trying to get more mids out of BMP (tone control schem inside)

[runmikeyrun]

Hey guys,

I built a BMP off another builder's schematic.  He has a different tone control section with a mid control added.  I'd like to know what I can do to get more mids.  Also, it seems like the tone control doesn't really do anything...?  Anyways, here's the schem, if you can offer me suggestions that would be great...  I'd like to get those huge mids that BMP are known for.  The mid control in the schem only seems to cut mids, not boost them.

[Johan]

make the upper 10nF smaller and the lower one bigger.. try half and double to start with.
the tonecontroll basicly pans between a simple low-pass and high-pass filter. by pushing their crossover frequencys apart, so they dont overlap, you should get more mids(if there are any more to be had)
J

[teemuk]

The way this tone control circuit works is that it splits the signal into two parallel RC filters, one low-pass the other high-pass; the potentiometer blends in between them. The filters are usually designed to interweave so that the corner frequency of low cut is lower than the corner frequency of the high-cut, which results into mid-range cut when in mid way of the dial.

If you alter the corner frequencies to match more closely you will get a linear response, if you alter them so that CF of low-pass is higher than the CF of hi-pass you will get a mid-range boosted response.

With that in mind, implementing mid-range control to either RC circuits is achieved by altering the RC circuit's corner frequency so that the two filters begin to overlap. But those added parts are still actually part of either low-pass or high-pass filter so such control will also affect other frequencies besides the mid-range a lot.

Download Duncan's Tonestack Calculator and see what affects what your self. That's the best way to learn.

If you really want a working and effective mid-range control then I would not try to implelement one to this tonestack circuit but build another circuit for the task instead.

[runmikeyrun]

thanks guys for the input.  I found this at Jack's site, might give it a try.  It's different than the way I have my tone control laid out. 



I do have duncans TSC but it doesn't have that mid control that I have on my tone control.  That's what I was hoping to play with to bring out more mids.

I've got some 'spirimentin to do.

[Electron Tornado]

Here's an article that describes a simple mod to give you flat mids:

http://guitarkitbuilder.com/content/big-muff-pi-mod-more-mid-range-tone

[aron]

What I would try on the Big Muff is a modified VOX tone stack. If you play around with the simulator, that tone stack can get some wild settings which I think would be perfect for the Big Muff.

[teemuk]

I do have duncans TSC but it doesn't have that mid control that I have on my tone control.

But that mid control is nothing more complex than just varying the shunt resistance in the CR chain. The TSC can easily show its effect: Just snapshot R2 as 10k, as 110K and as any value you want in between, eg. 60K, which would correspond to mid pot dialled to mid way, assuming the pot is linear.

[runmikeyrun]

I want to thank everyone for their replies.  I got it in a pretty good place... I kept the 100k mids pot, but wired it like in Jack's schematic- way more useful.  I also dropped the 1st 10n cap to a smaller value for more highs.  The tone stack functions much better now and has a wider sweep. 

other mods I did- switch to shunt the emitter resistor on Q3 to ground for a boost.  I also removed the diodes on Q3 for more gain.  Lastly, I put in a tone bypass switch, which gives it a LOT more gain, but sacrifices that tone section that I monkeyed with so much.  It sounds pretty good now.