From gstopp@fibermux.com Wed Dec 13 10:21:06 1995
    13 Dec 95 13:20:33 +0500
    15 Nov 95 19:10:31 +0500
5: 25 -0800
From: gstopp@fibermux.com
Date: Wed, 15 Nov 95 15:46:18 PDT
Encoding: 82 Text
Cc: kellyd@taco.andataco.com
Subject: Re: ODYSSEY CV-in mod?

     Okay I confess I modified my whiteface with CV/Gate IN/OUT jacks. I 
     don't like the "disable the local keyboard when you plug in the 
     external control" type of operation so I had to add some extra op-amps 
     piggy-backed onto some of the existing ones. It's not in front of me 
     but I do have my notes:
     
     CV input:
     
     Break the connection between the output of the keyboard sample/hold 
     buffer (A1b) and the CV pin on the backplane connector. Add a dual 
     op-amp (1458 etc.) configured as two series inverters so that you can 
     use the first one to sum the original keyboard sample/hold buffer 
     output with a signal from the CV input jack (added on rear panel). The 
     result will be upside-down so use the other inverter to right it again. 
     Use closely matched 1% or 0.1% resistors so you don't have to add 
     trimpots to make the gain exactly +1. You can use a DVM to match them. 
     However adding a trimpot to the external input is a good idea, 
     especially if you epoxy it to the inside of the rear panel sticking out 
     through a hole, to avoid having to open up the Odyssey if you move from 
     one external controller to another.
     
     CV output:
     
     Op-amp buffer on the above CV sum to an output jack.
     
     Gate input:
     
     The Odyssey's internal gate is created by a keyboard bus that goes to 
     +15 whenever any key is pressed. This gets cut down to about +10 by a 
     resistor divider, after an isolating diode. To add an external gate, 
     add an input jack to a diode to the juction of the resistor divider 
     (diode black line towards divider). This provides a "wire-or" 
     function. I'm not sure what the minimum gate requirement is but this 
     works for the MPU-101.
     
     Gate output:
     
     Op-amp buffer on the above resistor divider junction to an output 
     jack.
     
     Trigger:
     
     The ARP envelope needs a trigger to set the attack flip-flop. It is 
     derived from the rising edge of the external gate as follows: External 
     gate input jack to a 0.01uf cap, to an op-amp inverter with 10K input 
     resistor and 220K feedback resistor, to another inverter with 100K 
     input and 100k feedback, to a 0.01 cap, to a diode, to the keyboard 
     trigger bus (diode black line towards trigger bus). You can add an 
     external trigger here too just by adding another 0.01uf/10K input to 
     the first inverter.
     
     - Gene
     gstopp@fibermux.com
     
     
Subject: ODYSSEY CV-in mod?
Author:  kellyd@taco.andataco.com (Kelly Dunn) at ccrelayout 
Date:    11/15/95 8:18 AM
     
     
As I'm gearing up to sequence with my Odyssey, I'm going to 
install CV-in, GATE-in, TRIGGER-in & LFO-in mods. My question 
is..........(doing the GATE mod for instance).... 
Is this simply a matter of just breaking the trace between the  
internal gate source to gate destination (env), run leads from 
either side of trace-break out to a switching jack where, as long 
as a male plug is not inserted, signal runs straight thru as unit 
normally works but, when male plug is inserted, INTERNAL gate is 
disconnected & EXTERNAL gate (from male plug) is applied to gate 
destination (env)? 
Also.......if this IS correct, do I do the same for trigger, cv & lfo?
     
Someone please answer this plea as I'm not the only one waiting for 
an answer to these questions. I've seen other (unanswered) pleas for 
the same questions & I'm pretty convinced that if one of you AH experts 
don't answer, this could be the beginning of the end of ALL analogue 
mods as we know them. (not really, AH is such a cool place to live!)
     
Thanks much,
Kelly Dunn