I really hope people reading about my "LED incident" do not conclude that LEDs should be avoided. Not at all. I use plenty of them in my devices but they are mounted in steel/copper cases (not hanging outside the box 
) and there is no real reason to think they do any harm to audio.
chrissugar
) and there is no real reason to think they do any harm to audio.chrissugar
Jack Bybee, he knowns me, he knows I'm right
I've been talking to Bybee, all my life...
Gerhard
for more:
Genesis - Jesus He Knows Me (1991) - YouTube
They even have the Bentley or sth. like that
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It might have helped if John had said why he would have used two resistors for the LED he didn't fit. He mentioned power supply imbalance as a 'problem'. The LED wires acting as an RF conduit only got a mention later, after chrissugar introduced his story about a particularly severe EMC situation. Why does John love to be mysterious?
A forward-biased LED will need an awful lot of RF to disturb it, like any forward biased diode. Even an unbiased one needs more than a normal diode, because of the higher turn-on voltage. Some people have experimented with using LEDs instead of Schottky diodes for high-level balanced mixers, because they can better cope with RF power. I suspect it is the wires and not the LED which are to blame.
A forward-biased LED will need an awful lot of RF to disturb it, like any forward biased diode. Even an unbiased one needs more than a normal diode, because of the higher turn-on voltage. Some people have experimented with using LEDs instead of Schottky diodes for high-level balanced mixers, because they can better cope with RF power. I suspect it is the wires and not the LED which are to blame.
You are pulling the rug under the feet of some people here.
Some people here have a vendetta – condemning everything and everyone who, to their view, addresses things which are outside what they consider as 'good engineering'. When they are confronted with aspects which aren't included in what they consider as 'good engineering', they attack.
The diode's bias doesn't eliminate RF on the diode's return from polluting the 'ground' of the PSU and thus the entire amp.
Possibly, as much as possibly RF presented at any point of the amp's 'ground' will have the same negative effect.
The problem was caused by the fact that there was a LED in the front of the speakers, outside the faraday cage. The fact the RF entered the amp through the LED's wires is a side issue, it is obvious – the LED didn't produce RF pollution, it only enabled RF entering the amp, via its' wires.
I'm cynical about your professed level of audio knowledge and understanding.
Look at the human hearing mechanism.
Then consider that the minutest change in the most minute aspects of transient function is the single core component of signal that the ear utilizes and decodes.
Thus, every bit of what the signal does in order to get to that point where the transient is supported and 'placed exactly and correctly as it must be in time, shape, and level', all of it becomes critical.
Ultra critical, down to the micro level, in relation to another given micro level ....and in relation, on the micro level, to all the macro level that needs to be, at minimum, as correct.
Look at how an LED deals with transient function, regarding V and A and see what it reflects back to the power supply.
And if any sort of feedback regulation, or feedback of any kind is used, then said feedback it is chasing the horse AFTER it has left the barn and thus is over correcting a mistake, into being another mistake. specifically with respect to those all important micro levels.
Then, those micro levels are slewed in time and level, and thus the ear hears them as as a separate and elevated noise, and among the less aware, they will confuse this with detail information. When it is actually..distortion. (depending on the aspects of the correction, it might be interpreted as a lack of information and/or darkness)
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