I'm building something that would benefit from a midi-clock input, but also a analog clock input. In order to save space, i'd like to use a mini-jack with an adapter for the midi cable (as seen in the Arturia Beatstep pro for example) and have it double as a analog clock / gate input.
Seeing some synths have gate signals that go up to +15v, I'd need some protection in order not to fry the opto-coupler mandated by the midi input. A simple resistor in front of the ir-led won't do the trick: the forward current will either be too low in midi-mode, or too high in +15v gate mode.
I guess the capacitance of a zener prevents me from using that as voltage protection, because it will be too slow for the midi signal. Maybe there is some other thing I overlooked?