need advice : bias pot for Q2 in FF ?

[keith71]

Hi to every DIYers !

I'm trying to build a slightly modded FF. My idea is to make something similar to the sunface from analog man, those have a pot out of the box (not an inbox trim pot) wich can regulate voltage in Q2 emitter. I want to incorporate such a pot to my project.

My idea is to put a 10k pot instead the 8.2k resistor, to change the bias. Like this, I beleive I could minimize voltage to vary due to temperature, I'm I right ?

Do I risk to blow out trannies ? Do you think it is good if I put a 1k fix resistor behind the 10k pot to keep minimum resistance in the cicuit ?

Thanks in advance everyone

[phillip]

http://fuzzcentral.tripod.com/axisfacesi.html



The circuit that I have posted there is Silicon with an external bias pot, but it can also be applied to Germanium circuits as well.  The "fix" resistor is a trimpot so that 4.5V can be dialed in exactly when the bias pot is at the center of its rotation...the 10K bias pot also has a center detent position.  If you want to get rid of the temperature instability in the Germanium circuit, check out the Germanium Axis Face page:

http://fuzzcentral.tripod.com/axisface.html

I then moved the bias pot to the input to act as a series resistor to help remove some woofiness from the circuit when wanted.

Phillip

[keith71]

thank you phillip. I think I will do kind of an axis face clone if you agree. I have already order stoick caps values for my project, but I will change them if it's too bass-heavy.
By the way, how quick Ge transistor could die because of iron's heat ?

[petemoore]

PDQwuick....but you 'can' get away with it.
 In the infrequent instance I wouldn't use a socket for a Ge transistor, I use an alligator clip heat sink on the tranny leg [have to make sure your on the right leg or use 3 clips] that I'm soldering on.

[brian wenz]

Hello Hello  keith71--
    Put a metal clip of some kind on each leg of the transistor while soldering.  It will help direct the heat away from the tranny.  Try to solder as quick as you can, though,  because germanium can be damaged really easily by the heat.
Brian.