[sdiy] passive MIDI merge?

[Simon Gatrall]

I have what I think should be a straight-forward MIDI problem, but I 
can't find a good solution.  I have 13 MIDI devices in my studio and 
one Opcode Studio 4 interface (8 in/out).  I'd like to ba able to 
hook all of the external MIDI equipment to my computer with both the 
MIDI in's and out's.  If I didn't care about sending MIDI back from 
every device to the computer, I could hook everything up just fine 
using the thru's that some of my equipment has.  However, I like to 
be able to save patches and use the controllers on all of my gear, 
not just selected pieces.  Given that problem, I can think of a few 
options:

1) Buy another multiport MIDI interface (I just saw a used Studio 4 for $150)
2) Buy a MIDI merge unit that can handle at least 6 inputs. (around $200 new)
3) Build my own simple MIDI merge unit.
4) Sell all my MIDI gear and go all [software/analog] (take your pick);)
5) Build/buy a MIDI patchbay.

I think there must be a simple solution for #3 because I don't need 
an active merge.  There are two people at most in my studio at any 
given point, and we aren't both playing/tweaking knobs at the same 
instant.  Isn't there some simple way to combine MIDI signals if you 
assume that no two pieces of gear will be transmitting at the same 
time?  Does anyone have a schematic?

Solution #5 might also do the trick, but I'd prefer something that I 
don't have to touch again.

-s!mon