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Old 25th June 2012, 03:57 AM   #6391
popilin is offline popilin  Argentina
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Quote:
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Originally Posted by DF96 View Post
Not necessarily. Motorola were mainly hard-headed engineers, so it is very likely that their rule of thumb was derived in the way I explained i.e. the criterion was not 'sound quality' but x% droop in 10 ms (or 8.33 ms in US). This could be regarded as a ripple calculation, but ripple calcs usually assume full power sine-wave; I assumed full power square wave.

If your amp has good PSRR (including low power supply IM) then it may be the case that there is nothing more to be said: low enough ripple guarantees good enough sound. When people try to explain anything further they usually quickly fall back on myths and legends rather than genuine explanations. Now it may be that we don't know how much hum is low enough, or how much ripple IM is low enough, given that we can't have zero of either unless we use battery power. 'Too low to measure' is meaningless, as you can always measure lower if you try a bit harder.

Exactly.

My rule of dumbs is to design power supply according to sag and ripples that I can tolerate on max RMS power infinitely long. The same rule applies to power dissipation, both in power supply and output components, passive and active. Hi-fi designers usually assume short period of time for peak power levels, so they downsize power supplies, heatsinks, output components, also they assume that all channels can't work at once on full power. However, it is wrong, that's why amps with bigger power supplies tend to sound better. But let me repeat, it is not because bigger is better. It is because not enough is worse than enough.
Thank you very much to both of you, now I'm just dumb, but a little less ignorant.

From this side of the world, I propose nominees for "the gold electron prize" of the week.
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Old 25th June 2012, 04:38 AM   #6392
popilin is offline popilin  Argentina
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If you like higher ripple currents, sure. This is another audiophile legend, I'm afraid, one to which I succumbed for many years until I started looking more carefully at what was actually going on in the power supply. As well, adding capacitance until there's no more ripple (whatever "no more" means) is an invitation to make the overall system noise performance worse.

Maybe I'm just a nutcase, but the more sensible approach seems to be to specify the required noise level at the amp output, and knowing the power supply rejection of the signal circuit, work backward to see what acceptable ripple is. Then design the supply for something lower than the maximum acceptable ripple, but not too much lower in order to keep ripple current to a minimum.

Of course this is engineering, not "design."
OK, you're also nominated, but not get too excited, the prize is just symbolic, I have less of that gold in my wedding ring.
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Old 25th June 2012, 07:46 AM   #6393
dvv is offline dvv  Serbia
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I have some logic issues here.

I was led to believe that NOBODY in their right mind listens to steady state sine waves at full power for hours on end. Therefore, a full power operating mode is by deafult intermittent, unless our objective is to fry our speakers with the first few transients which come along.

After 40+ years of listening to music, I have never encountered a situation in which there were several large peaks inside of say 1 second, or 2 seconds.

Therefore, it seems to me that my amp will in fact be working at least 6 dB below its maximum power in any steady state mode. And even that is cutting it close, but never mind. We use very powerful amps in order to have the first say 25 Watts of power as clean as possible, the rest is just reserve for peaks.

I may have been misled in my beliefs by the logic of DIN 45500 standards, which defined "music power" as power capability with suddent peaks, 1 in 16 cycles, wihtout distorting more than 3% of THD. Meaning that you run your amp at nominal rated power and see what it does when 1 in 16 time intervals requires more. Hardly a perfect test, but far from being stupid either.

We tend to shy away from the fact that our AVERAGE DISSIPATED CONTINUOUS POWER is way below our absolute power capabilities probably because we have no way of knowing what might that be in any "average" situation and because we know all of the factors which come into play. It's effectively impossible to know in general terms, but I think it's safe to assume most folks are at around -10 dB mark or below, unless they purchased an amp initially too weak for their needs (in which case it's not our problem any more).

If so, then we need to design our power supplies so that they can respond to our real world needs, not theoretical models from a lab, and we can design these at will, the sky's the limit.

In that respect, industry designers are better informed than we are, even if they generally still tend to undersize for cost reasons only. Not defendinding anyone here, mind you, just noticing.

I think this discussion has moved on to theoretical grounds a little too much - we keep talkning as if we are about to run our amps into a 2 Ohm load with a -60 degree phase shift steady state all of the time, and for hours on end. All the time knowing that this will never happen.

Let's get down to planet Earth once again, shall we?

Nigel already has. I've followed him through evolution from a steady state 1 Ohm load driving capability to impulse capability - a reasonable move, as I see it, since beside Wayne's 1 Ohm speakers, I have never even heard of anything going that low, I mean, 1 Ohm is practically a short circuit. Sure, you can design for it, no doubt, but be ready not to faint when you work out the price of that baby. It's not going to be gentle.
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Old 25th June 2012, 11:02 AM   #6394
SY is offline SY  United States
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Originally Posted by dvv View Post
After 40+ years of listening to music, I have never encountered a situation in which there were several large peaks inside of say 1 second, or 2 seconds.
...

I may have been misled in my beliefs by the logic of DIN 45500 standards, which defined "music power" as power capability with suddent peaks, 1 in 16 cycles, wihtout distorting more than 3% of THD. Meaning that you run your amp at nominal rated power and see what it does when 1 in 16 time intervals requires more. Hardly a perfect test, but far from being stupid either.
Like most standards, it's a Procrustean bed. Unfortunately, real world source material is not made to DIN standards, and the increased use of compression has made things worse. THD is far less relevant than recovery from overload (e.g., blocking in cap coupled amps, "sticking" to rails in DC amps) and modulation of the signal from the increased ripple components and sag from the power supply.
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Old 25th June 2012, 11:11 AM   #6395
DF96 is offline DF96  England
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Lots of words have been used, but we basically still have three criteria, in descending order of uF:
1) use as much capacitance as you can afford, (with some adding "but not too much"),
2) get the ripple sufficiently low on continuous full power signals,
3) with real music you can get away with less than (2).

So far, only (2) and (3) have had engineering explanations and only (2) has the benefit of a calculation. A calculation for (3) would be like that for (2), but with the addition of something relating to duty cycle or music dynamic statistics.
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Old 25th June 2012, 11:42 AM   #6396
Pano is offline Pano  United States
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Originally Posted by dvv View Post
We tend to shy away from the fact that our AVERAGE DISSIPATED CONTINUOUS POWER is way below our absolute power capabilities probably because we have no way of knowing what might that be in any "average" situation and because we know all of the factors which come into play.
Please follow the link in my sig line.

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So far, only (2) and (3) have had engineering explanations and only (2) has the benefit of a calculation.
But it has not, so far in this thread, had the benefit of a precise number. We just say low enough ripple or quote some percentage. How do we determine what that is? How much ripple is good and how much is bad? Is the criterion "Not audible on my speakers at the listening position", or something else?

At some point we have to set how much ripple (or other fault) is acceptable to us, or to those who buy amplifiers.
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Old 25th June 2012, 11:48 AM   #6397
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Originally Posted by Pano View Post
a curve
Berendsen in Germany still offers a 150W stereo power amp type in two versions ; a regular with 60.000uF and a Special Edition with 100.000uF capacitance.
Back in the late '80s, early '90s, i audited their monaural Blue and Red editions on different loudspeakers.
Red or Blue was not distinguishable on an easy loudspeaker, the trickier loudspeaker model favored the pumped up Red brigade.
The thought process of the DIY’er

Interesting (to me) still are the geographic preferences ;
High VA/W numbers in the US, with a relatively large uF bank, e.g. Parasound amp models.
UK designers who favor soft powersupplies, relatively low size capacitors (and Nigel is unmistakenly British ).
Powersupplies as rigid as a tank, with steep electrolytic size, in the Germanic region.
Ultimately it's still the amp circuit that's the key factor.

The Marantz MA24 monaurals (Philips production) and Accuphase P102 from the 80s/90s are both Class A power amps.
Marantz does a nominal 60W, but was conservatively rated, the balanced design Accuphase produces 80W in 4 ohm.
Cost about the same at the time, have close to identical size power supplies, both 2 times 22.000uF and a similar size toroidal per channel (Marantz >3.5 J/10W for 4 ohm).
The Philies beat the Accuphase hands down, doubling the powersupply in the P102 wouldn't make it the winner.
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Old 25th June 2012, 11:51 AM   #6398
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We just say low enough ripple or quote some percentage. How do we determine what that is? How much ripple is good and how much is bad? Is the criterion "Not audible on my speakers at the listening position", or something else?
See post 6374.

FWIW, in my own gear, I design to a "lower than the noise floor from 16 bit source material" standard. But that's an individual choice, not a "rule."
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Old 25th June 2012, 11:58 AM   #6399
Pano is offline Pano  United States
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See post 6374.
Do you mean - "to what accuracy" ?

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FWIW, in my own gear, I design to a "lower than the noise floor from 16 bit source material" standard. But that's an individual choice, not a "rule."
That seems like a logical choice. Maybe not so easy to achieve, tho.
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Old 25th June 2012, 12:00 PM   #6400
SY is offline SY  United States
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Maybe not so easy to achieve, tho.
I manage, and I'm just a rank amateur.

I should qualify my statement- for a phono stage, I aim for within 1dB of cartridge thermal noise.
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