Changing the value of the feedback resistor in a fuzz circuit...

[alex_spaceman]

Hi everyone, here's a very simple and basic question... Hope it will be useful for future reference.

I've been messing around the Companion/Fuzzrite/Orpheum kind of circuit, but only have 2M2 resistors for the feedback loop (no 10M or 1M2). My question is, how does changing the value of the feedback resistor (between the transistors' C and B) affects the sound?

Thanks a lot and sorry for the very basic question.

[PRR]

> only have 2M2 resistors

Put two in series or parallel for 4M4 or 1M1. Compare and contrast.

[alex_spaceman]

> only have 2M2 resistors

Put two in series or parallel for 4M4 or 1M1. Compare and contrast.

Cheers, will surely give it a go!

Any good reads where I could learn and understand more about how the feedback loop with a transistor works at all? I'm sure trying different values will teach me quite a bit, but would be interesting to understand the basis behind it.

Thanks!

[brett]

Hi
for general info, look up "collector feedback biasing".
It seems strange, but that resistor isn't there for signal feedback. Gain in a common-emitter stage is set by the ratio of the collector resistor to the emitter resistor (or the internal emitter resistance if there isn't an external resistor).
The C-B resistor biases the base so that the transistor is turned on (a little bit). It carries a small amount of predominantly DC current to the base, which increases the voltage at the base to about 0.7 volts more than the emitter. Too small a resistor saturates the transistor and too large a value doesn't turn it on. Biasing near saturation and cut-off sometimes create extra distortion, and can be worth playing with.
cheers

Here's a bias calculator that's fun to play with: http://www.daycounter.com/Calculators/Transistor-Bias/NPN-Transistor-Bias-Calculator.phtml

[PRR]

> how the feedback loop with a transistor works at all?

Being comfortable with basic resistor concepts (like using two 2Meg resistors to make 1Meg or 4Meg) comes before transistor concepts.

I know that doing "V=2V, R=7, I=??" problems is boring, but it's important.