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From this question, I understand that the better solution to drop off the temperature dependence of the gain in variable gain amplifier is to set the potentiometer in a voltage divider configuration. The problem is that the gain is highly non-linear in that case. While long time temperature drifts are not an issue anymore, I am curious about the effects of long time mechanical drifts due, for example, to mechanical constraints release.

I want to use this trimpot in one of my circuits, but no reference to the intrinsic mechanical stability is made (or I missed it.)

What is your experience with this issue? Do they move with time? Does glue help with stability? Are there other tricks besides range limiting the trimpots?

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  • \$\begingroup\$ This seems like an X-Y problem. Gain is not made nonlinear by using a voltage divider feedback, however gain vs. pot rotation is somewhat nonlinear for reasonable gain trims. How much are you planning on changing the gain with the pot? \$\endgroup\$ Sep 14, 2023 at 2:16
  • \$\begingroup\$ I want to set it once and for all, I would like to have a gain range from x1.5 to x2.5 in the beginning and I will probably want something around 2, I was thinking adding two 1500 resistors on both sides of a 500 Ohm trimpot compared to the configuration 2 in the question I am refering to to limit the range of the trimpot, have a more linear relation between gain and trimpot. I was just wondering if I should take extra precautions like gluing the thing. \$\endgroup\$ Sep 14, 2023 at 3:06

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Glue (or paint) helps detect but does not stop "screwdriver drift". I don't believe it helps with undisturbed drift under relatively benign conditions.

Of course pots will drift, wiper resistance can vary and the kind of pot you linked to are probably more prone to changes from thermal mismatches (since they are not symmetrical like rotary pots with or without a gearing).

You can probably set the pot to 0.1% and count on it staying within about 1% over a year or two, as rough orders of magnitude. So if you want the gain to be accurate to within 1% you need to restrict the range by one means or another. Using it as a voltage divider reduces the effect of CRV (which is negligible for higher values of element resistance), and of pot element tolerance and temperature coefficient.

Adding resistors to the end of the pot reduces the range but can affect the temperature stability (and tolerance) if it's used as a divider. To reduce those effects, add an additional low tempco precision resistor in parallel with the element.

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  • \$\begingroup\$ Thank you for the answer, I do not know much about these trimpots, can you advise a similar part that is symmetric as you say and less prone to changes ? \$\endgroup\$ Sep 14, 2023 at 3:22
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    \$\begingroup\$ Bourns 3296 and similar (they are 3/8" or about 10mm x 10mm x 5mm) \$\endgroup\$ Sep 14, 2023 at 3:32

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