Simulcast low cut / bias issue

[Svenson007]

Hey there fellow pedal nerds

It’s been a while. So I am building a Simulcast for somebody. It’s all together (not boxed) and tested. It sounds fantastic with some Toshiba germanium’s I salvaged out of a Hammond organ a while ago. Those things are like a gold mine.

The problem I’m having is with the low cut and biasing? Once I get down to about the last 1/4 turn of the pot it starts to fart out and sound severely mid biased. All the way down yields zero signal. Right before that it sound like a crackly mess.I’ve built a ton of Duocasts and never had a problem

I’ve read somewhere that the circuit doesn’t tolerate leakage well. So I tried a couple other transistors yielding slightly better results.

Is this really just a keep trying transistor until all is well? Or should I be focused on the biasing resistor. Not sure which that is, I haven’t had a peak yet. Also I’m not the best with schematics compared to some of you guys. I also considered trying different pots, but not sure how that would work out. And since it’s for somebody else I want all the correct values. If it was a personal build I wouldn’t mind quite as much as I don’t use much low cut.

Anyways. I’d be forever grateful if somebody could shine some light on this. Whether you have built it or now.

Edit- This build is using the old V1 style pcb if that matters.

Thanks so much guys.

 

[Svenson007]

Hey there fellow pedal nerds

It’s been a while. So I am building a Simulcast for somebody. It’s all together (not boxed) and tested. It sounds fantastic with some Toshiba germanium’s I salvaged out of a Hammond organ a while ago. Those things are like a gold mine.

The problem I’m having is with the low cut and biasing? Once I get down to about the last 1/4 turn of the pot it starts to fart out and sound severely mid biased. All the way down yields zero signal. Right before that it sound like a crackly mess.I’ve built a ton of Duocasts and never had a problem

I’ve read somewhere that the circuit doesn’t tolerate leakage well. So I tried a couple other transistors yielding slightly better results.

Is this really just a keep trying transistor until all is well? Or should I be focused on the biasing resistor. Not sure which that is, I haven’t had a peak yet. Also I’m not the best with schematics compared to some of you guys. I also considered trying different pots, but not sure how that would work out. And since it’s for somebody else I want all the correct values. If it was a personal build I wouldn’t mind quite as much as I don’t use much low cut.

Anyways. I’d be forever grateful if somebody could shine some light on this. Whether you have built it or now.

Edit- This build is using the old V1 style pcb if that matters.

Thanks so much guys.

Never mind guys. I just socketed the transistors and tested many many transistors. ended up using the highest hfe silicon and germanium I could find. That’s what was apparently holding me back. There is a small chance I installed the germanium with the wrong pinout….. but I positioned the same kind of transistors in the duocast many many times. So I don’t see how that could be the problem

My really crappy multimeter tells me the germanium is 133hfe… I doubt it. The silicon is 640hfe.

If anyone could please let me know which resistor is the bias I wound be so stoked. Then I could use a trim pot to dial it in was easier. I’m okay with most schematics….

But I’m a little stumped which resistor biases the germanium. This schematic is a bit weird compared to other “normal pedals” to me anyways