August 21, 2016
Tech Time No. 007: Voltage-Controlled Cassette Deck...
by Chris Randall
Like the subject line says... I was curious as to how the Onde Magnétique OM-1 worked. Originally, I thought that these super cheap little decks might be powered directly from the sequencer. I went out and hit a few thrift stores and bought several and gave that a try, with success rates that varied between "not at all" and "fuckin' nope." (I believe I briefly referenced this failure in one of the other Tech Time videos.) So I just set that aside with a shrug and moved on to other things.
However, last night I was looking at the OM-1 video again, and I was like "oh. Duh. He's just throwing 0-5V at the speed pot." So I busted out the video camera and soldered a jack right to the pot, and sure as shit, works like a charm, as the video above shows.
Something I didn't mention in the video: this isn't 1V/Oct. It's more like 5V/Oct. Sequencer 1 actually shows the voltage value you're shitting out the CV outputs in linear mode, so I was able to just put a tuner on the ass end, and scroll the voltage values until it was tuned to 12TET. I got 14 semitones total out of it, which is plenty for demonstration purposes. But if you're going to attempt this, you'll need a sequencer that can output linear values in addition to 1V/Oct. Sequencer 1 is, of course, perfect for this sort of foolishness. I'm sure there are others that will work fine, but I don't feel like talking about them.
When it comes to the cassette itself, take the lowest note you want to play, and record a note a semitone below that (so you have some wiggle room) on your cassette, and you'll end up with a full octave above that note.
You can clearly hear the portamento in the note programming later in the video. This is a result of the time it takes the motor to move to the new speed. This is an electromechanical process, so it's not instantaneous. Something with inertia needs to be accelerated or decelerated, and this takes time. Hence, fixed portamento.