Adding a Baxandall tone stack

[bluefoxicy]

I've ordered parts for a Baxandall tone stack for my VJ, trying to reason out placement. The Tweed mod shows linkage to the volume knob but I don't think that's wise for anything other than a Princeton tone control; I've had considerable results with a capacitor switch in C1, so I'll likely put the Baxandall there.

 

I just made a few changes that resulted in very nice operation. R6 and R7 down from 1M to 100k; input filter set to 10nF (16Hz low cut); C4 from 22uF to 2.2uF (C3 uses 1uF); and put a 47k resistor in my NFB circuit. C1 used a switch to set .022uf or .0015uF, and this switch now actually has a strong audible effect, hence my decision to finally get a tone stack in there.

 

For the tone stack, I've decided to follow gain stage 1 with an IRF820 (NTE2398 actually) MOSFET set up as a source follower into the tone stack. This will provide 25 ohms of impedance; I'll stick a 33k resistor in front of that to create a 33k non-reactive load. It's not a gain stage, it's a current source (like a cathode follower), which a tone stack desperately needs. For R4 in the control I might use 100k instead of 180k, but likely not unless it sounds poor at 180k.

 

I'm not sure if I want to totally replace C1 with the Baxandall; I'm thinking I'll place its input after C1 and its output into R6, in series between the two. Thoughts?

[bluefoxicy]

Hmm.

 

http://users.adelphia.net/~thomasholley/Guitar/Guitar%20Input%20Stage.gif

 

Looks like I should follow the volume knob. This does make sense because of the NFB loop.

 

http://www.triodeguy.com/other_projects.htm has a baxandall practice amp that's kind of complex.