[sdiy] 50k Tapped Pots

[Michael Bacich]

On Aug 4, 2006, at 6:20 PM, <scottnoanh at peoplepc.com>  
<scottnoanh at peoplepc.com> wrote:

> Doesn't the SEM use a center tap, without a detent, to sweep the  
> response of
> the filter?


No, it uses a normal 3-terminal pot for panning through three filter  
responses.  The pot also has a switch on it that adds an additional  
Notch response when the pot is all the way counterclockwise.

You may be thinking of the filter in the EML-101, which does have a  
center-tapped pot for panning between four (?) filter responses.

The SEM, however, does have a center-tapped pot for modulation depth  
on each VCO (one for each VCO).  It's wired with the center-tap to  
Ground, the wiper to the mod source (LFO, etc.) and the two ends  
attached to two modulation destinations (via summing resistors).  If  
you turn it clockwise, the mod source modulates pulsewidth.  Turning  
it counterclockwise modulates the pitch of the VCO.  Centering it  
connects the wiper to Ground (the tap), and kills all modulation.   
It's nice -- unless you want both pitch mod and PWM at the same time!