more gain ideas

[Bieworm]

hi guys

Some time ago I built a tone king imperial clone. I had some fizz on the OD channel and the clean channel too when fully cranked. So I started tweaking with grid stoppers... ending up with a LPT PI instead of the paraphase PI that was in there.
Still fighting that fizz I came to realize that even if the fizz was gone I still wouldn't like the midbite thing  one bit. It has a good amount of drive, but totally overrides the tone control that resluts in a (intended, I know) middy nasty gnarl I don't think I like.
So.. I removed the entire OD channels components and started over with a normal 3 triode configuration with a volume and tone knob. The midbite now was used as part of the voltage divider between the 1st stage and the parallel triode 2nd stage. Now it starts to sound like I can do nice overdrives. But I would like to be able to dial in some more overdrive...

I have been thinking it over and over and came with following solutions. Starting from the changed circuit (schem 1)...

A. change the voltage divider values to allow more juice towards the grid of the 2nd (parallel) stage (schem 2).. I think it will give more overdrive, but  I'm not sure.. so that's why I'm asking this. But there might be another option...

B. separate the parallel 2nd stage and cascade those too with the same voltage divider configuration. I was thinking about using a dual ganged B500k pot to wire the 2 voltage dividers to. So increasing the gain would evolve progressively on the 2nd and 3rd gain stage. I wrote A500k on the schematic, but I was thinking about the B500k I have in my stuffbox... When I come to achieve the tone I like I might even pull out the dual ganged pot and add a correct value grid leak resistor between the 1st 2 stages, correcponding with the measured value of resistance the pot has at that position..

Any obvious problems I will encounter?

EDIT: is it perhaps better to start with removing the voltage divider between V1A and V1B and replace it with a A1M pot? Or even raise the plate resistor value? I don't need a lot of extra gain anyway.. so maybe it's better to remove some attenuation on the voltage divider..  that 470k is already attenuating the signal substantually.

[pdf64]

I think that however one might tinker around with the 'parallel 2nd stage' options, it won't provide a reasonable depth of preamp overdrive.

[Bieworm]

I think that however one might tinker around with the 'parallel 2nd stage' options, it won't provide a reasonable depth of preamp overdrive.

Been playing it for the past hour  comparing it to my 18W Tremolo TMB.  It's pretty good  but I'd like it to have a little more kick. Next time I'm opening it up I will try a higher plate resistor like 220k instead of the 100k. And the voltage divider replaced by a 1M pot will be tried too. I think I will be in the ballpark of what I want it to do... but the 18W Tremolo TMB kicks its ass no matter what. That is one mean amp man!!! It has that plexi vibe even on low volume.. hard to believe, but it's true. Josh has designed a heavenly circuit. In fact, I love it so much that I have built 2 .. one with and one without reverb 😃😃😃

[Bieworm]

I have tested all these modifications..
I settled for the mod where the voltage divider is changed for a 1M pot. There is a 33k between the lug and the grid and a 47k from lug 3 to ground. Pretty nice now. Except I think I'm going to swap the A1M for a B1M or at least a 1M reverse audio...

[kagliostro]

MerlinsBootstrapCathodeFollower

Something to be tried ?

Franco

[Bieworm]

MerlinsBootstrapCathodeFollower

Something to be tried ?

Franco

Thanks. I thought of that too.. even the cascode... but it won't be necessary.  It's pretty fine now.
I'm going to explore the amp for now like this. Thinking about tinkering with the clean channel for more mids. Starting with the slope resistor and the mid resistor...