SOLVED Dizzy gnat

[Mentaltossflycoon]

So I put together a dizzy elk inspired by @peccary 's build report. It works but I wanted to confer with y'all about the transistors. I bought some mp38 from Ukraine and they're all testing in a tightish range on my tc-1 (best I have rn, thanks again @fig). This means I have an ok selection of gain for Q1 and Q2 between 55 and 72 but Q3 should be more in the 100 range. I socketed them and have been digging around the small amount of germs I have and found an ac127 that's around 100 and an unbranded metal can around 120. No idea about leakage so I've tried a lot of combinations finding the best results with the highest gain mp38 (72) and a pair around 67 for Q1 and Q2.

It sounds amazing with everything maxed. The volume sustain knob seems to be fine but the other two have a major drop in volume when not cranked. I'm hoping this just means I need to keep on searching for the right set of transistors but if this sounds like another issue I'm hoping y'all will know what's up. I found little difference between any of the mp38 in Q1 and Q2. The unbranded in Q3 sounded ok and the ac127 sounded similar to the mp38. The rest of my germs are higher gain. Should I just finally order a Peak tester? I'm just not that germaniumy but I'm assuming I need a leakier Q3 than I have.

At full blast, I like it enough to box it as is but I feel like it isn't right.

 

[Coda]

I would bet its about finding the right transistors. I don't remember off without looking at the schematic, but the one of the knobs controls Q3 bias (Timbre? Sustain?)...what is the voltage at the collector of Q3?...

 

[Mentaltossflycoon]

70mv

 

[peccary]

I've built a few of these and to be honest they all really sound at their best with everything maxed out. I think it could easily be a one knob fuzz if you built everything dimed on the PCB.

That being said I don't remember a big volume drop being an issue with any of my builds and I can't test it because although I've built 6 or 7 of them they all seem to have run off. I can say that in my experience the GE diode has the biggest overall effect on the sound and feel of the fuzz and the transistors seem to be relatively forgiving. That's probably not your issue but it's a fun thing to kind of play around with to hear the differences at least.

Have you gone through it with a probe? If the volume drop is being caused by a wrong resistor or something that'd be an easy way to find it.

 

[Mentaltossflycoon]

Agreed on the diodes. Much bigger changes swapping those around. I have a black glass mullard in it now. I was kind of hoping you'd say it's a one trick pony anyway. I'll still get some smallbear goodness coming my way but it'll be a conservative order.

 

[peccary]

Agreed on the diodes. Much bigger changes swapping those around. I have a black glass mullard in it now. I was kind of hoping you'd say it's a one trick pony anyway. I'll still get some smallbear goodness coming my way but it'll be a conservative order.

It's definitely a one trick pony but it does it so well there's no shame in it. It'd be like being upset that your doomsday device didn't also function as an EZ Bake Oven

 

[Mentaltossflycoon]

Hmmmm... might just make it a one knob fooz. But it would be easier to just drill for 4 pots. Decisions decisions.....

If I were @Feral Feline I would have something to say about the path of least variable resistance.

 

[mdc]

I'm not sure what mods you've made from stock, but in my experience hfe and leakage aren't particularly important in tone bender MKIII/IV variants. It's the sound of one amp stage slamming into another, and the distortion comes from Q3 being (and this is a technical term) "blown the hell up." AFAIK when they switched to a Si version all they did was drop Si transistors into it with no other changes - it worked great and doesn't sound much (if at all) different from the Ge version.

They sound best with everything maxed or near maxed. Changing the bias will definitely affect the overall output, and I believe that's what one of the knobs on the dizzy tone does.

I love TBIIIs and their offspring, but they're definitely not versatile in any way.

vero-p2p has a fantastic spreadsheet with a lot of component values cribbed from various versions of this circuit so you can compare the differences. It seems to be a D*A*M favorite, so he's tweaked it in a lot of ways.

 

[Mentaltossflycoon]

I followed this.