MIDI-Thru problem ?

[tomg]

Hey Michael,  I know this sounds stupid but don't ground the thru 
jack. The midi spec says to ground the midi in jack only. This makes 
sure that the midi cables themselves do not create a ground loop. 

The truth is you don't really need to ground ether, the current loop 
will work without it but you might run into problems on long cable 
runs or radiate midi data into badly shielded neighbors. OTOH
midi ground loops can be a real problem.

Tom

> Hello dear listmembers,
> 
> i am again here to pest you with my silly questions:
> 
> After some struggling with various embedded processors and much
> help from you, i finally mamaged to biuld my first DIY MIDI device, a simple
> MIDI note --> 16 Gates converter box.
> It just works fine, but then i wanted to add a MIDI-Thru jack. So i looked at the
> MIDI.org schematic at http://www.midi.org/images/midihw.gif
> and added the output according to this.
> My circuit ist here: http://www.takeonetech.de/midi.gif
> 
> OK, the inputs to my onboard CPU does work and recognizes all MIDI data
> without problems, so i do think that there is no problem in the input stage - the
> signals do also look fine when i look at them with a scope.
> 
> But MIDI gear hooked up at the MIDI-Thru connector receives only garbage
> and erroneous data. After double-checking all parts, connectors and cables
> and verifying that the data at the thru-connector looks to me absolutely the same
> as the on as then in-connector, i am absolutely clueless.
> 
> Has anybody encountered such a problem yet ?
> 
> 
> -Michael Buchstaller