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Fast, soft recovery diodes

83.49.225.210
Posted on November 1, 2009 at 10:24:38
megalomaniac
Audiophile

Posts: 114
Joined: January 29, 2004
 What is it that makes these diodes sound better?

Is it the REVERSE RECOVERY TIME, or is it the RECOVERY CHARACTERISTIC (soft or hard)?

I have read in some websites that a slower diode may actually sound much better than a really fast one. Is this true?

Thanks for any input.

RE: Fast, soft recovery diodes, posted on November 3, 2009 at 20:20:04
casouza
Audiophile

Posts: 485
Joined: March 18, 2008
 This is not a direct answer to your question, anyway:
Schottky diodes are vastly superior to fast or soft recovery diodes, because esssentially there is no reverse current, therefore no diode-generated RF to pollute the power supply.

Good Schottky diodes are available up to 200 V PIV and hundreds of amperes.
In summary, for solid state circuits, Schottky diodes are the clear choice over fast or soft recovery diodes.

One can get the benefits of Schotttky diodes by using VoltSecond's Schottky tweak, even on high voltage tube power supplies:
http://www.audioasylum.com/scripts/t.pl?f=bottlehead&m=27654

I have performed this tweak on my 845 tube amp's bias, heater and B+ 800V supply, it works magic!

Reduction of harmonic energy., posted on November 1, 2009 at 12:06:42
Al Sekela
Audiophile

Posts: 8279
Location: Northern California
Joined: February 18, 2002
 Junction diodes store electric charge during forward conduction, and this charge is removed in the form of a pulse of reverse current upon reversal of the applied voltage. There are two consequences in mainstream electronic applications (not audio equipment power supplies): the pulse represents an energy loss mechanism in switching power supplies, and the shape of the pulse translates into an RF energy spectrum in applications where RF noise is a concern.

The steeper the trailing edge of the pulse, the more high harmonic content it has, due to Fourier's theorem. Thus, diode designs that minimize total charge in the pulse at the expense of a steep trailing edge will have lower energy loss but generate more RF noise. Designs that tailor the trailing edge to reduce RF noise may waste more energy in switching power supplies.

For audio use, both are still important. The pulses from diodes used as rectifiers stimulate associated power supply parts to ring. The charge magnitude may generate ringing even if the trailing edge is considered 'soft' for other applications. I think one would have to experiment with different available diodes to see which gives the most quiet results.

RE: Reduction of harmonic energy., posted on November 1, 2009 at 23:47:58
Ugly
Audiophile

Posts: 1420
Location: Des Moines, WA
Joined: August 22, 2006
 Couldn't one just use a tuned snubber circuit on the diode that's already there and achieve similar if not better results and avoid all the diode rolling in the process?

Yes, if one has a wide-band capacitor., posted on November 2, 2009 at 14:33:46
Al Sekela
Audiophile

Posts: 8279
Location: Northern California
Joined: February 18, 2002
 The snubber makes sense even with the fancy diode, but all caps have self-resonance frequencies that limit the upper harmonic damping.

Makes sense. n/t, posted on November 2, 2009 at 16:08:53
Ugly
Audiophile

Posts: 1420
Location: Des Moines, WA
Joined: August 22, 2006

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