Regarding hfe rule for Silicon Transistors in fuzz face

[fuzzymuff]

When using silicon transistors, does the hfe rule for Q1 (70-90), Q2 (110-130) apply as with germaniums?  Silicons are usually are much higher gain than germainiums.

[kaycee]

Not really,  you can get some low gain silicons and follow those values, but general silicons will have gains over those ranges. Try a 3904 in Q1 and BC108 or 2N5088 in Q2. Just because the gain is 2X doesn't make it twice as fuzzy. It's always worth bread boarding before boxing, I have a little test rig that I can pop trannies in and out before building.

[fuzzymuff]

Not really,  you can get some low gain silicons and follow those values, but general silicons will have gains over those ranges. Try a 3904 in Q1 and BC108 or 2N5088 in Q2. Just because the gain is 2X doesn't make it twice as fuzzy. It's always worth bread boarding before boxing, I have a little test rig that I can pop trannies in and out before building.

The reason I asked, was because Dunlop just announced a release at the NAMN show of the mini Fuzz Faces.  In the descrption indicated for the silicon was using "matched" transistors and the germanium using slight "mismatched" transistors.

http://www.jimdunlop.com/product/FFM1-silicon

The FFM1 Silicon Fuzz Face Mini is spec'd from a 1970 Fuzz Face in our own collection prized for its bright and aggressive Fuzz Face sound delivered by its matched BC108 silicon transistors.

http://www.jimdunlop.com/product/FFM2-germanium

The FFM2 Germanium Fuzz Face Mini is based on '66-'68 era pre-silicon Fuzz Faces famous for warm vintage fuzz tones provided by slightly mismatched germanium transistors.

[kaycee]

Well there might be something in it, but in the end it's all very subjective as to what  constitutes a good sound. If you just pick two silicons from a batch chances are their hfe will be similar anyway, convention as you note puts the lower gain in Q 1, probably based on measurements of existing units, whether they sound good or not!

My current FF has a silicon Q1 with an hfe of 65, Q2 is switchable between ge and si, the ge is 54 (lower than Q1) and the si 280, there isn't a huge difference in fuzz, probably due to the low Q1, but a fair difference in tone. How was this arrived at, a bit of experience and some experimentation and an idea of what I wanted from a FF, which is an articulate and responsive fuzz/overdrive and not an aggressive wall of fizz or mud. its certainly worth experimenting with though, Dunlop seem to be on a bit of a roll with the FF at the moment.

[fuzzymuff]

Well there might be something in it, but in the end it's all very subjective as to what  constitutes a good sound. If you just pick two silicons from a batch chances are their hfe will be similar anyway, convention as you note puts the lower gain in Q 1, probably based on measurements of existing units, whether they sound good or not!

My current FF has a silicon Q1 with an hfe of 65, Q2 is switchable between ge and si, the ge is 54 (lower than Q1) and the si 280, there isn't a huge difference in fuzz, probably due to the low Q1, but a fair difference in tone. How was this arrived at, a bit of experience and some experimentation and an idea of what I wanted from a FF, which is an articulate and responsive fuzz/overdrive and not an aggressive wall of fizz or mud. its certainly worth experimenting with though, Dunlop seem to be on a bit of a roll with the FF at the moment.

"Switchable transistors" on the fly?  NICE!!!!!!!!  How did you do this, if you don't mind me asking?  You have a youtube demo?  Is the tone difference similar to just making the tone stack caps switchable, via rotary switch or the tone is entirely different, I assume much more dynamic and changing how the pedal interacts with the guitar or your playing?  How did you compensate for setting the bias Q2 bias?

[zombiwoof]

As I recall, in the original Fuzz Faces, the silicon version had at least one change in resistor value, I'm guessing to make up for the higher gain of the silicon transistors.  Look up the schematics for the germanium and silicon Fuzz Faces and you'll see what I mean (Fuzz Central has the info on their Fuzz Face pages).

Al

[kaycee]

[/quote]"Switchable transistors" on the fly?  NICE!!!!!!!!  How did you do this, if you don't mind me asking?  You have a youtube demo?  Is the tone difference similar to just making the tone stack caps switchable, via rotary switch or the tone is entirely different, I assume much more dynamic and changing how the pedal interacts with the guitar or your playing?  How did you compensate for setting the bias Q2 bias?[/quote]

This is the fella, with circuit diagram, although this one is more based on the early Vox 2 tranny tonebender, it is essentially a FF and thus relates to your questions.
http://www.buildyourownclone.com/board/viewtopic.php?f=8&t=32845

Yes, it has an external bias and the in/out caps can be switched in pairs as the diagram shows, the transistor switching is as beavis:

http://www.beavisaudio.com/techpages/Switches/

About halfway down, I just use a DPDT toggle and don't bother with the LED.

Yes it covers a fair few tonal options which is what I wanted from it, I don't like one trick pony's

[Gus]

You might want to try this circuit. 
It was designed to work with most small signal silicon transistors.

[fuzzymuff]

Thanks Gus!!  I'll breadboard that ASAP.