38AWG and me...

[dBe]

A few years ago I was given three spools of wire by a friend of mine. I have a 5 pound spool of 35AWG and 2 smaller spools of 38AWG - a 1 pound and a 2 pound. The spools are very old, one has a 1948 date on it - as old as me. Since I have this newfound interest in guitar pickups, I have a few questions. They aren't ALL stupid, I'll try to find the answers to those by myself. Given that I understand the basics: wire diameter; wire area; resistance per foot; volume resistivity, etc., let me ask a couple of questions.

Have you guys wound with 38, other than trying to "do" a Charlie Christian pup? If so, what?

Ever wound on a Strat bobbin? P90?

If any answers are "yes", what were the results, objectively and subjectively,
ie, output, tone, et al?

If this has all been hashed over forgive me. I couldn't find any good references with the Search function.

Thanks,

Dave

[Possum]

....

you should give that wire to me :-) I'm actually just finishing up a Charlie Christian-in-a-dog-ear-P90 cover. didn't have any 38 and didn't want to buy five pound minium just to find out it didn't work, so I have some 40 heavy build, haven't listened to it yet.

Basically that heavy a guage isn't going to be useful for anything but a very large coil. For instance, with this new pickup even at 40 gauge all I can get on a big and very tall coil form is about 5.5K. On a strat pickup you'd probably get way less than that, and you would have a very bright very low power pickup. same with a P90. if you're going to tackle learning windng you should just go to stewmac and buy a small spool to try it out and work with something real. 38 guage is so thick it won't break easily and will give you false sense of security :-) 42 gauge wire is thinner than human hair and you'll find out fast that it takes awhile to get a handle on

[bbsailor]

A few years ago I was given three spools of wire by a friend of mine. I have a 5 pound spool of 35AWG and 2 smaller spools of 38AWG - a 1 pound and a 2 pound. The spools are very old, one has a 1948 date on it - as old as me. Since I have this newfound interest in guitar pickups, I have a few questions. They aren't ALL stupid, I'll try to find the answers to those by myself. Given that I understand the basics: wire diameter; wire area; resistance per foot; volume resistivity, etc., let me ask a couple of questions.

Have you guys wound with 38, other than trying to "do" a Charlie Christian pup? If so, what?

Ever wound on a Strat bobbin? P90?

If any answers are "yes", what were the results, objectively and subjectively,
ie, output, tone, et al?

If this has all been hashed over forgive me. I couldn't find any good references with the Search function.

Thanks,

Dave

Dave,

Why not try to make a low impedance pickup? You can wind humbucker bobbins with about 500 turns of AWG38 on each bobbin. Then connect to 5K volume and tone pots. The output will be a low impedance in the range of about 500 ohms to match a Shure A95U microphone matching transformer.

Put the matching transformer at the amp and you have a good high fidelity pickup with extended high frequencies due to the reduction in coil capacitance. This type of pickup will be quiet and work well near a computer.

The matching transformer provides a turns ratio boost to make the thicker AWG38 have the equivalent of the amount of turns of AWG42. This boosts the output level of the 500 turns of AWG 38 to be equivalent to about 5000 turns of AWG42 but without the capacitance effect of thousands of turns of the thinner wire.

This is what Les Paul did with his low impedance recording pickup. Do a search on this forum for "low impedance pickups" and see some additional information.

Joseph Rogowski

[David Schwab]

Joseph, does anyone sell one of those transformers loose? I've been wanting to experiment with a low Z pickup using a impedance matching transformer.

[dBe]

Well, guys, thanks for the replies. Dave, your answer is kind of what I expected, the thin, low output thing. Joe, I didn't even think about the low impedance alternative. I even have some Lundahl impedance matching transformers. I think I may try this. It won't take much effort and I have the parts.

On the other hand, the approach that I plan is making a P90 size bobbin 2.4 times the height of the standard bobbin. This will allow me to put the same number of turns on it as a standard P90. I have some polepiece screw keepers that I have made in the past that are mild steel, M6 electrical steel, copper and brass. With all of the magnetic materials available, this should give me enough to keep me out of trouble for a while.

I really do appreciate it.

Dave

[bbsailor]

Joseph, does anyone sell one of those transformers loose? I've been wanting to experiment with a low Z pickup using a impedance matching transformer.

David,

Radio Shack sells on for about $15.00.

This type pf transformer plugs into the high Z input of the amp. That way the cable sees a low Z output from the pickup to the transformer preserving the high frequencies normally lost to a high Z pickup going through the same coax.

The Shure A95U can be obtained at most music retailers such as Sam Ash or the Guitar Center.

The Shure A95U can be altered from a 150 Ohm impedance to a 75 Ohm impedance by opening the transformer and resoldering an alternate jumper connection. The instructions are on the web. Search for "Shure A95U" to see how this is done.

Changing this jumper changes the turns ratio of the transformer and the amount of voltage boost.

When you get ready to try this and need more information, post your questions on this forum and I will provide you with what you need to know.

Joseph Rogowski

[dBe]

Try this for the best TX that I know of, I prefer them to Jensens.

www.kandkaudio.com

HTH

Dave

[David Schwab]

David,

Radio Shack sells on for about $15.00.

This type pf transformer plugs into the high Z input of the amp. That way the cable sees a low Z output from the pickup to the transformer preserving the high frequencies normally lost to a high Z pickup going through the same coax.

I have one of those. I've been trying to get the case open, but it's being stubborn!

I need the just transformer without the metal plug/case.

[David Schwab]

Try this for the best TX that I know of, I prefer them to Jensens.

www.kandkaudio.com

Ah.. there you go. Thanks!

Lots of choices there... now to figure out which one to use.

[bbsailor]

I have one of those. I've been trying to get the case open, but it's being stubborn!

I need the just transformer without the metal plug/case.

David,

The Radio Shack is only 500 to 50K impedance and is not adjustable.

The problem with using this for bass is the inductance variation at low frequencies. You need to actually measure the loaded transformer inductance with a Extech LCR meter at 120Hz and match that to your low Z coil for the best performance. Put a resistor equal to the amp impedance on the High Z transformer output when measuring.

Transformers can be pretty tricky at low frequencies.

Removing the transformer from the case and mounting it in the bass or guitar instrument defeats the purpose of going low Z. It is best placed at the amp to minimize coax capacitance effects.

Joseph Rogowski

[David Schwab]

Removing the transformer from the case and mounting it in the bass or guitar instrument defeats the purpose of going low Z. It is best placed at the amp to minimize coax capacitance effects.

I agree, which is why I haven't bothered with transformers, but think about the Lace pickups, and that's more the idea I wanted to mess around with.

[bbsailor]

Ah.. there you go. Thanks!

Lots of choices there... now to figure out which one to use.

David,

Try the LL2914 which has 4 primaries mixed to one output. This is good for a 4-string bass pickup with the transformer mounted in the bass body.

Each primary is .2 ohms. The secondary is 68 ohms.

Use this for a single coil from each string. Use 4- 5/16" dia magnets that are .75" long. Wind 5 or 6 layers of 24 turns of AWG 22 magnet wire on each magnet and connect to each primary. These turns will be about .2 ohms. The LL2914 output will provide a 250 to 500 ohm output to feed to a transformer at the amp.


The LL2914 provides a 1:37 turns ratio. And if you use a matching transformer at the amp with a 1:10 turns ratio, you will have a total of 1:370 turns ratio (ideal, no losses). There will be some losses but not too much to be concerned about as the noise level will be very low.

Six layers of 24 turns of AWG22 will give you 144 turns X 370 and will provide some a very good output level. You can reduce the turns or layers on individual loud strings to balance the output level of the strings. You can even reverse the phase of two coils to hum buck external noise. With this, the 4 string magnets can be the same polarity facing up as the strings are independent, not synchronized with each other.

The is just some "back of the envelope" design parameters to get you started in the right direction.

Have Fun!

Joseph Rogowski

[Mike Sulzer]

Possum:
"For instance, with this new pickup even at 40 gauge all I can get on a big and very tall coil form is about 5.5K"

It is the number of turns that count, not the resistance. The larger the wire, the less the resistance per turn. The larger the wire, the fewer the turns on a bobbin of a fixed size, but the resistance difference overestimates the actual change in the number of turns.

bbsailor:
"Put the matching transformer at the amp and you have a good high fidelity pickup with extended high frequencies due to the reduction in coil capacitance."

In the normal high impedance pickup/cable, the cable capacitance is is larger than the pickup capacitance (maybe 800 pf versus 200 pf). A low impedance pickup is immune to the effects of cable capacitance at the frequencies of interest. On the other hand, the resonant frequency of the pickup/cable system is part of the sound of the guitar. Maybe you do not want more high frequencies.

[bbsailor]

Possum:
"For instance, with this new pickup even at 40 gauge all I can get on a big and very tall coil form is about 5.5K"

It is the number of turns that count, not the resistance. The larger the wire, the less the resistance per turn. The larger the wire, the fewer the turns on a bobbin of a fixed size, but the resistance difference overestimates the actual change in the number of turns.

bbsailor:
"Put the matching transformer at the amp and you have a good high fidelity pickup with extended high frequencies due to the reduction in coil capacitance."

In the normal high impedance pickup/cable, the cable capacitance is is larger than the pickup capacitance (maybe 800 pf versus 200 pf). A low impedance pickup is immune to the effects of cable capacitance at the frequencies of interest. On the other hand, the resonant frequency of the pickup/cable system is part of the sound of the guitar. Maybe you do not want more high frequencies.

Mike,

The sound of a pickup is a subjective opinion. With a low impedance pickup you minimize the noise being picked up by the thousands of turns of very thin wire as well as eliminate noise picked up in the cable and the high frequency attenuation of 330pf from a 10 ft coax cable. You can always add capacitance to shift the resonant frequency down and cut highes but once the tone pot is at maximum resistance you cannot add more highes. The low impedance approach is a design option that adds more highs without active circuits.

Sound quality is in the ear of the beholder. I am only addressing engineering design options that ultimately must be evaluated by the ear of the beholder.

Every design has tradeoffs as well as historical prejudices. Some people prefer a classic high impedance pickup sound.

I agree with you but my comments offer pickup designers and users a chance to try something new, if they want.

Joseph Rogowski

[Mike Sulzer]

Mike,

The sound of a pickup is a subjective opinion. With a low impedance pickup you minimize the noise being picked up by the thousands of turns of very thin wire as well as eliminate noise picked up in the cable and the high frequency attenuation of 330pf from a 10 ft coax cable. You can always add capacitance to shift the resonant frequency down and cut highes but once the tone pot is at maximum resistance you cannot add more highes. The low impedance approach is a design option that adds more highs without active circuits.

Sound quality is in the ear of the beholder. I am only addressing engineering design options that ultimately must be evaluated by the ear of the beholder.

Every design has tradeoffs as well as historical prejudices. Some people prefer a classic high impedance pickup sound.

I agree with you but my comments offer pickup designers and users a chance to try something new, if they want.

Joseph Rogowski

Joseph,

You are quite right that you can (and should) add capacitance to get the best sound for the particular application. This is an option that is often overlooked.

I partly disagree with you about the noise pickup. Low impedance pickups are much less sensitive to pickup from electric fields; there is no doubt about that. But for magnetic fields, I believe it works out to the same. Suppose you decrease the number of turns by some factor. The voltage pickup from both the strings and stray magnetic fields decreases by the same amount. The voltage gain in the transformer then amplifies both, and the signal/hum ratio is no different.