Diodes in Series + Forward Voltage Calculations

[Guitarfreak]

Identical diodes in series will have additive forward voltages, but how about different diodes with different forward voltages and clipping characteristics?

For example
Ge: Vf = .35V
Si: Vf = .65V

Ge > Ge = .70Vp
Si > Si = 1.3Vp

How about...
Si > Ge = ?
Ge > Si = ?

[Cliff Schecht]

The Vf of the diodes always simply add together. Order doesn't matter, they will act the same either way.

[Guitarfreak]

The Vf of the diodes always simply add together. Order doesn't matter, they will act the same either way.

Cool, thanks.

[Guitarfreak]

I just put a Ge diode in series with a silicon diode and the amount of gain and compression seems to have increased.  If what you said is true about additive Vf, then shouldn't the gain have decreased and the feel be a little less compressed?  It seems I have run into the opposite situation.

[ayayay!]

Depends on the pedal.  What are you doing this to?

Clipping is clipping, yes, but it depends on where in the circuit it's clipping.   

[Guitarfreak]

Oh ok, that makes sense I guess.  It's a BOSS SD-1 Overdrive and that would mean the clipping would be in the op-amp feedback loop.  Does that mean that I wouldn't experience the same clipping characteristics if it were a clipping stage similar to a DS-1 Distortion then?  How would it differ?

[Mark Hammer]

I just put a Ge diode in series with a silicon diode and the amount of gain and compression seems to have increased.  If what you said is true about additive Vf, then shouldn't the gain have decreased and the feel be a little less compressed?  It seems I have run into the opposite situation.

Nothing should happen to the gain.  Gain is produced by other elements.

If, however, you have done such a mod to a clipping stage in a Big Muff, or other pedal that uses two cascaded clipping stages, then increasing the forward voltage, and raising the clipping threshold in an earlier stage will result in hitting the subsequent stage with a hotter signal, which CAN create the impression of more clipping (or what you incorrectly refer to as "gain").

[Guitarfreak]

I just put a Ge diode in series with a silicon diode and the amount of gain and compression seems to have increased.  If what you said is true about additive Vf, then shouldn't the gain have decreased and the feel be a little less compressed?  It seems I have run into the opposite situation.

Nothing should happen to the gain.  Gain is produced by other elements.

If, however, you have done such a mod to a clipping stage in a Big Muff, or other pedal that uses two cascaded clipping stages, then increasing the forward voltage, and raising the clipping threshold in an earlier stage will result in hitting the subsequent stage with a hotter signal, which CAN create the impression of more clipping (or what you incorrectly refer to as "gain").

I have actually done extensive modding to a Muff circuit, fun stuff tweaking things here and there and getting a different feel.  Whatever you want to call it, the gain knob seems to have more of an effect at lower settings, and the feel seems tighter and more compressed.

[ayayay!]

If, however, you have done such a mod to a clipping stage in a Big Muff, or other pedal that uses two cascaded clipping stages, then increasing the forward voltage, and raising the clipping threshold in an earlier stage will result in hitting the subsequent stage with a hotter signal, which CAN create the impression of more clipping (or what you incorrectly refer to as "gain").

...what he said...

[new]

This is my experiment for forward voltage of diodes at differnt currents.