Some discussion came up on wattkins.com about tweed bassmans and that sort of pushed, overdriven sound some players get with them.
I had built this bassman sort of amp and decided to see if I could get that tone.
This, eventually, lead me down a path of tweaking the gain channel of the Nervosa a little bit more.
It seemed many people who use bassmans drive the front end with a pedal, not set for a lot of gain but to just drive it harder. So I tried a pedal into the normal input on the Nervosa and I could tell there was something to this.
I went in a slightly different direction and instead of a pedal I used the cascade mode, basically substituting the extra triode for the pedal.
I ended up turning the gain and master way up but turning the second volume down. This was a really cool sound! It had a big clear overdiven tone with a strat neck pickup.
The issue was the amp became super bright. I had a Marshall treble peaking circuit in there and a little .1uF cap on the middle triode when the amp is in cascade mode.
So the tweaks I did where to put that treble peaking circuit on a switch and to increase the .1 bypass cap to .47uF.
These two things really did the trick. I can turn off the treble peaking when I need to and the bigger bypass cap fattens up the tone nicely. Even when the amp is dialed in for more of a saturated tone it sounds better.
Here is the updated schematic:
Hi. I’ve been enjoying browsing through your projects.
Wrt. the Nervosa tone stack Shift switch: when the switch is in “100K” mode, shouldn’t the middle .022uf capacitor have another capacitor added in parallel – i.e., to get a total of .1 uf for the middle capacitor? The way you have the schematic drawn right now, it looks as if the middle tone stack capacitor is completely bypassed when the switch is in “100K” mode.
Interesting design btw. I built a similar hi/lo gain amp with switching built into the input jacks, JCM 800 style.
The way I have it the middle .1 cap is moved to before the tone stack and the rest of the tone stack is in series with it. So the middle is basically .1. I’m thinking of changing this though because the .02 caps are really less than .02 now because they are also in series with the .1. I’m probably going to change the .1 to something really big like a .47 and then add the .1 in the normal position.