[sdiy] CV inputs with bipolar "amount" knobs

[Harry Bissell]

I was talking about a pot with a center tapped element (not TOO hard to find...)
this is a four terminal device. If you ground the center tap, its like two
pots in one case. You can even have two different functions on the same pot...

envelope and lfo in opposite directions anyone ?

H^) harry  (shades of SEM)


----- Original Message -----
From: mark verbos <mverbos at earthlink.net>
To: David G. Dixon <dixon at interchange.ubc.ca>
Cc: 'Synth DIY' <synth-diy at dropmix.xs4all.nl>
Sent: Mon, 19 Jul 2010 18:08:47 -0400 (EDT)
Subject: Re: [sdiy] CV inputs with bipolar "amount" knobs


On Jul 19, 2010, at 5:50 PM, David G. Dixon wrote:

>> If it's a DC thing: as I understand it the only problem is, the null
>> point is not exactly in the middle of the pot travel. Crude way to
>> take care of this: mount the knob on the pot shaft so that the
>> marking on the knob is in middle position at the null point.
>
> I believe Harry was talking about centre-detent pots, in which case  
> you
> can't really choose the centre independently.  However, if you use 1%
> resistors and a decent opamp, I can't imagine this should be a  
> problem.  I
> mean, after all, if you need absolutely zero CV to your circuit,  
> unplug the
> damn patch cord!  If that's not good enough for you, then a 1k  
> trimmer off
> one end of the pot will do the job; which end depends on where the  
> "true
> centre" is relative to the detent.


A trim pot in parallel with the pot is easier.

BTW. is there any reason to have the pot after the opamps rather than  
sending the signal through a resistor to the wiper and then one side  
to an inverter and the other side into the summer like Buchla does?

Mark
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-- 
Harry Bissell & Nora Abdullah 4eva