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Transient Attack and Amp Design

I have observed with my new McCormack DNA-1 Deluxe (CJ Rev. 1 upgrade) that the transients are significantly better than my previous amps. Everything from classical, rock, and jazz has, for lack of a better term, better rythm and transients. (Granted, I have only owned mid-fi amps like Marrantz, Rotel, and Sunfire.)

I was wondering if the McCormack amp design explains the reason. It has eight caps on each output board instead of just one large cap for each channel. Maybe that means there is just more storage capacity? In any event, the amp is a heck of a lot more responsive than what I have heard in the past.

Is the multi-cap board topology more conducive to better transients or is this benefit dependent on the skill of the amp designer regardless of board layout?
jragsda

Showing 3 responses by almarg

almarg's avatar
almarg
9,670 posts
 
There are innumerable design variables that could relate to the good transient response you have noted. And we wouldn't have adequate visibility into most of them without at least having schematics and other detailed design documentation on the amps being compared.

If you haven't seen it, you'll be interested in this review of the DNA-1 that appeared in Stereophile in 1992. Robert Harley had observations about its transient response that were very similar to yours:

http://www.stereophile.com/solidpoweramps/520/

Regards,
-- Al
almarg's avatar
almarg
9,670 posts
 
Now does the transistor proximity to the storage cap(s) make a difference?

Atmasphere can speak to that more knowledgeably than I can, but I don't think that would make a significant difference. The concern would not be propagation delay (which would be a few nanoseconds at most, as you speculated), it would be that the inductance of the wiring or printed circuit board traces between the capacitors and the output devices would slow the transfer of energy.

But I don't think that would be a significant effect either. As a very rough ballpark the inductance of one foot of straight wire is around 15 nanoHenries, which would have an impedance of about 2 milliohms even at 20kHz, and much less at lower frequencies. The numbers would be somewhat different if printed circuit board traces were involved, rather than discrete wiring, but I would think they would still be totally insignificant.

What would be of potentially greater significance would be noise pickup on those runs, but that is presumably filtered out by much smaller decoupling capacitors (that have much better high frequency performance than electrolytic storage capacitors), which should be and presumably are located very close to the point of use in the output stage area.

Regards,
-- Al
almarg's avatar
almarg
9,670 posts
 
Kijanki -- Gee, that's the same calculator that I used! Playing around with it a little more, it looks like I must have set the units to mm instead of inches, to get the 15nH or so, although I thought I checked myself pretty carefully on that. In any event, thanks for the correction. Even at 500nH, though, the impedance would still be essentially negligible at audio frequencies.

Good points about the possibility of parallel resonant circuits, ringing, etc. Thanks!

Regards,
-- Al
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