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  1. Using AOUT with Buchla 1.2v/octave

    As you probably know, the AOUT module is set up to support 1v/octave scaling, and that has been fine for me when I was using it with a Serge modular system. But I have been wondering how I could use my AOUTs with my Buchla-ish modular synth, which uses 1.2v/octave scaling. I contemplated building an opamp based solution, boosting the voltage a bit. But this seemed a bit of a hack to me, so I spent a bit of time understanding the opamp based outputs from the MAX525 DACs. I realised that by tweaking a resistor value I could get the AOUT to put out 1.2v/octave. I've tested this for a bit with two different oscillators (258r and 259r) and it seems fine for my uses. I'm no electrical engineer though, so if this mod blows up your rather expensive equipment I'm afraid you're on your own... That said, for any other Buchla users who want to use an AOUT to output 1.2v/octave, just change RY to 1.8K on any channels you want. That should give you the extra bit of gain required, and then you can trim it to 1.2v/octave. FWIW I usually use the MBSeqV4 app, then use the nice new calibration stuff to get things super accurate. I'm able to get submillivolt accuracy over the whole voltage range. Top voltage is obviously a bit higher in this case, almost 13v from my measurements. That seems to have been fine in my system, but YMMV. Also, I have set my AOUT so that V1-V4 have this tweak (1.8K for RY), and I use them for controlling Buchla oscillators. V5-V8 use the 2.2K resistor for RY still, and I use those channels for modulation CVs and to control the Serge oscillators which run at 1v/octave. All in all I'm most happy with this system and am glad I don't have to mess around with adding more circuitry. Hope that helps someone in the future!