Some help with a 1974 Gibson Les Paul Signature (Low impedance pickups)

[bbsailor]

I'm a moderator in pickup makers.
I moved it over here.
Unless you are making pickups, more guitars are repaired over here in this area.
Also a lot of these guys also work on amps using transformers and the likes.
T
** I sent bbsailor a pm, he does low impedance pickups, maybe he will stop by, and can offer some ideas?

I just returned from my vacation.

Here are the rules of thumb to make low impedance pickups.

AWG42, typical of high impedance pickups, would need to be thicker for low impedance pickups to minimize restive losses. AWG32 has 10X less resistance than AWG42. Jack Casedy liked the sound of AWG 28 for his bass.

If a typical single coil high impedance (high Z) pickup has about 6000 turns, then a low Z pickup would have about 600 turns or one tenth the high Z turn number. The impedance varies by the square of the turns difference. A volume pot for a high Z 6000 turn pickup would be 250K but 600 turns of AWG 32 would require a pot value 100 times lower in resistance or 2.5K ohms. For humbucker pickups, just double the values in this example.

The Jack Casedy bass used a three position switch marked 50-250-500 to feed the pickup output into different taps of the input step up transformer mounted inside the bass. This technique uses matching and mismatching the pickup load impedance (50-250-500) to create tonal and volume differences. If you choose to minimize the coax cable losses, put the transformer at the amp using an XLR connector and 2 conductor shielded mic cable.

To provide any more relevant input, please describe your design restrictions or ultimate goals.

Joseph J. Rogowski

PS Post the details of your pickup design and bobbin size to better consider your options.

PPS: Read this: https://www.gearslutz.com/board/so-m...ansformer.html
This reference will give you another input to consider.

I believe that you need a mic input transformer that has multiple input primary taps of 50 ohms (possibly 75), 150 ohms, 300 ohms to 10K to 15K or even 20K ohms secondary.

To determine the turns ratio of published impedance specifications do this: Divide the input impedance into the output impedance and take the square root of that number. Example: 150 ohms input to 20K output is: 20,000/150 = 133.33. Square root of 133.33 is 11.547 turns ratio or approximate voltage boost.

I hope this helps?

[olddawg]

What a beauty.. kind of like a cross between an LP and an ES335! I still would drop some minis in it in a heartbeat!

[stairwaytokevin]

Cheers Big-teee, I was wondering if I'd posted in the right place! It is pretty cool looking and I'm going to keep pursuing the Jack Casady angle with Gibson, as well as the transformer idea. I must say a thank you to bbsailor for the enlightening post about the transformer. I've found a small mic line matching transformer (600ohm : 10k) that I'm going to try first and I should be able to work backwards from there to find the proper turns ratio. From what I understand now that'll be pretty critical This one even has a center tap on the primary so I can take a reading there as well, wonderful. I can always try another with a higher secondary, up to 25k at least if this one doesn't work out. I'll be using the guitar's original pickups so let's see what we can do

[bbsailor]

Cheers Big-teee, I was wondering if I'd posted in the right place! It is pretty cool looking and I'm going to keep pursuing the Jack Casady angle with Gibson, as well as the transformer idea. I must say a thank you to bbsailor for the enlightening post about the transformer. I've found a small mic line matching transformer (600ohm : 10k) that I'm going to try first and I should be able to work backwards from there to find the proper turns ratio. From what I understand now that'll be pretty critical This one even has a center tap on the primary so I can take a reading there as well, wonderful. I can always try another with a higher secondary, up to 25k at least if this one doesn't work out. I'll be using the guitar's original pickups so let's see what we can do

The center tap of the 600 ohm impedance is actually rated at 150 ohms for calculating the turns ratio.

I am glad I was able to help you.

Joseph J. Rogowski

[agabinet]

I am unfortunately in the same position as the OP -- I am the first and only owner of a 1974 LP Sig. and the electronics are not working. I'm no engineer, but per the drawing that three impedance selector looks like it's an "inductor?" Like the varitone on the LP Recording guitar . . . I think we are SOL with trying to replace the original parts. Mine has been converted to a 335 setup running through the high impedance output jack, but it needs an external transformer now.

If anyone can get parts out of Epi/Gibson for the Casady bass I'd love to know about it.

[bbsailor]

I am unfortunately in the same position as the OP -- I am the first and only owner of a 1974 LP Sig. and the electronics are not working. I'm no engineer, but per the drawing that three impedance selector looks like it's an "inductor?" Like the varitone on the LP Recording guitar . . . I think we are SOL with trying to replace the original parts. Mine has been converted to a 335 setup running through the high impedance output jack, but it needs an external transformer now.

If anyone can get parts out of Epi/Gibson for the Casady bass I'd love to know about it.

The Shure A95U series mic matching transformer is still available. Look it up on line. It uses an XLR connector for input and a quarter inch plug for output directly into the amp.

To convert your guitar, use a stereo jack in your guitar. Make an adapter cable with a stereo quarter inch plug using 2 conductor shielded mic cable. XLR pins 2 and 3 go to the tip and ring. Ground goes to XLR pin 1 and the ground of the stereo plug. This set up eliminates the high impedance capacitance of coax guitar cables on high impedance pickups by just having the A95U transformer out of the guitar and located at the amp input. Make sure that your pickups are low impedance.

I hope this helps?

Joseph J. Rogowski

[agabinet]

The Shure A95U series mic matching transformer is still available. Look it up on line. It uses an XLR connector for input and a quarter inch plug for output directly into the amp.

To convert your guitar, use a stereo jack in your guitar. Make an adapter cable with a stereo quarter inch plug using 2 conductor shielded mic cable. XLR pins 2 and 3 go to the tip and ring. Ground goes to XLR pin 1 and the ground of the stereo plug. This set up eliminates the high impedance capacitance of coax guitar cables on high impedance pickups by just having the A95U transformer out of the guitar and located at the amp input. Make sure that your pickups are low impedance.

I hope this helps?

Joseph J. Rogowski

Thanks Joseph, I have an inline matching transformer and it works very will in the current setup to make the Low impedance pickups sound fine. What I want to do, though, is restore my original electronics with the impedance selector . . . I'm working on it. It may be just a grounding issue.

[bbsailor]

Thanks Joseph, I have an inline matching transformer and it works very will in the current setup to make the Low impedance pickups sound fine. What I want to do, though, is restore my original electronics with the impedance selector . . . I'm working on it. It may be just a grounding issue.

See this link for the schematic. http://archive.gibson.com/Files/sche...PRecording.PDF All the tone changes are on the low impedance side of the transformer. Use a selector switch per the schematic to add various capacitance loads and the phase invert switch to put two pickups on but out of phase for a variety of thinner sounds.

Joseph J. Rogowski

[agabinet]

Les Paul Sig Schematic

See this link for the schematic. http://archive.gibson.com/Files/sche...PRecording.PDF All the tone changes are on the low impedance side of the transformer. Use a selector switch per the schematic to add various capacitance loads and the phase invert switch to put two pickups on but out of phase for a variety of thinner sounds.

Joseph J. Rogowski

Here's the schematic (or one of them) for the signature. It's not as complex as the recording or professional -- no decade control!

[52 Bill]

Looking at the photo of the original switch/transformer assembly, that looks like a UTC matching transformer. United Transformer Corp, New York.

If there are other photos available, there will be a number on the transformer case that may lead you to specs from one of their old catalogs or data sheets. Perhaps there is someone with the original part that will look at theirs and tell you the number.

[52 Bill]

As a follow up, the UTC "ouncer" model O-1 would seem to fit the bill.

There are a number of 1970's UTC catalogs scanned and online out there. Who knew?

[Do Something]

The Pick ups in your Guitar, are same pick up used in the Les Paul Signature Bass. Oddly enough while white and rectangular they are also were the same pick ups in the Les paul recording guitar, even those these were black and Oblong. The black and oblong pick up look like they are used in both the LP recording guitar and LP triumph bass but they are different. I have the LP recording guitar and the LP Triumph Bass and I also have one of the white pick up that I plan to use in a EB2 body to turn it into a Signature Bass Its confusing to be sure but I have check the resistance on all of them and It confirms what I have written,. For the bass project I have sourced the proper ohm Pots (hard to find) and several years back I scored three NOS transformers. The little buggers are rarer chicken teeth and were expensive..I think I paid $150 for each. One I used as an in line 3 stage transformer for both of the Les Pauls I have and the second will be incorporated in to my LP Signature Project. If I can find the third you welcome to it at the price I paid for it. If you keep your eyes open you could probably find a used one at a better price. I haven't seen any lately but if your patient one will pop up sooner or later. BTW you will have to buy the rotary switch separately but they are available everywhere. Check with Mouser.

FWIW . The Les Paul Signature looks like an ES-335 with an extended lower cut-away but inside it does not have the solid central block of wood under the pickups and bridge: instead it has a block under the bridge only. It also has a three piece maple neck instead of the usual mahogany. As a result it is bright with clear clean woody jazz tones reminiscent of the L5. A few early Signatures had the Les Paul Recording pickups installed, but most came fitted with the rectangular low-impedance type. The guitar came with individual low and high impedance output jacks on the front and side of the guitar, respectively. Even with the different setting on the transformer the output is low ... too low to drive a pre-amp so don't expect the usual LP humbucker tones. It is not very popular and is limited in its range. However it is a true classic. If you change you mind about restoring it instead opting to put regular electronics in please message me. Ill buy it from you at a price that will get you the modern guitar you want and I will restore it. Its not about making money but losing a bit of history. These treasures are slowing disappearing and once gone they are lost forever. I would leave it as an inheritance for one of my sons.

[Kurt Jaeckle]

I may have some parts for these LP signatures. I have one that is working and am restoring another. I tend to disagree with some on this thread, the guitar is very versatile, jazz to Tele like sounds. With a good jazz amp eg Henriksen they sound great. I would not switch out original parts on this classic, < 1500 made.

I checked with Gibson several years ago for a better wiring diagram, they just sent the abbreviated one in this thread. (Most of the people there were not born when this instrument was released !)

[Chuck H]

I may have some parts for these LP signatures. I have one that is working and am restoring another. I tend to disagree with some on this thread, the guitar is very versatile, jazz to Tele like sounds. With a good jazz amp eg Henriksen they sound great. I would not switch out original parts on this classic, < 1500 made.

I checked with Gibson several years ago for a better wiring diagram, they just sent the abbreviated one in this thread. (Most of the people there were not born when this instrument was released !)

I sure understand the frustrations with this sort of effort... All I can say is that this and other low impedance pickup efforts have ultimately been abandoned with the exception of additional preamps in the guitar. No amps or other gear has ever been offered by the industry to support the idea. So...

If this is a personal effort because you actually like the music you can make with these guitars, then good on you. Keep going and make some music. If, on the other hand, this is just killing time looking at an obscure, vintage ideal that Gibson experimented with I would say exactly this:

Gibson abandoned it pretty fast and no peripheral manufacturers supported it (ie: amps, pedals, etc.). So unless there's a personal love and usefulness for the tone of these instruments I think any pursuit of the original concept will remain unsupported in the industry. Which means any supportive gear will need to be managed (possibly designed and hand made) by the few aficionados who own and love them. Which has to a tiny number considering how many of these guitars were likely modified with higher impedance pickups.?.

Anyway, if this is a goal of personal artistry then get after it and use the guitar/s as they serve you. If it's anything else the I'm afraid this horse you're beating isn't just dead, it's forgotten.

No offense intended.

[LowImp]

Mr. Do Something,

Wonder if you still check this site?

I have a Signature that’s in the shop due to the bridge pickup not working, and I was curious if a pickup from a Epi “Cassidy” bass could replace it if needed (sounds like it would!)

If my guitar is repairable I’ll get it fixed; maybe to sell and replace with a 330-TD, Epi USA Casino or a Heritage 530. (I know I’d be making quite a change from low-impedance to a guitar with P-90s!)

Message me on this board if you’re interested and I can give you more details about my specific instrument.