Light-emitting diodes use different semicondutor junctions to provide different colors, and each has a different forward-voltage requirement, usually between 1 and 4 volts. The typical red LED requires about 1.7 volts. Semiconductor junctions that provide higher frequency colors require higher forward voltage bias.

The 20 mA red, standard red, are the ones you want. The internal resistance of the specialty red ones is not optimum for Audio use.
regards,
Douglas

What about using a string of regular silicon diodes? I've used them to bias circuits a lot, but the first time I saw an LED used for this was in the CCS on Bottlehead stuff. You get higher forward-bias voltage with an LED than a regular solid state diode but you can sure use a series string instead. I always thought the LEDs were used for effect as much as anything else.

I suspect that the Schotky would be quieterin fwd bias than a Si one would be. Nice suggestion I must say. If I didn't need a 20-30 of them in the new one ( instead of 6 red LED's ), I'e be solderig up a string.
regards,
Douglas

Saw this done this way on the Axiom Amp. Haven't tried it, but it sure looks interesting.

Joe