> Wouldn't a simple diode provide sufficient protection from negative
> voltages
>
> /Silas

In most cases a diode will be sufficient. In addition I'd recommend a serial
resistor to be on the safe side. I forgot to mention another peculiarity for
this modification: as the internal logic of the A-161 uses +12V the levels
of the signals (clock, reset) have be at least ~ 10V. 5V will not be
sufficient as for the regular gate/clock/trigger inputs of all A-100
modules.

Best wishes
Dieter Doepfer