Wikipedia says that modern (cheap) log potentiometers aren't actually logarithmic at all, but constructed with separate sections of fixed resistance tracks. Time for an investigation.
ETI Vocoder constructional project reproduced with permission from Wimborne Publishing Ltd. http://www.epemag.com
2 x 100K OHM Logarithmic Taper Potentiometer Pot A100K 100KA FREE SHIPPING http://www.ebay.com/itm/-/260902185815
2 x 10K OHM Logarithmic Taper Potentiometer Pot A10K 10KA FREE SHIPPING http://www.ebay.com/itm/-/280779174020
http://en.wikipedia.org/wiki/Potentiometer
http://www.geofex.com/article_folders/potsecrets/potscret.htm

By Julian

Youtuber, shed dweller, solar charge controller aficionado

12 thoughts on “Investigation: are log potentiometers really logarithmic?”
  1. Avataaar/Circle Created with python_avatars Harry says:

    What happens when we connect a fixed resistor in parallel with logarithmic potentiometer?. Any help ?. Thanks in advance.

  2. Avataaar/Circle Created with python_avatars R K says:

    The first slope is just bottom scale error.

  3. Avataaar/Circle Created with python_avatars Mr. S says:

    a smart design actually. thank you!

  4. Avataaar/Circle Created with python_avatars Haribo Starman says:

    Wouldnโ€™t this chart be upside down when talking about volume? I thought more resistance meant less volume

  5. Avataaar/Circle Created with python_avatars Space Walker351 says:

    I was testing some log pots under power and viewing the output with a digital scope set on a very slow sweep. Turning the control at as steady of a rate as i could by hand, the waveform resembled this. I thought that there had to be something wrong. I stand corrected. This verifies what i was seeing was to be expected. Thank you for explaining this. Oh yeah, cool test fixture too. Simple and effective.

  6. Avataaar/Circle Created with python_avatars Martin Kardos says:

    that's where my pencil broke

  7. Avataaar/Circle Created with python_avatars sophieeeee says:

    Can anyone explain to me why these instructives on log pots always show the resistance increasing with the volume? Surely the opposite muct be the case.

  8. Avataaar/Circle Created with python_avatars MURUGESAN R says:

    fantastic demonstration ……….

  9. Avataaar/Circle Created with python_avatars Revelation 13 Coming says:

    Can you please tell me if this pot has a click at the end of the turn…like to power something off? I need to find one like that. Thanks!

  10. Avataaar/Circle Created with python_avatars Bishka100 says:

    I read or saw an article somewhere and, much to my annoyance, I can't remember where, about converting lin pots to log. ย ย 

    By using a resistor between the wiper and one side or the other ย you could turn a lin pot into log or even antilog. If I remember correctly the fixed resistor should be about one tenth the value on the pot. So if you wanted a 100K log pot. you would use a 1M lin pot with a 100k resistor between the wiper and the right hand terminal ( as viewed from he front).

  11. Avataaar/Circle Created with python_avatars DossKat says:

    Little known fact about "A" taper pots- they're not logarithmic, it's just a common misnomer. They're correctly known as audio taper, hence the A50K, etc.

  12. Avataaar/Circle Created with python_avatars Poptart McJelly says:

    You can turn an analog pot into a logarithmic pot by just adding a resistor.
    If you need a 100k log pot you take a 150k analog pot and put a 300k resistor in parralel with the middle pin and side pin.

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