Axis Face Silicon with old npn's......OH yea!

[momo]

So in the spirit of trying to contribute, I just finished a Axis face from Fuzz central, tried a bunch of old trannys......so I found some good combinations and want to give you the results.
So if you come across some of these trannys, use them!
The best 'out of the ordinary' fuzz face tones were with a BC 108 with a BC 233 in second position.That is an awsome amount of gain, much more than I really need I guess, but the tone is awsome!
Another combination was with the same BC 108 in Q1 and a BC 149c in Q2.....now if you ever want to test a spkr, or get it in its "compressed zone" .......thats the config to get!....but warning, that one is a Big Muff killer! Its a good thing it has a .22 input cap, anything with more bass and I would not have a spkr anymore.

So I have done 3 Ge FFace, and this is my first npn one....I have to say, this is really really close to some Ge's......the other combinations were also good, but were kind of generic FFace sounding, the BC 108 with the BC 233 has mojo man, it has a funky tone with some bite if you want, or you can smooth it out with the said pot.
Cheers

[mac]

Did you measure hfe of those transistors?

mac

[momo]

Did you measure hfe of those transistors?

mac

Nope!...my test meter or ac meter, whatever you call it does not have provisions to test them, Im not aware of some kind of tranny tester for silicon like RG's Ge tester.....so basically I read the data sheets and tried to put some 70-100 Hfe spec on Q1 and 150-200 Hfe on Q2. I actually tested all configurations and for sure the lower Hfe on Q1 is the way to go, but all combinations exept my prefered one had kind of generic FFace sound, almost like a BigMuff if you play with the smooth pot and reduce the sting,sounded good but not original. Using the BC 108 followed by a BC 233 gave a great original tone, I would say a mix between a regular hot FFace and one of those nasty Fuzzes which I forget the name, maybe the Shizzle?.....some kind of bee buzz!
What I like is that its versatile, I can bee buzz if I want, compete with a BigMuff, or use my blender pot on my strat combined with position 4 on the switch(one before bridge position), that is a great Santana like tone, has sooo much sustain.....
Actually, talking about sustain, Im not experienced enough to know if I found some funky setup for sustain but I can pick a note and hold it FOREVER, it behaves like one of those magnet things you use on the string......you can feel it setting up, instead of having the note die down after a while, say you are holding the note but not activating it with vibrato, normally, at least on all heavy distortion I used, after a while, it dies down if you dont help it.
Well with this one, I can do that Buddy Guy trick and hold the non vibrato note forever!
I guess thats the huge amount of gain Im getting.
I would say the only thing I don't like is how the guitar pot behaves....the taper is too sudden, at 8.5 im almost chicken picking with thin sound, I mean its usable, but I would enjoy a longer taper or having more Fuzz at 8.5......is there anything I can tweak for that?

At the end though, its a silicon circuit and so Im really surprised at the Ge tones on that one and bonus I can put a dc jack for external power.....yea I guess you can do that with Ge's but I would be paranoid to plug in the wrong polarity.

OH, I would love to give you guys some clips, If someone can point me to a server that can host the clips.....
Cheers

[mac]

You can use RG test to measure Si. It is just a particular case with leakage current almost zero, and a bigger Vbe, you do not need to disconnect the base resistor. Remember that
ib=(Vcc-Vb)/2.2M
ic=(Vcc-Vc)/2.4k
hfe=ic/ib   (if leakage is almost zero)

IIRC bc108 are high gain transistors going from ¿200? to ¿800?
The only difference between my Si and GE FF is that the Ge "sawtooth" is more rounded, and therefore more harmonics.

mac

[momo]

IIRC bc108 are high gain transistors going from ¿200? to ¿800?

Hmmm, yea I checked again and your right!......so yea I realize that looking up the Hfe would talk more than just the specs, maybe I have a very low out of spec BC108?
Ill try to put up the tester on breadboard and see the results, whatever they are, this circuit will be boxed as is!

[Lachlan C.]

Glad you found a transistor combo that you like! If you want to get a better taper (i.e. a smoother transistion on the fuzz control) use a 1k Rev Audio pot. Alternatively, if you find if difficult to grab a rev audio pot dig into AMZ, GEOFEX, and Analog Alchemy re modifying pot tapers to taste by adding resistors to either lin or log pots.

- Lach 

[mac]

Note that Geofex test schem is for pnp devices. Just change the polarity of the PS. But if you're going to box it, do not waste time measuring

mac

[drewl]

I tried a bunch of oddball looking old NPN's I had lying around for this fuzz, but settled on a pair of low hfe
2n2907's.
Can't believe how good it sounds with plain old si transistors!
it's the red pedal on the right, the box was an RF coupler that was junk, that's why it's got a bunch
of screw holes!