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Old 24th June 2012, 05:42 PM   #6351
dvv is offline dvv  Serbia
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Quote:
Originally Posted by Pano View Post
I thought I did yesterday. See this post:
http://www.diyaudio.com/forums/showthread.php?p=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!
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Old 24th June 2012, 05:45 PM   #6352
Pano is offline Pano  United States
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I didn't miss it, just didn't understand it, sorry. I guess it's a BTL output, then? Maybe 50V rails?
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Old 24th June 2012, 05:48 PM   #6353
Pano is offline Pano  United States
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Quote:
Originally Posted by SY View Post
Of course this is engineering, not "design."
No, and they can have different goals. Of course you like to make fun of "design", but it does not have to be bad. One could accuse engineering of finding the minimum that will possibly work - for a little while. But it isn't always that bad, is it?
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Old 24th June 2012, 05:49 PM   #6354
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Quote:
Originally Posted by dvv View Post
Karan uses balanced ciruitry
1500VA + 132.000uF per channel.
Rails have to be +/-50V at least.

600W/ch > 2.75 J/10W
(in reality more)
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Old 24th June 2012, 05:52 PM   #6355
a.wayne is offline a.wayne  United States
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Dutchie,

What are you currently running for amplification ....?
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Old 24th June 2012, 05:54 PM   #6356
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Something grey.

(but my TT is half chromed, i'm pretty kitsch myself)
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Old 24th June 2012, 05:55 PM   #6357
Pano is offline Pano  United States
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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.

As point of comparison the first SS class-a amp I built was about 9.5 joules/10W
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Old 24th June 2012, 06:00 PM   #6358
DF96 is offline DF96  England
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Quote:
Originally Posted by dvv
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.

Quote:
Originally Posted by SY
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.
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Old 24th June 2012, 06:02 PM   #6359
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Quote:
Originally Posted by Pano View Post
more in line with the Motorola spec.
Ah, but the Karan top model has a much number.
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Old 24th June 2012, 06:07 PM   #6360
dvv is offline dvv  Serbia
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Originally Posted by Pano View Post
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.

Last edited by dvv; 24th June 2012 at 06:10 PM.
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