Sequential Circuits Pro One - Octave selection rotary switches

The octave selection rotary switches on the pro one works a little differently than most other.

They are in fact four position, DP switches, meaning that they have no common pin, the rotary action short circuits two and two poles.

The way the selector works, is that it selects 0, 1, 2 or 3 connections to the 1V reference voltage. In the various positions of the switch it means that:

• Pos 0 : pin 10 is connected to pin 2, and pin 5 is connected to 6, connecting the octave summer to R161, which in turn is connected to ground.
• Pos 1: pin 1-2 and pin 6-7 are connected, connecting the octave summer to the reference voltage through R162 (100k)
• Pos 2: pin 2-3 and pin 7-8 are connected, connecting the octave summer to the reference voltage through R163 and R164 (100k * 2)
• Pos 3: pin 3-4 and pin 8-9 are connected, connecting the octave summer to the reference voltage through R162, R163 and R164 (100k * 3)

Mouser.com sells a C&K switch with the number R20407RN02Q. I don't know if the kind of shaft is the correct length (it is .500", for a total height of about 1.05"), but the switching mechanism is the correct one. The same switch is sold by digi-key.com too.

NB: The switch has a 0.25" (6.35 mm) shaft. Other pots may use 6mm shafts.