Sub oscillator for CEM3394

[Duane R Balvage]

Hello all ...

I have a friend who has a SixTrak, and he was complaining about it's
lack of OOMPH in the bottom end department. So, I "borrowed" an idea
from my Juno-1 and put a sub-oscillator ckt. together.

Circuit desc.:

The CEM 3394 does NOT have seperate outputs for the waveforms, only a
VCA out. (it's a synth on a chip... see
http://www.synthtech.com/cem/cemdata.html
for more info.) Sooo... a simple flip-flop hookup was out of the
question.

This chip has the timing cap hooked up external to the chip (3000pF, if
I remember correctly),
so I thought I could pick off thecharging/discharging triangle off the
cap with an extremely 
high input impedance op amp (so as not to load it down unnecissarily).
Then I thought, "save a step (and parts) and make a comparator out of
the op amp." This worked... a nice square wave
resulted. I then fed this directly into a 4013 D flip flop with Qnot
tied to D to make a divider. Now I had a squarewave at 1/2 the initial
osc frequency. This is attenuated down by a 
100k/1k voltage divider, and a 47k trimmer pot (the ext. in of the 3394
can only handle about 80mV p-p). I bent pin 9 out of the socket,
attatched the output of the sub-oscillator circuit,
powered up, and turned up what used to be the noise/osc balance (is now
osc/sub osc balance).

It worked! I had to adjust trimmer 2 to get rid of distortion.

Oh, BTW you have to adjust trimmer 1 until you get a squarewave out of
the TL082...

so... I built 5 more, stuck 'em in his SixTrak, and he is now a happy
camper...

(he doesn't miss the "noise" generator too much.)

This circuit can be used in any synth that uses CEM 3394's, I.E. -

SixTrak, MAX, Multi-trak, Split-8

Akai AX-60, 73, VX90

others I can't think of right now ...

Anyways... Anyone who has one of these, and would like some more OOMPH
out of their synth
and don't mind losing the "noise input" ... see attatched GIF for
circuit.

		Hope someone can use it!

						- Duane



-- 
   "That boy's got a mouth like a cannon ... Always shootin' it off..."
                                
                             - Foghorn Leghorn
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       -------------/ ////  Duane R. Balvage   //// / /---------
                   /    _________________________  / /
                  / // / // /// // /// // /// / / / /
                 /___ //////////////////////////_/ /
                 \____\________________________\_\/

                     Intel Corporation, RA1-303
                   Portland Technology Development
       =========================================================

              Phone: (503) 613-8055    FAX: (503) 613-8261
                   E-Mail: dbalvage at ptdcs2.intel.com
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