Tribute JB-2 Wiring Question

We are fortunate to count Paul Gagon as a member here, so it seemed natural to give him a home to stretch out in and relax a little. Maybe exercise the grey matter and present a little history of the guitar and bass (amps too!) from his perspective as one of the eminent designers of our time.

Got questions? Great! Good questions might be, "What are the EQ mappings for the M Series preamps?" Or, "What was the thought process behind the MJ-4?" Troubleshooting questions should remain in the regular forums (he reads those too). Finally, please be mindful of how I feel about tech questions via PM or email.

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Tribute JB-2 Wiring Question

Postby jglunt2112 » Thu Mar 18, 2021 3:49 pm

I recently picked up a B-stock JB-2 direct from G&L, and the volume pot on the bridge pickup doesn't turn off all the way. I can turn both volumes all the way down and still hear it plainly., but the bridge pickup is the only one that clicks when I tap a screwdiriver against it with both pickups turned down. Is this normal? I ask because I figured the pot just wasn't grounded right, so I opened it up to check, and this isn't wired like any other jazz bass I've ever seen. Question #2: What happens if I wire it up like a regular jazz bass? The volume pots are just normal 250A pots as far as I can tell. Is there anything unusual about the pickups?...Jim
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Re: Tribute JB-2 Wiring Question

Postby Ken Baker » Thu Mar 18, 2021 5:15 pm

jglunt2112 wrote:I recently picked up a B-stock JB-2 direct from G&L...


Boy, you've been busy!

Is this normal? I ask because I figured the pot just wasn't grounded right, so I opened it up to check, and this isn't wired like any other jazz bass I've ever seen.


No. Turn both down completely and both should go silent. In stock condition and wired correctly, it should act like a Jazz Bass.

Question #2: What happens if I wire it up like a regular jazz bass?


It'll work as it should. Diagrams below.

The volume pots are just normal 250A pots as far as I can tell.


Yup. All are 250KA.

Is there anything unusual about the pickups?...Jim


Nope. They are Paul's take on a late-60s (as I recall) Jazz pickup.

PDF for printing.

Image for eyeballing.

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Re: Tribute JB-2 Wiring Question

Postby jglunt2112 » Thu Mar 18, 2021 5:49 pm

Ken, thank you for answering all my questions succinctly and specifically. About half hour ago I found the problem with the bridge pickup volume. The ground lug of the pot was not grounded to anything. I left the back of the bass open for tomorrow because there's something in this one that I didn't see on the wiring diagram you sent (And thank you for that, BTW). On the neck volume pot of this bass, across the two hot (not the one grounded) lugs, a tiny brown disk is soldered. I assume it's some kind of capacitor, but I'm not knowledgeable enough to know what it is for certain. I don't see that in your diagram, though I just did a cursory look at it because I'm hungry and fixing dinner. That really confused me...I'll take a closer look at it tomorrow and post another reply. Who knows, maybe I'll even upload a picture! (Oh, no, not again!!!)...Jim
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Re: Tribute JB-2 Wiring Question

Postby jglunt2112 » Fri Mar 19, 2021 6:34 pm

Tribute JB2 Wiring(2).jpg
Tribute JB2 Wiring(2).jpg (123.98 KiB) Viewed 190 times


I'm not sure if I've captured this correctly--my only notorious attempt to try to upload a photo to this forum is legendary in its futility--but this is the wiring on the JB-2 I bought. If you look really closely, you can see the bridge pickup's volume pot is not grounded, which is easily fixable, but the thing that really has me stumped is that little brown dot-of-a-thing that I think is a capacitor wired to the neck pickup's pot across the hot input lug from the pickup and the output lug. It's the little brown dot you can spot near the yellow wire. It has the number "210" printed on the bottom side. Does anybody know for sure what that is and why it's there? As far as I can see, it doesn't show up in the wiring diagram for a JB-2...Jim
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Re: Tribute JB-2 Wiring Question

Postby jglunt2112 » Fri Mar 19, 2021 7:30 pm

In cruising through wiring diagrams (I have to get a life :geek:) I see that on the LB100 Paul has a 201 cap drawn in between those two lugs on the volume pot, but no matter how hard I try to see it on his JB-2 wiring diagram, it just doesn't materialize. Is it possible that somebody grabbed a pot out of the wrong bin or was using the wrong wiring diagram when this bass was assembled? :oops: Is it possible that I actually stumbled across something I thought was a capacitor but it was actually just a mouse turd? :o What happens if I just remove it? (The capacitor AND the mouse turd)..Jim
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Re: Tribute JB-2 Wiring Question

Postby Ken Baker » Fri Mar 19, 2021 8:58 pm

A couple of things:

1. That little cap can be safely removed. In a circuit where it belongs, it helps to maintain a balanced frequency response at low output levels.

2. Another image, please. Wider so that we can see all the wiring and be able to trace leads.

I have a hunch this one has been modded.

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Re: Tribute JB-2 Wiring Question

Postby jglunt2112 » Fri Mar 19, 2021 11:32 pm

1. That little cap can be safely removed. In a circuit where it belongs, it helps to maintain a balanced frequency response at low output levels.


Low output level? I'm a bass player. Low output levels are for lesser mortals, like guitarists and keyboard players! Consider the cap removed!!

2. Another image, please. Wider so that we can see all the wiring and be able to trace leads.


I'll do that ASAP. Weekends are crazy busy for me, but next week I'll have time to take another shot.

Very sincerely, thank you for all your help!...Jim
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Re: Tribute JB-2 Wiring Question

Postby jglunt2112 » Mon Mar 22, 2021 6:46 pm

JB2 wiring 4.jpg
JB2 wiring 4.jpg (193.73 KiB) Viewed 171 times


Here's a photo from farther out. It's just re-sized from one I took the other day since the bass is in my studio and I didn't get over there today. Can you tell from this photo if this has been modded? The only thing I saw wrong was the ground lug on the bridge volume pot wasn't grounded to the chassis, and I certainly have no problem doing that. Oddly, the lug is tinned with solder, but it wasn't attached in any way to the chassis. I can also remove the cap that's on the neck volume pot. It seems odd to me to have one on the neck volume pot but not on the bridge volume pot. Let me know if you see anything else unusual or if you need a different photo to determine that. I know this one is still not optimal since I used a flashlight to keep the wires out of the way of the control pots. As always, I'm grateful for your help...Jim
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Re: Tribute JB-2 Wiring Question

Postby Ken Baker » Mon Mar 22, 2021 7:34 pm

Sorry to ask, but can you take another one? This time without the flashlight so I can visually trace the leads. You can email it to me full sized and I can update here as well.

Thanks!

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Re: Tribute JB-2 Wiring Question

Postby jglunt2112 » Tue Mar 23, 2021 9:54 pm

Hi Ken. I'll be glad to post a better pic as soon as I get the chance. No, I'm not mad about that. I knew the pic was probably not gonna work, but it was what I had and I thought I'd try to "sneak it past you." But there ain't no foolin' you! I serve as a worship leader at a little church in our little town (pop. 176) and also as the interim pastor at an even smaller church here. This being Easter season, I'm crazy busy right now. Thus, the pic I tried to sneak by you instead of taking the time to take some others that might work. So it might be a while before I get a chance to actually sit down and snap a photo. I just don't want you to think I'm mad at you. So many of the guys on this forum are great about sharing their experiences and know-how. I'm thankful for all of them, and you're at the top of the heap in that regard. I appreciate the help you've given me and others since I've been part of this forum. When I moved from the Albuquerque area to southeast Arizona, I lost my luthier, who is now 350 miles away. He was an expert who priced his services reasonably and was willing to dole out advice over the phone as well. So at my advanced age I'm having to learn a lot of the stuff I leaned on him for. You and others on this forum have been invaluable. Thank you...Jim
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