tonebender mkii transistor question

[nepalnt21]

planning on breadboarding the mkii fuzz, according to this page: http://fuzzcentral.ssguitar.com/mkII.php

honestly, im not sure which brand/ version i wanna go with, maybe i'll try out all three.

my question is: do all three transistors make a difference in tone? i have a few germanium pnp BJTs, but i am wondering if i could just use Si in one or two slots. which of the three make the most impact on the overall tone?

thanks

[PRR]

Q1 "has" to be "leaky" (or a new bias devised). The collector should come to 1V to 8V, not zero or 9V. (A Si part here would be hard-off, collector jammed at 9V.)

The other two will be different Ge or Si, but may be satisfactory either way.

[nepalnt21]

im pretty new to this: when you say collector should "come-to", are you talking bias? what do "hard-off" and "jammed" mean in this context?

edit*, ive collected that you mean yhere's a certain point where electricity wont flow? its been awhile since ive taken an electronics class... ive never used a transistor as a switch, only as component in boosters and distortions, afaik.

[Electric Warrior]

They are all set up for germanium transistors with a certain amount of leakage. You can make Q2 and Q3 work with silicons as well, but I don't know if it will sound the same.

Some of the fuzzcentral schematics have issues: These usually came with a 10k on Q1's base and a 47k on Q2's collector (with leaky OC75s) or 100ks in both spots (with lower leakage OC81Ds), no matter if Sola Sound, Marshall or Vox branded (the OEM versions used the same boards and circuit as the Sola Sound version when they were being made concurrently). Voltages for either version are in the same ballpark.

Also, their biasing instructions are way off. Here are voltage measurements from my vintage unit:

Battery: 9.67V
Q1 C -9.02V B -0.03V E 0V
Q2 C -0.17V B -0.08V E 0V
Q3 C -8.44V B -0.17V E -0.11V

[Mich P]

"Also, their biasing instructions are way off."

Sorry, but i'm not agree with that.
I've build this fuzz and i try differents biasing and the best
(to my ear)were the fuzz central option.
So, always try by your own.

[nation]

I recently tried Electric Warrior's method with OC75s in all three positions and it worked a treat. Initially I had two 100k resistors off Q1B and Q2C and tried biasing with a 10k and then a 25k trimmer replacing 8k2. The trimmer would only move Q2C by 0.5v at either end of the rotation and always around 8 and 9V and the pedal sounded bad with a lot of gating. Guitar volume roll off accentuated this and notes died quickly and abruptly.

I then put the 8k2 resistor back in and replaced Q1B with a 10K and put a 100k trimmer on Q2C as advised by EW. This made a world of difference, at 47k my Q3C voltages came into line with what EW posted above and the full rotation of the new bias pot allows me to go from 3V up to 9V on Q3C and great tones to be had between circa 40k and 60k on the trimmer. Not to say that it sounds bad at 4.5V but the real nice tones for me are in the 7.5V to 9V range. Only problem now is that I have a loud system type hum when I tune the trim pot to give me 4 and 7V which I need to work out.

[antonis]

im pretty new to this: when you say collector should "come-to", are you talking bias? what do "hard-off" and "jammed" mean in this context?

Paul tells you that now-days Si trannies exibit negligible leakage current so, in case of direct replacement into a circuit designed for "heavy" leakage BC junction should result in mis-bias, hence set at cut-off (or saturation, depending on specific circuit..) state.

ive never used a transistor as a switch,

So, don't do it now..
A transistor permanently set at cut-off state should be totally useless..