Moog 901 and 921 oscillators

On Friday, we had an opportunity to test Volta with the Moog 901A/B and 921A/B oscillators. This was also a test of MOTU's multi-point calibration system, which accounts for non-linearities in CV response range. Most oscillators we've tested are completely linear, as they should be. Vintage instruments can be a bit more finicky.

We were pleased to find both the 901 and 921 tracked accurately across a 5-6 octave range. Normally, several 901Bs are connected to a single 901A controller. Same goes for the 921. The A module takes the CV input and does the expo to linear conversion and feeds this to the B modules, and the B modules have an offset, but all track the same CV signal from the A module. I imagine this may have been a cost-saving measure as the expo to linear conversion was expensive and complicated. However, you have three oscillators, and one CV input.

This is all fine and well and good, provided all your B modules are calibrated precisely to each other. An optimum system for Volta would use a separate AB pair for each oscillator. That way, Volta can address the individual calibration irregularities of each oscillator directly. I can't imagine there are a surplus of 921As and 901As floating around, however.

A more radical option would be to treat the 901B and 921B oscillators as linear VCOs and remove the A modules from the equation entirely. Perhaps a Moog technician could lend their voice to a discussion about the possibilities of a reversible/non-invasive mod for Moog oscillators. I will say these oscillators sounded AWESOME.