Tube Screamer Without Drive Pot

[mremic01]

I was just messing around with a Son of Screamer circuit I built a couple weeks ago, and I forgot to connect the wires to the drive pot. It sounded great. Just a little tighter and more aggressive than normally. So I hooked up a switch to experiment and found that when the drive pot was maxed out, it was still a little tame compared to when the pot was completely out of the circuit. I'm thinking of incorporating this into future builds. I'm still pretty new to electronics and I'm not sure why this would happen though. Is there a reason that it does this? I imagine that the pot has some resistance even when it's dimed, but then I would think breaking the circuit there would cut off the signal too.

[earthtonesaudio]

Non-inverting gain is (1+Zf/Zi) where Zf is everything between the inverting input and the output, and Zi is everything between the inverting input and some nonvarying DC voltage (AC ground).

The drive pot is part of Zf along with the diodes and the small value cap.  Since it is in parallel with those other things, removing the drive pot increases the overall value of Zf.  There is sufficient conduction through the diodes to bias the op-amp and keep it from misbehaving too badly, but the gain is increased dramatically.

[HOTTUBES]

It would be cool to set that up on a foot switch for solo boosts etc . .......

[mremic01]

So is it safe to do then? It's not going to damage the IC?

I wouldn't call it a boost so much. At least it doesn't get that much louder. It just gets a little more aggressive sounding though. If I had to give it a name, I'd call it the 'unleashed' mod or something like that.

[earthtonesaudio]

It's safe.

[Steben]

response curve of a si + ge diode pair could be a nice copy of CMOS inverter amp stage.
Really high gain, yes. Ideall or a hard rock/metal pedal. Bad for an overdrive