ge + trimpot

[mat]

Hi!

I've read the FF article from geofex (great by the way!)

Anyway one dumb question:

Can i use germaniums for FF with trimpot added from 9V to the collector if the gain of the ge is not between 70-130 and have desireable results ?

Thanks,
mat

[petemoore]

Ge's should be low leakage and the 'right' hfe's for 'optimum' results, but you can probably stick whatever you have in there and see how it goes..

[brett]

Can i use germaniums for FF with trimpot added from 9V to the collector if the gain of the ge is not between 70-130 and have desireable results ?

Absolutely!

First; the collector goes to 0V in PNP fuzzfaces (or -9V if ground is considered 0V).  Don't connect the collector to 9V.

Si fuzzface variants use this trick.  If the hFE of Q1 is too high, put a small resistor (22 to 220 ohms) between the emitter and gnd (assuming you're building PNP +ve earth) to lower the gain.  For Q2, it not usually such a problem, but again, you can put a resistor (or trimpot/pot) between the emitter and the "fuzz" pot to lower gain (at a given hFE).

You could also mess with (reduce for lower gain) the 33k resistor on the collector of Q1.

These changes will affect the tone, but only slightly in my experience.
cheers

[mat]

Thanks alot brett and petemoore for your information.

The one i'm building is Tonebender MK2 pro -pnp negative ground version. Gotta figure the bias right.

cheers,
mat