AW: PAIA Hex VCA circuit

[Fraser, Colin J]

> -----Original Message-----
> From: BJ [mailto:zzynt at swipnet.se]
> Sent: 19 January 1999 07:05
> To: Magnus Danielson
> Cc: diylistan
> Subject: Re: AW: PAIA Hex VCA circuit
> 
> Quite interesting this hexa VCA thing, i had a fast 
> look into Don Lancaster "filter book" and there is
> a short description on how to use "various" things as
> a voltage controlled resistor.
> 
> One of them is a Mosfet and there Don is suggesting a 1Mohm for feed
> back
> to get the device more linear, he also mention this about to "rework"
> a 4049 to do the same thing but hexa times!
> 
> I just had a wery short look at the 4069 as well but 
> the input protection diodes may cause troubbles!!
> 
> How about using the Vdd pin as an AM modulation input??(Ohh!) ;)


Another novel use of the 4069 is in the Roland Tr909.
Have a look at the schematic for the Snare drum (
http://hardware.freepage.de/raf909/ , circuit analysis, snare drum...)

Follow the schematic from the label ENV1.
There are two voltage controlled oscillators built around a 4069 IC. The
supply voltage to the chip is modulated to produce pitch modulation of the
oscillators by the envelope signal.

The toms use the same idea, but with an extra osc.

Colin f