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1974 Gibson Les Paul Signature Bass Low Impedence Pickup Transformer Inquiry

The Retro Lab

New member
Joined
Apr 7, 2021
Messages
1
Well folks, it's about that cycle where once in a blue moon, someone comes along with an inquiry on one of these basses. I've done as much research as I can, all of which turn up dry, no results. Then why am I posting again? In hopes that *SOMEONE* out there has an answer / solution / *something* to get this thing up and running again. And that perhaps sometime between the last time someone posted something like this and now, *someone* has some info / solution!

SO, here's what I'm dealing with, as I acquired it:

I have a '74 Sunburst Les Paul Signature bass that came to me essentially as an empty hull with all hardware (and a fresh re-fret), and a baggie full of parts, consisting of the original pickup, an input jack, 1 potentiometer, a period correct looking unused 3 way selector switch for the 50/250/500, and some wire. THATS IT. Eager to try this thing out, I put the pickup in, wired it up straight to the input jack, hoping I could be in business. Well, kinda. Just whisper quiet. I know I know I know... it's because of the low impedance thing, which is why I'm here. I need to know what that is. Or what it can be. Ideally what it was. Preferably what I can put in there, mmm, now?!

I've seen a photo on Chicago Music Exchange's listing for a Les Paul Signature Model bass, which shows the transformer that I speak of. I will go to my grave that I've seen a photo of what this transformer was, and it was made by UTC, but for the *life* of me I can not find that photo again (shakes fist), and I do know that said photo did NOT have any further into illustrating what model UTC transformer it was.

Yes I've seen the schematic, yes I have spoke to Gibson about it, NO they do not have any further info on the 70-991 or 70-043 part numbers on said schematic. I spoke with Walter Carter at Carter Vintage Guitars in Nashville, as well as Tony the lead tech at Gruhn's Vintage guitars. Best take away from those two consultations was the referral of a gentleman by the name of JT Riboloff, whom was the head designer and main liaison between Jack Casady, Gibson / Epiphone on the development of the signature model Epi. Tried to trace him down through all usual suspect online mediums, no dice other than LinkedIn. ...which if he's like me, the last time he logged into linked in was when it was created, a hundred years ago. So, if anyone has any form of passing along JT Riboloff's contact info via email I would be extraordinarily forever grateful. It was expressed to me if that if there was any wizard on the planet with immediate knowledge of everything I'm in need of knowing, it's that gentleman. 9 out of 10 people I speak with have heard of this guy, just no means of connecting with him.

I have seen some folks post something about a Shure impedance balancing transformer used in-line, I would prefer to get to the bottom of whatever was SPEC first, if at all humanly possible. OR, if someone had some kind of practical workaround of permanently installing the guts of said Shure thing inside the bass itself, if that's even possible?

For an added plot twist- I have a friend who owns one of these. Lives in Montana, I'm in Nashville. Medium story short, he recently visited very briefly, and I made an attempt to remove the position potentiometer, to be able to wiggle the transformer thing out. I didn't have much intuitive luck in doing so, and in the interest of not knowing if there was a certain way to remove it, I for the life of me couldn't get it out of there, and had to leave it. SO CLOSE!!!

I do have some photos and video of the inside guts of my buddies LP Signature Bass, if it would be of any help here, I just don't see the ability to host media here within this post?

Cheers in advance everyone!


~Nick
 
Joined
Feb 25, 2021
Messages
72
Well, as you have friend who has one, I think a solution to your problem should be fairly easy. Have your friend measure the impedance at the output jack, with volume and tone on the bass turned up. The tone switcher/selector should be in the position, where it filters the sound the least (Apparently the 50 position).
Then you take your pu to a transformer winder, and tell him/her, what impedance you´d like to end up with. Will it sound EXACTLY like the original?. Probaply not, but it should give you a usable instrument.
This link: https://www.flyguitars.com/gibson/bass/Les_Paul_Signature_bass_controls.php says that the selector should be in the 50 position (The two others filters the lower frequencies), and that your friend should measure from the jack on the front of the bass. This is the measurement that is needed to determine which transformer you need. Also have your frind measure on the jack on the side of the bass, in the 50 position, and with tone and volume all the way up, it should measure like your pu directly on the multimeter. If there is a dramatic difference, then I´d suspect a defective pu.
Good luck with the project.
 
Last edited:

Norton

Member
Joined
Jun 18, 2019
Messages
41
You're looking for the UTC O-1 Transformer. It attaches to the back of the CTS 3 Position rotary switch with a little u-shaped strap.



 

Norton

Member
Joined
Jun 18, 2019
Messages
41
Oh, and for what it's worth since you mentioned not know the best way to install everything, all electronics were originally fed through the pickup hole not fished through the f-holes. Much easier to get everything in and out.
 
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