i always thought the led's color was just a function of the color of the encasement plastic.  if this is so, why do people say the different colors sound different?

also, is there a sonic difference between the 5mm and 3mm sizes?

just curious.

I found this on wikipedia:

Conventional LEDs are made from a variety of inorganic semiconductor materials, producing the following colors:

aluminum gallium arsenide (AlGaAs) - red and infrared
aluminum gallium phosphide (AlGaP) - green
aluminum gallium indium phosphide (AlGaInP) - high-brightness orange-red, orange, yellow, and green
gallium arsenide phosphide (GaAsP) - red, orange-red, orange, and yellow
gallium phosphide (GaP) - red, yellow and green
gallium nitride (GaN) - green, pure green (or emerald green), and blue also white (if it has an AlGaN Quantum Barrier)
indium gallium nitride (InGaN) - near ultraviolet, bluish-green and blue
silicon carbide (SiC) as substrate — blue
silicon (Si) as substrate — blue (under development)
sapphire (Al2O3) as substrate — blue
zinc selenide (ZnSe) - blue
diamond (C) - ultraviolet
aluminum nitride (AlN), aluminum gallium nitride (AlGaN) - near to far ultraviolet (down to 210 nm[3])


Although I never use LED's for clipping, so I don't have any expierience with  them, I can imagine there are tonal differences when using different colors,
considering the different materials used.

Quotealso, is there a sonic difference between the 5mm and 3mm sizes?

Don't know 

André

hmm.  so it would seem that you would have to know the source material in order to nknow if the different color would sound different.  there are several materials that make both red AND yellow, but some that only make red, etc...

Easiest way to know - experiment 

Build a clipping circuit like a Dist +, and try all different colors, 2 different colors, 1 LED/1 Si diode, etc etc.  The tone probably has more to do with the diode drop than the material, IMHO.  I don't like LED clipping, but some people do! 

Different color LED's have different clipping thresholds.  1.6v to 2v.  I think this is has the greatest effect on the differences people hear.   

Quote from: WGTP on February 05, 2007, 11:29:01 AM
Different color LED's have different clipping thresholds.  1.6v to 2v.  I think this is has the greatest effect on the differences people hear.   

That's it, plain and simple.  As the clipping threshold goes up, less and less of any picked note will be above the clipping threshold, given use of the same gain factor.  You CAN make a green or yellow LED, or a red one, clip the same *amount* as a germanium diode....IF you adjust the amount of gain applied to bring the signal up to the level needed to produce that amount of clipping.

Under some "ideal" set of requirements and circumstances for comparing different LEDs and non-illuminating diodes, there may well be some small audible and measurable difference in clipping "quality".  The vast majority of diode-replacements, however, are carried out under conditions that don't come anywhere near meeting those rather stringent requirements for valid comparison. As a result, 98% of what people discuss and describe when comparing different diode types really has to do with what happens when you raise/lower the clipping threshold without some concurrent change in the gain structure of the circuit or input signal level. 

Naturally, if you raise the clipping threshold, there will be a slightly "warmer" sound because of the reduction in clipping action.  A rather under-discussed aspect is that use of higher clipping-thresholds can often result in subsequent stages being hit with a hotter output signal, which can produce its own coloration.

The general recommendation you see for using red LEDs has to do with red having the lowest clipping threshold of the various commonly available colour types.  It is roughly equivalent to 3 silicon diodes in series, and would require approximately 3x the gain factor to achieve the same amount/extent of clipping (i.e., the clipping action of a diode over the same percentage of the lifespan of the note, given identical pick attack and pickups, strings, etc.).

I suspect the reason why you tend not to see use of other diode types is because we start to get into gain factors that begin to challenge the stability of op-amps and capacity of 9v-powered circuits.  Bringing a non-hot SC pickup to a level that results in germanium diode clipping is easy, and doesn't require so much gain that you start to worry about introducing too much hiss, or running leads near each other.  Once you have to introduce gains in excess of 500 to get where you're going, you have to start paying attention to noise management, etc., more carefully.  So, red doesn't completely eliminate all those headaches, but it certainly reduces their intensity.

hmmm.  given THIS breakdown:




aluminum gallium arsenide (AlGaAs) - red and infrared
aluminum gallium phosphide (AlGaP) - green
aluminum gallium indium phosphide (AlGaInP) - high-brightness orange-red, orange, yellow, and green
gallium arsenide phosphide (GaAsP) - red, orange-red, orange, and yellow
gallium phosphide (GaP) - red, yellow and green
gallium nitride (GaN) - green, pure green (or emerald green), and blue also white (if it has an AlGaN Quantum Barrier)
indium gallium nitride (InGaN) - near ultraviolet, bluish-green and blue
silicon carbide (SiC) as substrate — blue
silicon (Si) as substrate — blue (under development)
sapphire (Al2O3) as substrate — blue
zinc selenide (ZnSe) - blue
diamond (C) - ultraviolet
aluminum nitride (AlN), aluminum gallium nitride (AlGaN) - near to far ultraviolet (down to 210 nm[3])

"red" could mean 1 of many different materials that ALSO could be used for green, yellow, etc. 

so we are back to :  is it a function of COLOR or MATERIAL?

Material.  Colour is merely an artifact of diode material....and whatever plastic (and pigments embedded in it) goop sits between the diode proper and your eyeball.

makes sense. 

i feel a little better now.