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Old 16th October 2012, 11:19 AM   #1471
fas42 is offline fas42  Australia
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Quote:
Originally Posted by DF96 View Post
If you really can hear the PSU caps in a conventional SS amp then something is wrong: grounding, PSU caps too small, NFB take-off point or ground reference incorrect etc.
Actually, it's pretty easy to "hear" the PSU caps in a "conventional" amp, that classic loss of dynamics, or compression of sound that starts at a certain volume on most systems is the obvious symptom of the caps starting to fail to do their job properly. Which is why amps with monstrously oversized power supplies always impress people, because finally the power supply's "fidgeting" is at a low enough level to not disturb the amplifying circuit's functioning ...

It becomes easy to recognise this behaviour once you've modified a normal sized power supply to work properly: all of a sudden the amplifier sounds 10 times as powerful, even though nothing in the amplifying circuit has altered ...

Frank
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Old 16th October 2012, 12:49 PM   #1472
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Quote:
Originally Posted by fas42
compression of sound that starts at a certain volume on most systems is the obvious symptom of the caps starting to fail to do their job properly.
Sounds to me like an obvious symptom of the caps being too small. Note that the simulations and algebra both show that as audio power rises to the maximum possible for a particular transformer and power amp then the capacitor value becomes more and more critical and in fact rises without limit. Note that too high ESR, by dropping some voltage, also means a larger cap is needed.

No magic is happening, it is simply that the cap is not doing its job properly, as you say. Bigger cap or bigger transformer is the answer. Circuits really do obey circuit theory! You will note that I included 'PSU caps too small' in my list of things which might be wrong.

'Loss of dynamics' presumably means that the gain of the amp is varying with signal level. That is mainly an amp design issue, but it can be eased by bigger caps so the supply rail droops less.

I think the main problem is that people don't realise what actually sets the required cap size. They do average DC calculations, not realising that this can automatically put them a factor of 2.8 too low in current draw. Then the marketing men get involved so an amp/PSU which can do 100W on an isolated HF peak is then advertised as a 100W amp even though it can only do, say, 60W on sustained low bass. People treat it as a bad 100W amp when in fact it might be a very good 60W amp. Doubling the PSU cap size might make it an 80W amp. Doubling again makes it a 90W amp (roughly) but then people turn up the volume and start complaining that it can't do 150W on HF peaks (they are still limited to 100W). This also might be described as poor dynamics.
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Old 16th October 2012, 06:11 PM   #1473
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Quote:
Originally Posted by gootee View Post
What?!! Think again! That was MUSIC, NOT NOISE.

You originally said:



and I was merely pointing out that the connection is not tenuous at all.

The power supply current IS what you hear.


There was no "inferring by", no "reversed logic", no "faulty", and no "misleading", at least not on my part!

Whiskey Tango Foxtrot?!

How could you have thought that I was implying, as you said, "voltage fluctuations that are on the rails will show up at the load in the same way"?

I said NOTHING that could possibly be construed to have implied anything at all like that.
Ah, then it looks like I completely misread what you meant in your post. Mea Culpa. You are correct in that the current from the power supply to the amplifier is resulting in the music emanating from the speaker.

Here's what transpired from my point of view:
I wrote: "Remember, this is just the power supply. There is a tenuous connection to what you would actually "hear" from the amplifier, so do not do listening tests to "proof" your tweaks!!!" to Danielwritesbac in an EMail where I went on to talk about his power supply design. What I had in mind was him using a light blinker to test his supply, and his unorthodox cap in parallel with diode add-ons. I had in mind the amp PSRR at the time when I made the statement about a "tenuous connection" and I was thinking of ripple, or other non-DC component on the rails. I wanted to go back and change it later to be more clear, but you only get a few minutes to change your posts after you make them, and that time had passed.

I had in mind that ripple and other rail VOLTAGE fluctuations will not be discernible at the amplifier output because of PSRR, and that making a tweak in your power supply and then listening for the change in the sound coming out from the loudspeaker is not a good way to go about it IMHO.

I thought that you were invoking your current measurements from post 372 and saying that everything on the rails will come out at the speaker. This would not be true, unless it was a signal at the input signal of the amplifier, which is precisely what you were measuring/showing in post 372 - a (music) input signal resulting in current delivered to the load that mirrors that input signal (if I am understand your post correctly).

So again, my apologies for misconstruing your post as something that it was not.

-Charlie
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Old 17th October 2012, 02:32 AM   #1474
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Quote:
Originally Posted by fas42 View Post
Actually, it's pretty easy to "hear" the PSU caps in a "conventional" amp, that classic loss of dynamics, or compression of sound that starts at a certain volume on most systems is the obvious symptom of the caps starting to fail to do their job properly. Which is why amps with monstrously oversized power supplies always impress people, because finally the power supply's "fidgeting" is at a low enough level to not disturb the amplifying circuit's functioning ...

It becomes easy to recognize this behaviour once you've modified a normal sized power supply to work properly: all of a sudden the amplifier sounds 10 times as powerful, even though nothing in the amplifying circuit has altered ...
Frank
Hi Frank! That a great comment.
I'm looking at it trying to name one thing or the most likely thing that could cause what is described. Bass dynamics? Undersize transformer isn't good for bass dynamics. Compression? Well, that confuses me a bit. Compression sounds like: "YAAAAAA!!!!" and something is having trouble driving something else, most usually a computer without a buffer. There seems to be several fixes, but I do not know the cause.
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Old 17th October 2012, 02:45 AM   #1475
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Quote:
Originally Posted by DF96 View Post
'Loss of dynamics' presumably means that the gain of the amp is varying with signal level. That is mainly an amp design issue, but it can be eased by bigger caps so the supply rail droops less.
Hard to see how this could be, short of the amp clipping. Under clipping of course the amp's gain is reduced, but exclude that and for a typical NFB amp the feedback resistors' values would have to be altering.

I rather suspect 'loss of dynamics' is associated with the perceived noise levels rising in a program-modulated fashion. The rails have more noise (increased ripple) on them and this gets through to the output slightly delayed due to the reservoir caps. Without the delaying factor probably the extra noise would get subjectively masked - perhaps explaining the 'small res cap sounds better' observation. The mechanisms can be non-infinite PSRR and sub-optimal grounding and decoupling techniques.
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Old 17th October 2012, 03:56 AM   #1476
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Compression, as I hear it, and think of it, is the inability of the amp to resolve high frequency information correctly once past a certain volume. Driving rock records with lots of splashy cymbal work is an easy way to pick it; the shimmer is maintained up to certain SPLs, and then that sound just goes flat, the drummer might as well be banging on the bottom of a saucepan.

My first decent amp, 25 years ago, a Perreaux 2150B, theoretically had plenty of grunt, but you could hear the power supply start to collapse in this fashion even at moderate sound levels. So the initial big tweak was to rip out the usual caps of the day, two big, fat screwcaps, and replace with myriads of parallelled, small valued radials, with about 10 times the capacitance overall. This made a huge difference of course ...

Frank
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Old 17th October 2012, 04:54 AM   #1477
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Quote:
Originally Posted by DF96 View Post
Be careful of causality here. The current through the cap may be the same (apart from charging pulses) as that through the speaker, but neither is set by the cap; both are set by the feedback loop (if there is one, which is usually the case for SS amps). Now if you go 'non-feedback' things get harder, but that is only for people who take pleasure in making life harder for themselves.

If you really can hear the PSU caps in a conventional SS amp then something is wrong: grounding, PSU caps too small, NFB take-off point or ground reference incorrect etc.
Absolutely. The capacitors are passive and should be configured to be transparent and their currents are used to produce the sound and we hear the results of the work done by the currents and hope we don't hear anything that is not due to accurate reproduction of the source signal, as orchestrated by the amplifier that is using the power supply.

But unless the reproduction is ideal and perfect, we actually are always hearing "system effects", which most of us wish to minimize. We hear each component of a non-ideal system, to some degree, which we hope is negligible in every case.

If Daniel could hear an improvement in reproduction accuracy due to a power supply change, then he was first hearing the effect of something being wrong and after the change he was hearing the effect of it being less wrong (assuming his perceptions were accurate and correct).
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Old 17th October 2012, 05:11 AM   #1478
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Originally Posted by gootee View Post
But unless the reproduction is ideal and perfect, we actually are always hearing "system effects", which most of us wish to minimize. We hear each component of a non-ideal system, to some degree, which we hope is negligible in every case.
Exactly, Tom. As a system gets closer and closer to being a "good" system (hah!) I hear 2 characteristics changing: firstly, more and more detail is apparent, the sound picture becomes richer and fuller in all the subtle aspects; and secondly, that fine detail is fully "integrated" into the whole, nothing jars, sounds harsh or irritates - it's always musical, for want of a better word ... these 2 aspects are rarely in alignment in hifi!!

Quite often alterations can bring the first element to the fore, but not the second. The hardest trick is to get both happening together, which means all audible "system effects" are sufficiently minimised ...

Frank
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Old 17th October 2012, 03:51 PM   #1479
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Frank I would agree with the concept of detail or the ability to resolve small a signal in the presence of larger signals.

However, as soon as the power supply modulation increases to similar levels than that of the small signals it not only masks the small signals, but also mixes with them creating new spurious inter-modulation products which could be dissonance and of course fatiguing.
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Old 17th October 2012, 05:56 PM   #1480
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Originally Posted by CharlieLaub View Post
Your implementation of the diodes does NOT seem to be a practical approach, and I believe that the diode drop is reducing the PS rail voltage.
Not as much loss as regulators. However, I do apologize for not showing the "output diodes" as Schottky like MBR1045, or even a fast silicon, like an MR. Credit to diyaudio.com member "TheProf" for that idea. This is not intended for every power supply in every application. Let's not lose sight of the target. Remember, the application had a near zero length umbilical cable and possibly borderline size transformer.
However, if the transformer is about watts*3=va and the umbilical cable is long enough to even the odds, then the "power board output diodes" would be useless except for minor stereo separation enhancement.
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