[sdiy] Potentiometer linearity questionable..

[jpdesroc at oricom.ca]

Hi list,

I'm in the process of designing
the artworks for some of my DIY synth
VCO front panels. I found that the supposely
'10% linearity' of some pots like
Vishay/Spectrol cermet 149 are not that
linear in the 0-3 region (0-10 markings).
0 to 10 graded lines around pots
on my front panels won't just alligned
with some pot real values. I measured 20-30%
off values in the 0-3 range which is very disapointing.
Some pots have 300deg mechanical rotation
but loose around 5deg at each ends
which make around 290 of real cursor travel.
This does not allign with 0-10 marks.
When I look some Moog modules like
the 921A I wonder if the 'frequency' pot
was accurate around its mechanical
rotation ends..(?) Moog utilised
Allen-Bradley pots at that time.
Where they more 'linearity reliable'?
I thought Spectrol type pots were
just fine on that..
What do you think?
J-P