Hendrix Fuzz Face

[spaceace76]

So the infamous dunplop pedal using BC108 is not that true to history?!

No it isn't really that true to history. It's impossible to say what spec his FF's were anyway, so anything claiming to be a definitive Hendrix spec is purely for marketing. The dunlop 'octavio' pedal isn't the one used on BoG either. That design has never been released to the public, but supposedly shares similarities with the current RM Octavia. The one dunlop copied WAS made by RM, but not for Jimi, and not for BoG.

Did he use one of those BC108 FF?!

There are some tracks on the posthumous releases that have that distinct Si sound. I can't recall them right now, but I remember hearing that sound, usually with a slightly unruly response to it. They were obviously modded by RM.

[Renegadrian]

Chris, thx for your answer! 

Matthew, gonna try that res. mod, would a 3.9M be fine?! I'll experiment a bit...thx

[petemoore]

So the infamous dunplop pedal using BC108 is not that true to history?!
  That's an interesting history, many versions of it exist.
  Just like every other FF...what matters ?
0: That the Fuzzface circuit ever 'works at all'.
1: That it boosts.
2: It makes 'Fuzz'.
3: That it '*cleans up at the guitar volume'.
4: It is voiced so that the 'wooliness' doesn't mud the amp over/Fizz out.
5: That it can be replicated with no more care to bias/gain than say an opamp Ckt.
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0: Can be achieved by putting in Si transistors.
1: Again, Si transistors will do this easily.
2: High Gain Si transistors will do this every time.
3: This requires incredible luck or Circuit Work.
4: Examine and estimate capacitor values, as necessary, consider LP filter for Si.
5: Start popping in HG/LN transistors for consistant Fuzz, Boost and Bias to produce production line FF [I think this trick only worked once though].
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*3 is a little trickier to get, requiring the 'right' type of PU's and other guitar circuit qualities...to get it to really do 'that clean up thing'.
6: Learn your FF tricks, develop them.
  This is where the FF starts coming to life, providing one or more 'right' amounts of boost per Fuzz values, loading can occur at the input to provide a gain control at the guitar volume, outputting Hf's that are smooth enough to not grind eardrums, and bass that while less defined than some other Distorters [at highish gains] isn't swamping the amp/speakers with mud, making a FF that is an excellent match to the amp and guitar.
  With a strong tendancy to be very sensative to everything else in the signal chain, tuning FF's to work with various signal chains can produce profoundly diverse results.

[Gus]

Time to do some math

Look at

http://fuzzcentral.ssguitar.com/schematics/oneknobfuzz.gif

http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacenpnschematic.gif

What is the emitter current at the Q2 section?

Note the value of the gain pot and fixed resistor.

Ohms law is your friend.

Also look at the collector currents.

Build the one knob fuzz and check operation points. 

Look at the bias pot in some fuzz circuits I shared, look close at the vox fuzz schematic in GEOFEX "tech of the ff" ask why is there a 820 ohm added under the gain pot?