Ok, a little update on Space Echo CV inputs. They aren't CV inputs nor are they expression pedal inputs -- so dont go plugging CV into them.
The RE-301 manual states you plug the 'out' jack of a Roland FV-2 pedal into the 'remote' jack to control tape speed. The FV-2 is a simple volume pedal with a second pot that controls the minimum volume out. I initially thought "Huh? That makes no sense, you run stuff
through a volume pedal not out of it"
Did some detective work with the schematics for both the RE-301 and the FV-2:
The highlighted area shows the 'remote' input circuit on the RE-301. It's a mono switch jack that puts a 20k pot across ground through a 1.5k resistor. When you plug something into the jack the 20k pot is out of the circuit.
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The FV-2 also has a 20k pot so plugging the output into the RE-301 remote input essentially relocates the 20k speed pot outside the Chorus Echo. That's it. I assume the input and ouput jacks are mono switch jacks, so if something isn't plugged into the FV input jack then it's a continuous ground between the input and ouput jacks and the 20k pot in the pedal behaves exactly like the speed knob in the echo.
So if you plugged CV into the remote jack you'd generate some resistance but nowhere near enough to have proper speed control which jibes with people's accounts of 'something happening, but nothing useful'. CV may eventually damage some other components making the motor speed unreliable.
So, is there a way to convert CV into variable resistance? Yes! This is one of the best uses for a vactrol. Sure enough someone in the modular world makes such a beast:
VAC-PAK CV to Variable Resistance – A Circuit Bender's Dream! | Synthrotek
This was originally intended for circuit benders to have an easy way to control pots with CV but it'll work here just as well because you are doing exactly the same thing when you plug that volume pedal into the tape echo.
What this means is you can easily add CV control to the Space Echoes that don't have them (RE-101/201, RE-150, and their progenators the RE-100/200).
Total cost: about 20 bucks.
Not bad. Not bad, at all.