Transistor, confused

[Jyka]

Hi,

I just resolved a problem for the biasing of my ge trnasisor for fuzz face, now i'm wondering something else, do i have to test the hfe of the transistor in each circuit ? Flanger, delay ... And change the values of the resistor ?

[RobA]

No. In general, circuits that use transistors are designed so the hfe isn't a design parameter. If a circuit does depend on the hfe, it would pretty much be considered a bad design. Some of the early fuzz and boost pedals are an exception because you are looking to replicate a particular sound. But, pretty much nobody would design a circuit like that today. Part of the problem is also that Ge transistors are actually pretty bad at being transistors (even if we like the way they sound).

The only case of new design I can think up off the top of my head where you have to hand bias for a transistor is in JFET stages in distortions that act like tube amps. Even these are setup so that you bias them using a trim pot.