Originally Posted by bowlfreshener
I have heard the different colored LEDs have different effects on tone. I have heard lots of people using yellow LEDs and then a few using red ones in the clipping sections. I think some Landgraff mods involve LEDs.
This is true and observable, if you have a good ear.
All diodes have a voltage or current at which they switch on:
-Germaniums are notoriously low - this is why you get a ton of compression and typically a great reduction in output.
-Silicons (most common) and rectifier type diodes are generally next up the chain. Some folks swear they can hear a difference. Possibly, but I bet most of them wouldn't pass a double blind test.
-LED's are higher than most other types of diodes. A typical LED will take roughly 2.5 times the power of a silicon/rectifier type to switch on.
The immediate benefit of LED's is typically an immense reduction of compression, and a great increase of gain. By gain I mean clean signal, NOT distortion. Since you've got a greater range to work with before your signal clips, a pedal with LED's will typically clean up much better.
I find LED's to work best for asymmetrical clipping. I like to run a single silicon with a single LED. No goofy series combinations. This combination seems to give me a good balance of everything - enough compression, cleans up well, adequate gain, extra even order harmonics that symmetrical clipping will never be able to produce...
LED clipping has been out for awhile, actually. The Marshall Guv'nor came stock with it.
Many meters let you test diodes so that you can see how much voltage/current it takes to make them switch. Then you can go with whatever type fit within a "threshold" that you like.
The typical LED takes about 1.3 volts before it switches on. Ge takes about .3, rectos about .45, silicons are around .55 volts. Super bright LED's and some colors can take 1.7 volts and above!
You can't determine an LED's switching point just by it's dimensions or luminosity, though. I've found the little red (3 mm) ones to typically be on the high side, at 1.55 volts. Actually, big greens tend to be on the lower side.