Balancing volumes for 2 channels

[marcelomd]

Hi,

Some time ago I completed a 2 channel guitar preamp, documented here.

It sounds great. The problem is the huge difference in volume between channels. I have to crank both the gain and volume of the weakest channel to get to an acceptable volume.

Schematic for reference.


There's only one output buffer for both channels because of limited space.

I'm planning a second version of this preamp with separate output buffers. The idea is to give the weakest channel some more gain.

I tried simulating this in LTSpice, but couldn't reach a conclusion.
- Simulating an AC sweep, the first channel gain is obscene, because the simulation doesn't account for the clipping of transistors (I think).
- Simulating transients, the waveform clips earlier than I want (aiming for 500mV signal... I have hot pickups), but even if not clipping, the waveform is so deformed I can't draw any conclusions.

Is this the right way to go about it? I don't have access to a breadboard at this point, only the boards from the first batch.

Any suggestions?

Thanks!

[FiveseveN]

Set the gain of Q5 so the weakest (the clean I assume) channel is where you want it. Then attenuate the other one until they are balanced. You could try a 20~50K trimpot in parallel with C16.

[PRR]

A long-chain clipper has to be built as alternating gain stages and loss pads.



Note R63 R64, R74 R75, R83 R84 in the lower (and lower-gain) chain.

[Ben N]

A recovery stage after your clean channel passive tone stack and volume control should help - just like in the old Fender & Vox preamps that your design derives from. Also, have you considered a 1M volume pot?

[marcelomd]

A long-chain clipper has to be built as alternating gain stages and loss pads.



Note R63 R64, R74 R75, R83 R84 in the lower (and lower-gain) chain.

Hah... WTH. I imagine the guys at a Carvin meeting:
- How many tubes do we put in our new preamp?
- Yes

The bottom channel is nothing more than a Zvex Box of Rock + tonestack. The volume is more or less where I want, so I'll leave it there.