Help with a possible alteration to ADSR circuit

vockleya · Joined: Aug 18, 2013 Posts: 2 Location: Pennsylvania, US

I'm working on designing a synth that is completely analog, but controlled by a PIC microcontroller (or similar) and is MIDI capable. I am quite familiar with the digital side of things, but I could use a bit of help on a possible alteration to one of the analog sections. I have hit a rather large snag in the form of the non-existence of one of the necessary digital potentiometers for the project. The MFOS ADSR requires 1M pots, and I have been unable to find any 1M digital pots. Is there some way to change the circuit to use a different potentiometer, like 100k or 10k? Or could someone point me in the direction of a different ADSR that is compatible with the MFOS gear? Any help would be greatly appreciated.

vockleya · Joined: Aug 18, 2013 Posts: 2 Location: Pennsylvania, US

I just came up with an idea. If I use a 100k pot and add a 900k resistor to one end, that should effectively work like a 1M pot, but only be able to sweep the first 10%. That would mean the attack, decay, and release times can only be set between 0 and 2 seconds, but for my purposes, that is ok. I have included a quick schematic to show what I mean. Could this work, or is it as wrong as I suspect it might be?

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