Specific transistor query for Fuzz Face

[OwenF]

Hi,


Second post on the forum  . I am preparing a BOM for the next projects I want to undertake and I want to ensure I can source all the parts (ideally within UK/EU) before I commit to drilling enclosures for a pedal. Amongst others I plan to build, I want to breadboard a fuzz to get one that sounds right to me before I put it to PCB. I've looked at negative ground circuits as I have already made a mutli-output neg ground power supply, and the circuits that I am aiming towards are: Axis Fuzz (RM), Axis Face (from fuzz central) and 70's Boutique Fuzz (GGG). I may also mix and match some controls from Joe Gagans Easy Face.

The 2N2369 (PN2369A) I can get from musikding and the BD139 from bits box. However, my dad has tons of components left over from his TV days and I found about 100 BF392 http://www.datasheetcatalog.org/datasheet/motorola/BF392.pdf. I've noticed that the fuzzes tend to prefer lower gain transistors, however this datasheet states min Hfe of 25 and no Max, does anyone think this may be suitable for these circuits? I suppose the only way to know is to try it, but it would be great if I knew then I wouldnt need to order extra. Plus, would it be required to match transistors for these circuits (i.e. buy loads) or are silicons all pretty close?

Also, are there any other Fuzzes similar to the ones I've listed that people would recommend/have had successful builds?

Thanks for your time

[brett]

Hi
Figure 1 on that datasheet indicates that these are nice, low hFE devices that are probably good for vintage Si effects, including Si fuzzfaces.
There's also some renewed interest in piggybacking to get low and "bendy" hFE (search function is your friend).
IMO:
The RM fuzz is very nice, but a bit complicated for an early build.
The Axis Face is more manageable.
just my 2c...

[OwenF]

Thanks for that, it seems then it would be safe to try these without needing to get 2N2369's on order, then see how they perform.
Also, I searched your post on piggybacking and it seems that your discovery may allow me to use a common, easy to obtain high gain transistor in this circuit. Great, I think the next thing to do is to have a play.

Is there any reason that the Axis Face might be a simpler circuit than the RM fuzz. Im guessing here, but is it anything to do with the PNP used in the neg ground circuit? I wondered how this worked, although I understand the PNP is 'reversed'?

[petemoore]

  PNP/NPN are like mirror image of one another [roughly] and each has it's own PS requirements [ie polarity must be opposite, and anything with polarity then must of course follow to suit the circuit [ie caps need their - to be - in respect to their + lead at all times, anything else is 'reversed'...but starting with the right scheamtic for the components is st recomended.
  SI transistors are all low leakage so you can just stick 'em in a DMM which has Hfe checker/tester and get a useful reading on the Q gain there, easy.
  Most effects are - ground, so an NPN fuzzface [Axis face for instance] can work well with others without creating a short-out.