Leds For Distoriton

[ROBERTLATHAM1]

hey guys can anyone shed some light on how LEDs are used for distortion in a cicuit. i understand the clipping part but where in the circuit and how to contol them with a pot. or even how to get a gain control circuit on 12ax7 for tube overdrive.

[Paul Marossy]

I really have no idea how diode clippers are instituted in a tube circuit, but in opamp circuits, they are usually used in the feedback loop to clip the signal. Sometimes LEDs or MOSFETs are used instead of diodes. Here is a way to add a saturation control with diode clippers: http://www.muzique.com/lab/sat.htm

And this might be a good read for you: http://www.geofex.com/effxfaq/distn101.htm

I do know that certain Marshall amps use diode clippers, but I can't remember which ones. Maybe it'll come back to me.

Edited January 26, 2006 by Paul Marossy

[Steve Vai]

The channel switching JCM800s and any non RI amps built after that use diodes for clipping, so this includes the Silver Jubilees, JCM900s, and JCM2000s.

[Paul Marossy]

Thanks Mr. Vai!

[JohnH]

At the other end of the Marshall scale - my little MG10 practice amp has a red and a green LED inside to run the overdrive. It is not a bad effect if you like extreme metal in a very small box. Looking through the cracks around the knobs, they light up like a christmas tree when a medium power chord is played.

LEDs clip on similar principles to other diodes, but at higher voltages (about 1.8V or more, as compared to 0.6V for silicon), so it depends on the circuit as to whether they are good or bad.

John

[Paul Marossy]

Yeah, it's fun watching LEDs light up when they are used as clipping diodes.

[ROBERTLATHAM1]

thanks pual very good reading there much better understanding of the design now.