Mid Control For James/Baxandall Tone Stack?

[Daver]

Does anyone have a schematic or idea of how to add a mid control to the James/Baxandall type tone stack? Yes, I know they aren't identical. I've seen one where the grounded components for the bass and treble are tied together and attached to a pot to ground as the mid control. How does that sound? I worked on an amp that used a 2 Meg pot to bypass the tone stack as the mid control. That worked somewhat, but really changed the gain a bunch as you might imagine. I suppose I could add a T filter somewhere but thought that might be adding a lot of components and be a bit cluttered. Any ideas? Thanks!
Dave

[exclamationmark]

I believe there is a 'mid shift' circuit in Merlin's book somewhere. Basically it shifts the center frequency to the right or left. I always liked the baxandall for it's simplicity and logically, you don't actually need a mid control (unless you don't like the 20db loss or whatever the centre frequency is at). Turning the two knobs to the max has a fairly healthy mid scoop, while turning them down has the opposite effect. Really, it's actually a lot less interactive than the FMV/Marshall stack (which might be a good or bad thing depending on how you look at it).

I don't know about any further control of the mid frequencies, but you can certainly change the frequency response of the circuit by fiddling with some cap/resistor values.

[loudthud]

There is a mid control for the Baxandall circuit (the one in the feedback loop). Crate used it on some solid state guitar amps back in the 80s or 90s. There are one example in a National Semiconductor data sheet or AP note, I'll see if I can dig it up. The only example I know of in a tube amp is the JCM 800 Model 2001 Bass amp. Link: http://www.el34world.com/charts/Sche.../2001_375w.pdf The mid control is on the lower channel with the switch to set the frequency by selecting different capacitors.

[Daver]

Thanks for the help guys! I'll have to experiment with it and see what works best.
Dave

[loudthud]

Here is a link to a National Semi data sheet. The Baxandall type Mid control is on page 9.

http://www.national.com/ds/LF/LF353.pdf

IIRC there was an Audio Applications book that had a more detailed example with equasions. Still looking for that one.

[Wakculloch]

If you can find the circuit for a Carlsbro 50Top, this had a James style tone circuit with a mid control.

[Daver]

loudthud,
Cool! That could work out nicely. I will have to try it. Thanks!

Wakculloch,
I'll do a search and see what I can find. Thanks much.

Dave

[Shane]

Heres a link to the Carlsbro schematic its pretty much the same as Merlins shift thing with an added cap.
Carlsbro 50 Top Amp Schematic

Garnet sometime would replace the resistor in between the two pots with T- filter or add one after the stack.
Cheers
Shane

[balijukka]

here's one that works
Amp disasters & other things - All kinds of tube creations

jukka

[Daver]

Thanks, jukka!

[thetubedude]

This is just a Big NorCal thanks to you for sharing your knowledge!

There is a mid control for the Baxandall circuit (the one in the feedback loop). Crate used it on some solid state guitar amps back in the 80s or 90s. There are one example in a National Semiconductor data sheet or AP note, I'll see if I can dig it up. The only example I know of in a tube amp is the JCM 800 Model 2001 Bass amp. Link: http://www.el34world.com/charts/Sche.../2001_375w.pdf The mid control is on the lower channel with the switch to set the frequency by selecting different capacitors.

I would have never guessed that Marshall used the Baxandall tone-stack in anything, let-alone somebody
actually leading me by the hand to the original schematic. Thanks MAN! LJay Walton/Cotati CA by way of
Tucumcari NM

[loudthud]

The Marshall JCM800 Bass amp models 1987 (50W) and 1992 (100W) from the early-mid 80s had a Baxandall Treble and Bass controls and a passive mid control with Sweep control to change the frequency. Those are pretty rare. The schematics should be on the Hoffman site.

[hasserl]

Carvin uses this type of tone stack with Mid control in many of their amps. Check this one: http://www.carvinmuseum.com/pdf/amps...r%20REV-E1.pdf

[teemuk]

Hint: Google search 3-band baxandall.



The circuit extends to several parallel bands for mid-range controls. Most extensive I've seen so far has been a 5-band graphic EQ. At that stage it likely gets more useful to switch to resonant tone control circuits, though.

[jbefumo]

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.

Does anyone have a schematic or idea of how to add a mid control to the James/Baxandall type tone stack? Yes, I know they aren't identical. I've seen one where the grounded components for the bass and treble are tied together and attached to a pot to ground as the mid control. How does that sound? I worked on an amp that used a 2 Meg pot to bypass the tone stack as the mid control. That worked somewhat, but really changed the gain a bunch as you might imagine. I suppose I could add a T filter somewhere but thought that might be adding a lot of components and be a bit cluttered. Any ideas? Thanks!
Dave