Mid Control For James/Baxandall Tone Stack?

[Wombaticus]

I'm in the process of prototyping a new tube amp, and have been pondering the same issue. I was thinking of trying the basic baxandall circuit, followed by a mid control from the Matchless Chieftain (http://www.freeinfosociety.com/elect...sschieftan.pdf). Any feelings as to how/if this would work out, other than: "just try it"? 8^)

Thanks.

The Mid control from the Chieftain is called a "bridged-T", and was used quite a bit in Gibson amplifiers of a certain vintage. The potential issue with the bridged-T is the source impedance. If it's too high, the control will increasingly cause the trebles to alter along with the mids (which may or may not be objectionable to you). The safest bet would be to put the Bax and the Mid control between different gain stages so that you will have a more predictable source impedance for both.

An alternative to the standard bridged-T is the Framus style bridged-T with caps forming the "arms" of the T, with a fixed resistor to ground, and a potentiometer acting as the bridge (output taken from the wiper). See the RubyRiot schematic for an example: http://www.framus.de/media/manuals/A...UBYRIOT_V1.pdf This version isn't quite so picky about the source impedance, but it is rather more fussy about the load that it is driving... the bass will start to vary with the control as as the load being driven become heavier. So kind of the opposite problem of the standard bridged-T. On the other hand, it behaves very nicely indeed when driving into a fixed high impedance like a grid or grid stopper/grid.

As always with tone stacks, simulation is very helpful. Bust out your LTSpice, and go to town until you get curves that look like they will do what you want.