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Old 20th March 2012, 11:32 AM   #3801
dvv is offline dvv  Serbia
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@gootee

You may be interested to know that Dan d'Agostino uses a LOT of 47 uF capacitors to decouple his rails everywhere. I haven't counted them, but off hand, I'd say no less than 10 or more per rail, in addition to smaller value caps. The main PSU uses 6,800 uF caps in parallel, if memory serves, three in parallel per each rail. But, given the fact that EVERYTHING is electronically regulated, and that his supply lines are rather high, even those seemingly not-too-big caps in fact provide a LOT of energy storage when added up.
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Old 20th March 2012, 12:01 PM   #3802
dvv is offline dvv  Serbia
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In a design note from Motorola, I think the one in which they propose two power amps, there's a good sideline on how to calculate your capacitor requirements.

Not scientific, more a rule of the thumb, but most useful nevertheless.

Essentially, they say that experience has taught us that we need 1...2 Joules of energy for every 10 Watts of dissipated power, depending on how complex and demanding the load is.

So when Wayne () sits down to work it out, he can easily "double down" as he pleases. Since one knows what the rails will be, and assuming we use plus and minus rails, PER RAIL capacitance can be worked out using a simple formula:

Joules = (V+ x V+) Farads

If my rails are +/- 50V, and I use 10,000 // 10,000 uF // 3x2,200uF for each device, I can have:

(50 x 50) 0.0266 = 66.5 Joules

good enough for 332.5 Watts into an evil load dmanind the maximum from the amp, to 665 Watts into a pristine clean and easy load.

Over time, this formula has shown itself to be very true indeed.

Obviously, it applies to the power supply only, for this to REALLY happen in REAL life, you also need beefy power tranformers, powerful rectifiers and an amp output stage capable of actually delivering this kind of power.

For power amp transformers, again there's a rule of the thumb - use as many VA in the transformer as you want watts out. If you want a 2x150W amp, minimum transformer value should be (2x150)2 = 600 VA for a stereo amp.

Not scientific, but hey, it works.
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Old 20th March 2012, 12:06 PM   #3803
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Quote:
Originally Posted by ThorstenL View Post
Hi,



With respect, having HD content at -90dB in an Amp also has no other effect than self satisfaction. Despite repeated requests by me you have not offered anything that demonstrated either that such low levels of HD reliable produce "good sound" or indeed that such low levels of HD can be delivered to the listner using any available speaker...

Ciao T
Yet it has also not yet been demonstrated that amps with large THD sound or low or no feedback sound better, in fact there are more hi end amps demonstrating very low THD and higher feedback winning awards than the other method........ makes one think
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Old 20th March 2012, 12:08 PM   #3804
Previously: Kuei Yang Wang
 
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Dejan,

Quote:
Originally Posted by dvv View Post
The only problem here, Thorsten, is that commerical devices with small caps usually also have small transformers - NOTHING like the Goldmund. Then again, for one Goldmund, you could buy like 10+ of such devices.

Let's not mix cranberries with watermelons.

Which is why you plan to use 144,000 uF instead of 13,600 uF.
There are two issues here.

One is the evidence that low value power supply capacitors limit power delivery (they do not, undersized mains transformers do however).

The other issue what I personally, as supposed High End Guru and merchant of questionable (according to some) audio ideas, concepts and devices plan to do for myself. I mean they'd revoke my High End Guru licence if I made the Amp with a 250VA Torroid and 4 * 4,700uF, even if it did deliver 180W into 8 ohm (one channel) and was adequate with music...

Less tongue in cheek, as a rule (I have yet to find exceptions), there are no limits up to which one may increase PSU capacitance AND power transformer size (other than practical/monetary), with some benefit. Though at the levels I intend to use we are already pretty far past the point of diminishing returns.

Then again, there is something to an amp that runs of eight stacked 12V SLA Batteries (for +/-48V) that is hard to get with mains powered amp's...

Ciao T
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Old 20th March 2012, 12:14 PM   #3805
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by dvv View Post
Since one knows what the rails will be, and assuming we use plus and minus rails, PER RAIL capacitance can be worked out using a simple formula:

Joules = (V+ x V+) Farads

If my rails are +/- 50V, and I use 10,000 // 10,000 uF // 3x2,200uF for each device, I can have:

(50 x 50) 0.0266 = 66.5 Joules

good enough for 332.5 Watts into an evil load dmanind the maximum from the amp, to 665 Watts into a pristine clean and easy load.

Over time, this formula has shown itself to be very true indeed.
As I happen to have 36,000uF per rail and 56V rails it would seem I'm well past that (twice actually). So I should be fine for 665W into a nasty load, which is probably quite nice for an Amp I'd call notionally 150W... Maybe my mains transformer is a wee bit undersized.

Ciao T
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Old 20th March 2012, 12:18 PM   #3806
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by homemodder View Post
Yet it has also not yet been demonstrated that amps with large THD sound or low or no feedback sound better, in fact there are more hi end amps demonstrating very low THD and higher feedback winning awards than the other method........ makes one think
Well, first, there are by far fewer Amplifiers of (for example) the SE DHT no-NFB variety and Sturgeons rule applies. So the statistics you quote do not help us much.

As to: " it has also not yet been demonstrated that amps with large THD sound or low or no feedback sound better", I think the solution for everyone is to go and listen. We must also realise that we do not listen amplifiers, but to whole systems.

Ciao T
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Old 20th March 2012, 12:31 PM   #3807
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Quote:
Originally Posted by DF96 View Post
Unless your waveform contains an infinite number of finite discontinuities or any infinite continuities you can use Fourier and it will perfectly preserve the waveform. All music waveforms are bandwidth-limited (if only by the microphones) so have no discontinuities, therefore a Fourier transform fully contains the information in the waveform. Whether this is useful or not is a different issue, because a problem is best tackled in the way which works best, but let's not have any loose talk about Fourier not capturing things like envelope. It might not do it in a useful way, but it does do it.
Music waveforms are non-periodic. Fourier transform, strictly speaking, can not be applied to non-periodic functions. But it is nevertheless applied, with definite degree of accuracy. A devil is in the limitations of its applicability. For some cases limitations are not essential, but they are essential for exploring audio perception.
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Old 20th March 2012, 12:51 PM   #3808
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Quote:
Originally Posted by ThorstenL View Post
Hi,



Well, first, there are by far fewer Amplifiers of (for example) the SE DHT no-NFB variety and Sturgeons rule applies. So the statistics you quote do not help us much.

As to: " it has also not yet been demonstrated that amps with large THD sound or low or no feedback sound better", I think the solution for everyone is to go and listen. We must also realise that we do not listen amplifiers, but to whole systems.

Ciao T
I take my stats from reading about 15 audio publications from tubes to solid state, a lot of the facts about the circuits are unknown to the writers of these so they just state the little the manufacturer tells them.

The 2 best amps I have listened to are on opposite sides of the fence. One a french amp with very high feedback Lavardin (more so then usual) and one with fairly low NFB a electrocompaniet monster I own. Each one has its stronger and weaker points but I cannot say that one or the other sounds better because of the amout of feedback used or their THD figures.
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Old 20th March 2012, 12:56 PM   #3809
jcx is offline jcx  United States
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not true as engineers know - yes the math is a little more complex to satisfy pure mathematicians but can still be made to work for bandwidth and time limited continuous signal representation

the simple gedankenexperiment version: for recorded music we can just loop the recording - instant "infinitely periodic" signal to analyze

Windowing functions are well studied - you can calculate the time domain "flitering" loss - can be way below real signal thermal noise, beyond recording microphone bandwidths

the time series and the full complex Fourier repesentaion of a Digital Audio signal are exact Duals - no information is lost in the conversion from one ot the other (finite rounding errors can be made small by working with long enough wordlength)

sorry for your "conspiracy theory" - but engineers do test, verify, use tools that really do work with real world signals, electronics - just how do think the 3 Mbaud DSL signal is made to work over voice telephone twisted pair??

by a million mathematically illiterate monkeys with soldering irons?? – that’s more the DiyAudio “just try it” version


(a little overlapping editing - SY has given the example before - its still a good example to "debug" your "nonperiodic" signal objection without heavy math)

Last edited by jcx; 20th March 2012 at 01:09 PM.
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Old 20th March 2012, 12:58 PM   #3810
SY is offline SY  United States
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Quote:
Originally Posted by VladimirK View Post
Music waveforms are non-periodic. Fourier transform, strictly speaking, can not be applied to non-periodic functions.
Actually, it can. Any function of finite duration can be made periodic without changing the physics. For example, let's say I want the frequency spectrum of Roland Kirk's performance of Seranade to a Cuckoo. It's 4:32 long. Call the time domain function SC(t). The boundary conditions are SC(0) = SC(4:32) = 0, since the song starts and ends. Then put SC(t + 4:32) = SC(t - 4:32) = SC(t). Voila, a periodic function!
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