[sdiy] Good precision pot choice for VCO CV panel tuning ??

[Oren Leavitt]

On 9/15/2010 2:09 PM, Jean-Pierre Desrochers wrote:
>
>
> Hi list,
> I'm about to build some VCO's for my DOTCOM modular
> and I'm wondering what brand of 100k precision pot I'll use
> for freq panel tuning.
> My VCO panel layout will be like the original Moog 921A module
> with the tuning pot shaft using 320deg mechanical rotation.
> (Original Moog used Allen Bradley pots, now PEC pots).
> So now I need a 100k (maybe 50k) linear pot
> with 320deg mechanical/electrical travel that has
> at least 5% linearity to follow the panel layout.
>
> I know a lot of you talked
> on some earlier posts about the good Vishay 148/149 series quality
> with 300deg shaft mechanical travel, and +-5% linearity.
> But that linearity doesn't show on both shaft travel far ends.
>
> So I need your opinions on the following possible pot:
>
> http://www.potentiometers.com/pdf/SP22E.pdf
>
> Tolerance 10%
> Independant Linearity 1% !!!
> Electrical/mechanical Rotation 320deg
> Conductive plastic
>
> Price, avaiability, distributor...
>
> Any thoughts on that choice?
> Thanks
> JP
>

Hi Jean,

I personally have been using the PEC pots more and more. I really like 
the solid feel and "setability" of them and do not mind spending a 
little extra for them. Very sturdy too (Having fixed/replaced many 
broken plastic shafts in the past).

I would say just buy a few of the SP22E's and try 'em! Our opinion's and 
tastes are different. Maybe you can ask for a sample?

An added tip for linearity, any load on the wiper is going to throw it off.
If the pot is used as a voltage divider, what I do is place a high input 
impedance buffer between the wiper of the pot and the input (typically a 
CV input). This effectively removes all loading from the wiper. Do this 
especially if you're using a multi-turn pot and turns-counting dial. The 
indication on the dial will correlate nicely.

- Oren