitry, choosing instead the bias kit from DynakitParts that allows adjusting each tube individually.
It's a very nice kit, complete with everything needed except tools, solder, and tubes. It even comes with a free Dynakit ball cap. https://www.dynakitparts.com/shop/st-35-kit-120-vac/
I did purchase the optional tube cage as shown above, but I doubt that I will ever use it. Some future owner might though. I might open up the solid sheet metal sides and install matching perforated metal if I can get a small quantity of it.
A discussion of tube lifespan and possible power supply mods is here: https://www.diyaudio.com/community/threads/dynakitparts-st-35-power-supply-mods.398189/
The first "upgrade" was to purchase a 14/3 power cord. The kit comes with an adequate 18/3 power cord with inline rocker switch, but I will be installing a switch on the chassis instead, ideally a rocker switch on the front panel if I can find one that will fit.
Today I mounted four larger rubber feet to the bottom of the chassis. The ones that come with it are very, very small, making it hard to lift or move the amplifier because you can't get your fingers under it. I just happened to have four new rubber feet from some other project in my parts box and some screws and washers that fit, so that worked out great.
The two power supply diodes look a bit skimpy by today's standards, so I'll order a couple of 3A diodes if I don't have any in my parts box.
The four coupling caps (C4 and C5) that came with the kit probably are fine, but I'll upgrade those with something a little nicer like the ones shown in the video at the bottom of this post. I'm not sure what those are though. What's a good cap to use without busting the budget and given the obvious space contraints? If Mouser sells something good, I'll be placing an order from them anyway so I could save on shipping charges.
I can't stand silver audio components, so everything is now satin black, including the choke and the quad cap. I have decided for a variety of reasons to stuff different capacitor values into a quad cap can that I emptied out, rather than use the included 60/40/20 uF 450VDC 100uF 25VDC quad cap. The 100uF section isn't used with the bias upgrade kit, so I only need three caps not four. I have retained the terminals and locking tabs unused and undamaged. I bought a cap that had a sticker on it instead of stamped values on the can so I can make a decal to show the values that I actually put inside along with the date.
I have completed the artwork for a new set of white decals to go on the satin black chassis. I haven't had them printed yet because I may use triple binding posts for the speakers instead of just the 8 ohm outputs, and I may be able to fit a power switch on the front.
My first technical question is, with modern equipment, C1 is no longer necessary, correct?
I'll be ordering some 6P14P-EV or 6P14P-ER tubes for it. The ST-35 runs the tubes quite hard, and those military ruggedized versions of the EL84 can handle it.
I'm not sure if there is any real need for the CL-90 inrush current limiter, but it seems to be a popular option.
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Update: here is the final schematic as-built. Parts in red indicate additions/changes vs. the kit.
It's a very nice kit, complete with everything needed except tools, solder, and tubes. It even comes with a free Dynakit ball cap. https://www.dynakitparts.com/shop/st-35-kit-120-vac/
I did purchase the optional tube cage as shown above, but I doubt that I will ever use it. Some future owner might though. I might open up the solid sheet metal sides and install matching perforated metal if I can get a small quantity of it.
A discussion of tube lifespan and possible power supply mods is here: https://www.diyaudio.com/community/threads/dynakitparts-st-35-power-supply-mods.398189/
The first "upgrade" was to purchase a 14/3 power cord. The kit comes with an adequate 18/3 power cord with inline rocker switch, but I will be installing a switch on the chassis instead, ideally a rocker switch on the front panel if I can find one that will fit.
Today I mounted four larger rubber feet to the bottom of the chassis. The ones that come with it are very, very small, making it hard to lift or move the amplifier because you can't get your fingers under it. I just happened to have four new rubber feet from some other project in my parts box and some screws and washers that fit, so that worked out great.
The two power supply diodes look a bit skimpy by today's standards, so I'll order a couple of 3A diodes if I don't have any in my parts box.
The four coupling caps (C4 and C5) that came with the kit probably are fine, but I'll upgrade those with something a little nicer like the ones shown in the video at the bottom of this post. I'm not sure what those are though. What's a good cap to use without busting the budget and given the obvious space contraints? If Mouser sells something good, I'll be placing an order from them anyway so I could save on shipping charges.
I can't stand silver audio components, so everything is now satin black, including the choke and the quad cap. I have decided for a variety of reasons to stuff different capacitor values into a quad cap can that I emptied out, rather than use the included 60/40/20 uF 450VDC 100uF 25VDC quad cap. The 100uF section isn't used with the bias upgrade kit, so I only need three caps not four. I have retained the terminals and locking tabs unused and undamaged. I bought a cap that had a sticker on it instead of stamped values on the can so I can make a decal to show the values that I actually put inside along with the date.
I have completed the artwork for a new set of white decals to go on the satin black chassis. I haven't had them printed yet because I may use triple binding posts for the speakers instead of just the 8 ohm outputs, and I may be able to fit a power switch on the front.
My first technical question is, with modern equipment, C1 is no longer necessary, correct?
I'll be ordering some 6P14P-EV or 6P14P-ER tubes for it. The ST-35 runs the tubes quite hard, and those military ruggedized versions of the EL84 can handle it.
I'm not sure if there is any real need for the CL-90 inrush current limiter, but it seems to be a popular option.
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Update: here is the final schematic as-built. Parts in red indicate additions/changes vs. the kit.
Neurochrome LM3886DR Build
- Chip Amps
- 522 Replies
Hey guys,
a few months ago now after a failed attempt at buying a chipamp.com kit, Tom mentioned he would be making the LM3886DR Kits, so I immediately put my name down for the first one. It turned up quite a while ago, however I've had a busy few months and haven't had a chance to start putting it together until now.
Cutting the box open, everything was individually bagged and labelled from Mouser - so much more convenient than trying to figure out a handful of components. Thanks to Tom for helping me out with getting all components along with my boards.
Printed off the design documentation - super comprehensive and walks you through every step of the build (including about as much information on the chip as you're going to find anywhere). Easy enough to follow that providing you can solder, it's pretty hard to go wrong building this kit.
Started populating the boards with resistors. Again, having everything bagged and tagged makes this process super easy.
Power resistors in. Left 5mm gap for airflow around the resistors.
All caps in.
Connectors and inductor in.
LM3886 in (easy to solder, was annoying trying to lift it a pinch off the board for clearance - more due to my fat hands than any issues with the kit).
Chip attached to temporary heatsink for testing. Definitely overkill, but I had it floating around. Checked DC offset at the output - 3.5mv; perfect.
Attached to a test speaker and lab power supply. At the start of testing I was hearing some terrible things - the cone flapping around, continual cracks and pops, etc. Figuring I had something wrong I went through and verified all components with no success - turns out I had a faulty signal generator! Switched over to another one and it was perfect.
-----TBC-----
a few months ago now after a failed attempt at buying a chipamp.com kit, Tom mentioned he would be making the LM3886DR Kits, so I immediately put my name down for the first one. It turned up quite a while ago, however I've had a busy few months and haven't had a chance to start putting it together until now.
Cutting the box open, everything was individually bagged and labelled from Mouser - so much more convenient than trying to figure out a handful of components. Thanks to Tom for helping me out with getting all components along with my boards.
Printed off the design documentation - super comprehensive and walks you through every step of the build (including about as much information on the chip as you're going to find anywhere). Easy enough to follow that providing you can solder, it's pretty hard to go wrong building this kit.
Started populating the boards with resistors. Again, having everything bagged and tagged makes this process super easy.
Power resistors in. Left 5mm gap for airflow around the resistors.
All caps in.
Connectors and inductor in.
LM3886 in (easy to solder, was annoying trying to lift it a pinch off the board for clearance - more due to my fat hands than any issues with the kit).
Chip attached to temporary heatsink for testing. Definitely overkill, but I had it floating around. Checked DC offset at the output - 3.5mv; perfect.
Attached to a test speaker and lab power supply. At the start of testing I was hearing some terrible things - the cone flapping around, continual cracks and pops, etc. Figuring I had something wrong I went through and verified all components with no success - turns out I had a faulty signal generator! Switched over to another one and it was perfect.
-----TBC-----
Attachments
Can I use miniature tube as driver with adapter in my amp?
- By Maximus89
- Tubes / Valves
- 35 Replies
Here’s a schematic. I’m not a DIY guy I’m simply here to ask the experts and I’d appreciate input.
I have generally found I get the top end I like out of miniature tubes vs the octal or larger tubes and since my 6550 Tung Sols lack that extended highs I want- hoping I can use adapters for the 6BX/L7 drivers. So could a 5687 tube work with an adapter? Any other options? 6CG7?
May as well ask while I’m here. I also have matching transformer coupled preamp which uses 12AY7/6072. Curious if i can safely use a 12AT7 or European equivalent? What about a Western Electric 420a or 396a/5670 via adapters? 5687?
Could the preamp handle a different rectifier other than the 6x4?
Thanks in advance
I have generally found I get the top end I like out of miniature tubes vs the octal or larger tubes and since my 6550 Tung Sols lack that extended highs I want- hoping I can use adapters for the 6BX/L7 drivers. So could a 5687 tube work with an adapter? Any other options? 6CG7?
May as well ask while I’m here. I also have matching transformer coupled preamp which uses 12AY7/6072. Curious if i can safely use a 12AT7 or European equivalent? What about a Western Electric 420a or 396a/5670 via adapters? 5687?
Could the preamp handle a different rectifier other than the 6x4?
Thanks in advance