I poked around a little bit with my multimeter.
Following the traces back, the middle opamp, the 4558DD, appears to be connected the L/R audio input on the bottom of the PCB where the potentiometers are located. Strangely enough, if you check between the left and right inputs there is continuity! The blue wire connects to the L/R channels on the bottom of the PCB where the connector comes in from the input stage. The left and right channels go through the blue wire to the main board and have continuity through a set of resistors! You can see this in the image below, where the thick blue wire comes from the left side. The red and white wires connect to a set of resistors. If you follow the resistors on the other side of the board and then back through to the back of the board, there's continuity between the two resistors. You can see this in the image right below where the red and white wires attach, there is a single trace that bridges the two resistors.
However, the good thing is as theAnonymous1 has noted, you can easily bypass the pots. I think it does sound better bypassing the pots.
The last 4558DD opamp closest to the front of the receiver appears to be connected to the auto power on circuit. And I don't think it's in the signal path.
I did order some polypropylene caps to replace the input caps and the input caps to the chip. Otherwise all of the other caps appear to be decoupling or power caps. This appears to be a well built amp. I'm looking forward to when I have it fully broken in.
Following the traces back, the middle opamp, the 4558DD, appears to be connected the L/R audio input on the bottom of the PCB where the potentiometers are located. Strangely enough, if you check between the left and right inputs there is continuity! The blue wire connects to the L/R channels on the bottom of the PCB where the connector comes in from the input stage. The left and right channels go through the blue wire to the main board and have continuity through a set of resistors! You can see this in the image below, where the thick blue wire comes from the left side. The red and white wires connect to a set of resistors. If you follow the resistors on the other side of the board and then back through to the back of the board, there's continuity between the two resistors. You can see this in the image right below where the red and white wires attach, there is a single trace that bridges the two resistors.
However, the good thing is as theAnonymous1 has noted, you can easily bypass the pots. I think it does sound better bypassing the pots.
The last 4558DD opamp closest to the front of the receiver appears to be connected to the auto power on circuit. And I don't think it's in the signal path.
I did order some polypropylene caps to replace the input caps and the input caps to the chip. Otherwise all of the other caps appear to be decoupling or power caps. This appears to be a well built amp. I'm looking forward to when I have it fully broken in.
mqualia said:
Pretty much the whole front part of the board is for the auto-on/bridge circuit and the power supply for the opamps. Every last bit of it can be bypassed by just connecting directly to the inputs of the TA0104A. I think I might go back to this option.
I really like this amp (all 3 of them). The only real fault I can find is the high gain of the Tripath chip. It would have been nice if they made it adjustable(other than attenuating the input).
I'll post a pic of my new choice of coupling caps soon. It's sure to make you cringe.
Great idea. I think that this is what I might do also. All one needs is an input resistor and cap. Some people in another thread have already done it to their Carver Pro ZR1600.
http://www.audiocircle.com/circles/index.php?topic=5413.0
I think that what I might try is simplifying the signal path to what is on the reference board.
RCA -> ferrite bead -> 38.4Kohm MKP -> 0.47uf 630v polypropylene -> TA0104A inputs.
The input inductor would removed from the input board and replaced by the ferrite bead and new 38.4Kohm resistor. The 47uF input cap would be replaced by the 0.47uF polypropylene. Then the 4.7uF non-polars be removed and the signal would run directly to the TA0104A inputs.
I've ordered the parts and I'll post an update after I try this.
All of my parts arrived. I tried to emulate the signal path on the reference board and it seemed to work okay.
RCA -> ferrite bead -> 38.4Kohm MKP -> 0.47uf 630v polypropylene -> TA0104A inputs.
However, the inputs were picking up some noise possibly from the board or transformer. When I get the chance again, I'm going to try using some RG59 and see if it's cleaner. Also instead of modding the input board again, I'm going to mod the pass-through board after disconnecting it from the input board. There's enough room to work on the pass-through board and it already has decoupling caps on it. This would allow keeping the regular inputs as stock and switching back and forth if I want.
RCA -> ferrite bead -> 38.4Kohm MKP -> 0.47uf 630v polypropylene -> TA0104A inputs.
However, the inputs were picking up some noise possibly from the board or transformer. When I get the chance again, I'm going to try using some RG59 and see if it's cleaner. Also instead of modding the input board again, I'm going to mod the pass-through board after disconnecting it from the input board. There's enough room to work on the pass-through board and it already has decoupling caps on it. This would allow keeping the regular inputs as stock and switching back and forth if I want.
There may be more things you can do to try to reduce noise besides the input stage. One thing especially might be the low voltage power supplies. I would imagine that there is plenty of switching noise right under the chip. Try placing 0.1uF || 0.01uF ceramic caps tied right from where V5 goes into the chip that are bypassed to ground. I wonder if the internal 2.5V reference for the op-amps get noise on them that the external 5V might not have...thus creating some non-common mode noise that could travel through to the output. I've designed an amp and board with the TK2150...I'm gonna take another look at it to see the noise issues and commonalities of it to the TA0104...more later.
There already appears to be a ceramic decoupling cap on V5. I left the decoupling caps on the input stage, when I modded the bypass board. I also tried to isolate the noise by running the inputs from the back of the board perpendicular to the board to see if I could isolate the inputs far enough to reduce any noise. None of these helped to reduce the hum. The hum isn't there with the stock inputs.
I did move the 0.47uf polypropylenes to the input of the chip and there was no additional noise. It appears they'll need a bit of breaking in but otherwise will be fine.
I might try to replace the 47uf Elna Cerafines on the input board with some Rubycon ZA's, but I think that will be the end of my modding.
I found that this value is too small for the cap to the input of the chip. It was rolling off the low frequencies. I ordered some 4.7uf polypropylenes to replace the original caps.
I also ordered some 47uf Rubycon ZA's to replace the caps on the input board and Vishay VN60D's to replace the resistors in the signal path.
So we'll see how this all goes. Should be good.
Re: Amp 7t noise
When you say "when the volume is down" do you mean the volume of your source, or the volume controls on the amp? Is the noise still there with the source disconnected?
This amp does have a bit of noise that will not go away by using a "noise suppressor"(ground loop isolator). I think the noise is due to a mix of a bad ground scheme and the high gain of the Tripath chip.
Jeff,
The green LED is a fault indicator. It might also act as a clipping indicator. If the red power button on the front panel ever turns green this also indicates a fault.
wooffer said:
When you say "when the volume is down" do you mean the volume of your source, or the volume controls on the amp? Is the noise still there with the source disconnected?
This amp does have a bit of noise that will not go away by using a "noise suppressor"(ground loop isolator). I think the noise is due to a mix of a bad ground scheme and the high gain of the Tripath chip.
Jeff,
The green LED is a fault indicator. It might also act as a clipping indicator. If the red power button on the front panel ever turns green this also indicates a fault.
The hum noise is present when the amp7 is disconnected from the source. The noise level is variable and goes up and down when the level controls on the amp are adjusted. I tried a ground loop suppressor from Radio Shack but it did not help much. I might try a cable video isolator since the unit is near the TV satellite box. It is really a minor nuisance.
I am surprised that I have apparently tripped a circuit breaker on the amp7 a few times that shut the sound off. Sound would promptly play again after turning the amp off and on again. It was only pushing 50 watts according to the meters, the power light was red not green, and there was no apparent clipping occurring. I am running a pair of Realistic Mach Ones (165 watts each) and a set of speakers with two 12" woofers apiece. I thought the amp7 could handle it. I am using a Carver HR 752 (100 wpc) as an amp and preamp. I have the pass through on the amp7 going back to the Carver to power a third set of less powerful Acoustic Research Holographic Imaging speakers. I simply turn these speakers off when I crank up the amp 7, but I wonder if the pass through back to the preamp might be the source of the amp7 circuit tripping off. Also the same aforementioned hum is fed back through the Carver unit and is more apparent on the AR speakers than on the speakers hooked up to the amp 7. Some Troubleshooting is in order.
I am surprised that I have apparently tripped a circuit breaker on the amp7 a few times that shut the sound off. Sound would promptly play again after turning the amp off and on again. It was only pushing 50 watts according to the meters, the power light was red not green, and there was no apparent clipping occurring. I am running a pair of Realistic Mach Ones (165 watts each) and a set of speakers with two 12" woofers apiece. I thought the amp7 could handle it. I am using a Carver HR 752 (100 wpc) as an amp and preamp. I have the pass through on the amp7 going back to the Carver to power a third set of less powerful Acoustic Research Holographic Imaging speakers. I simply turn these speakers off when I crank up the amp 7, but I wonder if the pass through back to the preamp might be the source of the amp7 circuit tripping off. Also the same aforementioned hum is fed back through the Carver unit and is more apparent on the AR speakers than on the speakers hooked up to the amp 7. Some Troubleshooting is in order.
no hum
I would like to give thanks for response to my posts. I reduced the problematic hum by moving the satellite box away from the amp7. Then, by adding a 75 ohm to 300 ohm antenna transformer between the coax cable and the satellite box the hum was reduced to almost inaudible. There have been posts related to amplifier hum and in this case it was not the amp but the satellite box. Perhaps this info may be of some help. dplay.com has more info in an article titled "Them hummin' cables". After about 150 hours of use the amp 7 sounds great with terrific sound on the low end and good sound stage. Wooffer
I would like to give thanks for response to my posts. I reduced the problematic hum by moving the satellite box away from the amp7. Then, by adding a 75 ohm to 300 ohm antenna transformer between the coax cable and the satellite box the hum was reduced to almost inaudible. There have been posts related to amplifier hum and in this case it was not the amp but the satellite box. Perhaps this info may be of some help. dplay.com has more info in an article titled "Them hummin' cables". After about 150 hours of use the amp 7 sounds great with terrific sound on the low end and good sound stage. Wooffer
Hummmm.
Gotta humm problem also.
I tried an rca ground loop isolator (from wallyworld), and that only had limited help. If I disconnect the inputs altogether, there is still a little noise, but it is attenuated.
All the audio gear is connected to the same mains, I tried looping all the chassis together with a piece of 16 gauge wire, etc.
Just a function of that high gain chip?
I wonder if this is the problem that sunk this thing to begin with?
Gotta humm problem also.
I tried an rca ground loop isolator (from wallyworld), and that only had limited help. If I disconnect the inputs altogether, there is still a little noise, but it is attenuated.
All the audio gear is connected to the same mains, I tried looping all the chassis together with a piece of 16 gauge wire, etc.
Just a function of that high gain chip?
I wonder if this is the problem that sunk this thing to begin with?
I've bought 3 of these units and they all have some hum from the transformer. One was rather loud and I sent that back but the other 2 are only audible if up close to the unit. I don't get any hum throught the speakers, is that what people are hearing?
Thiis is a terrific amp that really sounds detail and dynamic. I wasn't too convince that amps played a major role in making such a audible difference, but this amp proved me wrong. I don't think that I will go back to "regular" amps after experiencing digital. What a bargain to boot, hope it is relaible in the long term.
Thiis is a terrific amp that really sounds detail and dynamic. I wasn't too convince that amps played a major role in making such a audible difference, but this amp proved me wrong. I don't think that I will go back to "regular" amps after experiencing digital. What a bargain to boot, hope it is relaible in the long term.
Thank you for the fault info theAnonymous1!! 
I have noticed this amp dues hum when my preamp is turned off..
(inputs float high or something??)
Soon as I power on my preamp the the Amp7 is silent (Except for the sound of music or whatever when I play the source)
I also noticed this bad boy is really picky about ground..
I get a hum on my system when it is hooked to the DVD player..
Disconnecting my dish from ground eliminates this hum. (Just did this for a second as an experiment.) I need to figure out my ground problem there...
This hum was not there on my Amp Three by AudioSource.
Really Picky about ground...
I have noticed this amp dues hum when my preamp is turned off..
(inputs float high or something??)
Soon as I power on my preamp the the Amp7 is silent (Except for the sound of music or whatever when I play the source)
I also noticed this bad boy is really picky about ground..
I get a hum on my system when it is hooked to the DVD player..
Disconnecting my dish from ground eliminates this hum. (Just did this for a second as an experiment.) I need to figure out my ground problem there...
This hum was not there on my Amp Three by AudioSource.
Really Picky about ground...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.