Epi Jack Casady volume pot replacement (again)

Discussion in 'Basses [BG]' started by Lobster11, Feb 24, 2014.


  1. Lobster11

    Lobster11 Supporting Member Supporting Member

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    Apr 22, 2006
    Location:
    Williamsburg, VA
    My beloved Jack Casady, which I've had and loved for 6 or 7 years now, has finally developed a problem that evidently is quite common: The volume pot no longer controls volume. I've done a pretty extensive search here at TB and across the Interwebs to try to find out what replacement pot I need, and so far have learned the following:

    1. It is difficult, and takes forever, to get replacement pots from Epiphone/Gibson.

    2. The few people who have succeeded in doing so have usually found that the replacement pots have the same problem anyway, so that's not a reliable solution.

    3. It is also difficult to find the correct 2.5 audio-taper pot elsewhere -- it apparently is something of a rare bird -- though some people have posted links to online electronics distributors that appear to carry them. However, it isn't clear in these cases if these potential replacements are compatible in other ways -- for example, whether they have the right kind or length of shaft and can accommodate the original knob -- nor whether they in fact do work properly.

    What's particularly maddening is that every relevant thread I have found comes to an abrupt end before revealing a clear, reliable solution. I cannot find a post anywhere in which someone confirms that they replaced the pot with Part XX from Vendor YY and that it works fine. (The closest I found was someone who found a replacement pot that worked properly, but that wouldn't accommodate the original knob; he had to replace the knobs, too.)

    So... Is there anyone out there who has successfully solved this problem -- or found a luthier who could -- who can give me a definitive answer on this? I plan to have a luthier do the actual replacement, but I'd like to be able to provide this information to him so he doesn't have to waste time trying solutions that have already been tried and failed. Thanks!
  2. Grissle

    Grissle Supporting Member

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  3. jeffbonny

    jeffbonny _____________ Gold Supporting Member

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    Vancouver, BC
    After much ****ing around and trying several different pots that seemed close in spec I ended up going with stock replacement pots from Epiphone. They were a special order that took several weeks to materialize but none of the others I found had an even taper. I really wish Epiphone would publish the exact values for the Casady electronics so we could find higher quality aftermarket pots because it's no secret the stock ones suck big time....or better yet just charge a few buck more and OEM mil spec pots.
  4. Lobster11

    Lobster11 Supporting Member Supporting Member

    Joined:
    Apr 22, 2006
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    Williamsburg, VA
    That's what I feared. And I've read too many reports from people who said they got stock replacement pots from Epiphone that were also faulty that I don't want to go in that direction either.

    Do you happen to remember which other alternatives you tried but found unsatisfactory, so I can be sure to avoid them?
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  6. jeffbonny

    jeffbonny _____________ Gold Supporting Member

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    They were 2.5K audio taper pots from 2 different ebay vendors...no local electronics seemed to be able to track any down. I believe though that they might have actually been linear taper pots because they all displayed the same more or less on/off behavior. Too bad because they were mil spec and had that "lifetime of service" feel. I also tried as a volume a 2k snap-in pot for an amp that thinned the sound out a bit and wasn't ever going to really fit the bass anyway.

    I could live without a tone control but I'm a habitual onboard volume user. What I have is working for the time being but I'd like to solve this permanently with a high quality part. I wonder if contacting Jack Casady and asking him to find out the specs would get any results? Epiphone has ignored all my direct inquiries. I've thrown a lot of energy into this but I'm kind of at a loss now.
  7. takeout

    takeout

    Joined:
    Dec 27, 2002
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    Kansas City area
    Subbed. Same question, tone pot. I hate going in and out of this thing, tying fishing line to parts, etc.
  8. Lobster11

    Lobster11 Supporting Member Supporting Member

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    Apr 22, 2006
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    Thanks for that. I guess I'll take up the fight from here. I'll go ahead and see if I have any better luck with the folks at Epiphone (not holding my breath), and maybe I'll pm some other TBers who, like you, have posted about similar problems in the past. I'll report whatever I learn here, so watch this space.

    In the meantime, if anybody else out there has any ideas about what/where to try -- or not to try -- please chime in!
  9. mongo2

    mongo2

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    Downdashaw
    That gave me an idea.

    According to the Casady schematic I have, the potentiometer for the tone control is the same value as the volume control so the tone control potentiometer could be swapped into the volume role and do without the tone control until an adequate replacement can be found.
  10. Lobster11

    Lobster11 Supporting Member Supporting Member

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    Speaking of tone pots, I'd actually like to replace that (with a higher-quality part) too. Mine works okay but has always been scratchy, and now I'm afraid that at some point it's likely to suddenly fail like the volume pot did.

    Which raises the issue as to whether, notwithstanding what the schematic says, the tone pot is (should be) the same as the volume pot. My electronics knowledge is limited, but my understanding was that it was pretty much industry standard for volume pots to be log-taper and tone pots to be linear-taper, and that there are good reasons for this in terms of the psychophysics of sound perception. No?
  11. jeffbonny

    jeffbonny _____________ Gold Supporting Member

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    Yes this is completely doable. The tone and vol pots appear to be the same.

    I tried a 250k pot onboard the Casady and it functioned only as a hard on/off switch...no tapered volume control whatsoever. However the Casady works fine with an external 250k passive volume pedal. I'm not electronics savvy enough to understand why this is but it seems to me that you could emulate the output of the Casady with resistors instead of pots to fool a 250k pot into working onboard? What am I missing here?
  12. mongo2

    mongo2

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    Both are usually log taper.
  13. mongo2

    mongo2

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    Back to the Casady schematic...

    As I thought the pickup (which is a low impedance design) and the volume and tone controls are on the low impedance side of the varitone/impedance matching transformer which sits between the volume/tone controls and the output. The transformer matches output impedance for use with the input of an amp so it makes sense that the 250K volume pedal works normally. However since the pickup and volume/tone controls are on the low impedance side of the transformer replacing them with a 250K will produce the effect you noticed.

    My SWAG is that if the volume and tone controls and their RC networks were to be relocated to the high impedance (output) side of the transformer, the 250K values just might work, perhaps with a bit of adjustment to their RC networks. I'll have to try it if the volume/tone controls ever crap out on my Casady.
  14. Templar

    Templar Supporting Member

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    Interesting thread, guys. Too bad it's such a headache fixing a broken Casady. Hopefully, someone will locate a source for quality replacement pots.

    Barring an easy fix someday, if mine craps out on me I'll be taking a hard look at a Darkstar conversion (maybe even twin DS).
  15. Steve Dallman

    Steve Dallman Supporting Member

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    Mar 5, 2006
    Location:
    East Central Wisconsin
    A 5k audio pot should work fine for either volume or tone. If necessary a resistor could be added to adjust the resistance down or adjust the pot taper. If a suitable 5k audio pot was found, you could use your tone pot for the volume and use the 5k for the tone.

    Think standard passive bass. A 500k pot will work where a 250k is used, but with a little added brightness.

    Heck, even a 10k should work. But a 5k would be closer.

    A 5k linear taper could be changed to a suitable audio taper using a resistor. This article gives a lot of good information.

    http://www.geofex.com/article_folders/potsecrets/potscret.htm
  16. Lobster11

    Lobster11 Supporting Member Supporting Member

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    Ah, thanks for the correction. I definitely want the replacements for both pots to be the same taper as the originals, which were fine in that regard.

    BTW, this prompted me to do a little research, and I now see that there is a long history of confusing (and often acrimonious) TB threads debating the audio-vs-linear thing. So let's drop that topic and speak of it no more here....
  17. Lobster11

    Lobster11 Supporting Member Supporting Member

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    Thanks for that; I'll definitely keep this in mind as a backup plan. The bass certainly doesn't need to be any brighter, but as long as the pot allows me to roll off some of those "extra" highs I'd be fine with that.
  18. Pimpernel Smith

    Pimpernel Smith

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    May 25, 2012
    Location:
    In the Pond
    lobster11:

    You are doing a good service for us Casady bass owners.
    I encourage you to keep this diary going until you find the correct pots, and then let us all know where you got them.

    Additionally, do you have a link to the schematic of the JC bass?

    If so, I'd like to see it and print it and keep it in my bass case, should I need it in the future. I've had my JC bass since 1998, and so far everything works properly - I play it every night.

    But, I'd like to have the information for when the time to have it repaired comes.

    It really begs the question: Why doesn't Epiphone have these available for quick and easy replacements?
  19. mongo2

    mongo2

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    An internet search will yield what you seek.
  20. Lobster11

    Lobster11 Supporting Member Supporting Member

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    Williamsburg, VA
  21. jeffbonny

    jeffbonny _____________ Gold Supporting Member

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    Location:
    Vancouver, BC
    Here it is just for the sake of this thread's continuity.
    [​IMG]

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