Mike Bungo Posted July 2, 2021 Share Posted July 2, 2021 Hi everyone I've bought a used JC Bass and I'm looking to order new volume and tone pots whilst its on it's way to me as I'm told that the volume pot is either on or off with no in between. Would anyone know the pot shaft sizes i.e. width and height ect I believe that they are also 2.5k and I understand that these may be hard to get hold of so any help with advice on an alternative would be great And finally....... Am I ordering Audio or tapered and if so for which pots Many thanks in advance Mike Quote Link to comment Share on other sites More sharing options...
neepheid Posted July 2, 2021 Share Posted July 2, 2021 Can't help you with pot tapers, but if you look at page 157 of this amazing bass wiring cookbook then you'll find a great wiring diagram which might help you in your quest: http://www.ak-line.com/medium/Bassschaltungen.pdf It's in German, but even if you don't know the language the pictures are still useful. 1 Quote Link to comment Share on other sites More sharing options...
neepheid Posted July 2, 2021 Share Posted July 2, 2021 I would say that I would hold off buying a replacement until you've tried cleaning the existing pot out with some switch cleaner - spray some in then give the pot a good twirl back and forth through its travel and see if that brings it back to life. However, the description of all or nothing does possibly suggest a broken track, and no amount of magic spray will help you there. 1 Quote Link to comment Share on other sites More sharing options...
ikay Posted July 3, 2021 Share Posted July 3, 2021 There's a long thread on TB about this very problem - https://www.talkbass.com/threads/epi-jack-casady-volume-pot-replacement-again.1057712/ Finding replacement pots (2.5k log) seems to be next to impossible but on page 3 there are a few alternative suggestions: SUGGESTION 1 There is a solution. If you get stereo 5K pots (which are way easier to find than 2K5) and wire both halves in parallel you get the desired value. I think the fact that you have two separate pots in parallel may also reduce crackle as they wear. SUGGESTION 2 Order a good CTS / Orangedrop combination as for a PB (two 250K's, 0.047muF), remove the 2.5K pots and connect the JC Electar pick-up directly to the rotary switch input. Connect the transformer output to the two new pots as you can find in any PB scheme, then to the output. Before changing anything, confirm yourself that you can find the right wires in this "old-world telephone exchange"! Result: - no cracks anymore! - the sound is not changed, except for the effect of the tone pot. Depends on the rotary switch position and input impedance of your amplifier or device. But that was also the case before modification (some years ago I posted a question about this, but few JC-bassists seem to use different amps, I guess...). - no more searching for the right pots, the new ones are regular. - the JC Bass seems not critical for changing the wiring, the sound is still in your fingers. 1 1 Quote Link to comment Share on other sites More sharing options...
gary mac Posted July 3, 2021 Share Posted July 3, 2021 Before ordering I would hold off and check whether you can get full size pots through the F hole. It might be that you can get them installed through the pick up rout but I'm not sure. I know that with some of the Epiphone guitars that I've worked on, installation was through the f hole aperture and that can be a tight squeeze. 1 1 Quote Link to comment Share on other sites More sharing options...
rmorris Posted July 5, 2021 Share Posted July 5, 2021 On 02/07/2021 at 11:51, Mike Bungo said: I believe that they are also 2.5k and I understand that these may be hard to get hold of so any help with advice on an alternative would be great 2.5k ? Ohms ? Quote Link to comment Share on other sites More sharing options...
neepheid Posted July 5, 2021 Share Posted July 5, 2021 15 minutes ago, rmorris said: 2.5k ? Ohms ? Yes. Are there any other units of resistance? Quote Link to comment Share on other sites More sharing options...
ikay Posted July 5, 2021 Share Posted July 5, 2021 Here's a selection of 2,5k log pots from Mouser: https://www.mouser.co.uk/Passive-Components/Potentiometers-Trimmers-Rheostats/Potentiometers/_/N-9q0yp?P=1yzekj1Z1yzvm31 The Bourns one at the bottom of the list looks like it should do the job. Quote Link to comment Share on other sites More sharing options...
rmorris Posted July 5, 2021 Share Posted July 5, 2021 4 hours ago, neepheid said: Yes. Are there any other units of resistance? No. I was questioning the value, not the SI unit. 2.5k - I'm reading that as 2500 Ohms (2K5). Most pots in passive basses are min 250 kOhm (250K) and often 500K or 1M0. 2K5 is likely less than the DCR of a passive pickup. Even active EMGs typically spec 25K. 2K5 would be possible with active circuitry but other considerations eg power consumption of a battery powered circuit often lead to higher values of potentiometer resistance being used. Quote Link to comment Share on other sites More sharing options...
ikay Posted July 5, 2021 Share Posted July 5, 2021 The JC electronics are different to a regular bass. It has a low impedance pickup with a tapped transformer to change the impedance and tonal characteristics via a 3-way switch. Vol and tone pots are 2.5k log. I found this wiring diagram on the web. 1 1 Quote Link to comment Share on other sites More sharing options...
rmorris Posted July 5, 2021 Share Posted July 5, 2021 6 minutes ago, ikay said: The JC electronics are different to a regular bass. It has a low impedance pickup with a tapped transformer to change the impedance and tonal characteristics via a 3-way switch. Vol and tone pots are 2.5k log. I found this wiring diagram on the web. Right. I see. That is proper interesting from an electronics approach cf the standard Hi-Z passive. Many Thanks. Quote Link to comment Share on other sites More sharing options...
Mike Bungo Posted July 9, 2021 Author Share Posted July 9, 2021 Hi Again guys Thanks for all of your help. I am lucky to have 2 Casady's but please read on as to why I'm lucky White - 2014 owned for a while and this thing sounds amazing. I also have full control over the volume and tone so no issues here Gold - 1998 (Just bought) And the volume & tone are pretty much on or off with no in between. I can solder real well but I don't understand electronics. I spoke with Guitars North West and purchased replacement Alpha 2.5k pots and the packet is labelled (Volume & Tone). I've taken my time and fitted these by taking out both looms from each guitar so I could closely check the wiring but the problem is exactly the same. I am in the process of replacing both the capacitors and the one resistor to eliminate any issues with these BUT Whilst reading up on this side I came across an article about types of pots used on bass guitars and my scenario is mentioned. Not in a bad way but in a way that gives you an immediate drop in volume and treble tone if needed so the question is was this older guitar possibly designed to be like this and was this a spec requested by Jack Casady when working with Epiphone????? Your views would be very welcome before I just build it up and make adjustments on my amp....... Many thanks Mike Quote Link to comment Share on other sites More sharing options...
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