[sdiy] Panning with LM13700

[microtonalsynthesis at yahoo.com]

Dave,
The input CV is 0 to +5V and that needs to be split at zero volts. One CV is positive only and the other is negative only. If you look at the chart in the THAT AN120, you'll see that you cannot simply derive one CV from the other. They are symmetric across the vertical axis, not the horizontal axis. The breakpoint circuit is almost symmetric but there are additional offsets applied for the left CV generation. Every offset adds to the DC error and therefore adds to the panning and volume error. 
John

    On Thursday, January 12, 2017 1:58 PM, Dave Manley <dlmanley at sonic.net> wrote:
 

 Is there a separate diode breakpoint circuit for the left and right channels? Is that the cause of the mismatch?

If so, can you use one circuit for the left and then derive the right from that?

-Dave

On January 9, 2017 8:17:05 PM PST, microtonalsynthesis at yahoo.com wrote:
Tom,
I think you are on the right track with the microcontroller version. I've been simulating the THAT AN120, which is just a simple diode breakpoint generator. But the amplitudes never match up for the given circuit, with differences of 50% or greater depending on the setting and the left or right channel. In reality I think this circuit will need multiple trimmers to get everything right. Considering it is modifying CVs that go into an exponential control circuit, just small errors can be significant.
John 

   

   
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