Buzzaround/Elka Dizzy Tone gating issues

[KingSG55]

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!

[idy]

Maybe measure the voltages on those transistors.
Kit, so those are "preselected" sets of transistors?
Are they socketed?

[KingSG55]

Hi! I'll try to de-solder them but I know they are around 70 hfe for Q1 and Q2 and 130 for Q3. Leakage, I don't know.

When I'm taking the voltage readings, do I need to crank the balance knob and have input and output plugged in?
Also, the set that I use (three Ac125s) is the same set from my Buzzaround build, and now when looking back, transistors maybe could be the problem somehow. Or maybe I should use some trimpots to bias the Q3? Not sure really, I'll try to get the readings first.
Thanks!

[KingSG55]

Ohh..so I tested the voltages..
Q1 and Q2 collector sits at around 3,78-4V and Q3 is around 1V when the balance is completely cranked. Probably that's the reason I get those issues. Should I change some resistors for trim pots to adjust the bias? I have tons of trimpots around.

I'm just not completely sure which resistors to change.

[antonis]

[mac]

Try lowering the 22uf interstage cap.

Also tweak that 18k going to the battery --> a 25k-50k pot wired as a variable resistor to find the better value.

mac

[KingSG55]

Hi friends! I've tried all of your suggestions. I even tried to change Q3 for (tested 6 transistors in total). Nothing works for some reason

Maybe Q1 and Q2 are too leaky?

[Rob Strand]

Hi friends! I've tried all of your suggestions. I even tried to change Q3 for (tested 6 transistors in total). Nothing works for some reason

Maybe Q1 and Q2 are too leaky?

I'm pretty sure Mac is on the right track.  Did you try his suggestion?

Another possibility is to reduce the value of the sustain pot.  Instead of changing the pot you could experiment by resistors across the pot, ie. from the cap + terminal to ground.

I saw a schematic with a 4u7 cap and a 100k pot.   That's going to speed things up by a factor of 10 over what you have.   You could try 4u7 and a 150k across the 250k pot.

[KingSG55]

Okay, I have tried every suggestion posted here, even built another board with the same components, I even tried Buzzaround variant on PCB with the same transistors and the problem remains. In the meantime I've built 2 Tonebender MKIII's and tried Ac125s and they work beatifully there. I really can't figure out what's going on.

I also have 2 50k bias pots instead of 18k resistors and on every setting the issues is present. At this point I think it's the leakage problem with Q1 and Q2, I can't measure them but knowing I tried 6 other transistors for Q3 it has to be the issue with Q1 and Q2. This is one of the weirdest builds ever

Maybe I'll just order matched set of trannies, if you have a good dealer in EU please send a link.

[PRR]

Have we noted that the battery is *backward*, positive ground?

[KingSG55]

Yeah, it won't work the other way around.

[mac]

This is one of the weirdest builds ever

Wierd biasing and Germs... what could go wrong?

mac

[Rob Strand]

It's not obvious where the problem is, or what part of the circuit is causing it.   The leakage alone won't be the cause but leakage combine with some other component might.   The most likely cause is the cap between the the second transistor and the third transistor/diode.   The long time constant would point to that as well.  Also, coupling caps can cause this type of behaviour.  However your tests show otherwise.

What about making that cap 100nF just as a test?

If your diode is around the wrong way it might cause problems.   Have you tried different diodes.  Maybe even a silicon diode, even just for a test.

The fact the Tonebender MKII works is more puzzling.   The two circuits differ mostly in this suspect region!   Perhaps you could try adding a resistor say 10k to 100k between in series with the cap ie. between the cap + and the sustain pot.

Thinking outside the box, there could be something about your amp which is doing it.  Try adding a 100k to 470k resistors in series with the output lead, or adding a volume control at the output.   The intent here isn't so much a fix but to see what has an effect on the 2 second noise modulation in your wave sample.

[KingSG55]

Hey Rob, first of all, thank you for your time. I tested more things in meanwhile, 20 other transistors, re-checked all the solder joints, built 2 more circuits (same components) and the problem remains. I have tried 2 other amps and 2 other guitars.

Do you think I could try to replace all of of the caps to bigger ones (especially power-filtering ones)? Or just the ones you mentioned? Thank you.

[KingSG55]

Okay, one more thing: I noticed it only happens when sustain is set a bit higher. I'm providing the sound recording here: https://drive.google.com/file/d/10pg9733s5isGfx8rFkvmJvcte3fmqJnx/view?usp=sharing

Btw. this is one of the best sounding fuzz pedals ever (IMHO). I've had millions of fuzz pedals and nothing comes close really. I really want to nail this one so I can put it on my board.

[KingSG55]

Hey Rob, I also tried to use silicon diode - the result is the same. I'm thinking capacitors could do it.

Quick thought: can 1M pulldown resistor mess with this circuit?

[KingSG55]

Here's the soundcard recording - just listen to that sustain..
https://drive.google.com/file/d/14VjJLGfRqmL_lqx6Y3sqbiRmQ_0pBL1z/view?usp=sharing

There's also that weird issues present - also tried different cables and amp/cab are out of the equation for sure.

[mac]

The Sustain pot changes bias and the 22uf cap time constant.
Besides there is the possibility that some of the electros caps leak.

The TB MkIII Sustain does not alter bias, and the Balance is gone, replaced by a fixed 10k/10k divider and a custom Volume pot.
And the interstage cap is 220nf.
Higher chances of diy success.

One thing you can try is to flip the Sustain pot by connecting the wiper to the interstage cap. This way bias will remain fixed. Most likely you'll need to find a pot value, or a resistor across the pot, that bias Q3 "properly" (check tomorrow weather at the Weather Channel ).

mac

[bmsiddall]

Try an audio probe at Q1 base, Q1/2 collector, Q3 base and see where the phenomenon kicks in.  Apologies if previously suggested!

[KingSG55]

Thank you for your suggestions!
Major discovery right before I went to bed - when I press my finger against this part of the board the pedal is dead silent/gated.

I'm thinking it's something with the cap/sustain 3.
I'll provide an audio recording later so you can hear it.

Btw. upped all of the electolytics to 100 uF except that one.