Very low hFE germanium for Q2 in fuzz face - Hendrix sound

[luap77]

Hi,

I though I might share an interesting observation about the classic fuzz face circuit. I've come across some superb PNP germaniums with hFE's between 12 and 100. Typical hFE is around 30-45, and typical leakage is no more than 2uA (not a typo). I tried two different transistors from this batch (hFE=27 and hFE=46) in the Q2 position in my fuzz face clone fitted with 2SA102 for Q1 (hFE=70, leakage 100uA) and got the most wonderful Hendrix-like tones I've experienced to date.

Q2 is classically the higher gain transistor in the FF circuit, with a recommended hFE of 100-140, so if you are trying this make sure that you don't put the low gain transistor in the usual position (Q1).

BTW, this observation came about when I initially tried to Darlingtonise two of these low gain Ge's for fitment as Q2. The Darlington pair sounded nice (typical smooth FF), but for whatever reason I popped one out of the pair (hFE=27) and used it standalone for Q2. Sound is VERY close to the intro lead in All Along the Watchtower (MIJ Strat). Swapped this with the other half of the Darlington (hFE=46) and got the heavier fuzzy sound down pat. Both combinations clean up really well due to the low gains and leakages. Put in the 50k variable resistor in series with the input (variable impedance trick, ala '69 pedal) and you get a true AC/DC brown sound. Very versatile indeed.

Sorry I can't post sound samples, but if you try this you won't be dissapointed. The hard part is going to be tracking down the low gain, low leakage Germanium.

Paul E

[rockgardenlove]

You know, I get the best Hendrix tone with a 160 hFE in Q1 and a 145 hFE in Q2.  The measurements might be a bit off as when I measured I didn't have a perfect 9v battery, but this really does sound great.  My hFEs are way higher, but Q1 is higher on mine too.  Interesting.   

[brett]

Hi
I totally agree that low hFE in Q2 can make for interesting tones.  At least for hFE = 10 and upwards.

Here's my 2c.  A couple of years back, RG suggested "piggybacking" transistors to get low hFE.  2 devices in parallel, but with the collector of one unconnected reduces the hFE.  But it reduced hFE more than anyone expected.  Two devices of 200 give about 10 when connected like this.  To remedy this, and give hFE values more like 100, a resistor (e.g. 10k) was introduced between the emitters.
But when first I using this method, I didn't think the low hFE readings (about 10) were right, because I'd used the first piggybacked devices in a fuzzface, and it worked fine (it was also the first fuzzface that I'd built, and I'd never heard one, so I didn't know what it should sound like).  That pedal had a BD139 (hfe=150) for Q1 and two "piggybacked" BD139s (hFE about 6 maybe?) for Q2.  I boxed this circuit up and nearly sold it until great enthusiasm erupted for piggybacking and I realised that it was a part (albeit small) of DIY stompbox history.

How did it sound?  Very smooth.  Kinda like a germanium fuzzface meets the tube-sound-fuzz (and neither working flat out).
I'm not sure, but I may have later modified the circuit in that box by adding a piggyback "boosting" resistor, and increasing the gain of Q2 somewhat.  In any case, that circuit was my first piggybacked transistor, for at least a few days it had a Q2 with hFE of about 6, and I thought that all fuzzfaces probably sounded like that one: mild and smooth and full.

cheers