Fuzz Bias?

[aT19er]

Hey everyone,

I just started a build on a fuzz face and read about how the transistors can be biased differently. Looking at guy shots of originals I haven't seen any trim pots of any sort.

Is this something I should consider adding?

 

[Shiny_Beast]

for ge ones absolutely. Even for the si ones if ya want

 

[BMF Effects]

for ge ones absolutely.

This.

 

[aT19er]

I'm kind of hung up between some NKT275 and BC108 transistors. In either case, where would I add the trim pot to and of what value?

 

[CavityCreep]

I think it's a 10k pot in place of the 8k2 resistor.

 

[Laurie]

I think it's a 10k pot in place of the 8k2 resistor.

It is indeed.

The NKT is a Germanium PNP device. The BC108 is an NPN silicone device. Very different tone, and different power supply requirements (the NKT requires positive ground).

The tone of a fuzzface is critically dependent on the gain of the transistors.

Lots of good background info here:
http://www.geofex.com/article_folders/fuzzface/fffram.htm

 

[BMF Effects]

I think it's a 10k pot in place of the 8k2 resistor.

10k or 25k will do ya just fine.

Lots of good background info here:
http://www.geofex.com/article_folders/fuzzface/fffram.htm

I would say required reading.

 

[aT19er]

I think I'm going to side with the BC108 transistors, thanks for the Fuzz Face literature.

Are there any notable differences between brands of transistors like there are in tubes?

 

[FuzzFaceJ]

the most important thing in transistor selection for a fuzz face (or any fuzz face based fuzz) would be the gain structure of each of the two transistors (or so this is what I've read from several builders)

this is apparently more important than many realize

it's a good idea to put a bias trimpot on there regardless of which transistors you choose, if anything just for the versatility it would allow

you can get tons and tons of different tones with a bias control

you should make a germ fuzz face too down the line, trust me you'll want both, they both are awesome in their own way!

 

[Laurie]

I think I'm going to side with the BC108 transistors, thanks for the Fuzz Face literature.

Are there any notable differences between brands of transistors like there are in tubes?

Yes... but as noted previously it is the gain of the transistor that is more critical.

One way to approach it is to buy a number of different transistors from different sources and install sockets in your board. Try different combinations until you find the one you like best. You'll find BC108's on eBay and on google searches.

Trust me on this - stuff that loks good "on paper" can sound like crap, and things that look like they'll never work will sound good. All in the ear of the beholder, as they say!

 

[FuzzFaceJ]

Dingo is dead on

I don't have those famous NKT transistors in my GE fuzz face, and it still sounds amazing

 

[CavityCreep]

I did check out the soundclips of Dingo's fuzzfaces - great builds, advice very much worth taking

Same of course goes for BMF (have been impressed with the Sisyphuzz for a while)