Transient Attack and Amp Design

Hi Steve, I think there is plenty of evidence out there to support your position regarding smaller caps!

Steve, at the risk of gushing, I am honored that you have responded to my thread. Kudos on an outstanding, musical amplifier in the DNA-1.

In the old Stereophile review (noted above in this thread), your DNA-1 design is noted for its treatment of distortion spectra. Here are JA's comments:

The Test CD also features signals with distortion spectra representing "tube"-type THD, "solid-state"-type THD, and a mixture of harmonic and subharmonic distortion typical of a planar speaker driven at high levels. My experience with generating the signals for the disc using the Audio Precision System One Dual Domain suggests that the situation is more complex than RH describes. While the DNA-1 does have some upper partials present, these are not isolated but are accompanied by the lower partials in an almost regular descending series. This is typical of tube amplifier performance, tending to sound smooth and "fat" rather than grainy.—John Atkinson

I suspect, but have not read, that you have departed from the "tube" distortion spectra approach in your later designs, notably the DNA-500. Is this so? If so, would you please comment as to your reasoning?

Alamrg

Inductance of 1 foot of straight wire is not 15nH. According to this calculator:
www.consultrsr.com/resources/eis/induct5.htm
it is between 330nH for 0.1" Dia to almost 500nH for thin wires.

Large capacitors have large inductance. Bypassing them with film caps creates parallel resonant circuit (inductance + lossless cap) that tends to ring. It is always better to use bunch of smaller caps in parallel to further reduce already smaller inductance and to lower resistance (ESR).

There are better quality caps like slit foil type (used in Hypex kits - very expensive) where foil has cuts to prevent eddy currents and to lower inductance (losses).

Power supplies require large capacitance because they are unregulated. Regulated SMPS running at 100kHz is fast enough to response to any current demand at 20kHz in spite of small capacitors.

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