Mid Fq control for 3-band Baxandall

[juan_felt]

Hi!

I´m working on a new overdrive project with a 3-band baxandall tonestack and I´d like to add a middle frequency control.
The schematic is similar to these.. What should I modify to change the mid freq while keeping the same levels?

http://smg.photobucket.com/user/rickydon/media/3band.gif.html
http://audio-perfection.com/wp-content/uploads/3-Band-Tone-Control1.png

Thank you in advance!

[GibsonGM]

The .005 and .022u caps' values in the first pic can be altered to get different mid responses.  Why don't you 'build' this in LT Spice or another sim program, and play with those values to see what you get?

In the 2nd graphic, there's more going on.  They're simulating pots with 2 resistors (the RLF and RMF-tagged resistors).   You can also sim that one up, and try changing C1 C2 C3 and C4, if you like.   

If you can find some info on "bridged T" filters, that would be good so that you can learn how to actually calculate response.   Just 'changing' the values won't do what you want - there is a 'balance' involved to keep the response even and predictable (math).   Check GEOFEX (link at top) for info on this, I believe R.G. did quite a bit on parametric EQ's etc.  The first schem. is the easiest way to do what you're describing, IMO.    Or one of R.G.'s gyrator-type things using 1 transistor.

[Rob Strand]

The Baxandall's with a mid control are hard to adjust because all the bands interact.
One way to do frequency control is to switch caps in parallel with the two mid caps, keeping the ratio of the total capacitance of each position the same.  The resulting frequency response isn't as good as you would think due to the interactions.

Beyond that I suggest a two-band Baxandall followed by this parametric,

http://www.diystompboxes.com/smfforum/index.php?topic%3D95483.0

A two-band Baxandall with the same behaviour as the three-band, say with the mid pot set flat, will not be the three-band circuit with the mid control components removed.   You are best matching up the behaviour with a circuit sim like pspice or ltspice.

[armdnrdy]

If you want Bass, Treble, and Mid controls...why don't you check out a Fender/Marshall/Vox tone stack?

This configuration has been used in overdrive circuits with great success. The Catalinbread Dirty Little Secret being one.

[DavidRavenMoon]

Fender tone stacks are boost only for the B/T and cut for the mid.

But that wasn't his question. He wants to be able to change the mid frequency.

[Derringer]

can't vouch for how it sounds, but check out the BAX plus Mid tonestack that Weber put into their Orange inspired amp kit.

http://www.tedweber.com/media/kits/6o100_schem.jpg

[Derringer]

The Baxandall's with a mid control are hard to adjust because all the bands interact.
One way to do frequency control is to switch caps in parallel with the two mid caps, keeping the ratio of the total capacitance of each position the same.  The resulting frequency response isn't as good as you would think due to the interactions.

Beyond that I suggest a two-band Baxandall followed by this parametric,

http://www.diystompboxes.com/smfforum/index.php?topic%3D95483.0

A two-band Baxandall with the same behaviour as the three-band, say with the mid pot set flat, will not be the three-band circuit with the mid control components removed.   You are best matching up the behaviour with a circuit sim like pspice or ltspice.

can you repost the link for the parametric ? that link only redirects me to the front page

thanks

[tca]

The peavy standard has a mid shift + mid control before the 2 knob Baxandall ... but is passive you will need to add another stage to recover the signal.

http://assets.peavey.com/literature/manuals/standard.pdf

Cheers,

[Rob Strand]

New link is:
http://www.diystompboxes.com/smfforum/index.php?topic=95483.msg827441#msg827441

(I think the issue is related to Aron updating the forum.)

[BubbaFet]

Check out how Ampeg does it on their Portaflex PF-350 bass preamp --> http://www.bmamps.com/Schematics/ampeg/Ampeg_PF-350_Preamp_Schematics.PDF

Supposedly Ampeg's new Scrambler bass-DI pedal, uses the same preamp, with their scrambler circuit tacked on.

[Eddododo]

http://www.albertkreuzer.com/pics/el/pre/schem/preamp_sch21.gif


look at the op-amp baxandall