PAIA Hex VCA circuit

[Stewart Pye]

Hi there,

Arrgghh, using the 4049 as voltage controlled resistors. I tried this last
year for a phaser. I kind of got it to work but had some problems. I'll
take a look at my notes and see if I can do it now. Do you have the 4049
data sheet???? This might help you.( it contains the internal schematic )
If you could post the hex VCA schematic that would be great.

Regards,

Stewart Pye


At 16:30 17/01/99 -0600, Mark Smart wrote:
>Hi everyone.
>
>After forgetting about it for a year and a half, I have dived back into my
>GR-300 guitar synth hacking project. I have been messing with this circuit
>invented by PAIA which uses a 4049 CMOS chip to create six VCA's which mix
>into one output  (the output comes out the ground pin!). What I'm using
>this for is to mix together pulse and square waves derived from the
>GR-300's internal sawtooth waveform. My saw-to-pulse converter and octave
>dividers create three pulse waves which oscillate between 0 and +15 volts.
>
>This circuit mostly works execpt that there is noticeable leakage between
>channels which is especially bad at low volumes. I have three
>signals, the pulse wave, the /2 square wave, and the /4 square wave. When
>you turn on the control voltage for the /4 square wave, it comes on, but
>with a noticeable amount of the /2 and pulse signals leaking in. I would
>appreciate the advice of anyone who is familiar with this PAIA hex VCA
>circuit. I could also post a schematic at some point maybe. I tried
>lowering the 4.7 Meg resistors to 2.2 Meg, and this helped some, but did
>not eliminate the problem. My biggest problem in debugging the circuit is
>that I really don't understand how it works very well. The description
>which came with it does not go into that much detail. It does not specify a
>limit on CV or audio voltage ranges. The basic idea of the circuit is that
>the FET's in the CMOS inverter gate are used as voltage-controlled
>resistors, and somehow the audio inputs mix inside the chip and come out
>the ground pin.
>
>I would appreciate any advice. Also thanks to the people on the list who
>have helped me in the past in my sporadic forays into synth-building. 
>
>
>************************************************
>*     Mark Smart                               *
>*     Electronics Engineer                     *
>*     And Musician                             *
>*     smart at medusa.nn.com                      *
>************************************************
>