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"J" taper vs. "A" taper pots.

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  • "J" taper vs. "A" taper pots.

    What is the difference and does it matter in amp tone/volume controls?

  • #2
    Actually I never heard of a "J" taper and wonder if it's a standardized term, but ..

    an A or audio taper aka "logarithmic" taper is typically used for volume controls. Actually all audio pots have a J-shaped or exponential taper (looks similar to the V/I characteristic of a diode) meant to compensate for the logarithmic sensitivity of the human ear.

    Caveat: In Europe A taper traditionally meant a linear taper. B-taper was used for log pots.
    Last edited by Helmholtz; 10-14-2020, 10:15 PM.
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    • #3
      Here are some of the J taper pots: https://www.tubesandmore.com/product...er%3DJ%20Taper

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      • #4
        About potentiometer taper

        http://www.elby-designs.com/webtek/documents/tailoringpotentionometers.pdf

        https://eepower.com/resistor-guide/resistor-types/potentiometer-taper/

        https://www.islproducts.com/design-notes/potentiometer-taper/

        https://www.strat-talk.com/threads/best-volume-pot-taper.387421/

        https://www.diystompboxes.com/smfforum/index.php?topic=73819.0
        What is "J" taper?
        https://www.diyaudio.com/forums/parts/316967-substitute-taper-taper-pot.html
        Substitute "A" Taper for "J" Taper Pot
        https://www.crazyparts.de/electronics/cts-tvt-custom-pots/index.php
        CTS "VT" Vintage Taper Series Pots
        https://www.boxguitar.com/en/pots/4550-cts-pot-solid-shaft-250k-j-taper.html
        J taper is a softer audio taper where you have around 30% resistance at noon, as opposed to the 10 to 15% found in more conventional audio taper pots. You could think of it as an in-between the linear and audio taper.
        Who does not know and knows that he does not know - teach him Confucius)
        Who knows and does not know that he knows - wake him Confucius)

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        • #5
          They seem to be audio taper pots. Without a precise definition any new term is meaningless. I tend to think that J-taper is a marketing invention. It's a proven marketing stratety to offer solutions for made-up problems.

          I'd need to see a graph of the taper.
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          • #6
            https://imageshack.com/i/pmtlxUUvj

            https://www.tdpri.com/attachments/2019-05-13-png.608077/
            1)
            http://web.archive.org/web/20190720065820/https://www.ctscorp.com/wp-content/uploads/450G.pdf
            graph page 3








            Last edited by vintagekiki; 10-14-2020, 11:24 PM.
            Who does not know and knows that he does not know - teach him Confucius)
            Who knows and does not know that he knows - wake him Confucius)

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            • #7
              Looks as if CTS J-taper is between linear and audio taper, meaning that output is higher than a standard audio taper but lower than a linear pot at mid setting.
              - Own Opinions Only -

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              • #8
                Originally posted by Helmholtz View Post
                They seem to be audio taper pots. Without a precise definition any new term is meaningless. I tend to think that J-taper is a marketing invention. It's a proven marketing stratety to offer solutions for made-up problems.

                I'd need to see a graph of the taper.
                Not so, they exist, are alive and well.
                It *is* a "Log/Audio" taper pot, actually its mirror image, itīs Exponential (to counteract le Logarithmic ear response) but instead of typical (and most useful) 10% of full resistance at 50% rotation.which provides vey useful 20dB attenuation (1:10) , perfect for regular volume controls and Fender or James type tone controls, they haveb 30% at center, so 10dB.

                It allowed Fender to "sound louder than others" when compared side by side, with typical "all pots on 5" setting.

                Using Linear pots would have allowed for even more "impressive" results but then with only 6dB between 50% and 100% the trick becomes too obvious.

                Yes, the "between Linear and Log/Audio" description is not NASA quality buy useful in practical terms.

                As a side note, Log pots are NEVER Log because that would require continuous variation of resistivity (not resistance) along the track; the time tested and accepted convention is to use two linear tracks in series, one 10% resistivity of the other.

                I have personally manufactured potentiometers at the Argentine Philips factory (after Philips lost interest in actual manufacturing, they sold their machinery and one of their ex-Engineers bought it, together with licensed technology and original supplies) .

                process starts by coating long strips of Pertinax, phenolic paper board material, with proper resistive ink (colloidal graphite floating in raw phenolic varnish)
                Application is by mirror polished stainless steel rollers, which by capilarity leave a very thin and uniform layer.

                Then that strip is cooked in a controlled temperature oven.

                If you coat full width with a single ink/paint you get a linear pot.

                If you use 2 different ones, meeting in the center, you get a Log/Antilog (A curve or C curve) , you van easily get thisn so called J curve, no big deal, process is the same , just pick needed paint.

                I manufactured for myself "S" taper pots, best for active gain and Equalizers.

                Again, no big deal, only problem is that since you have to load machine tanks with resistive paints, you waste some and itīs **expensive** , you have to fire the oven and wait a lot for it to stabilize, etc. , you need a certain minimum batch size to justify it.

                Japanese/Chinese typically ask for 5000 units minimum, I had to coat custom strips for a 1000 pot batch, although I actually finished only 200.
                The rest of the process: punching Pertinax "omega" shaped tracks, riveting terminals, assembling shaft/wipers, closing it in the case and riveting it shut is standard for any type.

                Sadly open Customs, no Tariff, etc. led to the *destruction* of our Electronics Industry, this guyīs factory shrinked and shrinked until only him and his son remained, when I needed something custom I was invited to dress in blue overalls and do it myself.

                Oh well, delights of "globalization"

                We paid 30.000 dead for the "privilege"
                Juan Manuel Fahey

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                • #9
                  In other words except the log and lin, the others are the custom pot.
                  Who does not know and knows that he does not know - teach him Confucius)
                  Who knows and does not know that he knows - wake him Confucius)

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                  • #10
                    J taper = 30% log;
                    standard audio taper = 10% log
                    Jack Briggs

                    sigpic
                    www.briggsguitars.com

                    forum.briggsguitars.com

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                    • #11
                      There is also a "D" taper. I've seen these potentiometers (all of Japanese origin I think) on passive guitar tone circuits from Ibanez and probably Yamaha too. I think they must be another variant of a logarithmic curve but they worked especially well in that function.

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                      • #12
                        very interesting.....I had asked Fender before about the pot codes and was never really given a suitable answer....until now....

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                        • #13

                          Not so, they exist, are alive and well.
                          No doubt.

                          It allowed Fender to "sound louder than others" when compared side by side, with typical "all pots on 5" setting.
                          I would call that a marketing trick.


                          I manufactured for myself "S" taper pots, best for active gain and Equalizers.
                          Symmetrical "S" taper pots are also used in Wah-wah pedals.

                          Last edited by Helmholtz; 10-16-2020, 04:27 PM.
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                          • #14
                            Originally posted by J M Fahey View Post

                            It allowed Fender to "sound louder than others" when compared side by side, with typical "all pots on 5" setting.
                            Also also allowed a million Fender amp owners to say "why does it jump from very quiet at 1 to insanely loud at 2?"

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                            • #15
                              Not so much on old Fender amps, J taper is still contollable, but on modern ones, yes, Linear taper Master control makes them unusable.

                              Lots of people offer mods (which involve replacing pots by proper ones, such as J or A) or simply put an external Master volume in a small box and insert it in the effects loop.

                              J taper is a marketing trick as helmholtz says, and in general works, straight using a linear one is stupid, it simply annoys users.
                              Juan Manuel Fahey

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