Nelson Pass designed this ACA to be a newbie friendly amp....
there is only one voltage that mattered, that is the 1/2 of b+ at the output nodes, and this is the only measurement that mattered and that if you are able to get this, then the amp works...everything else is just extraneous...
after this, you can get your music immediately with speakers and program input....
we have built over 70+ boards of this ACA amps and so far, one mosfet was defective from get go, one mounted the mosfets backwards, and that was about it, everything else went fine and worked the first time after voltage adjustments....
incidentally, the voltage adjustment itself if you are able to do it is the confirmation that you did the build right the first time....that is why in our boards, the values of the resistors, capacitors and semicons are printed right on the board itself so that you need not have to look at the bom from time to time....
there is only one voltage that mattered, that is the 1/2 of b+ at the output nodes, and this is the only measurement that mattered and that if you are able to get this, then the amp works...everything else is just extraneous...
after this, you can get your music immediately with speakers and program input....
we have built over 70+ boards of this ACA amps and so far, one mosfet was defective from get go, one mounted the mosfets backwards, and that was about it, everything else went fine and worked the first time after voltage adjustments....
incidentally, the voltage adjustment itself if you are able to do it is the confirmation that you did the build right the first time....that is why in our boards, the values of the resistors, capacitors and semicons are printed right on the board itself so that you need not have to look at the bom from time to time....
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We like to torture builders by having to look up the values for parts on the PCB.
It’s part of building electronics, so good to learn, but also every time we printed the values on PCBs in the past, the values would change at some point! Then we’d have to correct things with written notes, that people would overlook, since they found it more appealing to just follow the values on the board....
Basically there’s nothing foolproof!
It’s part of building electronics, so good to learn, but also every time we printed the values on PCBs in the past, the values would change at some point! Then we’d have to correct things with written notes, that people would overlook, since they found it more appealing to just follow the values on the board....
Basically there’s nothing foolproof!
Thank you guys for your help and comments.
Yes the ACA is a simple design but as you can read on previous posts the "UN-symmetrical" issue is still strange. up to now i have the impression that both channels are not really symmetrical-one = R channel is worse.
yes at single supply its important to set up the DC bias at 1/2 the supply but this forced a unsymmetrical signal. Why?
i am still interested to solve this because of learning not because the ACA sounds bad
.
chris
Yes the ACA is a simple design but as you can read on previous posts the "UN-symmetrical" issue is still strange. up to now i have the impression that both channels are not really symmetrical-one = R channel is worse.
yes at single supply its important to set up the DC bias at 1/2 the supply but this forced a unsymmetrical signal. Why?
i am still interested to solve this because of learning not because the ACA sounds bad
.chris
The sine waveform is unsymmetrical at very high power output because of high distortion. From what I have read, the unsymmetrical waveform is due to the phase of the second harmonic, according to this article:
Understanding Distortion: A Look At Electronics, Part 2 | Wall of Sound | Audio and Music Reviews
Quoting the article:
Depending on the phase of a second-order harmonic, it can impose varying effects on the original signal. Should the harmonic be in phase, it can tilt the waveform by sharpening the positive 0-90 degree and 180-270 degree slopes while flattening the points at 90-180 degrees and 270-360 degrees of each cycle. If the harmonic is out of phase with the signal, it can produce tilted waveform in the opposed fashion. If the harmonic is 90 degrees out of phase it can cause one half to becomes rounded while the other is sharpened, as depicted in the first Figure above. These are very different effects which have received very little discussion in the public eye.
Understanding Distortion: A Look At Electronics, Part 2 | Wall of Sound | Audio and Music Reviews
Quoting the article:
Depending on the phase of a second-order harmonic, it can impose varying effects on the original signal. Should the harmonic be in phase, it can tilt the waveform by sharpening the positive 0-90 degree and 180-270 degree slopes while flattening the points at 90-180 degrees and 270-360 degrees of each cycle. If the harmonic is out of phase with the signal, it can produce tilted waveform in the opposed fashion. If the harmonic is 90 degrees out of phase it can cause one half to becomes rounded while the other is sharpened, as depicted in the first Figure above. These are very different effects which have received very little discussion in the public eye.
.............i am still interested to solve this because of learning not because the ACA sounds bad
chris
If you suspect the small JFET then why not just swap them between channels and see if the fault swaps over.
It's a stopgap to reduce Id of Q4. No longer needed since the new jfets are ready.
Thank you guys for your help and comments.
Yes the ACA is a simple design but as you can read on previous posts the "UN-symmetrical" issue is still strange. up to now i have the impression that both channels are not really symmetrical-one = R channel is worse.
yes at single supply its important to set up the DC bias at 1/2 the supply but this forced a unsymmetrical signal. Why?
i am still interested to solve this because of learning not because the ACA sounds bad
chris
if you think that is a problem, you can veer away from 1/2 b+ a bit until you get symmetrical outputs.....with a dummy load and a sine wave input signal, you can adjust the pot to have symmetry looking at your scopes.....
this 1/2 b+ thing is an age old practice aimed at getting the maximum output swing, if you want maximum symmetry then you can adjust the pot also....
irfp240 https://www.vishay.com/docs/91210/91210.pdf
the datasheet says gfs has a minimum of 6.9, so between devices the spread can be what? 1.5 x? 2x? 3x? etc., etc...
you can test them if you want identical results if you can, me i never bothered....i just stick them in and listen...
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Is that in response to my question?
If so - I do not understand it, and still not 100% sure whether or not I understand the wiring correctly...
Yes, that was to answer your question.
The wiring is shown here:
Amp Camp Amp V1.6 Build Guide - diyAudio Guides
If you also look at the schematic you will see that "+OUT" is connected to ground.
The wiring is shown here:
Amp Camp Amp V1.6 Build Guide - diyAudio Guides
If you also look at the schematic you will see that "+OUT" is connected to ground.
hi tony
thank you for your comments.
maybe you miss some posts before.
i did the DC bias setting to get an symmetrical wave = DC Setting 9,1V..... but the Q2 get therefore 15V to waste and Q2 gets 90°C
chris