Germanium Transistor cross reference

[TarheelTechinTraining]

Hey fellas. I'm looking for a cross reference from silicon transistors to germanium transistors. Mostly its for sh*ts and giggles but I've heard germanium trannys and diodes distort more organically than silicon. Thanks everybody,Greg

[Steve Conner]

Others might disagree, but I'd say that germanium transistors perform differently enough that the idea of cross-referencing with silicon ones makes no sense. For example, it takes 0.2 to 0.3V to turn on a germanium transistor, vs. 0.6V for a silicon one.

The earliest germanium devices were so slow that they struggled to make it above middle audio frequencies. The Dallas Rangemaster was more of a midrange booster than a treble booster. Probably the most famous example of an effect that sounds better with a germanium device, but there are other cases where they do indeed "distort more organically".

[Alan0354]

I played with germanium diode for distortion, it sure sound quite different from silicon diodes. I am not sure about the more organic thing, it's about the whole design, not just the components. I just don't believe it is better or worst, just sounds different.

[TarheelTechinTraining]

Thanks for the replies. Yes Alan I agree different. I noticed when I was modding a pedal the main mod was based around the clipping diodes, from silicon to germanium.
Just wondered if the transistors are like the diodes, different sound from silicon. Thanks again,Greg.
PS Steve I love your quote, Tesla Rocks !!!

[madkatb]

Here's a link to Keeley's Fuzzhead. Switchable Silicon/Germanium clipper so you can hear the difference.
Fuzz Head Audio Demo by Paul J. Priest

[R.G.]

On the topic of switching between silicon and germanium to "hear the difference", this is one of those things you have to be careful about. The forward voltage of a germanium diode and a silicon diode differs so much that if you use clipping diodes, you have to pre- and post-amplify by different amounts to get even notionally equal drives on the diodes and output signal levels.

The same thing applies to use of silicon versus germanium transistors. The bias currents and voltages to get even similar operation is so different that you have to arrange to rebias (at least) to switch between devices. That means that the silicon and germanium devices must have different biasing network parts, and so an exact test is not strictly even possible. Especially in a commercial device which has (presumably) internally matched up the drive levels and bias levels. This is such a dramatic change that apples to apples comparisons are hardly even possible.

Wolverines and house cats are both mammalian, clawed carnivores of comparable (... heh, heh, heh...) size. They're a little different in results, though. Hard to make a wolverine to house cat substitution guide.

[Alan0354]

I think the original post is about compare the sound, not putting both in one. Yes, I worked on D Allen's pedal that has a choice between Ge and Si diode, the output level is very different, you cannot just switch in and out.

As For transistor, I never even try Ge. But if Vbe is the only thing, that should not be too hard. If you want to be switchable, connect the collector and base of the two transistors in parallel, then use DPDT to switch in one of the emitter resistor for one of them. The resistors should drop at least 1V with bypass cap. The values of the two resistor is set to give the same collector current so there will be no DC shift when switching to prevent a popping sound when switch.

If gm is different and you worry about the gain, then use different emitter resistor without bypass to compensate the gain.

BUT as a former guitarist and pedal designer, it is my opinion that I don't put too many bells and whistle in one pedal. It is too complicated, it is more important to get one good sound than many sound. Want both sound, get two pedals. It is like so many people trying to get many combination of pickups in a guitar, but in reality, the most sort after sound are just simple neck pickup alone. Fender came out with thew S1 switching that you can switch any combination you can imagine. All I read were people taking the S1 circuit out from the guitar.

If the circuit is too complicated, the quality of sound might get lost somewhere in the spider web.