gain control in express amp

[phsyconoodler]

I wonder if a 'gain' controlcould be added to the express circuit where the v2 cathode goes to ground?
I'm looking at that 100k resistor and simply installing a pot in series with that 100k would throttle back the gain and become a nice control over the massive gain of the circuit.

Anyone tried that yet? It might not sound good but it just might.I realize that a master volume would do a similar thing but it doesn't really throttle back the gain and the gain at V1 is not that much different than an AB763 Fender circuit.
My thinking is that a pot of say 100k would do the trick wired as a resistor.
Any thought on that?

Don't get me wrong,I love the circuit as is,but control is always a plus IMHO.

Edit:maybe where the 150k enters the grid of V2?

[sliberty]

Sorry for not answering your question directly, but I would do it differently. I have had great success with gain reduction by using a split plate load resistor. So if I were to approach a variable control of some sort,mi would try to do some variation of that split plate load concept.

[phsyconoodler]

I'm thinking it should work as well as the Dumble method with a pot in series with the V2 grid.

[Firestorm]

Gain of a fully- bypassed preamp stage is all in the plate resistor. It can be split or even made variable (with a cermet pot). Unbypassed, you can fiddle with Rk, but the plate load is still more effective. Still might have to adjust the Rk to keep the bias right.

If you do something to the grid, that's a volume control; nothing wrong with that and you can bring it out to the panel.

[phsyconoodler]

Hmmm....But it works like a gain control on a Dumble amp and it's pretty much just controlling signal to the grid.
I guess it's like pre and post gain in a peavey amp?

[ChrisM]

Dumble's don't use a variable resistance setup like you're showing. They use a standard variable voltage divider.

Your method is altering the "classic" TW high pass filter.

[phsyconoodler]

Yes,I see that now.It would be better just to use a PPIMV.

[rock_mumbles]

How about this:
http://ampgarage.com/forum/viewtopic.ph ... st+gradual

[phsyconoodler]

Not exactly what I'm looking for.
How about replacing the 150k voltage divider that goes to V2 pin 2 with a 250k pot as a voltage divider?

That could be front panel mounted.
Any thoughts/

[Firestorm]

Not exactly what I'm looking for.
How about replacing the 150k voltage divider that goes to V2 pin 2 with a 250k pot as a voltage divider?

That could be front panel mounted.
Any thoughts/

I think that has been tried. But note that is principally a filter, so if you change the R, you also change the frequency response.

[phsyconoodler]

So the plate ov V1B coupled to the grid of V2 using the .022uf coupling capacitor is a filter as well as a coupling to the next stage?

Hmmm...What about a gain control before the cap?
Or even on the plate of V2 ? There has got to be a way to control the gain before it goes to the PI without upsetting the frequency too much.Maybe?

[Reeltarded]

Yeah, mixer. Put a pot at the tail end of the coupler then out to the next point.

You are going to end up with 300VDC on your front panel if you keep messing around.

[phsyconoodler]

I don't have any intention of putting plate voltage to a pot on the panel.
As we all know these amps are freakin loud and gainy,it's all about taming the beast to make it more versatile,not about turning it into something else.
I just want some control beyond the volume pot on my guitar.
It's not about volume,it's about gain and distortion.
These amps sound lovely clean too,and everywhere inbetween.

[Reeltarded]

Have you ever played an amp with a pre-stage pot at the input?

This would work for you if you are trying to match an instrument. Lower the signal there. Works.

[Clyde]

Like a guitar volume pot?