• Re: Tone controls and 'anti-log' potentiometers

    From Peter W.@21:1/5 to All on Sun Oct 3 10:01:40 2021
    No more so than any other pot - just a tad more difficult to make. Point of the choice, initially, was to make the pot travel more linear to the human ear, vs. electrically. They are easily obtained in most common values, other than the fact that the
    Brits, like the French, when they made their electronics copied no one, and no one copied them.

    I would first try cleaning the pot. I do not know how the treble-circuit is designed in that radio - other than the pot-resistor wants to be in-circuit in many designs, so it could be as simple as something in the wiper. Further, if the overall pot
    value and current-handling capacity is correct, the only difference between OEM and a replacement - anti-log or not - would be the response-to-travel perception.

    Peter Wieck
    Melrose Park, PA

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  • From Ralph Mowery@21:1/5 to All on Sun Oct 3 13:11:32 2021
    In article <i4njlght4300h0hb0c6t9iceun3oe3b6q1@4ax.com>, cw9877@gsm.com
    says...

    Does anyone know if anti-log pots are more prone to failure? I bought
    an old vintage broadcast radio that has separate bass and treble
    controls and for some reason they've used an anti-log pot for the
    treble - and it doesn't do nothing. Apart from that, the radio seems
    fine so I'd like to get it fixed. I've never encountered 'anti-log'
    pots before (never even heard of them) and am just curious as to if
    they're more likely to fail.




    Pots like anti-log, log, linear are just ways of how the resistance
    changes as the knob is turned.

    Many audio type pots will be log or anti-log so that as they are
    turned the results seem linear to the ear as the ear is not a linear
    device,but more of a log type of device.

    A linear taper pot will be turned just a little on one end of the
    rotation and a lot on the other end of the rotation to get the same
    effect.
    The resistance of a linear pot will change the same ammount no matter
    where on the rotation it is. A log and anti-log pot will change
    resistance very much on one end and not much on the other end of the
    rotation for the same ammount of degreese the shaft is rotated.

    So the taper should not make any difference in the life of a pot.

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  • From Chris M. White@21:1/5 to All on Sun Oct 3 17:43:52 2021
    Hey gang,

    Does anyone know if anti-log pots are more prone to failure? I bought
    an old vintage broadcast radio that has separate bass and treble
    controls and for some reason they've used an anti-log pot for the
    treble - and it doesn't do nothing. Apart from that, the radio seems
    fine so I'd like to get it fixed. I've never encountered 'anti-log'
    pots before (never even heard of them) and am just curious as to if
    they're more likely to fail.

    Thanks all,

    Chris.

    PS: the radio in question is a Hacker Sovereign II from about 1970
    made in liddle ol' England.

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  • From Chris M. White@21:1/5 to peterwieck33@gmail.com on Sun Oct 3 18:15:57 2021
    On Sun, 3 Oct 2021 10:01:40 -0700 (PDT), "Peter W."
    <peterwieck33@gmail.com> wrote:

    No more so than any other pot - just a tad more difficult to make. Point of the choice, initially, was to make the pot travel more linear to the human ear, vs. electrically. They are easily obtained in most common values, other than the fact that the
    Brits, like the French, when they made their electronics copied no one, and no one copied them.

    I would first try cleaning the pot. I do not know how the treble-circuit is designed in that radio - other than the pot-resistor wants to be in-circuit in many designs, so it could be as simple as something in the wiper. Further, if the overall pot
    value and current-handling capacity is correct, the only difference between OEM and a replacement - anti-log or not - would be the response-to-travel perception.

    Peter Wieck
    Melrose Park, PA

    Thanks. I came across the relevant schematic fragment online showing
    the tone controls for bass and treble. I can't see how they work
    unless they form some sort of elementary network with the 2.5uF C11.
    Hard to say with those pesky sockets in the way of the signal path.
    It's about a third of the way down the page in this document:

    https://www.microscopy-uk.org.uk/mag/artjan13/iw-radio2.html

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  • From Ralph Mowery@21:1/5 to All on Sun Oct 3 14:17:21 2021
    In article <cvojlgdenm5kj60jajnsubdkj5937f8vrm@4ax.com>, cw9877@gsm.com
    says...

    Thanks. I came across the relevant schematic fragment online showing
    the tone controls for bass and treble. I can't see how they work
    unless they form some sort of elementary network with the 2.5uF C11.
    Hard to say with those pesky sockets in the way of the signal path.
    It's about a third of the way down the page in this document:

    https://www.microscopy-uk.org.uk/mag/artjan13/iw-radio2.html





    From the looks of things there is no way to tell how the base and tresle controls work. They are shown to go into the block diagram to the right
    of the 2 batteries. There could be anything in that block.It is
    doubtful that the C11 has anything to do with the 2 pots.

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  • From Phil Allison@21:1/5 to Chris M. White on Sun Oct 3 13:57:18 2021
    Chris M. White wrote:
    =================

    Does anyone know if anti-log pots are more prone to failure?

    ** I do.

    I bought
    an old vintage broadcast radio that has separate bass and treble
    controls and for some reason they've used an anti-log pot for the
    treble - and it doesn't do nothing.

    ** So you can't say if it is a cut or boost ?

    Apart from that, the radio seems
    fine so I'd like to get it fixed. I've never encountered 'anti-log'
    pots before (never even heard of them) and am just curious as to if
    they're more likely to fail.

    ** Rare to see one in a tone circuit.

    But very common the the "gain" control of mic pre-amps.
    Here the gain increases as the resistance reduces, so a normal log pot has to operate anticlockwise.

    BTW when you have a sample size of one, probability theory does not work.



    ...... Phil

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  • From Chris M. White@21:1/5 to rmowery42@charter.net on Sun Oct 3 22:02:52 2021
    On Sun, 3 Oct 2021 14:17:21 -0400, Ralph Mowery
    <rmowery42@charter.net> wrote:

    In article <cvojlgdenm5kj60jajnsubdkj5937f8vrm@4ax.com>, cw9877@gsm.com >says...

    Thanks. I came across the relevant schematic fragment online showing
    the tone controls for bass and treble. I can't see how they work
    unless they form some sort of elementary network with the 2.5uF C11.
    Hard to say with those pesky sockets in the way of the signal path.
    It's about a third of the way down the page in this document:

    https://www.microscopy-uk.org.uk/mag/artjan13/iw-radio2.html





    From the looks of things there is no way to tell how the base and tresle >controls work. They are shown to go into the block diagram to the right
    of the 2 batteries. There could be anything in that block.It is
    doubtful that the C11 has anything to do with the 2 pots.

    Thanks for your observations. That explains a lot. I'll need to order
    a service manual for this radio off the Web as there's no free
    downloads for this model available anywhere. Until that arrives,
    there's nothing more I can do.

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  • From Phil Allison@21:1/5 to Ralph Mowery on Sun Oct 3 14:00:10 2021
    Ralph Mowery wrote:
    =======================

    So the taper should not make any difference in the life of a pot.

    ** Don't be so sure.

    Most reverse log pots are made by installing the carbon element from a log pot upside down.
    That has an effect on reliability.


    ...... Phil

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