Clipper variations

[m-theory]

On T/S type overdrive circuits, I've experimented quite a bit with various different combinations of clipping diodes, including various combinations of silicon, germanium, and leds.  I have yet to try either Schotky or mosfets.  I'd like to get some input on those from those who've tried them.  So far, I've tried 134a, 1n914, 1n4001, 1n4002, and both red and yellow LEDs. 

I'm heavily partial to the aggressive, "marshell-esque" sounds that a red 3mm LED provides, but I'm not opposed to trying something else that might be interesting.  I prefer a more "open" tone, so I really don't care for the traditional T/S variant, and even adding a 3rd 1n914, while certainly making the sound more "tube-like," isn't really as aggressive and open as I prefer. 

I'm very curious about both schotky and mosfets, and whether or not either can produce anything as aggressive, or close to as aggressive and "open" as red LEDs. 

[anti-idiot]

Reply #9 on: October 28, 2005, 06:14:22 PM
   
G+D - S = diode conneted mosfet = very soft knee = as used i the Shaka B.
This is the different one. The gate shorted to drain means that the "diode" doesn't start to conduct until the gate/drain is more than the threshold voltage more positive than the source (positive for N-channels, negative for P channels that is). So the forward voltage of these diodes is usually 1.5 to 3V. The knee of conduction is quite soft, and so diodes using this don't go from full off to full on, they gradually turn on. This happens to be quite good for soft distortion. This is the only FET diode connection worthy of any special study or pursuit IMHO. The others are just too similar to ordinary diodes.

It's this connection that needs the series ordinary diode to keep the body diode (connection 1) from conducting when the signal reverses.

i love the sound of leds, they sound "natural", but it's hard to have some almost-clean-almost-crunch sound. i haven't tried mosfets, but u should give it a try.

[Mark Hammer]

The "sound" of ANY diode will be largely a function of the gain applied to the input signal and the actual absolute level that hits the diode.  If you could control/adjust for what the diode needs to achieve the same degree of clipping, then I imagine many diode types probably would have some small nuanced differences in clipping quality.  Given that most people who swap these diodes out for those hardly ever adjust the gain structure of the pedal to compensate, 95% of what they are typically hearing is not the "sound" of the diode itself, but rather the sound made when the clipping threshold and signal are a given "distance" apart, and when the resulting output signal pushes the amp by X amount.

While LEDs of various colours CAN be used, generally speaking, there is insufficient gain and voltage swing available from a pedal using a 9v supply to achieve any significant clipping with LED colours other than red, since it has the lowest forward voltage.

[m-theory]

The knee of conduction is quite soft, and so diodes using this don't go from full off to full on, they gradually turn on. This happens to be quite good for soft distortion.

Based upon this description, I would say that mosfet is probably not the ticket for me.  I like the aggressive nature of a red LED clipper.

While LEDs of various colours CAN be used, generally speaking, there is insufficient gain and voltage swing available from a pedal using a 9v supply to achieve any significant clipping with LED colours other than red, since it has the lowest forward voltage.

I've only tried yellow and red, and prefer red.