     This circuit is a modified version of the Soundblaster MIDI interface
that has been floating around the Internet (which has the opto-coupler input
wired wrong, by the way!). It has been tested extensively with the older
PAS 8-bit card and the newer PAS16's revs C and D. The later versions of
the PAS16's were very sensitive to substitutions of the 6N138 optocoupler.
In all, 8 different substitutions were made for the 6N138, and all worked
on the 8-bit PAS, but NO substitute worked on the PAS16. After checking
the specs on the opto-couplers I assume the newer PAS16's need the extra
gain that the 6N138 gives.

     The 6N138 opto-coupler is available from Allied Electronics, 7410 Pebble
Drive, Fort Worth, TX 76118 for $1.43. The other items in the parts list
were ordered from Radio Shack for a total cost of $3.19. Midi cables are
available at Radio Shack for $4.99 each. Jacks, circuit board and an
enclosure for the project will add another eight or ten dollars depending on
how neat you want your interface. I spent a little extra in order to
eliminate dangling wires from the interface by including a 15-pin D-connector
male to female 6-foot cable for $9.50 and male and female jacks for 95
cents each from Allied.

     One item that I did not draw in the circuit is the addition of a power
on/off switch in series with pin 8 on the 15-pin D-connector. This was
necessary for my MIDI keyboard since it will not go into MIDI-mode unless
the MIDI interface is turned on last. The switch eliminates plugging and
unplugging the D-connector in order to trigger my keyboard. This may be
just a quirk in my keyboard which is a Radio Shack Concermate 1000 MIDI
synth.

     The accompanying midimutt.gif file is a 2-color 640x700 GIF containing
schematic diagram and a parts list. For those curious, it was drawn
freehand using Neopaint v2.1a. If I can be of assistance to those attempting
to build this circuit, you may reach me through E-Mail at:

     apete@maine.maine.edu

     Best Wishes,

                     Art

