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Fisher 400CX-2 potentiometer

Discussion in 'Fisher' started by vendo81, Nov 29, 2018.

  1. vendo81

    vendo81 AK Subscriber Subscriber

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    On Ebay there is a person selling a new version of the volume pot (with on/off switch) for the Fisher 400cx-2, 400c, X-1000, etc...

    Of the half dozen or so 400cx-2 preamp's I've owned, 3 had volume pots that wouldn't track correctly. One channels volume would track differently than the other. The switch was another problem but they are available with a little searching.

    I've been using one for several years that tracks really well but have one boxed up that tracks terribly. It tracks so bad that one channel is still heard when all the way down and they don't track the same until at the 11 or 12 o'clock position. Replacing the volume control without the correct taps would cause you to lose the loudness function. I did this on the boxed up preamp so the volume worked as it should but lost the use of the loudness switch. Hopefully the taps on this new pot would bring back the loudness function.

    Has anyone tried one of these for fit and for how well they perform? I thought I'd ask before ordering a couple.
     
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  2. bhamham

    bhamham AK Subscriber Subscriber

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    Thanks for posting this vendo. Just had a look at the ebay seller's site and his pots look very promising. I need one for a 500-B but wouldn't mind having an extra or two. I don't know what the loudness tap is for the preamps with reference to your post, but he has the tap for the amps/receivers at 125k. For some reason I thought it was lower than that, like 75k.

    I'll see what others have to say before hiting the buy button.
     
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  3. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Keith, are you talking about that Capt Fant******** guy? Seems he has new pots for all kinds of Mac and Fisher gear, have never done business though. He has 2 Screen names on that site. Hope you find one! :) Al
     
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  4. fred soop

    fred soop Super Member

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    If the tracking is not extremely bad, you can play some games with a fixed resistor on the loudness tap. Disconnect the control completely. Connect a 9 V battery to the top end of both sections and its return to the bottom (ground) end of both sections. Now, set the control at your most common listening position, 10:00 for example. Measure the voltage between each wiper and ground. The section with the higher voltage needs to be reduced by adding a resistor between the loudness tap and the ground connection. Calculations are complex and iterative, so best just to experiment. Something on the order of 220K - 330K is a good starting point. Note that if the pot tracks well at higher volumes, this "fix" will actually make it worse but at higher volumes, the unbalance may be less obvious.

    [​IMG]
     
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  5. vendo81

    vendo81 AK Subscriber Subscriber

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    Hello Al. Yes that's the guy. If they are exact matches they would sure be needed by many. The volume imbalance issue makes things unlistenable. The fix Fred Soop posted looks like a great thing to try as well.
     
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  6. vendo81

    vendo81 AK Subscriber Subscriber

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    Great idea Fred! It's common to find pots doing this and many times impossible to find a good replacement. I'll make note of this.
     

     

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  7. vendo81

    vendo81 AK Subscriber Subscriber

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    Yes, the resistance of the taps and how smoothly the pots work are the items I'm questioning. I know several people that don't care about the loudness feature but I use it often.
     
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  8. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    It's a shame Alpha or another big potentiometer maker couldn't be persuaded to make a line of these - lots of stereos through the 70's have these issues.

    The Alpha dual 500K audio pot is less than 5 bucks. With a longer shaft, switch and loudness taps, they should still be able to keep the cost under $20. I went through some experiments on one of the dual audio taper Alpha 500K pots, one can add loudness taps with some effort - not too bad, and pull a power switch from another new Alpha Pot. Shaft needs an extender, but they make another pot with the right length - it's just permanently assembled, so hard to swap over and have a robust, long lived connection.

    I once saw someone selling Dynaco amp pots modified as I describe on eBay

    Point is, they already make all the parts to do this separately except the loudness taps (they may have some pots with loudness taps, I just haven't seen them).
     
    Last edited: Nov 30, 2018
  9. vendo81

    vendo81 AK Subscriber Subscriber

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    Yes Matt I wish some big potentiometer maker would make these with quality/quantity and at a decent price.
     
  10. 1rebmem

    1rebmem AK Subscriber Subscriber

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    I bought one from Capt Fantastic for my 500B. The tracking was about the same as the original using an ohm meter so I installed it and it works fine.
    With the original, the volume would cut out briefly when I touched the control. Even after multiple cleanings.
    Jef
     
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