In the wah article, Mr Mojo appears in the guise of a faulty inductor which interacts postively with a fuzz face and can never be recaptured cause no modern inductor has those faulty characteristic anymore (except Teese?). In the Fuzz Face article, the ultimate dictum most people put over their bed is the magic hfe range for fuzz face. This is the crucial paragraph:
I've really been looking for that sweet spot, but from the beginning builders were reporting great ff's with silicons and extremely high hFE's, initally even Jack Orman thought low gain to be essential to FF sound - though all the time people were building great si fuzzes with enormous betas:R.G. [i]Technology of the Fuzz Face[/i] wrote:I've done a lot of circuit simulation on the FF, twiddling the values of the transistor gains, and looking at the clipping waveforms and resulting harmonic spectra. There is a definite sweet spot for musical sounding clipping at transistor gains of about 80-110. If you allow combinations of one high and one low gain device, the range widens out to 70 or so on the low end and perhaps 130 on the high end. Keeping in mind that preferences for distortion tone are definitely a matter of personal taste, the range of gains for unselected AC128's in this circuit would produce some really clunky-sounding devices.
This seems to be borne out in practice. Mike Fuller, maker of the Fulltone "69" pedal, posted his preferences for Fuzz Face transistor gain to the usenet news groups, and they fall right in this range. He noted that he feels that he can affect the relative amount of symetrical versus asymetrical distortion by selecting for non-identical gains in the two positions. (Mike also prefers transistors with only certain colored epoxy sealant, which I can't see making any difference except coincidentally, but then, who knows?)
11/18/1997 5:29 AM Jack Orman - Ampage
I've heard from people who made the FFace with 2N3906 trans. and were satisfied with the sound. However, its hfe of 200 sounds like a little much. I've heard that the best sound comes with the first transistor hfe= 85 to 95 and the second one at 100+. The MPSA18 has an hfe of 500! But then again, the BC108C trans. that are in my original 1972 FF also have an hfe of 500...
The AC128 PNP Ge's that were in the original model rate out at 90.
(...)
regards, Jack
I conclude from this that the prime requirement for a transistor to function well in an original fuzz face circuit is not the correct gain, but rather the correct amount of leakage to bias the base.11/19/1997 R.G.
Every MPSA18 I've ever measured has had an Hfe over 1000.
The "two different gains" data was also posted by Mike Fuller about the FF some time back on the newsgroups. The first one can be as low as 70 and the second can be up to 140 (assuming that this is real gain, and not leakage as measured on a DMM gain test). In theory, the mismatch changes the amount of asymetry in the clipping.
the first transistor's properties dominate the "soft" distortion sounds, the second one's dominate the "harder" distortion settings. The soft distortion is the result of the mushy saturation of the voltage feedback first stage, and the harder distortion is the result of the cutoff clipping of both first and second transistors.
(...)
Ge is indeed leaky. My last batch of AC128's was 75% unusable because of leakiness. Leakiness is exactly the same effect as putting a large value resistor from the collector supply to the transistor base, it simply adds extra current into the base - and hence the collector - of the transistor. As a result, the bias points shift. If this were the only problem, you could deal with it by tweaking the bias point. In fact, you see this in many "Golden Age" fuzzes, which have Ge transistors with NO bias into the base; it's not zero biased, the leakage is biasing it. The real problem is that the leakage shifts with temperature, and this fact makes speculation on the effect on sound unnecessary.
Further evidence that a certain amount of gain is not imperative to create a fuzz effect, can be found on the other end of the spectrum. It's the famous Piggybacking thread
[quote="Brett @ diystompboxes:"Piggybacking" trannies for lower gain
« on: 06-01-2004"]Simple. Or so I thought.... Well, my Hornet had Q1 and Q2 hFEs of 130 and 340, so I piggybacked then with 2 extra tyrannies of hFE = 200 and 340, respectively. The Hornet was now more of a Wasp, and sounded great. I bundled it up and sent it off to the guy I was building it for. Then I started to wonder what I had done to the hFE of those transistors. A few checks revealed some things that STUNNED the *^%@ out of me.
I found that piggybacking two similar transistors (PN100s, hFE=350 and 430) to those I'd used for Q2 in the Hornet gave a hFE of either 6 or 12, depending on which transistor piggybacked on which. So piggybacking DIDN'T HALVE THE GAIN. Also, the Hornet worked great with a hFE at Q2 of about 10. (What!!??)[/quote]
Adding a resistor between the emitters, allows you to increase the gain. I did some experiments with some various silicon transitors
- Take two identical transistors, tie the BASES together, cut off one COLLECTOR, connect a 3k to 6k resistor to the EMITTER of the collectorless devices, and connect that to the EMITTER of the other transistor. By varying the resistance, you can dial in the gain you want... It is my experience that identical transistor work better in getting a good fuzz sound.
So, if we can mimic both leakage (big resistor between B and C) and low gain with silicon, where's that germanium mojo? This is a question I've been asking myself some time now. The piggybacking experimenters at diy were happy to find low gain silicons and settled for that. Which is fine, but...
Is there reason to assume germanium still has something to offer? Is this a path worth persuing?
just throwing a bone, hope nobody gets hit
