Those limiters don’t allow much more than the “nominal” peak currents drawn by a typical singe-driver, full range speaker. They are the RIGHT solution for an instrument amplifier. Hi fi and PA users tend to require lower Z loads and they would be activating all the time, quite audibly. The solution is either relax the protection (cheap) or double/triple up on output transistors (expensive).
Thank you very much for that explanation. I will study this and probably ask some follow up questions!
Can you explain what you mean by relax the protection? Or how you would do that with this circuit?
And this is one of the reasons I think building a SS guitar amp that is to be over 20W is a waste of time. Those Yamaha's come up for sale here for $200 and under, often not sold. And for SS amps of the vintage they are not bad. With a dirt pedal up front it will hang with a drummer no problem. I just dropped off a Randell RG200 for $150 (threw in a 2x12 cab).
Oh oh, had an idea. Memories of the 100 buck challenge coming back. A tube amp in the 30-40W range for $200? Is it doable? Just kidding, do not want to hijack the thread.
Hi fi amps often have the current limits to high values which will not fully protect the output transistors. They’re good for accidentally brushing the speaker wires together for a split second while music is playing at a sane level. But not much more. Or delay the action for several hundred milliseconds. It’s just a resistor/capacitor value change, pretty much.
Maybe the main point I am pushing was not clear enough, so here it goes again, with a little basic Math added.
In no particular order (all points matter anyway):
1) the speaker is 75W, 16 ohm
2) so it needs 34,6 V RMS at speaker terminals= 49V Peak
3) power and driver transistor drop amounts to about 4 V so now we need minimum rail voltages of 53V
Add at least 2V for drop across ballast resistors plus current sending one, if used.
So now we are talking 55V rails, under full load, and add a couple V (at least) for ripple.
4) unregulated simple PSUs drop around 15% from idle to full load if average quality.
10% if very good (toroids, big caos) , 20% if cheesy cheap.
So 55V*1.15 (to keep it simple)= +/-63-65V rails unloaded.
A TALL order if you ask me.
5) compare that to apparently suitable early "60-100-150W" suggestions
3886/Elliott: excellent amps but both +/-35V rails: very weak for a 16 ohm speaker.
"150W amp" , unknown supply ... assumed unsuitable unless it has high supply
Tda7294: unsuitable if used "plain" at some +/- 40V rails, good if bridged.
IcePower module: probably do fine, depends on model.
6) we see speaking "Amplifier Watts" alone can be very misleading, Power Supply specs RULE
There is a thread around asking "how many volts do you need for your System?"
In my view, that is the proper question to ask 👍🏻
In no particular order (all points matter anyway):
1) the speaker is 75W, 16 ohm
2) so it needs 34,6 V RMS at speaker terminals= 49V Peak
3) power and driver transistor drop amounts to about 4 V so now we need minimum rail voltages of 53V
Add at least 2V for drop across ballast resistors plus current sending one, if used.
So now we are talking 55V rails, under full load, and add a couple V (at least) for ripple.
4) unregulated simple PSUs drop around 15% from idle to full load if average quality.
10% if very good (toroids, big caos) , 20% if cheesy cheap.
So 55V*1.15 (to keep it simple)= +/-63-65V rails unloaded.
A TALL order if you ask me.
5) compare that to apparently suitable early "60-100-150W" suggestions
3886/Elliott: excellent amps but both +/-35V rails: very weak for a 16 ohm speaker.
"150W amp" , unknown supply ... assumed unsuitable unless it has high supply
Tda7294: unsuitable if used "plain" at some +/- 40V rails, good if bridged.
IcePower module: probably do fine, depends on model.
6) we see speaking "Amplifier Watts" alone can be very misleading, Power Supply specs RULE
There is a thread around asking "how many volts do you need for your System?"
In my view, that is the proper question to ask 👍🏻
Just to clarify, do you think building a solid state amp over 20 watts is a waste of time because there are 2 versions?
It’s common for revisions to be made.
If I could build a tube power amp for $200 I would! I think I’d have to get lucky finding used parts. I’ve looked at the AX84 stand-alone power amp. I may attempt to build one someday.
I know solid state power amps aren’t as straight forward but I assumed they would be cheaper
Thank you for sharing this information. I will keep this to n mind. Maybe replacing the speaker with an 8 ohm one or using 2 16 ohm speakers would be better.
say what....the build quality was good but not bulletproof, the original OR80 had the F.A.C. control (sorry don't remember the proper long version of that acronym) a bass rolloff that was a multipole switch that was pure bunk, it was constantly intermittent, most i've seen where jumpered/bypassed and the send and return for external echo/reverb where real fussy about what impedances they where seeing.
they have revised the TT.... A LOT i know i saw quite a few of the early models on my bench and even with the revisions it's still not what i would consider a "rock n roll" or roadworthy amp....there sure cute sitting on a 4x12 cab in the den.
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Soild state is cheaper. But it is also possible to build a tube power amp for $200. It won’t be huge and won’t be using conventional 6L6 or EL84 tubes, and probably not as your first tube amplifier. 200VA Power transformer -$52. 4K a-a output transformer (AS-0505) $26. Pair of 6LU8 $16. Plus tax and shipping, and then the rest of the glue to put everything together. I had this putting out just shy of 30W, running open loop with no problems with OPT saturation.
Bandits are excellent amps but supply runs around +/- 40V, power amp puts out some 75-80W into 8 ohms , mere 100W into 4 because transformer is tightly spec'd and drops a lot.
As you live in the US, cant touch the used market. Some e-pay examples;
https://www.ebay.com/itm/256434580564
https://www.ebay.com/itm/115952374412
https://www.ebay.com/itm/176328438652
https://www.ebay.com/itm/256434561069
Tube?
https://www.ebay.com/itm/364835654496 $100 free shipping isnt awful for a 6BQ5 PP amp.
Point is, all the basics are there and if fundamentally working, you can learn a lot correcting, changing into something else.
I saw somebody say it. Why a solid state power amp. Years ago, I was asked to join a band and be the music arranger and director. I had all the guitars I needed but, I really didn't have a stage rig. I needed an amp. I went to my local Music toy store and since I wasn't sure what would happen to the band in the long run. They had a used 200W SS Yamaha combo amp. I figured it should be fine at least for a while. After all the other guitar player was only using a Pevey 100W Classic tube amp.. Bar bands, go figure. As the night gets longer , the band gets louder. It didn't take me long to figure out that that Hunk of a Pevey amp was burying me. The short answer, he had the Dynamic Range!!! The amount of inverse feedback in a tube amp is minimal compared to a SS amp.As far as the 500W Bass amp. Remember he needs that power because the wavelengths of the Bass are substantially longer than your guitar. As far as building a tube power amp. You can half A** building a tube amp and it will likely perform reasonably well. You get off on SS and you will cook a lot of stuff. I am showing my age here but, I will site the old Sunn Coliseum series amps. If you have ever seen or had the ill fate to own one you have probably seen it literally catch on fire and burn. Tell me, when is the last time you saw a Fender Twin or Marshall Plexi on fire. For that matter even a Pevey Tube Classic. Think on it real hard. If you need to ask questions, feel free to talk to me. I am also sure there are lots of others here that will be willing to pitch in as well.
Regards,
Jamie
Regards,
Jamie
Before building anything, make a spreadsheet, or even paler list of all of the expensive parts. Look at all of the possible ways to get to the volume level that you want / need. If the solid state route appeals to you, the 16 ohm load is a cost adder because of the higher voltage needed in the power supply and other parts. Look at the cost of duplicating your current 16 ohm cabinet and speaker. Running two speakers will increase the apparent volume for a given power level, and you can make more power into an 8 ohm load with a given SS amp.
If there are two speakers, then there can be two power amps. Back in the 90's Sam Ash opened a new store in a shopping center in Margate Florida. We were in the area, so we stopped in. There was a bunch of stuff in the storefront window to be given away that day, and "you must be present to win." The drawing was about 2 hours away and the parking lot was empty, so my wife, myself, and my daughter registered for the drawing and walked over to a restaurant for dinner. Upon returning we discovered 31 people including ourselves waiting for 30 different things to be given away. Those are good odds for all but one person! We walked away with a Shure microphone that I still have, and acoustic guitar that I sold cheap, and a "Brownsville 212" guitar amp. Brownsville was apparently a short lived Sam Ash house brand. the 212 was LOUD but sounded pretty bad when cranked loud. My daughter played her JV-1000 keyboard through it, which sounded far better than the Gorilla Banana guitar amp that she was using. Of course, I had to rip into the Brownsville to see how they were getting "100 watts." There were TWO chip amps mounted on one heat sink, and one fed each speaker.
I'm still going to build a new guitar amp. Experiments and test circuits are being built now. I look at that Hughes and Kettner Triamp MKIII and wonder what's in a $4000 guitar amp. The schematics for older Triamps can be found on the net, as can zillions of other designs, but my new amp will not be any of them. There are some circuits being developed that have not yet been seen in a commercial amp. I started a "new amp" thread. Progress may be sporadic at times, the 1 X 12 cabinet is done, and a 1 X 15" + 2 X 6" cabinet for a biamped guitar setup is nearly done (been on rain delay for almost two weeks). Anyone up for a two hundred buck amp challenge, or even an informal exchange of low budget ideas like those that sprung up in the original HBAC?
My new amp thread is here:
https://www.diyaudio.com/community/threads/tubelab-wants-a-new-guitar-amp.408097/page-9#post-7644466
A tube amp in the 30-40W range for $200? Doable, yes. Remember that the original HBAC rules just counted the electrical parts, the cabinet, chassis and speaker were not included in the total price. Hijack this thread, No, I won't mention it again here.
Bait? Want more motivation for making a 30 to 80 watt guitar amp? I have a large quantity of the guitar amp specific open frame OPT's seen in the amp head here. They are rated for "80 VA from 82 Hz to 5000 Hz 6600 ohms to 0-4-8-16." They work well at 3300 ohms to 0-2-4-8, which is how I usually run them. Stuffing over 100 watts through one for guitar use seems OK, but don't play bass through one beyond about 35 watts. I will sell small quantities to interested builders. They weigh a little over 5 pounds each so shipping isn't cheap and international shipping is probably not viable. See the listing in the Swap Meet section here:
https://www.diyaudio.com/community/threads/tube-amp-opt.411473/#post-7654793
If there are two speakers, then there can be two power amps. Back in the 90's Sam Ash opened a new store in a shopping center in Margate Florida. We were in the area, so we stopped in. There was a bunch of stuff in the storefront window to be given away that day, and "you must be present to win." The drawing was about 2 hours away and the parking lot was empty, so my wife, myself, and my daughter registered for the drawing and walked over to a restaurant for dinner. Upon returning we discovered 31 people including ourselves waiting for 30 different things to be given away. Those are good odds for all but one person! We walked away with a Shure microphone that I still have, and acoustic guitar that I sold cheap, and a "Brownsville 212" guitar amp. Brownsville was apparently a short lived Sam Ash house brand. the 212 was LOUD but sounded pretty bad when cranked loud. My daughter played her JV-1000 keyboard through it, which sounded far better than the Gorilla Banana guitar amp that she was using. Of course, I had to rip into the Brownsville to see how they were getting "100 watts." There were TWO chip amps mounted on one heat sink, and one fed each speaker.
The amp head in the picture was built for the original Hundred Buck Amp Challenge. It squeezed in just under $100 and made about 20 watts. The lone knob on the far right is a Parts Express attenuator to let the amp play at full crank without upsetting the neighbors. 20 watts was loud through the 4 X 12 cabinets that I had at the time. When the amp was built, it used an Antek power toroid for the OPT it worked pretty good but resulted in about 17 watts of power. I had stolen that transformer for another project, and the amp went dark for over 10 years. I decided that I needed a new guitar amp, so I slapped a real guitar amp OPT in that amp and fired it up. Some of the pots are bad, but it works well and gets plenty loud with a single 12 inch speaker.
I'm still going to build a new guitar amp. Experiments and test circuits are being built now. I look at that Hughes and Kettner Triamp MKIII and wonder what's in a $4000 guitar amp. The schematics for older Triamps can be found on the net, as can zillions of other designs, but my new amp will not be any of them. There are some circuits being developed that have not yet been seen in a commercial amp. I started a "new amp" thread. Progress may be sporadic at times, the 1 X 12 cabinet is done, and a 1 X 15" + 2 X 6" cabinet for a biamped guitar setup is nearly done (been on rain delay for almost two weeks). Anyone up for a two hundred buck amp challenge, or even an informal exchange of low budget ideas like those that sprung up in the original HBAC?
My new amp thread is here:
https://www.diyaudio.com/community/threads/tubelab-wants-a-new-guitar-amp.408097/page-9#post-7644466
A tube amp in the 30-40W range for $200? Doable, yes. Remember that the original HBAC rules just counted the electrical parts, the cabinet, chassis and speaker were not included in the total price. Hijack this thread, No, I won't mention it again here.
Bait? Want more motivation for making a 30 to 80 watt guitar amp? I have a large quantity of the guitar amp specific open frame OPT's seen in the amp head here. They are rated for "80 VA from 82 Hz to 5000 Hz 6600 ohms to 0-4-8-16." They work well at 3300 ohms to 0-2-4-8, which is how I usually run them. Stuffing over 100 watts through one for guitar use seems OK, but don't play bass through one beyond about 35 watts. I will sell small quantities to interested builders. They weigh a little over 5 pounds each so shipping isn't cheap and international shipping is probably not viable. See the listing in the Swap Meet section here:
https://www.diyaudio.com/community/threads/tube-amp-opt.411473/#post-7654793
Attachments
Mr. Tublab snuck one before me, thinking along the same lines though.
You may have to go off the beaten path to get it below $200. We would like to reduce shipping costs, if there is a electronic distributer near you it could save you some money. Since we have a budget to meet I think the first thing is to find an inexpensive output transformer. No 16 ohm tap, we will see if any consensus can be found for it on 16 ohms.
Fender Original Hot Rod Deluxe and Blues Deluxe output transformer. 40 watts. Equivalent to #050438. $59.95
40W 4.25k 8/4 ohms
https://www.tubesandmore.com/products/transformer-fender-output-hot-rod-deluxe-and-blues-deluxe
We would like about 430V for the BD. Looked up the Hammond replacement for a PT and find it has 300V @ 250MA. So we need to get 75 watts out of it.
A little short of voltage, $70.53
| P-T1182H117 | 80 | 234V C.T. @ 342ma |
|---|
https://www.tubesandmore.com/products/transformer-hammond-toroidal-power-110v-220v-secondary
Let us try for a cheap power transformer. $23.39 I know nothing about the quality though. 80VA
| Voltage - Primary | 115V, 230V | |
| Voltage - Secondary (Full Load) | Parallel 115V, Series 230V | |
| Current - Output (Max) | Parallel 700mA, Series 350mA |
Or 100VA $34.08
| Voltage - Primary | 115V, 230V | |
| Voltage - Secondary (Full Load) | 120V | |
| Current - Output (Max) | 850mA |
Say we flip the primary and secondary around, might get 210V out, using a voltage doubler.
Let us see what Digikey has for the BD OT.
$76.01
digikey.com/en/products/detail/hammond-manufacturing/1750JA/3869290
The next expensive part is the chassis. If you can bend some sheet metal you can save a fair amount. Then comes the filter caps, other than the tubes the rest of the parts are not too expensive. Not to say this is the way to go, just an example of how to skin a cat another way.