first project - passive midi switcher

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aeonsound

New member
Joined
Jan 19, 2009
Messages
3
hello all!

please be gentle as this is both my first post and my first project...  :) apologies if my queries are stupid/obvious/irrelevant...

i would like to build a 1-input, 4-output passive midi switcher, to send midi from my soundcard to my various outboard gear. the idea is to do something passive (so i don't need to worry myself with power issues) and non-audio-carrying (so it won't be too criticial in terms of grounding).

at the moment i have an ABS plastic case, 5 x 5-pin DIN terminals, and a 3-pole, 4-throw rotary (Lorlin) switch. however i still have a few questions, and i'd really really appreciate your collective input!

1) is it ok to simply connect all the DIN pin 3 (the 'ground' pin for MIDI) to one common ground, as indicated in the schematic? or do i need to send the pin 3 through the switch as well?

2) would that be a star chassis ground, i.e. one washer to which all grounds are connected?

3) is it really that simple, or am i missing something? is that all there is to MIDI switching?

4) the MIDI hardware specification notes that inputs and outputs should be opto-isolated. is this necessary for my switcher, or will this have been done at my soundcard output and synth input points?

5) i managed to grab some sticky-backed metallic tape which my work were throwing away, which i'm going to line the case with - does that sound ok for shielding purposes?

i would be super grateful for any help or advice :) thanks!

aeonsoundmidimal.jpg
 
It's ok, just connect all grounds together, no need to switch the various grounds
The opto-isolator has to be present in MIDI input only, not MIDI output, it is for avoid ground loop
you don't need to implement an opto-isolator here, as it is probably already implemented in your synth MIDI inputs

 
thanks very much!

i bought a 3-way switch just in case ;) but glad to hear it, that makes things easier.

once all the grounds are joined, do they need to be connected to a chassis ground?

 

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