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Marshall LED's ,, Diode clipping....

4/10/1999 6:36 PM
David Manson
Marshall LED's ,, Diode clipping....
Has anyone played around with the led's in their marshall.. replacing them with different ones or or putting more in a series... would like to know if anyone has tried this before,,,  
4/14/1999 12:48 AM
Dave Stork

You might want to try different colors of LEDs, believe it or not. My understanding is that the LEDs that give off shorter wavelengths (brighter colors) have a lower forward voltage drop. This could very well have an effect on the sound. You might want to try some yellows or greens or even some of the blues which have become available recently. You could mix them in pairs for a skewed clipping characteristic. For Christmas gigs, I recommend green and red :-)
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4/14/1999 12:55 PM
Mark Buckingham

longest wavelength: red  
shortest wavelength: blue
4/14/1999 2:10 PM
David Manson

What kind of difference in the sound does mismatching the diode pair make... if one has a higher voltage than another -- will it not distort until it reaches the higher threshold?  
I'm looking for something with a tight bass type of distortion -- nothing flabby sounding... but that sorta sounds neat -- different color diodes...
4/22/1999 9:08 PM
If the mismatched diodes are in parallel and facing opposite directions, you end up with asymetrical clipping, as one half of the signal clips at one forward voltage, while the other half clips at another. In series, the clipping voltage should be the sum of the forward voltages.
4/14/1999 3:18 PM
Jack Orman

Different colors have different forward voltage drops. See the measurements at:
4/18/1999 8:51 AM

In most modern (late model JCM800, 900 and 2000)Marshall amps the distortion is produced with LED's and a bridge rectifier. A pot wired as a variable resistor between the normally grounded leg of the bridge and ground will give you better control. Try pots between 5k and 50k. Also some models have a preset tone stack before the distortion generating circuitary. Replace the fixed resistors with pots and you will have even greater control.  
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