Experimenting with fuzz face: Questions re: biasing and polarity

[Rick899]

I built another fuzz face. I built this one with sockets for the two electrolytic caps, the transistors and the 470 resistor that is changed to 330 for Si circuits.

By building the pedal with sockets for these specific components, I expect to be able to make it either NPN or PNP and/or Si or Ge  simply by reversing the polarity of the caps and/or changing the  transistors and the 470R resistor.  Will this work to change the pedal back and forth from PNP to NPN or Ge to Si?

On this pedal I also (in addition to a 10k trimpot/1k resistor instead of the 8k2 resistor) substituted the 33k resistor for a 25k trim pot and a 12k resistor. I couldn't find any data on this,  just references to doing it. Is this because a trim pot in place of the 33k makes no difference so no one does it?

Q1/Q2 Voltage measurements after biasing Q2C to -4.50V are as follows:
Q1C: -1.29; -.57; E: 0
Q2C: -4.50; B: -1.29; E: -.70

Without adjusting the 25k trimpot, the measurements for Q1 are almost the same as the measurements of the other 2 fuzz faces I have built and of others I have read about online. This is what makes me think that there is no benefit to changing the 33k for a trim pot.  Questions:

Are the Q1 voltages I got with the trim pot adjustment as it was right out of the bag just a coincidence?

Can  Q1C voltage be set to an optimal number so as to yield positive sound benefits?   If so, to what voltage should Q1C be adjusted to? 

Can the Q1C voltage be adjusted to whatever voltage makes it sound the best to one's ear? 

Where does the -4.50 V measurement for Q2C come from?  Is that voltage a function of the internal physics of the design of the fuzz face?  Or is that the voltage at which a lot of trial and error has shown that the fuzz face sounds best?

Thanks for any feedback on my questions. I am trying to understand the fuzz face as completely as possible.

[Davelectro]

While using old, really low gain silicon transistors I was never able to get less than 1.6V for Q1's collector. Wonderful tone, though.

[pinkjimiphoton]

yah, you should be able to switch between silicon/ge, pnp and npn i would think. just change the polarity of the caps, and if ya used any diodes, that too.

i know fuzzfaces don't use diodes, but there's so many variants out there, ....

[LucifersTrip]

I expect to be able to make it either NPN or PNP and/or Si or Ge  simply by reversing the polarity of the caps and/or changing the  transistors and the 470R resistor. Will this work to change the pedal back and forth from PNP to NPN or Ge to Si?

don't forget to flip the battery

Q1/Q2 Voltage measurements after biasing Q2C to -4.50V are as follows:
Q1C: -1.29; -.57; E: 0
Q2C: -4.50; B: -1.29; E: -.70


Are the Q1 voltages I got with the trim pot adjustment as it was right out of the bag just a coincidence?

no, it was prob close to 33K

Can the Q1C voltage be adjusted to whatever voltage makes it sound the best to one's ear?  

exactly...

Where does the -4.50 V measurement for Q2C come from?  Is that voltage a function of the internal physics of the design of the fuzz face?  Or is that the voltage at which a lot of trial and error has shown that the fuzz face sounds best?

9 (battery)/2
again, it's what you like the best for your particular setup. 4.5v is an excellent  starting point

Thanks for any feedback on my questions. I am trying to understand the fuzz face as completely as possible.

you did read this already?
http://www.geofex.com/Article_Folders/fuzzface/fffram.htm

[Rick899]

Luciferstrip:

Yes I read that article. I forgot to mention that on this one I added part of the Fuller mod, i.e., the 50k pot before  the input cap, which I read about in that article.

About the polarity issue .... Flipping the battery is a problem because of the way the 9v battery snap connectors are made and because it is soldered into the circuit. What is the easiest practical way of doing it?  How about taking two battery snap connectors and soldering  the red of one to the black of the other, etc.,   that would allow one to flip the battery, wouldn't it?

How about a power supply other than a 9V battery. I have DC jacks wired into the pedals ....  For a NPN pedal one could just daisy chain it with other pedals on a One Spot, but how about a PNP pedal?  Can you use a One Spot with a PNP pedal without modifying the pedal as long as there are no  other pedals connected to it?  Or is there another way of using a 9v power supply like a One Spot  on a PNP fuzz face?

[LucifersTrip]

Flipping the battery...What is the easiest practical way of doing it?

with a DPDT switch

For a NPN pedal one could just daisy chain it with other pedals on a One Spot, but how about a PNP pedal?
 Can you use a One Spot with a PNP pedal without modifying the pedal as long as there are no  other pedals connected to it?  Or is there another way of using a 9v power supply like a One Spot  on a PNP fuzz face?

you can't chain npn & pnp together...do searches here & you'll find a million people asking about that one. the pnp has to have a separate supply, like a battery.   you can use a DC jack but the +/- will be reversed inside on the wiring compared to your npn wiring. also, remember, some walwarts are positive center and some negative.