Voltage controlled band pass filter?

[yerblues]

Hi everyone,

I have a feeling this one might be way too far out in left field, but I was wondering if anyone has any experience using voltage controlled bandpass filters with guitar (like the MoogerFooger for example). I built a simple one myself recently, but unfortunately I don't have anything to generate a control voltage.

I was hoping to be able to use an audio signal taken from a tape player, convert it to a voltage, and use that as the control for the filter. I've looked into frequency to control voltage converters, but I can't find much that seems to apply here. If anyone happens to know of a schematic for a simple frequency to voltage converter that would do the trick in this particular application, I would really appreciate taking a look at it.

Thanks!

[Mark Hammer]

About 75% of the "autowah" pedals out there are precisely what you describe: a voltage-controlled bandpass filter with some source of control voltage. The control voltage is the envelope of the input signal, although there is often little reason why one could not interrupt the path and substitute an external signal for the guitar/input. Read this paper to see an illustration and explanation: http://www.geofex.com/Article_Folder...ch/ecftech.htm

The control voltage CAN be, but doesn't HAVE to be, proportional to the fundamental frequency of the the control signal. All commercial autowah pedals, including the Moogerfooger Lowpass, use the overall input amplitude to sweep the filter. Although it is possible to derive a control voltage proportional to the fundamental frequency, that is a MUCH more complex process than a mere envelope follower.