wish I could see it , drill a couple holes . Put Vbe out on wires , have a EF2.
But , it is IP !
OS
Much to think about thank you gentlemen.
For the purpose of science I am tempted to implement the changes suggested above and see if I can get something stable.
Regarding the boards; my plan was always to redesign Rods board with a few modifications to allow the use of a PP cap at the input instead of mkt etc.
This was supposed to happen after proving I can build the amp. If it was going to be beneficial I could bring this part forward to allow the necessary modifications.
For the purpose of science I am tempted to implement the changes suggested above and see if I can get something stable.
Regarding the boards; my plan was always to redesign Rods board with a few modifications to allow the use of a PP cap at the input instead of mkt etc.
This was supposed to happen after proving I can build the amp. If it was going to be beneficial I could bring this part forward to allow the necessary modifications.
Perhaps a better approach might be to state what I wanted out of this build.
I wanted a discrete design that is relatively simple to build. I've done chip amps, so I wanted a step up on complexity.
I want something that will happily put 100w into 4R speakers
I want something that sounds nice which is to say a bit if H2, winning the distortion Olympics doesn't interest me.
I want something stable, bullet proof stable.
I want something that uses my current PSU and output transistors since that is what I already have.
If another design will meet these goals better than a modified P3A, then that is probably where I need to go.
I wanted a discrete design that is relatively simple to build. I've done chip amps, so I wanted a step up on complexity.
I want something that will happily put 100w into 4R speakers
I want something that sounds nice which is to say a bit if H2, winning the distortion Olympics doesn't interest me.
I want something stable, bullet proof stable.
I want something that uses my current PSU and output transistors since that is what I already have.
If another design will meet these goals better than a modified P3A, then that is probably where I need to go.
I am really surprised Rod did not include an output L in this amp. If you’re going to design and build an amp without an output L you really need to take other precautions.
https://hifisonix.com/power-amplifiers/audio-amplifier-output-coupling-inductors/
https://hifisonix.com/power-amplifiers/audio-amplifier-output-coupling-inductors/
Interestingly, in the original version, there is an output inductor.
https://sound-au.com/project03.htm
https://sound-au.com/project03.htm
Go modular - crazy stable (EF3) output stage (below) , add any design on the forum to it.
But you could win the "distortion Olympics " with it , if you wanted to.
And .... I have through-hole input stages that also plug in to it...
OS
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Me too. Wanted to see how it developed before committing time and money. Also my pending project list is... long. Probably too long.
One thing is clear though, P3a is definitely off the list...
There is no need to bash P3A especially if you haven't attempted a build or have failed its build.
It is a relatively simple design except maybe for the Sziklai outputs which require special care to avoid oscillations.
Over the last 30 years, it has been built by many including inexperienced ones such as myself.
My P3A has been on daily use flawlessly over 10 years, still works and was only decommissioned recently to make room for a latfet amp.
If your fail this one, you should not be proud and chances are high that you will fail more complex builds.
I have, for the record, never built a P3A. But I have one in my simulator, and with the recommended transistors (ancient bd139/140 for VAS and drivers!) you don't have the above stated problems. And the DC offset is 7.5mV.
But that leaves the C6 'bandaid'. Rod Elliot says in the project description he needs this cap just on the bottom CFP, else the thing will oscillate, and he doesn't actually understand why. Does anyone here? and why is it that CFP like to oscillate around 7Mhz?
CFP is a local feedback loop. Linear amplifier oscillation is always about gain and phase shift around a loop (as distinguished from things like blocking oscillators and or multivibrators). IIUC its usually the negative side that tends more towards instability. Just the way the two transistor's characteristics interact in that configuration. That and possible interaction with the load, etc.
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Because the Vbe is not bypassed. 100nF added and the oscillations stop. I advised this on post 5. The CFP is stable, see the step responses
Post in thread 'Stability testing my new Rod Elliot P3A' https://www.diyaudio.com/community/...ing-my-new-rod-elliot-p3a.403473/post-7462178.
If the amp got destroyed because the output got shorted. This why the VAS got also destroyed. See also
Post in thread 'The Blameless CFP' https://www.diyaudio.com/community/threads/the-blameless-cfp.402614/post-7449527
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Wasn't bashing it. Clearly it's stability is finely balanced and selection of active devices is crucial to achieving that stability. My time is limited and debugging and modifying p3a just doesn't float my boat.
So it's off my to-do list.
That's NOT bashing p3a.
Does this design work with BC550/560 and BD139/140 type of transistors (while obviously not placed on your SMD board)? What about the output devices?
Good. I must have been lucky then by using successfully different outputs from my stash.
You would have to ask maybe Jeff in the thread for that stuff: https://www.diyaudio.com/community/threads/jamjar-an-hpa-1-inspired-power-amp.345668/ Please PM if more info needed.