[sdiy] (OT) Doepfer MIDI-CV oddity

[Paul Perry]

Great pictures, Colin, very eloquent, worth quite a few words.
As an aside, this is the kind of thing that makes life hard for 
manufacturers- whereas a lone DIYer can tweak the load resistor until it 
runs, if you are manufacturing, you have quite a possible range of input 
signals & loads to consider, and as you can see it isn't just a matter of 
being able to get a particular part - it had best be a particular 
manufacturer, as well ;-(

I had trouble when I changed the manufacturer of a CD4046 phase locked loop 
chip that I was using as a VCO..

paul perry Melbourne Australia (happy ex-manufacturer)

----- Original Message ----- 
From: "Colin f" <colin at colinfraser.com>
To: "'Tom Wiltshire'" <tom at electricdruid.net>
Cc: "'Synth DIY'" <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, January 19, 2011 9:45 PM
Subject: Re: [sdiy] (OT) Doepfer MIDI-CV oddity


>
>> I did quite a bit of research looking for MIDI input circuits
>> based on the 6N138/9 and found a large range of resistor
>> values used.
>
> I've been there too...
> Take a look at this image:
> http://www.colinfraser.com/images/6n139-fairchild-vs-vishay.jpg
>
> It's a scope trace of the output from a 6N139 in a MIDI input stage.
> Top trace is a Fairchild part, bottom is a Vishay.
> These two are just swapped over in the same circuit.
> All other values are the same.
> So clearly, all optos are not.
> Fairchild worked perfectly, Vishay was hopelessly unreliable, missing more
> bytes than it managed to receive intact.
> I've always stuck to Fairchild since.
>
> Cheers,
> Colin f
>
>
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