[sdiy] (OT) Doepfer MIDI-CV oddity

[Jerry Gray-Eskue]

Oh I forgot to mention that rebuilding the pulse train Also adds a delay in 
the data stream which can be yet another problem for real time stuff like 
MIDI...

----- Original Message ----- 
From: "Jerry Gray-Eskue" <jerryge at cableone.net>
To: "Ullrich Peter" <Peter.Ullrich at kapsch.net>; "Colin f" 
<colin at colinfraser.com>; <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, January 19, 2011 8:39 AM
Subject: Re: [sdiy] (OT) Doepfer MIDI-CV oddity


>> 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.
>
> This is true of any communication link that uses an "analog" repeater, if 
> you use a device that regenerates the digital pulse train using a system 
> clock you get a correction of the distortion at that stage.
>
> ----- Original Message ----- 
> From: "Ullrich Peter" <Peter.Ullrich at kapsch.net>
> To: "Colin f" <colin at colinfraser.com>; <synth-diy at dropmix.xs4all.nl>
> Sent: Wednesday, January 19, 2011 6:17 AM
> 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
>>
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl 
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Colin f
>> Sent: Wednesday, January 19, 2011 12:58 PM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] (OT) Doepfer MIDI-CV oddity
>>
>>
>>> As an aside, this is the kind of thing that makes life hard for
>>> manufacturers-
>>
>> Yep, that's why I'm so well acquainted with the range of 6N139s...
>>
>> Another new factor in the MIDI equation is that some PC interfaces drive 
>> the
>> line with a lower voltage supply.
>> MIDI is a current loop, so in theory you just need to reduce the series
>> resistors and 3.3v pull up on pin 4 should be no problem.
>> But if the forward voltage drop on your opto is higher than usual, you 
>> might
>> find the margins of operation sooner than you'd like.
>>
>> Cheers,
>> Colin f
>>
>>
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