[sdiy] MIDI notes filter which is also a MIDI converter for Junos ?

[Roman Sowa]

I dare to disagree with you.
Adding an opto isolator in any kind of MIDI-powered translator is highly 
irrational. It simply replaces plain MIDI cable, so ground at the end of 
the chain is exactly the same as it was in case of pure cable. Ground 
loop can appear only if there's some 3rd connection to the device, and 
there is none in this example.

5V at MIDI OUT is determined by by 1.2V voltage drop on the opto's LED, 
3x220 ohm resistors that are usually found in every MIDI IN-OUT loop, 
and 5mA standarized requirement for logical zero. I don't think any 
manufaxturer would risk incompatibility problems using lower voltage at 
MIDI OUT jack.

But, there's alwas but, there are many devices that simply turn off the 
5V at the DIN jack when no MIDI is transmitting. This is mostrly true 
for USB/MIDI cables, and even more sophisticated interfaces. In this 
particular case it will not work.

Roman

W dniu 2013-12-29 02:25, rsdio at sounds.wa.com pisze:
> Dave,
>
> I prefer to encourage DIY efforts, but this design violates the MIDI
> specifications in multiple ways.
>
> First of all, there is no opto-isolator on the MIDI input, which risks
> ground loops between your synthesizers. Is there any reason you did not
> use the standard chip?
>
> Second, powering a circuit from the MIDI cable is a hack that was never
> sanctioned by the MIDI Manufacturer's Association (to my knowledge - if
> it has been added to the spec, please let me know). In this age of 3.3V
> devices, there's no guarantee that a MIDI output will actually be 5V. As
> long as a device delivers the required 5mA of the MIDI spec, then  it's
> theoretically possible for the output to be less than 5V. Of course, the
> example MIDI schematics do show 5V, but that supply voltage is never
> mentioned in the text as a requirement. Fortunately, your circuit does
> provide the option of external, regulated voltage.
>
> Brian Willoughby
> Sound Consulting
>
>
> On Dec 20, 2013, at 17:03, Dave Brown wrote:
>> This is a real DIY solution but I had similar needs for filtering stuff,
>> transposing, etc. so I designed a small MIDI-powered processor
>> system.  The
>> MIDI received stream is parsed to each of the base commands which then
>> reassemble them for transmission.  You can do whatever you want to the
>> MIDI
>> stream with it.  The schematics and code is public and on my site at
>> http://modularsynthesis.com/processor/processor.htm
>>
>> There isn't much to the schematic if you just want a filter: processor,
>> crystal and caps, a couple of resistors, and a couple of diodes.  You can
>> leave off the LED, reset circuit, and of course the switches.  I have a
>> variety for whatever specialty I need.  This is probably more DIY than
>> you
>> are interested in.
>>
>> I use them for changing expression messages to volume messages, filtering
>> active sensing, transposing midi channels, keyboard splits, and just
>> messing
>> around - hence the keyboard reverse.
>>
>> Dave
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>