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Old 20th September 2012, 11:18 AM   #1291
fas42 is online now fas42  Australia
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Originally Posted by danielwritesbac View Post
Perhaps one does not get stunning clarity and epic soundstage without coming to similar/same conclusions as Ott does in his book?
My "thing" (hahh!!) is that you can get perfect sound by having a perfect system ...

Definitions:

Perfect sound - no audible deficiencies, sounds as least as good as the "real thing". Throw any DBT at it, whatever, never fails to satisfy ...

Perfect system - enough problem areas have been investigated, sufficient weaknesses eradicated, all the tricky, subtle things that a lot of people miss, have been dealt with to an adequate level

So endeth the lesson for today, , ...

Frank
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Old 20th September 2012, 12:58 PM   #1292
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Originally Posted by fas42 View Post
Of course not possible, I was just quibbling with the term, "desired impedance" - this should just be as small as possible, or else do the design and simulation work to find out how much you get away with it not being "perfect", i.e., zero ...

Frank
Frank your right my choice of words could have been better.
How about maximum impedance resulting in modulation of the amplifier output to less than audible levels.

I still claim that its this "less than audible levels" that is difficult to define. I don't know how one can do "design and simulation work" without defining this.

In my opinion the digital world is a good place to compare and take from. The techniques used there are just analog designs to maintain this impedance below some defined required level. We don't have to go as far (GHz range) and use all their measures (multilayer PCB's with "predetermined" amounts of embedded plane capacitances, multiple vias in pads etc).

The point is these digital designs start with defining the required impedance. It is not easy but using analog models for their switching and driving effects, in conjunction with meeting the components noise margin a required impedance curve can be derived.

When looking at impedance peaks especially with low esr and esl components the interconnect parasitics can't be ignored. My experience is there is much more damping in a built circuit than accounted for in most simple simulations.

Hope this helps
-Antonio
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Old 21st September 2012, 04:21 AM   #1293
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Magnoman, yep. the literature to look at is "signal integrity". herewith a couple of good ones:

Signal Integrity Characterization Techniques, Resso & Bogatin
Signal & Power Integrity Simplified - Bogatin
Digital Signal Integrity - Young
Signal & Power Integrity in Digital Systems - Buchanan

the last one is not the greatest book (its clearly a copy-n-pasta book) but has the advantage of being almost free - my 2nd hand copy cost me < $5 ($30 to ship to NZ though)
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Old 21st September 2012, 06:47 AM   #1294
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Default Reciprocity failure

Paralleling 2 caps cuts the inductance in half and that's an excellent idea for less noise other parts of an audio circuit, but did not help the individual units make less noise and did not make the caps charge at precisely the same time, since they're not quite perfect. SO how many caps can you parallel before reciprocity failure occurs turning the good idea to bad? Same question as how many slightly different noises can we stack before the slight differences add up to awful?
Ah, practicality invades.
The earlier idea of a horde of 1000u caps directly at the outputs of an audio amplifier board, was a good idea with the very worst dullest performance. Well, we're going to need to revise that to a smaller number of bigger caps, but then the question of how many persists.
How many noises are tolerable?
How many noises are needed?
Symmetrically and considering several larger values, I've guessed six as a rough estimate for the maximum number of caps that should be in a paralleled grouping, although more caps/groupings could be added with the separation of a long trace, a cable, a diode, or a resistor. However, the Real number of caps that can be paralleled before the good idea turns bad, will vary depending on the model and value of cap.
But, do we have a rule of thumb for it?
Maybe a guideline? Something simple?
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Last edited by danielwritesbac; 21st September 2012 at 06:49 AM.
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Old 21st September 2012, 02:27 PM   #1295
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Daniel,
There you go using those big words again, reciprocity.....

Point well taken though, that is why I poorly asked the question what the limit was in adding N number of small caps together to equal the equivalent capacitor values we are looking at. How did you settle on the number 6 as the upper limit though, experience or just a gut feeling? This subject like others has many factors taken together that can become N to a power more difficult when we look at the entire picture.

Steven
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Old 21st September 2012, 02:45 PM   #1296
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The idea of reciprocity occurs in some electromagnetic and network theorems. I don't know if any of them involve paralleling lots of capacitors. I suspect he meant a different big word. Monotonicity, perhaps?
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Old 21st September 2012, 03:52 PM   #1297
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Reciprocity failure means, wasn't re-scalable indefinitely. For example multiply a cookie recipe to make a far larger batch of cookies, and then get surprised that they're quite weird and really flat. It can also mean when the inverse square law doesn't work as expected when at the extremes of supposedly linear photosensitive materials, and the term is most commonly seen when push processing film or using non-standard temperatures for bulk processing speed. In any of that, multiplying was going on, but there was a hidden difference included that got multiplied by a different proportion and made for poor results. For 20 parallel 1000u caps, the hidden difference is the manufacturing variances now awfully multiplied 20 times despite the assumption of perfect and there's dull audio consequences.
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How did you settle on the number 6 as the upper limit though, experience or just a gut feeling?
I was looking at historical data and many different power supplies to find the amounts of parallel caps that support real examples. But, due to variable manufacturing tolerances of caps, a generally six parallel max is an unreliable estimate because it could be more for tight tolerance caps or less for looser tolerance caps. The more differences between individual caps, the more bad news we get and none are perfectly identical. It is perhaps, just a clue that if we're thinking of exceeding six for assuming perfect caps in parallel, then it may be time to do something better instead, with real components. I'd like for someone to propose a more accurate way to estimate.

Earlier, I was talking about a range of 2, 4, 5, or 6 same model parallel caps larger than 1000u (I meant in the range of 2,200u to 10,000u with a total range of 4,400u to 60,000u). Just notice the largest scale example is 60,000u and the transformer purchase was a fail if that isn't enough capacitance and so adding more caps is not needed, but rather the right size transformer could do a lot better.

And, earlier, I was asking a question.
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Last edited by danielwritesbac; 21st September 2012 at 04:04 PM.
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Old 21st September 2012, 04:34 PM   #1298
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Reciprocity failure is a term from photography, about exposure derived from aperture and time. When you parallel lots of caps you get the benefit of the Central Limit theorem which means that the result tends to the mean. Variations are not multiplied but diluted.

When anyone describes sound as 'dull' then I sometimes wonder "does he mean accurate?". However, in this case dullness could perhaps come from the extra inductance from all those extra cap connections.
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Old 21st September 2012, 04:55 PM   #1299
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Quote:
Originally Posted by DF96 View Post
When you parallel lots of caps you get the benefit of the Central Limit theorem which means that the result tends to the mean. Variations are not multiplied but diluted.

When anyone describes sound as 'dull' then I sometimes wonder "does he mean accurate?". However, in this case dullness could perhaps come from the extra inductance from all those extra cap connections.
If it is subtractive and in both cases, there seems to be, instead of 20 noises, there's 20 reference failures, in which case, it could be possible to select a "just right" bypass cap to restore the HF performance of the cap bank.
Do you think so?
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Old 21st September 2012, 05:18 PM   #1300
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As usual, I have difficulty translating your posts into the language of conventional circuit theory. If what is "subtractive"? "20 noises", "20 reference failures"?

Adding a bypass cap to a circuit with too much inductance could make things worse, unless enough damping is present. As others have said, the cap bank itself is not always the best place for any bypass. The outcome depends on many things, including the detailed layout.
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