[sdiy] (OT) Doepfer MIDI-CV oddity

[Ullrich Peter]

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!

Ciao
Peter


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Ullrich Peter
Sent: Wednesday, January 19, 2011 1:18 PM
To: Colin f; synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] (OT) Doepfer MIDI-CV oddity

Hi!

And the 6N139 switching times can further be optimized by used a bias resistor on the 
base of the opto-receiver transistor.  Without this receiver the 6N139 is quite slow.
I normally use a 15k resistor from pin 7 to GND.

The maplin MIDI thrubox has this base resistor in it and works very fine. I had the same 
circuit without the resistor in my own thrubox and had problems.

The problems get bigger and bigger the more MIDI gadgets are connected in series as 
the MIDI pulses get more and more distortions in each thru stage.

Ciao
Peter

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