[sdiy] (OT) Doepfer MIDI-CV oddity

[Tom Wiltshire]

On 19 Jan 2011, at 12:33, Colin f wrote:

> 
>> 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.

I wasn't aware of such significant differences between manufacturers, so thanks for that Colin. Very useful to know. 
I made the (not unreasonable, I don't think) assumption that parts with the same part number are functionally identical. But these differences explain why you see such a variation in resistor values, at least.

One question for you, Peter. You give us your preferred resistor values, but could you tell us what your preferred 6N139 is?

Thanks,
Tom