[sdiy] (OT) Doepfer MIDI-CV oddity

[Colin f]

> I had a look at my preferred 6N139 circuit: The pullup is 1k.
> The difference with/without the base resistor is like the 
> difference between Vishay and Fairchild Colin showed us!

I used to use the bias resistor, but found I had to adjust the value for
reliable operation with different optos, so I gave up on it.
That was before I realised there were such differences between the 'same'
parts.
If you pick one maker's chip, find the optimum set of values and stick with
them, life should be sweet.

Cheers,
Colin f