[sdiy] (OT) Doepfer MIDI-CV oddity

[Ullrich Peter]

Hi!

I used different manufacturers. The manufacturer I use normally is SHARP - they 
have a light green or light yellow color (so not black as most others...)

They look like these optocouplers (but of course different part number and pin count...):
http://img.cn.china.cn/0/0,0,112,54032,356,323,1379a9f8.jpg

Ciao
Peter

-----Original Message-----
From: Tom Wiltshire [mailto:tom at electricdruid.net] 
Sent: Wednesday, January 19, 2011 2:05 PM
To: Colin f
Cc: Ullrich Peter; synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] (OT) Doepfer MIDI-CV oddity


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


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