Reverse Audio Taper Hack

Discussion in 'Amp Tech Center' started by SSL9000J, Oct 17, 2018.

  1. SSL9000J

    SSL9000J Tele-Meister

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    Greetings! Whilst sourcing parts for a Vibro-Champ clone currently under construction, I found myself vexed by the scarcity of options when it comes to the infamous reverse audio pots for the tremolo circuit. Particularly because the amplifier is going inside a wood speaker cabinet with the controls on top, necessitating longer bushings on the potentiometers. Not a big deal for 250K or 1meg audio taper, and I'll even accept a 25K linear if it fits. But that confounded 3meg reverse audio!

    So anyway, I found this helpful resource that seemed worth sharing. (It's an article titled "The Secret Life of Pots.") The author, R.G.Keen, tells you everything you ever wanted to know about potentiometers but were afraid to ask. About halfway through, he explains different types of tapers, and how to modify them by adding a resistor to the pot, creating a voltage divider. It's a bit technical and there's math :eek: but useful for tinkerers such as we.

    [​IMG]
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  2. wanderin kind

    wanderin kind Tele-Meister

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    cool stuff, thanks!

    James Brown uses that in the 72 Coupe>

    r.gif
     
  3. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    You could of course just use the readily available CTS 3M reverse taper, and extend the shaft with a shaft coupler.
     
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  4. Old Tele man

    Old Tele man Friend of Leo's

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    ...however, it is NICE a 'trick' for the DIY amp designer/builders to be able to "tweek" the response (change-vs-rotation) of his/her's amplifiers.
     
  5. Bill Moore

    Bill Moore Tele-Afflicted Silver Supporter

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    I have mixed/matched shafts/wipers to get the characteristics I needed.
    I recently had to "make" a pot to fit an old SS amp with a "spider" type mounting, and an SAE thread.
     
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  6. wanderin kind

    wanderin kind Tele-Meister

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    you could also custom build a stepped rotary switch with fixed values, these makes repeating the same speed easy, dial in the resistor for Born on the Bayou and then the resistor for Scratch My Back and you hit the note every night,
     
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  7. SSL9000J

    SSL9000J Tele-Meister

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    True, although the challenge with mounting the pots directly to the cabinet isn't so much the shaft being too short as the bushing not having long enough threads to reach all the way through the wood.
    IMG_20181018_075332.jpg
    I may try to mount the pots to a metal plate and attach it to the inside of the cabinet, if all else fails. (Top pot is actually a Clarostat 2M linear. Scored a box of them off FleaBay a while back for something like 16 bucks.)
    Great idea! Might have to practice on a few expendable pots first.
    Let's not forget "I Had Too Much To Dream Last Night!" I thought about this too.
    A wealth of great ideas on this forum, as always. Many thanks!

    PS - here's the cabinet. It's... had a few previous conversion attempts.
    IMG_20181018_080758.jpg
     
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