Buzzaround (Gnat Fuzz)/Elka Dizzy Tone gating issues

[lmajcen]

Hi guys! I need some help with some issues that I've encountered in my build.

So, let me start by saying I've built a Gnat (Buzzaround) PCB kit from Musikding/PedalPCB and it's having the exact same issue as my Vero built Elka Dizzy Tone. Whenever you stop playing the gating kicks in but then few miliseconds later I can hear a hum that gets a bit louder and then it stops. I have no idea why this happens, tried using different supplies/adapters/batteries and it's the same.
Now, this is where it gets interesting. The only same type of components used in both builds are transistors (AC125s and the Ge diode which I'm not sure which one it is). Everything else is different.
Here is the link to the audio recording of the issue: https://drive.google.com/file/d/1uqr4pqbQj-cJ0zw4tLU4TlXr99ocnvl8/view?usp=sharing

However, I really, REALLY love the sound of this pedal, it's the perfect fuzzbox for my needs! Hopefully I can fix it and box it and use it. Thanks!

 

[Cybercow]

Gating and farting with Ge BJTs is generally caused by two primary reasons:
1) The device(s) is(are) not properly biased.
2) The leakage factor of Ge devices and how that is exacerbated by temperature fluctuations.

Germanium devices are temperature sensitive and when subjected to temperature change, they tend to behave in an unexpected manner. And their temperature sensitivity can greatly affect their leakage. The leakage factor & temperature sensitivity of Ge devices is the primary reason the industry moved to silicon instead of germanium.

You would be well served to examine the leakage of those AC125s and consider a bias adjustment.

Some good clear photos of your build might be helpful too.

 

[lmajcen]

Hey!
Okay I've tried pedal when the temperature is super hot or super cold and the effect is the same - the problem with gating.
Maybe I'll try to post some voltages later today, do you need a readings with the balance knob cranked or at any position? Thanks!

 

[lmajcen]

Hmmm, so I get 3.78V at Q1 and Q2 collector but on Q3 I get 1V when balance is completely cranked. It seems like that's the problem, I have tried 6 other transistors for Q3 and every single change resulted in the same issue.

 

[Cybercow]

It's NOT the transistors, UNLESS their leakage values are too high. Anything over 300µA is suspect. The biasing resistor values need to be addressed if the leakages are less than 300µA.

Again, any good, clear, close-up photos of the circuit board and connections?

 

[peccary]

If you have different GE diodes I would recommend trying them in the circuit. I have built a few Dizzy Tones (NPN versions) and the diode has a huge influence on the gating in those pedals.