Les Paul Lo-Z pickups

[Sweetfinger]

FWIW I recently repaired an early to mid 70's Ibanez copy of a Les Paul Recording. I thought that Ibanez would likely have stuffed high z coils in the thing under bigger covers, but they were huge lo z coils with a matching transformer for the high z setting. The coils were about 10 ohms DC resistance. Aside from being a bolt-on, fairly accurate I guess.

[bbsailor]

FWIW I recently repaired an early to mid 70's Ibanez copy of a Les Paul Recording. I thought that Ibanez would likely have stuffed high z coils in the thing under bigger covers, but they were huge lo z coils with a matching transformer for the high z setting. The coils were about 10 ohms DC resistance. Aside from being a bolt-on, fairly accurate I guess.

Sweetfinger,

Do you remember if this 10 ohms is for each coil or for both coils in series?
Approximately what wire size was this pickup using?
How much larger was the wire window on the Ibanez low-Z pickup bobbin than a conventional high-Z pickup bobbin?

Generally, when you know the low-Z coil DC resistance you can get an idea about the number of turns. If each humbucker high Z coil uses 4000 turns then an equivalent low Z coil will have about one tenth the number of turns (assuming a 1:10 matching transformer turns ratio) and the wire size needs to be selected to fit that low-Z 400 turns, in my example above, within the available wire window area. However, low Z pickups use larger bobbins and selecting the right size wire is important as it tends to act as a passive pre-equalization without adding any gain noise.

Thanks

Joseph Rogowski

[Sweetfinger]

The repair job was mostly cosmetics and control harness related -didn't entail much to do with the coils, so I didn't take any wire guage measurements. It was BIG wire though, maybe 22 guage? I don't recall that the coils were stacked, but the 10 Ohms was per coil. They had a huge alnico magnet and the wire was wrapped around the magnet till the whole coil fit snugly inside the cover. They were essentially stuffed in and potted. This guitar had gotten hot enough that the wax softened and let the coil assembly drop down out of the cover. I heated it back up and stuffed 'er back in while I had the hood open.

[David Schwab]

So I got my LP recording pickup parts today. Here's some pictures.

Judging from photos I've seen of LP Triumph bass pickups, the cover and bobbins here don't match up. The bobbins are smaller than the cover, more so than I would have expected, and when stacked on top of each other, they poke out the back of the cover slightly. The real pickups have the back filled with epoxy, so either the covers are deeper or the bobbins are different.

I have seen these red bobbins in a photo of "the log", so I'm guessing the bass had different bobbins.

But I should be able to get them to work, or I'll make new ones.

I also got a rough carved maple neck for an '81 LP bass.

[JasonG]

I think the bobbins are smaller to accommodate the 8 wires that need to be fed out the bottom of the pickup.

[David Schwab]

[edit]

The more I look at this photo, I can see the smaller bobbins and also the fact that they are protruding from the cover ... so I think these parts are right.

And really do need room for all those wires.

[bbsailor]

[edit]

The more I look at this photo, I can see the smaller bobbins and also the fact that they are protruding from the cover ... so I think these parts are right.

And really do need room for all those wires.

David,

The best information about low impedance pickup details in in a 1962 Burns pickup patent number 3,249,677 (go to google patents). In this patent he says that the thicker wire SWG 34 to 38 can be wound around one, two, three or six string poles. He states that he uses 300 to 500 turn of SWG 34 to 38 at less than 1 ohm for a single pole coil. I don't know how he does that. I calculated AWG 30 which is 9.69 ohms per foot or 116.28 inches. I have a single coil bobbin that has a wire window of .375: high by .125" wide that fits a .125" diameter magnet. I can only fit 150 turns and stay under 1 ohm. At 300 turns I am at 2 ohms.

Burns gets into using transformers turns ratios between 20 and 400 in a unique switching arrangement where he keeps the low impedance transformer sides switched in parallel with the coil while the secondary high impedance side is switched in series to boost the voltage and increase the effective turns ratios. This matching and mismatching provides various tonal possibilities much like the multiple taps on the Triumph Bass low Z pickup.

Carefully read and analyze what he is saying in the patent and you will see turn numbers and resistances that are in line with our previous discussions.
At the extreme turns ratio of 400 to 1 that represents a 160,000 impedance ratio (400 X 400) that when reflected into a 1 meg ohm amp input impedance reflects back about 6.25 ohms. Use this scaling example for other transformer turns ratios, coil resistances and coil turns discussed in this patent to obtain one of the most detailed low impedance pickup disclosures.

I hope this helps?

Joseph Rogowski

[David Schwab]

Thanks Joseph,

Lots of good info there, as always. I have a copy of that Burns patent.

I'm trying to recreate the Gibson pickups as closely as possible though, just because I always wanted a LP Triumph bass. I might not even like them, who knows?

But I'm also going to experiment with other low Z bass pickups not following the Gibson design.

[bbsailor]

Thanks Joseph,

Lots of good info there, as always. I have a copy of that Burns patent.

I'm trying to recreate the Gibson pickups as closely as possible though, just because I always wanted a LP Triumph bass. I might not even like them, who knows?

But I'm also going to experiment with other low Z bass pickups not following the Gibson design.

David,

Norman Crowhurst, a noted early audio expert in 1953, wrote a paper for Audio Engineer Magazine, January, 1953; Making the Best of an Audio Transformer, said: "In any audio circuit, frequency response is usually considered first. Generally, it is desireable that this should be a flat as possible for as wide a frequency range as possible, but sometimes deliberate narrowing of the band or correction for deficiencies elsewhere is required". Since a single musical instrument is only producing a small section of the audio spectrum, the mismatches offered by Burns and in the multiple taps of the Triumph Bass pickup seeks to do what Crowhurst observed above, providing deliberate tonal variations.

The starting point in design of a low Z pickup is to know the total number of high Z pickup active coil turns that contribute to it's output voltage. Then assuming that you are using a 1 to 10 turns ratio transformer, scale the number of low Z turns to be one tenth of the high Z pickup turns. That is the starting point and then doubling the turns and doubling it again gives you the Triumph coil resistances of 16, 32 and 64 ohms for each coil but it is 32, 64 and 128 ohms when the coils are in series, humbucking. However, the bottom coil may not be adding any or much output. Hook up the bottom coil only through a transformer and let us know if the bottom coil produces any output alone?

Joseph Rogowski

[David Schwab]

David,

Norman Crowhurst, a noted early audio expert in 1953, wrote a paper for Audio Engineer Magazine, January, 1953; Making the Best of an Audio Transformer, said: "In any audio circuit, frequency response is usually considered first. Generally, it is desireable that this should be a flat as possible for as wide a frequency range as possible, but sometimes deliberate narrowing of the band or correction for deficiencies elsewhere is required". Since a single musical instrument is only producing a small section of the audio spectrum, the mismatches offered by Burns and in the multiple taps of the Triumph Bass pickup seeks to do what Crowhurst observed above, providing deliberate tonal variations.

Yes, and also as seen on the LP Signature/Epi Jack Casady using the tapped transformer instead of the pickup.

I've also noticed that sometimes reducing the low end response to about 75Hz (the usual rumble filter found on mic preamps) sometimes gives a punchier bass tone.

The starting point in design of a low Z pickup is to know the total number of high Z pickup active coil turns that contribute to it's output voltage. Then assuming that you are using a 1 to 10 turns ratio transformer, scale the number of low Z turns to be one tenth of the high Z pickup turns. That is the starting point and then doubling the turns and doubling it again gives you the Triumph coil resistances of 16, 32 and 64 ohms for each coil but it is 32, 64 and 128 ohms when the coils are in series, humbucking. However, the bottom coil may not be adding any or much output. Hook up the bottom coil only through a transformer and let us know if the bottom coil produces any output alone?

Since I'll be winding this, it shouldn't be hard to figure out what transformer to use.

I'm also guessing that the bottom coil might not be doing much. The top and bottom coils also have a steel plate between them. I'm probably not going to epoxy the pickup into the case, so I might end up trying a few ideas. I was planning on using 28 AWG, since that's what seems to be referenced most of the time. 34 or 38 would probably be easier to deal with.

I also don't know what magnets were used in the real thing. I have some ceramics that will fit the bobbins, so that's what I'll be using.

But as I said, my intent was to try and duplicate the original pickup as closely as possible without having a real one for comparison. I'm doing this more for fun than research, but I'm expecting to learn a few things along the way. This is my first foray into large wire gauges and transformers. I saved a lot of your past posts for reference.

[clementc3]

Cream-colored Gibson/Electar/JCB-1 Low-Z pickups?

The info here about the LPR low-Z pickups is great (although I didn't quite get to all of the math in my class on electricity back in college).

Does anyone have any information/data/specs on the cream-colored low-Z pickups that are on the Gibson and Epiphone Les Paul Signature guitars (the hollow-body 330-LP hybrids) and the Jack Casady Signature basses ("JCB-1" pickup)?

The covers look similar (the Gibson LPS cover says "Gibson" and the Epiphone LPS says "Electar"; I don't know what the the JCB-1 cover says) but there are significant gaps in time between the production of the Gibson LPS (1970's), the Epiphone LPS (1998 - ?) and the JCS (1998 - present) so they might be quite different from each other (plus the bass pickup might be much different than the guitar models).

Thanks!

Clement Chen

[bajaman]

I think one of the main reasons that the Les Paul recording guitar was a failure sales wise, was the complete absence of a top end resonance or tone signature if you prefer.
Everyone knows the tone signature of a high impedance Les Paul or Fender Strat or Telecaster etc. Many guitarists have different guitars for there own unique sounds.
The Les Paul recording with its stacked (separated by an iron spacer) and tapped low impedance coils had a sterile (would have been fantastic for an acoustic jazz guitar sound) lifeless tone signature with a complete absence of any top end resonance - I remember them well - they were not well liked by rock and blues guitarists.
The Les Paul triumph bass was a different story - it had a great natural sound - unfortunately everyone was playing Fender precisions at this stage (except Jack Bruce with his mudbucker sounding EB3). Fender had the best sounding bass at that time - Gibson missed the boat
I have the wiring diagram and measurements of the Les Paul Triumph bass pickups (taken from a friend's brand new bass in the early 70s) I must dig them out - they may interest some of you guys.
cheers
bajaman

[bbsailor]

I think one of the main reasons that the Les Paul recording guitar was a failure sales wise, was the complete absence of a top end resonance or tone signature if you prefer.
Everyone knows the tone signature of a high impedance Les Paul or Fender Strat or Telecaster etc. Many guitarists have different guitars for there own unique sounds.
The Les Paul recording with its stacked (separated by an iron spacer) and tapped low impedance coils had a sterile (would have been fantastic for an acoustic jazz guitar sound) lifeless tone signature with a complete absence of any top end resonance - I remember them well - they were not well liked by rock and blues guitarists.
The Les Paul triumph bass was a different story - it had a great natural sound - unfortunately everyone was playing Fender precisions at this stage (except Jack Bruce with his mudbucker sounding EB3). Fender had the best sounding bass at that time - Gibson missed the boat
I have the wiring diagram and measurements of the Les Paul Triumph bass pickups (taken from a friend's brand new bass in the early 70s) I must dig them out - they may interest some of you guys.
cheers
bajaman

bajaman,

Yes, additional technical information would be most helpful, particularly coil resistance and impedance for all coil taps as well as the transformer resistance and impedance for all inputs and output.

Thanks

Joseph Rogowski

[bajaman]

This is all I have - feel free to ask questions - I traced this out when I was still a teenager - long long time ago - lol

[bajaman]

please feel free to redraw the above attachments for more clarity.
cheers
Steve

PS: Joseph - I read with great interest your home made alumitone pickup construction techniques - have you done any further research on these?
I am currently (no pun intended) working on a humbucker design using a small current sensing toroidal coil and the EMG active differential preamp - just waiting for my miniature rare earth magnets to arrive!!
The sensing coil has 500 turns and is listed as AS104 (if I remember correctly) from rscomponents. I am thinking of using a gain of 10 times for the active differential preamp and feeding it from this coil.
More later (with some pictures)
cheers
Steve