Moog Music Forum

This is a questions for any Moog CV experts out there. What's a safe current draw on Moog CV's (MP-201, Etherwave etc.) I'd like to try a dead simple vactrol setup with an LED and photoresistor. I've seen one reference for 0.5 mA but I can't find anything in the MP-201 manual.

Any insight would be greatly appreciated!

I don't know what the maximum output current is on MP-201 or Etherwave but you woud need at least several mA to get anything from an LED - possiby up to 10mA.

Are you trying to get a linear change in the photo resistor caused by the CV output level? If so, you'll probably get nothing (or very little) from the LED until you get close to its 'forward voltage' (could be 1.5V-ish), so it wouldn't be linear across the full CV range.

I may not have understood what you're trying to achieve...

Thanks, those are both good points. I was estimating something like 20 mA. for the LED. Lineararity is less of an issue- this would be for circuit bending/hardware hacking applications more than acurate pitch tracking.

A typical blue led (as used in flashlights) will draw 1 ma when powered from a red jack of my Voyager, which is the max the CV can supply, the led would draw more if it could (the load).

Bright enough to make a controller with a CDS cell. I got a picture of this somewhere I think in this forum.

Made a new pic anyway... cheapest light controller ever... and it works great.

2 TRS plugs

1 CDS cell (5 for a few bucks at Radio Shack)

1 blue led on a swivel head (from a reading light, 1 dollar at the dollar store).

You can either move the swivel head or put your finger between the light and the cell for touchless operation.

Seen here in action controlling the LFO rate of a CP-251.

Awsome, that's close to what I was thinking of- did you wire the LED directly to the jack or use a resistor in series? I want to modulate the LED's brightness with Moog CV and my photo cell will be attached to another device.

makers wrote:I want to modulate the LED's brightness with Moog CV and my photo cell will be attached to another device.

Isn't that the principle of Vactrols? Anyone correct me, but if so, you can find some info online through googling that word.

Yep, that's what I'm looking to do- drive a vactrol with Moog CV. It should't be much trouble to build a simple circuit to control the LED side of the vactrol with a transistor but I was wondering about skipping that altogether and hooking a vactrol directly to CV.