cv to midi???

WeAreAs1 at aol.com WeAreAs1 at aol.com
Mon Nov 8 23:10:22 CET 1999


In a message dated 11/8/99 7:37:03 AM, you wrote:

<<  The DX-7 breath controller input jack provides three things: the ground
ring, the "excitation voltage" on the tip, and it picks up the controller
response voltage on the "middle ring".>>

It should also be noted that the Yamaha Breath Controller unit itself 
contains active circuitry (a couple of opamp inverting gain stages, with gain 
and offset trimmers), and this circuit is powered from the "excitation 
voltage" part of the wire.  I think they use a resistive divider to derive a 
psuedo-bipolar supply for the opamps from the single -10v line.

The original DX7 footpedals had some sort of light bulb, photoresistor, and 
moveable light shutter arrangement in them, which Yamaha had been using in 
their organs since the the late 1960's!  I have a Yamaha YC-30 organ, which 
was designed around 1968, which has almost the exact same volume pedal as 
those made for the DX7.  You always needed to bring a spare bulb to gigs, 
because if it burned out, you'd have no sound (although you could open the 
pedal and point a flashlight into it, in a pinch situation).  Obviously the 
light bulb was working on some kind of current loop - probably the same in 
the DX7.  The obvious advantage these pedals had was that they didn't have a 
moving potentiometer to wear out.  This was especially import back in the 
60's, when potentiometer technology wasn't as good as it is today.

For later model Yamaha keyboards, such as the DX7II and subsequent models, 
Yamaha came up with a more reliable passive potentiometer-based pedal, though 
these units still used the same three-conductor ground, voltage, and return 
arrangement.  Interestingly, you can use the new passive pedals on old model 
Yamaha's, but you cannot use the old photoresistor pedals on the new model 
yamaha's.  Maybe the new models have too much internal current limiting to 
properly ignite the light bulb?  (kind of like those pesky Korg's, with their 
temperamental MIDI outputs that refuse to provide power for cute little 
external MIDI boxes... Maybe they can sense it's not a Korg product.  "Pocket 
Pedal?  Sorry pal, we don't provide free power for CANADIANS.  Bring your own 
batteries, eh?")

It would be good for us to do some kind of survey of the various CV input 
arrangements found in some of the most common MIDI keyboards, then maybe we 
could come up with a sort of universal CV input interface adaptor that would 
let us turn all our cold digital machines into useful parts of our warm and 
fuzzy analog modular systems.  As previously noted, Barry Klein really gets 
into this idea at length at his website, with discussion about using the DX7 
and Kurzweil K2000 as voltage-controlled "analog" synths.  (I think he should 
append the idea to include an analog Gate input as well.  It could be done by 
simply placing a couple of 4016 analog switches across the middle C key 
contacts.  You could even get voltage-controlled attack velocity if you made 
a little 555 timer arrangement to control a variable delay between the 
opening and closing time of the two key contacts)

Michael Bacich




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