Effects of transistor leakage besides false gain reading?

[TrekFX]

Are there negative effects to transistor leakage upon actual circuit performance? Say, in a fuzz would transistor leakage raise noise/hiss? I understand how leakage affects the testing of gain (and understand how to measure and correct for it...) but was wondering what "real-world" ramifications might be upon the signal.

Tanks!

[davebungo]

Could you expand a little?  Are you talking about BJTs or FETs.  In the case of a BJT, there is always current (in a normal amp circuit) flowing in and out of the transistor terminals so I don't get exactly where this leakage occurs that you are referring to.  In a FET circuit, there may well be gate leakage (as well as a small capacitance across the terminals) which could affect bias if you used high resistance values in the bias circuit. :?

[R.G.]

Are there negative effects to transistor leakage upon actual circuit performance?

Leakage is largely the reason we (the electronics world in general) don't use germanium any more. Leakage is an uncontrolled current that leaks through the device that makes it harder to turn off, hard to bias where you want it, and thermally unreliable since leakage is what leads to thermal runaway.

Leakage is the devil personnified as far as electronics devices go.

Say, in a fuzz would transistor leakage raise noise/hiss?

Depends on the source of the leakage. If it's just that you couldn't make a collector base junction that didn't leak some conductors, it is relatively benign to audio. However, surface contamination leakage is perhaps the major contributor to germanium device noise, and high leakage is usually an indicator that there's some surface contamination in there. Surface contamination leakage only gets worse with time, and hisses like crazy. Bad juju.

Silicon leakage is about 10**3 times less than germanium, and all modern silicon devices are glass passivated, so their surfaces are coated in a high purity layer of silicon dioxide, so surface hiss is almost nonexistant.

was wondering what "real-world" ramifications might be upon the signal.

Two major effects: high hiss from surface contamination and unstable bias in the face of temperature variation. This last one can drift your fuzz face from sweet distortion to ugly, blatting, choking distortion as it gets hot.

Use leaky devices if that's all you can get, but don't think it's no big deal. Cope with it, but look for low leakage devices in germanium. If you have leaky silicon, toss it and replace it. Any measurable leakage in silicon means it's already been damaged and is living on borrowed time.