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CV output PID controller (aka "let's make a janky ER-301 expander")

CV output has long topped many people’s ER-301 wish list. But how to sneak a DC voltage past the AC-coupled outputs?

The classic method:
Attenuate some noise such that the amplitude is equivalent to your desired DC voltage, then extract that voltage using an envelope follower. And as I confirmed last night, such a method works just as well on the ER-301 as it does elsewhere.

My completely unnecessary method:
As above, but mult the resulting DC voltage back into the ER-301. Take that voltage and compare it to your setpoint. Consider the difference between these as “error”. Feed the error into three mixer channels which act as proportional, integral (low-pass filter as integrator), and derivative (microdelayed error comparison to extract slope) terms. Use this as your control signal over the attenuation of your noise.

This resulted in a hilarious, poorly-tuned, ringing mess of a control voltage. Much “worse” than the classic method, but somehow much more fun. And that is probably the end of my “janky ER-302” story since I greatly prefer its neighboring Teletype for CV duties :slight_smile:

[GIF incoming!]


Ack, my GIF is too big to embed. I’ll host externally later.

I bet this method could be used to (crappily) extract multiple DC voltages from a single ER-301 output. “Simply” control the amplitude of multiple tones, mix together, and route that chord to something like the SMR with each channel tuned to provide an envelope follower for one of the tones filtered out of the whole.

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Did a similar experiment some time back, and got pretty good results, though I didn’t use noise and didn’t attempt to control anything as sensitive as pitch with it.


I think I pretty much reached the same conclusion as you. Neat experiment but I haven’t once used the technique after making the video.