[sdiy] Oberheim OB-Mx calibration ROM and instructions posted

[Aaron Lanterman]

[I posted this to AH but figured there'd be enough interest here to  
repost it here.]

Courtesy Tom Virostek.

See here: http://users.ece.gatech.edu/~lanterma/obmx

The calibration procedure is pretty complex and requires a scope (and  
preferably the voice board extender card that lets you get to the  
board while the unit is on). The OB-Mx uses some digital pots with  
built-in nonvolatile memory. I had always assumed that these were  
recalibrated upon booting up the OB-Mx, but it turns out they are set  
in this calibration procedure. I suspect that a lot of errant voice  
boards that are out there just need recalibrated. Maybe some of them  
were sloppily calibrated to begin with - who knows.

- Aaron

P.S. One caveat is that Lynx Crowe told me he recalled there being  
some runs of voice boards where Gibson used the wrong sort of  
capacitors in the oscillator section, resulting in boards that went  
out of wack as the temperature changed. He couldn't recall exactly  
what or where.