Les Paul Lo-Z pickups

[bajaman]

just looking at my schematic two posts back - I think I have omitted a wire connection from the junction of the 39 ohm and 680 ohm resistors and the top of the transformer winding - woops
David - at last your question has been answered - the coils are 1000 ohms each with two taps 500 ohms and 750 ohms
bajaman

[bajaman]

Just saw this in another thread:
http://music-electronics-forum.com/a...ph-recbass.pdf
Same as I traced way back when - I am sure those coil resistances are correct though
bajaman

[bbsailor]

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

Steve,

There is no need to make these very low impedance current loops be wired as a humbucker with two string loops. A single coil is still very quiet. Just run a ground wire from audio ground to the CSE187L transformer case and then to one side of the low impedance loop that is around the magnet(s).

I find that those little flat .125" thick by 1" by .75" with a 3/16 hole in the center to be very effective whn put three wide so the 1" axis lies in line with the strings. Onc loop of thick wire (awg 12 to 6) is connected to two CSE187L current transformers (CT) and it allows you to put a one CT on each side of the string loop and then switch the outputs in series and parallel to get different sounds. This CT output falls in the range of conventional microphone levels on mic preamps (about 5 mv) and matching transformers. When properly grounded, it is pretty hard to get noise out of these things.

Joseph Rogowski

[David Schwab]

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

Here's what I have.

I colored that one in back in the 70's so I could follow the wires.

I threw in the photo just for the shock value!

[bajaman]

for the bobbin size measured in my previous post you should be able (if my maths are correct to wind a total of 14,000 turns of 30 AWG single enamel wire giving a total resistance of approximately 1000 ohms per coil.
The taps would be at 7000 turns and 10500 turns.
hope this is useful for you David
cheers
bajaman

[David Schwab]

I just got a roll of 28AWG wire for experimenting.

Does anyone know what would be a suitable transformer to use for a LP Recording type pickup?

I know it depends on the impedance of the pickup, but I was wondering if anyone had some knowledge of what kind of transformer was used.

[clementc3]

Suitable (actual?) transformer for LP Recording pickup

I too have been looking for the answer to David's question (what did Gibson actually supply with the Les Paul Recording guitars?) for some time now and I haven't been able to nail anything definite down yet.

In post #14 of this thread J. Martin says:

I bought my LP Pro in 1973, but I had already been making my own low impedance pickups before that. I used ceramic bar magnets I got from Edmund Scientific and wound the bucker coil on an extra piece of steel that came with the magnets. I think I used #30 or #32 wire. I used what Gibson used to match the pickups to the amp, a Shure inline mic transformer. It worked best jumpered for 50 ohms. I molded the pickup assembly into a clay like substance that got baked in an oven at around 200 deg F.

I have a Les Paul Recording guitar for which another member said that I can use the Shure A95U which comes wired for low-impedance input in the 75-300 ohm range. The Shure A95U looks like the photos of the original Gibson-supplied transformer but so would any aluminum-colored cylinder so that's not definitive. The Shure A95U certainly seems to work well for me out of the box, wired for 75-300 ohms.

I have seen another recommendation elsewhere (like J. Martin's comment) that changing it to 19-75 ohms (by re-soldering a lead) is better but I haven't tried it to hear the difference because I don't trust myself with a soldering iron yet.

There are two others that I know of, the Electro-Voice E-V 502CP at 150 ohms and I saw one at Radio Shack at 900 ohms (I think) but I think the Shure A95U is more likely to be in the right ballpark.

[David Schwab]

I've been looking for a transformer that's smaller, since the Sure unit is in that cylinder, and I found this:

Altran C-3402-2 Audio Transformer

Looks like similar specs.

[clementc3]

Transformer for LP Recording type pickups

The Altran is small enough to fit inside the body of the guitar; I should look inside my LP Recording & see if I can figure out where & what the built-in transformer is.

I am sure that you have seen Dave Gould's Les Paul Recording Guitar Users Forum which states

"The main difference between the Personal/Professional models and the Recordings is that an Impedance Transformer was built in to the body. However, this did not alter the fact that these guitars still performed at their best when plugged into a mixing desk at Low Impedance setting or, when used with an Amplifier, with a suitable Impedance Matching Transformer at the amplifier end of the connecting lead."

and

"The effects produced are drastically reduced when the internal transformer in the (Recording model) is used."

I have read (but I am not up to speed on the underlying electronic theory) that the length of the cord after the transformer and before the amp affects the signal significantly. I will say that the Decade switch on my LP Recording has no detectable effect when I use the internal transformer, while it does have a noticeable effect when I use the Shure A95U at the amp end of my guitar cord. However, even when I use the internal transformer the LP Recording guitar has an incredible tone that I would call "clean" and "pure", but maybe I have been drinking the LP Recording low-impedance pickup Kool-Aid ...

I guess it depends on how far you want to chase after the "low-impedance tone". Give us a report on your results when you have them!

[David Schwab]

However, even when I use the internal transformer the LP Recording guitar has an incredible tone that I would call "clean" and "pure", but maybe I have been drinking the LP Recording low-impedance pickup Kool-Aid ...

I guess it depends on how far you want to chase after the "low-impedance tone". Give us a report on your results when you have them!

My perspective is from making replacement bass pickups. So the pickups will have to exit the instrument in a typical fashion, kind of the way Lace Alumitones work. So I want the transformer in the instrument.

But if you were going direct, bypassing the transformer would be a good idea.

Another way to look at it is the transformer is part of the tone, like with the Les Paul Signature instruments.

Now it's time to try winding some of this wire.. the stuff is huge!

[bbsailor]

I've been looking for a transformer that's smaller, since the Sure unit is in that cylinder, and I found this:

Altran C-3402-2 Audio Transformer

Looks like similar specs.

David,

Wire the two primary transformer inputs in parallel for the 150 ohm setting. This will give you about a 1 to 8 turns ratio.

Try using the Radio Shack Magnets, 5 per pack, 1" X .75" X .187" with a .187 hole in the center. Arrange them 3 wide with bobbin material. Cut holes to line up with the magnet holes. It makes winding them very easy. You can make the pickup with a single set of three magnets or six magnets for putting on more wire (wider wire winding area). Arrange the magnets for the same pole on all magnets facing the strings.

Joseph Rogowski

[Joe Gwinn]

I've been looking for a transformer that's smaller, since the Sure unit is in that cylinder, and I found this:

Altran C-3402-2 Audio Transformer

Two things strike me.

First, the can is mumetal. Mumetal is very sensitive to mechanical strain, so make sure to mount the transformer so the shell is not stressed. Soldering to a small piece of circuit board, with the board screwed to the guitar body, should work. Or, glue the transformer to the body with a thick blob of silicon rubber adhesive, ensuring that the rubber layer isn't too thin (to allow the wood to change size without tearing loose from the mumetal case). But do not clamp the transformer into place.

Second, typical guitar pickup signal levels can be far higher than typical microphone level inputs seen by such transformers, and one may be in danger of saturating the transformer core, which may yield a harsh sound. On the other hand, guitars are not exactly high-fi, so one can run a far stronger signal than typical for a fancy low-impedance mic. I didn't see a maximum signal level mentioned, so I would ask the manufacturer how total harmonic distortion varies with signal level and signal frequency.

[paradoxjon]

does anyone have info on the Les Paul Signature '73-'74

thanks!

[clementc3]

You may have already seen this page on the whole range of Les Paul low-impedance guitars:

Les Paul Recording Guitar Users Forum

About 2/3 of the way down is a short section regarding the Les Paul Signature.

A schematic is here (in the lower right corner of the jpg):

http://www.guitar-parts.com/images/lespaul.jpg

Information on the cream-colored low-impedance pickups is impossible to find as far as I can tell. I have an Epiphone Les Paul Signature with similar looking (but possibly quite different) cream-colored "Electar" (one of Epiphone's proprietary brand names) pickups. The Epiphone LPS only has one high-impedance output jack while the (real) Gibson LPS also has that and also a low-impedance output jack which completely bypasses the internal transformer.

On my Epi LPS the 50-250-500 rotary switch selects different taps of the internal transformer with VERY significant changes in tone. (Can anyone here explain the science behind this for me? )

For the sake of completeness here are two other sites with lots of information about Les Paul low-impedance guitars:

Woody's Gibson Les Paul Recording guitar page

Les Paul Personal

I have had a good experience using the Shure A95U transformer with the low-impedance output from a Les Paul Recording guitar (to enable one to plug into a regular guitar amp) and I would think you can use this with the low-impedance output from a LP Signature. I use the Shure A95U in its off-the-shelf 75-300 ohm configuration; it is reportedly a simple task (if you know what you are doing, which I don't) to change the internal wiring for 19-75 ohm input, which is supposed to be even better.

Please post here if you find more information about the Les Paul Signature!

[David Schwab]

The very early version of the Les Paul Signature had the same shape pickups as the Recording guitar. The they went to a rectangular shape.

I have no idea what's inside.