the Anti BMP-tonestack Wah, a cool building block filter/stand alone wah

[iainpunk]

hey, i was playing with the tonestack calculator online
http://www.guitarscience.net/tsc/bigmuff.htm
and found a cool looking frequency response that reminded me of a wah frequency response, but upside down.



so to turn it in to a wah, i put it in the feedback loop of an opamp, like so:



at first i didn´t have the input attenuation, so it clipped constantly, even when playing softly. so i added -35dB passive attenuation, which works fine for me. you can change the topology for the powersupply and Vbias to your own likings, but this seems to work well. the frequency sweep looks like this, its not really as vocal as other wah´s but its a great building block filter. 

the orange line going haywire in the high frequency is not actually available due to R4 limiting the pot´s response, this is so i dont accidentally fry my ears with a really nasty feedback coming from my amp.

here is an immage with both combined so you can keep them together in your schematics folder

[Mark Hammer]

Fascinating!  I would imagine that the component values can be tinkered with to shift or limit the range of sweep to be more "vocal".  That could include strapping fixed resistors between the pot wiper and one or both legs of the pot to alter resistance changes in either direction.

[iainpunk]

Fascinating!  I would imagine that the component values can be tinkered with to shift or limit the range of sweep to be more "vocal".  That could include strapping fixed resistors between the pot wiper and one or both legs of the pot to alter resistance changes in either direction.

yeah, moving the two filters further out from each other would probably make the wah more vocal, since the peak would be larger compared to the flats/shelves, but i really like this as a %^&*ed wah in between two overdrives, or after a fuzz because its less extreme.