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When using a standard carbon potentiometer as a variable resistor it will 'crackle' if exposed to a small DC voltage.

The DC is unavoidable and the circuit functions as desired except for this 'cosmetic' noise problem.

Is there any type of variable resistor that will be immune to this DC induced noise or at least less susceptible to it? Reducing it significantly will be acceptable.

The circuit requires at least 0-4k range of resistance and as little more than that as possible.

I have not tested any potentiometers with plastic, cermet etc. tracks , or any high end/high precision potentiometers.

I have considered using a rotary switch with resistors but it will cause a DC pop proportional to change in resistance when switched.

Very small steps in resistance would be needed to reduce the pops to acceptable levels I think, probably too small to be realistic with a mechanical switch but maybe possible with an R-2R DAC. Such an elaborate solution would be an absolute last resort.

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  • \$\begingroup\$ What is the application? Why is there DC then, why can't it be removed? If you have DC, then any change in resistance changes the DC operating point and any sudden change in resistance causes current changes and thus voltage over resistance will vary and it will crackle. If you tell what the signal is and what it is used for, it may already have a solution - such as LDR to control it linearly. \$\endgroup\$
    – Justme
    Mar 24, 2022 at 17:13
  • \$\begingroup\$ Conductive plastic is supposed to be the best in this respect. \$\endgroup\$
    – DKNguyen
    Mar 24, 2022 at 17:42
  • \$\begingroup\$ manually adjustable I/V resistor for audio signal, the signal unipolar with an offset current. I had briefly checked out LDR, they seemed like they would solve the noise issue but maybe lacked precision, did not look further into them because I could not find any on Mouser, where I buy all my parts. Should I reconsider? <10r - 4000k range, 2 channel with similar precision and channel matching to potentiometer. \$\endgroup\$
    – Albert
    Mar 24, 2022 at 17:49
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    \$\begingroup\$ Since it is audio, typical procedure is to remove DC bias, adjust volume, and if necessary, then apply suitable bias again. Why can't this be done? \$\endgroup\$
    – Justme
    Mar 24, 2022 at 17:51
  • \$\begingroup\$ It is possible. I can use a fixed resistor perform I/V for the maximum voltage and then use an AC coupled variable resistor to reduce the AC gain. I still prefer for the variable resistor to be direct coupled however. @DKNguyen thank you, I hoped to hear this. I will test a conductive plastic pot, hopefully it enough to bring the noise to an acceptable level. \$\endgroup\$
    – Albert
    Mar 24, 2022 at 18:03

2 Answers 2

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For DC, add a capacitor across the wiper:

schematic

simulate this circuit – Schematic created using CircuitLab

Note this will not work for AC signals, like audio.

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  • \$\begingroup\$ it is for audio but thanks. \$\endgroup\$
    – Albert
    Mar 24, 2022 at 18:04
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These Carbon & metal wipers are the noisiest Pots, followed by Wirewound then metal film for lowest noise but also lowest power rating.

So WW might be best choice if your DC power is too high.

Journal reference

https://www.brighthubengineering.com/hvac/47392-types-of-potentiometers/

  • buy a can of WD40 to lubricate it.

My Stereo Pots only got noisy after 20 yrs and WD40 fixed that. But if you exceed the power rating in a Metal Film pot at low R, it will melt.

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  • \$\begingroup\$ Reminds me of the old joke- You can fix anything with duct tape and WD-40. If it moves and you don't want it to use duct tape. If it doesn't move and you do want it to use WD-40. And now if your pot's noisy the WD-40 works too. \$\endgroup\$
    – John D
    Mar 24, 2022 at 17:31
  • \$\begingroup\$ I remember getting my MGB running in the early '70s during an icy snow storm with arc shorts visible on the distributor and working when frozen with the hood up and dying a few minutes later, coming home late at night from U of M. then I remembered I had WD40 . Voila. I cleaned the distributor outside cracked plastic with carbon trails, and got home safely rather than freeze in a blizzard -20'C. No joke it was a blizzard and no traffic except me on the highway. in Winterpeg. FYI @JohnD A little EE wisdom saved my life \$\endgroup\$ Mar 24, 2022 at 17:34

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