FAT GERMS: postscript notes

[Steben]

I know there won't be many FAT GERMS-copies in the future, yet for those who want to build it just a quick note:

In the FG of which you can hear sound samples on the net, there is a 680ohm (!) resistor going from power (in this case "-", it's PNP) to the circuit like a "sag" resistor in tube amps. Off course it forms with a 100µF cap a RC filter to block out ac hum, but 680ohm is quite big.

Knowing this - the first AC128 stage draws 0.4mA and the second 1.6mA - there is a voltage drop around 1.3V !. This means the circuit runs on about 7.5V-8V and not 9V. Biasing the first stage to 7V (like rangemasters) is not as good as 6V in this case (but let your ears be the judge, right ;-) ). Anyhow, when the input signal goes up the Q1 emitter current decreases and the Q2 emitter current goes up again but more than on Q1 (amplified signal). This means the total current draw on the circuit goes up -> increasing the voltage drop on the 680ohm resistor -> lowering the power voltage -> lowering the positive gain! When the signal goes down you get the opposite -> increasing power voltage -> lowering negative gain. This means a compression on both signal polarities, right?

Maybe that's why it all sounds so smooth?.............