Aionfx "Epsilon" Silicon Fuzz Face - Q1 Bias Troubleshooting

[mattypalm]

With the "Epsilon" Silicon Fuzz face from Aionfx, I'm not able to set the Q1 bias correctly. The Q1 trim pot has a range of about 1.25 V to 1.65 V, when the voltage (according to instructions) should be 0.7 V. I'm a real noob - do I just need to change the trim pot?

I used the 2N3903 and 2N3904 lower gain transistor option.

[antonis]

Hi & Welcome..

I can't say anything about "correct" FuzzFace clones biasing but I can't figure out the way of good working Si BJTs with V_BE 200mV only..
(unless they work as asymmetrical clippers..)

[abc1234]

0.7V sounds wrong for what I assume is an NPN Fuzz Face.

Bias Q1 to around 1.4V and Q2 to around 4.5V, and listen to the results.

Source: My own experiments with NPN silicon Fuzz Faces and threads like https://www.diystompboxes.com/smfforum/index.php?topic=104888.0.

[idy]

Is it working? Sounds like what?

It does look like the PCB is designed and marked for transistors like yours, that pinout EBC... but a pinout mismatch is one super common problem we would want to eliminate.

Si transistors "always" will have a "diode drop" between base and emitter, around .6v difference. If not, something is wonky.

Check and double check your solder joints and maybe pass the magic wand (soldering iron) over the joints to reflow and make good. Double check resistor values. Read the trouble shooting thread (Welcome to the Forum!)

And then post the voltages for all three transistors.
Q1
E:
B:
C:

When you get to Q3 the pins are D, S, and G, left to right facing the flat side. If you have a 2n5457.

Interesting and unusual is that Epsilon has a bias pot for both transistors. Most mad scientists only mess with Q2. Fuzz face have a funny bias arrangement where the voltage on the base of Q1 comes from a feedback loop with the emitter of Q2.

[PRR]

https://aionfx.com/project/epsilon-silicon-fuzz/

I do not see how Q1 can be alive at 0.2V on the Base. This may be a typo, perhaps from a Ge version.

[mattypalm]

Thanks for your responses! abc1234 you're totally right about 1.4v being the correct voltage. This was confirmed by Aionfx who kindly helped me out as well, and told me how to set Q1 correctly.

Should have played with the pedal more, and trusted my ears, cos it sounds awesome.

PRR I believe you're right about it being a typo from the Ge version, they're gonna update it now.