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Old 19th July 2012, 12:02 PM   #41
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Quote:
Originally Posted by Lazy Cat View Post
one more practical example
The ventilation slots under the capacitors are a nice touch.
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Old 19th July 2012, 12:03 PM   #42
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by PChi View Post
I think that the power supply and amplifier need to be looked at together.
Agree

Quote:
Originally Posted by PChi View Post
With large loudspeakers the bass response needs to be within a fraction of dB down to tens of Hz for no differences to be heard. That is difficult to achieve with a realistic sized output coupling capacitor so again a difference might be audible.
I don't think our ears are that sensitive at 10's of Hz to tiny variances although I've never tried it myself, besides in any normal listening environment the interaction of the speaker with the room boundaries make multiple dB changes to the flatness of the frequency response that are far in excess of any flatness issues from the amplifier (unless damping factor is so low that the speaker-amplifier combo produces it's own bumps in the FR due to impedance changes in the speaker with frequency).

My own thought on PSU cap sizes is that ripple is a bit of a red herring for the majority of gnf class AB amplifiers since they have very good PSRR. Class A is a different beast and the current draw requirements are so different from Class AB that I don't think one set of 'rules' works for both.

I believe that the frequency response of the power supply is more relevant. The output impedance as a function of frequency along with the transient response of the power supply to current demands from the output stage are more likely to affect the overall sound than low level ripple-induced hum. The use of chokes in the power supply can change these things drastically. I've never used a Shunt Regulator, but I suspect they level the playing field by maintaining a low output impedance and good transient response over a wide frequency range. They are power greedy though.

And the transient response is not about the caps, it's about the whole shebang, the transformer, rectifiers, caps, wiring and all of the associated parasitics. It seems to me, power supply design can be as complex and as important as the amplifier.
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Last edited by Bigun; 19th July 2012 at 12:07 PM.
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Old 19th July 2012, 12:04 PM   #43
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Lazy Cat View Post
Example is CSA PCB in attachment. Nothing new but just one more practical example from the real build.
If the power transistors are mounted between the big caps
this is an exemple of how it should not be done...
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Old 19th July 2012, 03:02 PM   #44
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by Nico Ras View Post
I have also heard of this rule of thumb, and we are on the opposite ends of the earth - is there a reasoning behind the rule (I was told this story in the 60s, but at the time it was only 1000uF/amp maybe easier calculations) Assuming all things equal, could the ripple only be responsible for "smearing" the sound. Does amps with better PSSR sound better than amps with lesser PSSR using the same power supply,.......
How much ripple maters depends on the rest of the amp. For example if the input stage and voltage amplifier stage are fed by a constant current source ripple would matter LOT less than if a simple resistor were used. A well designed amp should be very tolerant of power supply ripple.

But filter caps have another effect other then filtering out ripple, the caps are the power supply for the transistors. Transient response depends on having a low impedance power supply and having a few paralleled cap electro caps bypassed with film caps and proper wring can make for a lower output impedance. It depends on details of how this is done.

Those people who hear a difference when they add more capacitance may be hearing he lower output impedance and not the added capacitance. (Remember that ESR adds just like any other paralleled resistance.)

Other power supply effects matter too. For example mode switching noise and high order harmonic of that noise need to be "squashed" and some time high ESR caps work for that, Many times a resistor in series with a film cap is used to damp this radio frequency ringing on the supply. Again peole who change out filter caps may be effecting this and hearing more or less RF noise in the supply but thinking they are hearing the effect of more (or less) capacitance.
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Old 19th July 2012, 03:33 PM   #45
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Quote:
Originally Posted by wahab View Post
If the power transistors are mounted between the big caps
this is an example of how it should not be done...
Andrej, your views have earned much respect on the forum, thank you for your comments.

Hugh, I respectfully disagree with your discarding the diode front end decoupling merely on grounds of simulation unless the simulations where carried out using a complex stimulus and a power source with finite impedance and you were able to distinguish between signal and signal modulated power rail.

The reason I am saying this is because I believe that the width/depth/sound-stage/imaging is a direct result of very low amplitude information contained in the recorder signal. By modulating the power rails due to large currents being drawn by low frequency or other high level signals, masks or smears the low level stuff in such a way that we lose the ambiance (provided of course that it was recorded in the first place).

This has nothing to do with the PSSR of the amp, it is not mains or ripple related, but high power signal related, it would not manifest itself in the FFT simply because the power supply rails are "singing in tune with the high intensity stuff"

Now I believe that Tom and Andrej (and yourself) may have unknowingly (or knowingly) solved the problem with a distributed power supply. I also believe that your earlier amps may have attracted a good following because they were capable of resolving the "ambiance" as it was recorded.

Guy's I am speculating here, but the reasoning seams plausible and I have definitely experienced a chalk and cheese sound difference between the battery and the power supply simply because the battery rails I believe were rock solid and modulation was not present on the small signal power lines. Therefor I would like to state an opinion in that I believe that the power supply has much more effect on the character of the sound than the amp itself.
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Last edited by Nico Ras; 19th July 2012 at 03:41 PM.
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Old 19th July 2012, 05:21 PM   #46
PChi is offline PChi  United Kingdom
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Quote 'I don't think our ears are that sensitive at 10's of Hz to tiny variances although I've never tried it myself, besides in any normal listening environment the interaction of the speaker with the room boundaries make multiple dB changes to the flatness of the frequency response that are far in excess of any flatness issues from the amplifier (unless damping factor is so low that the speaker-amplifier combo produces it's own bumps in the FR due to impedance changes in the speaker with frequency).'

In an A/B comparison of electronics the low frequency response needs to be flat to not hear any differences between A and B. True it's academic because the differences are less than the Loudspeaker / room interaction.
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Old 19th July 2012, 06:10 PM   #47
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Where is AndrewT ? Its been nearly a month now since he was last on here.
Andrew posted (about a month ago) that he was taking an extended holiday. Just how extended we don't know but best wishes to him.
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Old 19th July 2012, 06:21 PM   #48
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Nico Ras View Post
I would like to state an opinion in that I believe that the power supply has much more effect on the character of the sound than the amp itself.
The tube guys have known this for 70 years already
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Old 19th July 2012, 06:23 PM   #49
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Default assumed simplicity

Attached is an example of a power supply
Click the image to open in full size.
The 10NF capacitor ensures that some high frequency noise is cleaned up. The rectifier exibits good high frequency behaviour (it isnt switched by the remaining high frequency noise) because the large 10,000uF shouldnt have low impedance at those frequencies. Thus we have a well behaved supply giving us something close to D.C.

Something close to D.C. will not mind interconnecting cables and will safely charge the on board 33uF capacitors. These capacitors are sweet as they respond fast enough in the high frequency region to buffer the interconnecting cables. Thus What the amplifier sees is a stable DC supply.
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Old 19th July 2012, 06:27 PM   #50
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Quote:
Originally Posted by Bigun View Post
The tube guys have known this for 70 years already
an audio amplifier is, fundamentally, a voltage controlled current source

of course the power supply is very crucial.

i for one am putting 2*15,000 μF on my 2*40 W chipamp

yeah the capacitors themselves will cost at least twice as much as the IC
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