Hi,
This is done in fuzz pedals, that generate distortion. When replacing
them, you need to adjust several resistor values too!
A silicon transistor is generally a "better" transistor, but it is the
"bad" part of the germanium transistor that is being used. It
saturates more, the gain depends on the currents more. And it is
slower.
The transistors are driven into saturation. The silicon transistor
goes up to the power supply, then clips and give sharp edges. this
gives a very sharp, mean sound.
But the germanium transistor saturates and can't even reach the power
supply voltage, it shows characteristics that look more like a
distorting tube, rounding off the peaks. But there is more to it: a
germanium transitor is much slower, has higher capacitances (i think
that that may also have to do with the older manufacturing processes).
This causes the edges of the clipping to get really round. And at the
same time, very high harmonics are not generated anymore.
So what does it do:
It generates distortion, but only a couple of harmonics (more even
than uneven harmonics), making the sound more pleasant. It gives more
"warmth". And still "power" as it works in the mid-frequency region.
It gives a sense of a "full" sound.
And now I have a great tip for you, and all you germanium distortion
enthousiasts out there: you can add a very small capacitor to the
base-collector of the distorting transistor to influence the warmth of
the sound! Notice that the capacitance must only be a couple of pf as
it is being multiplied by the transistor due to the Miller effect.
You can use this capacitor too to use another germanium transistor
(one that is cheaper than the ones that are always used) and adjust
the sound so they sound the same.
You can also influence the sound by adjusting the bias, so the
transistor will either generate even or more uneven harmonics
depending on wether distortion is on both up and down voltage, or only
one.
If you have any questions about how to calculate resistor values, feel
free to ask me. Email me at (and remove both the "byespam"'s) to
[email protected]
Pieter