Switch Cap Low Pass Envelope Filter

[rring]

I put this together a few weeks ago for the heck of it. It consists of subcircuits I have used before in other designs. It produces some really nice low pass envelope effects. The variable attack is quite useful  but can be omitted. A 10k resistor is a good choice to replace it, if this is done. The clk generation circuit uses the CD4046 and not the 74HC4046, this is because the  VCO in the 74 series part goes crazy near the high end of the control voltage range and abruply oscillates way too high for the switch cap filter work correctly.

I have files for a 1590b layout at www.circuitsalad.com. It does not have the variety of sounds that a Mutron has of course , but for guitar the low pass characteristic is by far the most useful (just an opinion) - so the small footprint, simplicity and small set of controls may make it attractive.




Here is a classic "Jerry Garcia noodling" sound clip:
http://circuitsaladdotcom.files.wordpress.com/2013/12/envelopefilter-demo.mp3

[Mark Hammer]

That sounds nice.  The sample is very reminiscent of the MXR Envelope Filter, and the schematic suggests more control.

I can't access the web-page (work filters  ).  How many poles does it have, and is there a means to adjust resonance?

[rring]

Its a 5 pole filter with a butterworth  type curve. There is no feedback loop to create resonance or variable Q but the 5 pole filter has nice sharp knee. The adjustable attack is helpful because you can get  sounds more akin to using your foot on a wah pedal as opposed to the more snappy response as in the sound clip.

[Mark Hammer]

One of the pleasing aspects of a 4-pole lowpass (whether diode ladder or some other topology) with resonance is that it can mimic a bandpass, when the resonance is cranked, without the thinness that happens when a bandpass sweeps up too high.  It would be great if you could find a way to get some resonance in there...which doesn't mean it sounds bad, as is.

How would one go about reversing the direction of sweep?

[rring]

Yes that makes alot of sense - will have to look at that. Yes the reversing of direction would require a different peak detector structure - this one utilizes ground sensing and can only work with positive excursions. Lots of choices here to do that - as I write - I am thinking - you  could just add a unity gain inverter stage after the peak detector set to a max VCO voltage. As the peak detector V goes up the VCO voltage will go down. An op amp or a cheapo transistor would work. Add a switch and repitition of the input stage with some value adjustments - I think that would work.

[Kipper4]

Sweet. another for the later list me thinks
Thanks