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. That pedal had a BD139 (hfe=150) for Q1 and two "piggybacked" BD139s (hFE about 6 maybe?) for Q2. 10k) was introduced between the emitters.īut 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). To remedy this, and give hFE values more like 100, a resistor (e.g. Two devices of 200 give about 10 when connected like this. But it reduced hFE more than anyone expected. 2 devices in parallel, but with the collector of one unconnected reduces the hFE. A couple of years back, RG suggested "piggybacking" transistors to get low hFE.
I totally agree that low hFE in Q2 can make for interesting tones.
The hard part is going to be tracking down the low gain, low leakage Germanium. Sorry I can't post sound samples, but if you try this you won't be dissapointed.
#Darlington transistor hfe 600 series#
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. Both combinations clean up really well due to the low gains and leakages. Swapped this with the other half of the Darlington (hFE=46) and got the heavier fuzzy sound down pat. Sound is VERY close to the intro lead in All Along the Watchtower (MIJ Strat). 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. 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).īTW, this observation came about when I initially tried to Darlingtonise two of these low gain Ge's for fitment as Q2. 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. Typical hFE is around 30-45, and typical leakage is no more than 2uA (not a typo). I've come across some superb PNP germaniums with hFE's between 12 and 100. I though I might share an interesting observation about the classic fuzz face circuit.
0 kommentar(er)
