Anybody tried bypassing V2 in an Express clone?

[ForcedFire]

I was considering adding a switch to take V2 out of the preamp circuit so the preamp is just V1 with the tonestack driving the PI.

Anybody try this? From my simulations it still overdrives the power amp pretty quickly.

[ForcedFire]

I just did this mod. I drilled for a heavy duty Carling DPDT between V2 and V3. The switch is wired to completely bypass V2 out of the circuit which gives a bit more room on the volume pot before the power amp distorts. I kept the 0.0022uF cap in the circuit.

The Deluxe Reverb that is very similar to this has a 1nF coupling cap to the PI. I might add a second 0.0022uF cap on my V2 bypass switch since I seem to have a ton of bass with V2 bypassed.

I'll post some pics later.

[M Fowler]

I have never done that or considered it before, how did you like the change?

Mark

[ForcedFire]

It's pretty interesting. Definitely changes how the amp breaks up.

It's a much lighter overdrive but still has really good harmonics. Less noisy too, obviously.

I didn't have any large high voltage caps on hand (around 1uF) so I have DC on the switch. I imagine it would pop insanely loudly so I only flip it on standby.

The Deluxe reverb couples the second gain stage to PI with a 220k resistor and 0.047uF cap and then there's another 0.001uF cap on the PI. I only have the 0.0022uF cap in the bypass mode and it's too bassy. I just did a couple of time domain simlations and it looks pretty good with a 220k or 470k resistor in parallel with a cap. I have to run the AC simulations to figure out what values I want to use.

[jaysg]

The Deluxe reverb couples the second gain stage to PI with a 220k resistor and 0.047uF cap and then there's another 0.001uF cap on the PI. I only have the 0.0022uF cap in the bypass mode and it's too bassy. I just did a couple of time domain simlations and it looks pretty good with a 220k or 470k resistor in parallel with a cap. I have to run the AC simulations to figure out what values I want to use.

Can you post a schematic on this? I'm having trouble envisioning it. For example, if the .0022uF after the tone stack recovery is still there in bypass, is the shunt resistor still there...together they kill a lot of low end.

[EL34junkie]

I threw a cap around the 56k res in between the 1st and 2nd 12ax7 and it had good gain. We did it with aligator clamps but we are going to wire it in as a foot switch. The guy I built it for loves the amp at 10 but wanted more gain at lower volume.