BMP Tone Control Mod

[jishnudg]

Just tinkering with the Duncan amps tone control simulation, and thought it'd be nice if a 3 knob version of a BMP tone control could be made, like this - -

http://i64.photobucket.com/albums/h169/jishnudg/70bdb4a4-6d2b-4544-8af9-c2b614171e07_zps1a68ed5c.jpg~original

Basically adding some degree of variability to the LP and HP filters.  Would love some comments on this!

Thanks!
J.

[nocentelli]

I think the two pots will be interactive: The upper "tune1" pot is the standard way of implementing a midscoop/midboost control, but the lower "tune2" pot will also have this effect making it somewhat superfluous. If you're going to the effort of committing three pots to a tonestack, you might be better off with a bass/middle/treble set up.

[jishnudg]

There's actually a small error in the schematic - - it should be 100k "Tone"  well, if the "Tone" pot is set one way or the other (not in the middle) shouldn't one of the two filters (the one the tone pot is set towards) be dominant? The Idea here was to have a single Tone control, but be able to set its extremes...would this do that well?

[GibsonGM]

It will DO it, but how 'well' is going to be subjective.   Like Nocentelli said, this will be interactive....the setting of one 'tune' pot will definitely affect the control of the 'tone' knob.    So you have 3 parameters going on at all times.  You COULD simulate this in LT or your favorite software, and do a sweep showing how it's all going to move.

However, the easiest way to get an idea of what this will do would be to breadboard the tone stack, with a simple buffer or something in front of it.  Then you can physically mess around with it.   It will "work", but it will be difficult to dial in what you like, I think.  Could be frustrating, more so than the previously-mentioned BMT would be.   

Perhaps breadboard it, find the values you think are good for the "tune" resistances, measure the pot values and then replace with regular resistors instead of a pots?

[nocentelli]

With the values you've chosen, the 100n cap in the highpass filter path would allow most of the guitar's bandwidth to pass (i.e. right down into the middle+bass frequencies - a 4n cap is usually used here, which would roll off most of that): If the tone control was fully clockwise, and the "tune1" pot at maximum resistance, almost all the guitar's sound would be audible with the very low end rolled off by the 100k pot - Reducing the resistance of "tune1" would then act as a quasi bass control, rolling off more bass and then low middle as the resistance goes down.

Set to the other extreme of the tone pot, the 220n-to-ground cap is so large (BMP value = 10n) that most of the treble AND a lot of middle would be rolled off, and you would be left with an extremely woolly and indistinct signal - Rotating the "tune2" pot would just slightly alter how extremely woolly the sound would be.

The BMP tone control is a clever and relatively versatile control, but it is limited by the compromise that more bass = less treble and vice versa: The "presence" control mod aka midscoop/boost (see link below) adds a bit more variation to it, but there is not much scope to take it a lot further than that without dumping the combined LPF/HPF single pot altogether.

http://www.muzique.com/lab/tone3.htm