VC Panning querie...

[Scott Bernardi]

Here's a VC panning circuit that uses two OTA's:
http://members.home.net/sbernardi/elec/vcpan.html

OTA's have three "inputs" - a +Vin, -Vin, and the control current. The
control current input sits a couple of diode drops above the negative
supply, so the best way to drive it is with a transistor (usually a
pnp). 
The +/-Vin inputs can take both positive or negative voltages, but at
only a few tens of millivolts before they are driven into saturation;
therefore its common to put voltage dividers in front of them (100K to
220ohm).
The LM13600 and LM13700 have "linearizing diodes" in them which allows
to be driven with much higher input voltages, say with a 100k/10k
voltage divider. To activate them, you tie a resistor (say 15k) from the
+Vcc supply to pin 2 and pin 15.
The schematic above is actually an older design that doesn't take
advantage of this.

Hey you other DIYer's- where's that nice tutorial on OTA's that I've
seen out there?

Ken MacBeth wrote:
> 
> Anyone know of any Voltage Controlled Panning
> circuits/schematics out there? I've, personally found
> this a hard thing to implement. I have an idea to use
> a pair of voltage controlled companders contained
> within a single NE571. Looking at the specs for this
> thing (571) it would apprear to be voltage
> controllable. The other option is to use two 3080s one
> recieving an inverted control, but, alas here is where
> I screw up! My understanding of 3080/13700 is that
> they only work from OV down to the negative rail. I
> know that this must be wrong! Any help out there?!!!!
> 
> 
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-- 
Scott Bernardi
sbernardi at home.net