Sound Quality Vs. Measurements

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And that's basically what I was looking for. ;)

For some reason when you ask for a rule of thumb or general practice, people fly into a fit and want to hit you over the head about "no Magic Answers" or "You can't generalize" or some such. Sheesh..... All I wanted to know is if anyone had noticed a relation between energy stored/output power and sound quality. (Sound Quality vs Measurements). It appears that no one posting here thinks in those terms, fair enough. Tho we can see that someone at Motorola did.

FWIW, many deluxe amps have much more than 1.5 joules per 10W. Is it just overkill?

Indeed? Please give one or two examples of having more than 1.5 Joules/10W and we can try to find out if that's an overkill.

Theoretically, as you add more and more capacitance, at some point you will reach a state which would equal full electonic voltage regulation, even if that point would, pricewise, be higher than with electonics. I mean in terms of effects - quite simply, your nominal power output into say 8 and 4 Ohms would not cause any appreciable voltage drop (sag) of the powers supply lines. I fear that would cost you a pretty penny indeed, but it is possible.
 
I beg to differ a little . Say whatever maximum current will be . Times it by 1.5 for safety . Job done . The manufacturer will give the ripple ratings . Then add caps as your ears require . I would admit that the currents that might be required baffle most of us . Would anyone like to say ? Lets talk daft speakers and stupidly high wattage's ( 1 ohms 600 W ) . One problem is that the big amps draw current at the crest of the sine wave . Sometimes the caps hardly get a look in . My friends in the PA world use 3 phase power as it helps replenish the caps more often . They find there comes a time when no matter how big the caps are 3 phase does it better .

A quick, sure fire way to bankruptcy, Nigel.

On a per item basis, NOTHING in an amp is as expensive as capacitors.
 
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.

I beg to differ.

Measuring say THD and/or IM at say 0.001% under worst case conditions is going down to academic values. I honestly see no point fighting now to make that 0.000,9%. That's just making the inaudible even more inaudible.

In my book, that is simply brainless. I prefer to stay on this side of sanity.
 
I beg to differ a little . Say whatever maximum current will be . Times it by 1.5 for safety . Job done . The manufacturer will give the ripple ratings . Then add caps as your ears require . I would admit that the currents that might be required baffle most of us . Would anyone like to say ? Lets talk daft speakers and stupidly high wattage's ( 1 ohms 600 W ) . One problem is that the big amps draw current at the crest of the sine wave . Sometimes the caps hardly get a look in . My friends in the PA world use 3 phase power as it helps replenish the caps more often . They find there comes a time when no matter how big the caps are 3 phase does it better .

Are you calling my speakers daft .. :)

Ok , they are , but the sound isn't , my findings , too much hurt the top end , too little muddies the sound , so I agree with John , there's no set formula, now how do we combine the two ..?

Ohh.....

Battery power kills dynamics , been there done that .....!
 
Bigger is better. :D

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."
 
I thought I did yesterday. See this post:
https://production.diyaudio.com/community/index.php?posts/3070031/

Or am I not understanding Motorola's 1.5 joules/10W? I see that as 0.15 joules per output watt.

You may have missed my response.

Karan uses balanced ciruitry, meaning he has two complete small power amps driving the output "+" and "-" side in tandem. His actual supply voltages are much smaller that way. I never took the trouble to measure them.

BTW, for the op amp haters, he uses BB 2604 op amps for just about everything, including his power amp input stages. So there! :D
 
dvv said:
Measuring say THD and/or IM at say 0.001% under worst case conditions is going down to academic values. I honestly see no point fighting now to make that 0.000,9%. That's just making the inaudible even more inaudible.

In my book, that is simply brainless. I prefer to stay on this side of sanity.
I agree. Someone said that we should add caps until ripple is too low to measure. I was just pointing out that 'too low to measure' is not a meaningful criterion. You are saying that is not a useful criterion either. So I think we agree.

SY said:
Of course this is engineering, not "design."
Yes, although I would add a requirement for sufficiently low ripple IM in addition to sufficiently low ripple. The two are obviously related but are not the same thing.
 
Yep, that puts it much lower than I thought, and more in line with the Motorola spec.
Surprising how much capacitance it takes to get there.

A lot!

Consider. I will be using +/-56V rails for the output section. It's the only one which will be running from, as John put it, raw DC, i.e. capacitors only.

Using Motorola's formula, I should use 22,000//10,000 uF, for a total of 32,000 uF per line, or 64,000 uF per channel. With my voltages, that's almost exactly 50 Joules per side.

For my nominal goal of 200 WPC into 4 Ohms, that's 2.5 Joules per 10W of dissipated power, more than enough to keep a stiff upper lip with just about ANY nominally 4 Ohm speaker out there.

And quite enough to ride out almost any impulse output into 2 Ohms or a bit less for the 40 miliseconds it needs until the current limiting kicks in at 1.8 Ohms.

However, that's a total of 128,000 uF for a nominally 100/200 WPC into 8/4 Ohms amp. Not at all a common figure, the industry is happy with just one pair of 15,000 uF feeding both sides (e.g. Yamaha AX 592 integrated).

But also not an unprecedented figure. Studer/reVox's A740 power amp from 1975 (or so) was also a nominally 100/175W into 8/4 Ohms, and used twin 33,000 uF caps per channel, with three custom packaged pairs of Motorola 250W devices per channel.

I wish I could lay my hands on a sample, and they are very rare, so even if you run into one, it will be rather expensive even on e-bay or its clones.
 
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