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.

 

[Feral Feline]

Hi lmajcen, I saw your post in Peccary's modifications-thread. The schematic didn't show, only the vero layout:

I'm still trying to fix my Dizzy Tone clone from this schematic:
Everything on the pedal works, my bias is around 1V when maxed out on Q3, sound is awesome..but there is a single problem with it, if you hit the strings super hard and stop them with your palm immeditately after, there is a weird gating sound (sounds like a phase for a second). It seems like the capacitor is charging and discharging..no idea. Tried over 20 sets of transistors (proper hfes and leakages), as well as diodes.
I'm slowly losing my mind with this pedal
I also built Gnat Fuzz, and the same exact thing - pedal is sounding awesome, just that small thing that I mentioned above.
Is that maybe how the effects behaves? I have no idea anymore, thanks!
View attachment 79915

As Chuck D Bones said in Peccary's thread: "Follow the troubleshooting protocol. Provide pix of your board. Tell us what part numbers you used for your transistors and diode. Measure the collector voltages on Q2 & Q3."

What schematic are you working from? Can you post pics of your build?

 

[lmajcen]

Hello! I'm sorry, will post a schematic now, photos tomorrow (because I'm not home at the moment).
About the parts:

Currently I'm using matched set of Soviet transistors:
Q1 hfe is 57 (no leakage)
Q2 hfe 75 (no leakage)
Q3 hfe is 108 (leakage around 300-400)

I do have more sets ready as well (some AC125s).
Diode that I'm using is 1N34A. Voltages for Q1 and Q2 are 3.78V and for Q3 1V when the balance is completely cranked.

I use A5k for Balance, 1M for Attack and C250k for sustain.
For the reference I can also use my Super Electric Dizzy Tone by Jimmy Behan which is tuned to have a bit more sustain and less gating (Still using SFT308 in Q3) his pedal is super quiet even after hitting the strings pretty hard and stopping them immediately.
I also tried to bias 18k going to the Balance pot, at one point the noise stopped but the sound was pretty bad but I noticed when I tweaked that value that the speed of the noise generated is changing. One more funny thing to mention, whenever I pressed my finger against the vero where the 25uf/100uf between the -9V and the +Ground is the noise wasn't present.
Thanks a lot folks, I will be posting the pics soon.

Schematic that I'm using is this one:

 

[Feral Feline]

You might have a cold solder joint at the 25µF/100µF point, pressing on the vero flexes it enough to make good contact but as soon as you let go... I'd heat up those joints and

 

[lmajcen]

Oh my, after a constant year of pain, I accidentally found the issue! It was "biasing" issue indeed. Once more I put the trim pot instead of the Q3 collector resistor and turned it slightly until I found the perfect spot. When I did turn it it changed how fast/slow the gate was kicking in and I found a spot where it worked...It was slightly below 18k (around 13-15k). Oh and yes, it sounds amazing, ordered a proper big enclosure and will be posting pictures soon!!!