Low Impedance Pickup Research

[charrich56]

Charlie,


The flat LoZ pickup at the end of a fingerboard - really a nice idea. Hide it invisibly under some thin veneer, perloid, MOP or the like. The Nanomag design is something like that, isn't it?

Yes, the Nanomag is usually on the end of the fingerboard and can be made to blend in visually with the dark fingerboard. The examples are the Epiphone Ultra III or Ultra 339. It is also a low to medium impedance, high fidelity pickup. I do like this design and have a generally high regard for Shadow products although they do tend to be a bit expensive.

Back to Joseph's ideas and hence to our main topic: where could we hide the current transformer when using a single loop pickup on, say, an archtop fingerboard? We would have to solve the question where to go with the cable and with the plug - it is a sacrileg not to leave the top of an acoustically usable archtop intact.

If the pickup is at the end of the fingerboard, the current transformer can be mounted to the underside of the pickguard on a jazz archtop instrument. That is a reasonable and often used place to mount volume controls, jacks, etc. so that they do not compromise the top vibration or esthetics of the top. I have a couple of the CSL current transformers and they are fairly small, so this is feasible.

If the instrument doesn't have a pickguard, we are obviously in trouble and have to use a "floating" pickup usually attached by mounting ears to each side of the neck/fingerboard. This does create the problem of where to put the current transformer.

One of the interesting possibilities here is a flat low-Z sidewinder design similar to what Mike was suggesting earlier- this would not require a transformer if wound to the 150-250 ohm impedance range. Basically a low-Z version of the very nice pickups made by Elmar in Vienna - Original Flatpup. Extremely flat guitar pickups. Outside the box! . There's a thread on these here in the forum. http://music-electronics-forum.com/t37623/

BTW: although electrically not optimal i would prefer a stereo jack connection in the guitar instead of the XLR. Smaller, lighter. Possible to mount under the pickguards of a Jazz archtop (not of all - i need to use a 3.5 mm jack on my guitar).

The stereo 1/4" jack is a possibility but I did want to make sure you knew that there is a miniature version of the XLR connector that you might consider. Switchcraft : Mini XLR Connectors

And something regarding the market: would You think that Jazz Archtop players are more on the conservative side or more open to modern developments? And the archtop luthiers? I actually have never noticed an active Jazz archtop other than my own guitar.

A lot of jazz guitarists I think are traditional and want to get mellow tone. I think jazz archtop guitarists would be in that category. But at least some jazz artists aren't playing archtops at all. You are almost as likely to hear jazz played these days on a Telecaster as a jazz archtop. And part of the reason might be that in live sound situations, electrified archtops can be difficult beasts to tame because of feedback.

If someone offered the ability to both get a mellow traditional tone and a high fidelity near-acoustic tone with more dynamic range and expressiveness, and lots of tones in between, in a single instrument with simple controls, I think at least several artists would gravitate toward it even if it didn't look exactly like a traditional archtop. I think that Rick Turner's guitars are definitely the embodiment of this idea. But they are so non-traditional in appearance they still won't appeal to a certain number of jazz players, which is a shame, because they are outstanding instruments from what I hear, and not even as expensive as many traditional archtops.

The archtop market is so small that it would be difficult to judge how luthiers would react to developments in pickups and electronics.

-Charlie

[rjb]

One of the interesting possibilities here is a flat low-Z sidewinder design similar to what Mike was suggesting earlier- this would not require a transformer if wound to the 150-250 ohm impedance range. Basically a low-Z version of the very nice pickups made by Elmar in Vienna

I like the "FlatPup" design a lot.
But, for this application (low-Z floating archtop pickup with differential outputs), would that particular sidewinder design have any practical advantage over an even smaller single coil pickup?
After some sketching and calculating, I figure the smallest practical "flatpup" bare coil (4.5mm thick, using 1/8"D magnets and 200 turns of 34AWG for a DCR of ~20 ohms) would be about 1/2" across.
Would something like suggested here be smaller, physically sturdier, and more efficient?
http://music-electronics-forum.com/t23205/#post195848
I guess my real question is, do you really need a humbucking configuration if running a low-Z pickup into a a mic input?

[bea]

At least in the studio signal to noise ratio will be important, won't it?
I'm not quite sure, but good dynamic microphones also have noise compensation (i.e., humbucking) coils, don't they?

To the (acoustical) jazz archtop: IMO the only solution that can live aside floating minihumbuckers are invisible pickups in, for example, the fingerboard. The latter only when they actually do reproduce the acoustic tone.

[Mike Sulzer]

I guess my real question is, do you really need a humbucking configuration if running a low-Z pickup into a a mic input?

Low impedance and balanced configuration are for rejecting interference in the form of electric fields, and have no effect on interference resulting from magnetic fields. You need a humbucking configuration for the latter.

[charrich56]

Low impedance and balanced configuration are for rejecting interference in the form of electric fields, and have no effect on interference resulting from magnetic fields. You need a humbucking configuration for the latter.

Yessirree. You really do want humbucking even if the instrument is never played live on a stage or in a club. And the "flatpup" sidewinder design looks to be a very good way to get the two coils for humbucking action, in a minimum height pickup which is what you need for an archtop, dobro, or similar.

However there are and have been both very low height conventional humbuckers and single coil pickups. The Barcus-Berry wasn't the only game in town. Benedetto and I think Bartolini probably still have them.

http://www.theguitarsherpa.com/categ...ar-pickups.htm

You could probably do a conventional vertical-coil humbucking pickup with self-bonding magnet wire (bobbinless) and neo or ceramic magnets that would be pretty short, reasonably small in height and width, and would be within the reach of a hobbyist/experimenter/small shop to be able to fabricate. It would really depend on how much height you had to work with. It may be as much as 3/8" or even a tad more on some archtop designs.

BTW one cool thing you can do with a low impedance coil (less than 36 AWG or so) and self-bonding magnet wire is that you can run a pretty large current through the coil windings and completely fuse the coil together just by resistance heating. Or, just cook the coil or PU for a while in an oven. Once you worked out current and/or time, easy, cheap, no messy wax or varnish to pot the coils, and if you wanted, no bobbin if you wind on a removable form. And you would end up with a darned good, solid, non-microphonic, reliable coil that would hold its shape.

I guess we are a bit far afield of Joseph's ultra low Z single turn pickups, though.

-Charlie

[bea]

I guess we are a bit far afield of Joseph's ultra low Z single turn pickups, though.

Aside from the discussion on the hum sensitivity, yes, indeed.

[bea]

Just a question toward the actual pickup type in discussion: how large can the distance of the pickup to the strings become? Is it possible to place such a pickup hidden under the soundboard?

[bbsailor]

Just a question toward the actual pickup type in discussion: how large can the distance of the pickup to the strings become? Is it possible to place such a pickup hidden under the soundboard?

Bea,

Here is where your experimentation can lead you to another view of guitar pickups where the mechanics of fitting a low resistance string loop under the strings and connected to the current transformer (CT) can help you make a wide bandwidth, low noise lowZ pickup. Your choice of magnets that you place in the center of the string loop will affect the output and string balance.

As a first step, try to visualize this. Obtain a piece of scrap rosewood block 2.25 inches wide by 0.5 inches wide by normal fingerboard height. Place a groove around the perimeter of this block to accomodate a thick wire used as the string loop. Bend the hairpin shaped loop down 90 degrees spanning the B string so that the current transformer primary is vertical and directly under the B string. This will allow the transformer to hang into the sound hole and this pickup to appear as a small extension of the fingerboard. Depending on the magnets you use, the effective distance to the strings will be different. I find that rubberized magnet material with a single loop of AWG 11 connected to a CSE187L works well on an acoustic guitar when located even with the fingerboard top. See the attached photos on one of my previous posts. It can be mounted on any acoustic guitar without any permanent modifications.

The purpose of introducing this low impedance pickup approach was to offer an alternative to making high Z pickups which tend to have a resonant hump in the midrange. This design, rather than focusing on matching to high Z amp inputs, as has been historically done, focuses on matching to the low Z XLR mics that are rated at nominal 150 ohms with actual input bridging impedances at the mixer input of 1500 ohms to 2400 ohms. By making the string loop with heavier wire, you can adjust the output impedance of the CSE187 (CT) to be near 200 ohms (plus or minus 50 ohms) and have a way to voice the overall tone of the pickup with heavier wire favoring the lower frequencies.

I can imagine a luthier making an acoustic guitar where the magnets are embedded on the underside of the fingerboard end with a single loop of AWG 11 or a creative copper plate cut to fit available space. Then the CT can be located under the fingerboard just in front of the guitar hole opening. I doubt that you will be able to get much of a signal from this or any other pickup, if the pickup magnet top and loop coil are more than .625 inches below the strings. The final test is to experiment and try it. Let us know if you try it.

Joseph Rogowski

[rjb]

See the attached photos on one of my previous posts.

Unfortunately, I fear those photos disappeared during the Great Attachment Vanishment.
Could you possibly post them again?

[bbsailor]

Unfortunately, I fear those photos disappeared during the Great Attachment Vanishment.
Could you possibly post them again?

See post #153 in this thread for the photos. They appear to still be there.

Joseph Rogowski

[rjb]

See post #153 in this thread for the photos. They appear to still be there.

Joseph Rogowski

Oops. Sorry. I don't know how I missed them.

[charrich56]

Bea,


I can imagine a luthier making an acoustic guitar where the magnets are embedded on the underside of the fingerboard end with a single loop of AWG 11 or a creative copper plate cut to fit available space. Then the CT can be located under the fingerboard just in front of the guitar hole opening. I doubt that you will be able to get much of a signal from this or any other pickup, if the pickup magnet top and loop coil are more than .625 inches below the strings. The final test is to experiment and try it. Let us know if you try it.

Joseph Rogowski

Joseph,

Would it be an idea to add about 2 1/2" to the loop length but adding it vertically so that the CT can be embedded further into the guitar? I do realize the loop length is a sensitive parameter in this design for a given wire size.

I can see how on a round hole acoustic things would work fine the way you are describing, but on an archtop, if the CT were floating or just installed under the top, the only top penetration would be two small holes for the loop wires, and the whole loop and magnetic structure could float at the end of the fingerboard and be much closer to the strings. This would have to be built in during construction of course.

One might be able to make something pretty creative and aesthetic with copper plate and small magnets for an archtop if the CT could be hidden either under the pickguard or under the top. Or maybe even embedded into the neck before the neck/body join.

-Charlie

[bbsailor]

Joseph,

Would it be an idea to add about 2 1/2" to the loop length but adding it vertically so that the CT can be embedded further into the guitar? I do realize the loop length is a sensitive parameter in this design for a given wire size.

I can see how on a round hole acoustic things would work fine the way you are describing, but on an archtop, if the CT were floating or just installed under the top, the only top penetration would be two small holes for the loop wires, and the whole loop and magnetic structure could float at the end of the fingerboard and be much closer to the strings. This would have to be built in during construction of course.

One might be able to make something pretty creative and aesthetic with copper plate and small magnets for an archtop if the CT could be hidden either under the pickguard or under the top. Or maybe even embedded into the neck before the neck/body join.

-Charlie

Charlie,

Try playing with a few CSE-187L current transformers and make a 2.125 inch long to 3.625" on the straight side hairpin loop with a .375 inch spacing to match the CT primary spacing. Join the string hairpin string loop to the CT with solder or better with thin wall hobby copper tubing. Locate some common craft magnets Magnets - Master Magnetics, Inc. part number 07001 .25" X .25" X .785". Tape 2 or 3 magnets to the hairpin loop and slip under the strings just behind the fingerboard. Attach 2 conductor shielded cable to the CT and an XLR connector, attach to a mic mixer and listen, modify and learn about a different way to look at making guitar pickups.

Yes, putting the CT 2.5" deeper into the guitar body will add another 5" to the string loop. You will then need to use heavier wire. Try to keep the added hairpin string loop near or less than 600 microohms. AWG 11 is 105 microohms per inch. The output impedance is calculated by squaring the turns ratio: 600 microohms is 0.000600 X 250,000 is 150 ohms plus the impedance of the 250 microohm installed primary on the CSE-187L is another approximately 80 ohms (including a small leakage inductance) for a pickup output impedance of about 230 ohms, well within the limits of low impedance microphone ratings.

Triad makes an embedded .75" cube version. The CSE187L-P can be visibly mounted near the string loop and provide more mounting flexibility.

The big challenge is to find commerciall off the shelf parts that will fit in a pickup application that meet your space and mounting requirements. Once you understand how fast these CT pickups can be made, modified and mounted, you can begin to explore how the thickness of the string loop wire affects the overall tone of the pickup. Look at the Lace Alumitone for the Stratocaster and the Humbucker and see how the width of the alumium string loop (the pickup frame is the string loop) is different, resulting in a different tone in these pickups. I found some AWG 11 magnet wire (Surplus Sales of Nebraska) that works good. You can also use AWG 10 to 8 plain copper wire from Lowe's or Home Depot for the string loop. Place a mini 1 K pot (as a variable resistor) on the CT output and adjust the load to change the level and tone of the pickup.

How much space do you have under the pickguard to potentially fit a CT and what is distance from the string loop to the CT?

Joseph Rogowski

[bea]

Yes, putting the CT 2.5" deeper into the guitar body will add another 5" to the string loop. You will then need to use heavier wire.

[/QUOTE]

or two or more loops in parallel (in contrast to serial like in a coil), correct?

What about the distance from the strings?

The application i asked was for a CGB where the PU should be mounted under the top. No soundhole or whatever.

The other application - mine, mentioned earlier during this thread: imagine an archtop with holes for standard humbuckers, similar to, say, an ES-175. Imagine that the acoustic sound is better with these holes open. Imagine a loop in shape of a humbucker mounting frame, and hence pretty far away from the strings. Will it be possible to get a sufficient singal from such a setting?

[bbsailor]

[/QUOTE] or two or more loops in parallel (in contrast to serial like in a coil), correct?

What about the distance from the strings?

The application i asked was for a CGB where the PU should be mounted under the top. No soundhole or whatever.

The other application - mine, mentioned earlier during this thread: imagine an archtop with holes for standard humbuckers, similar to, say, an ES-175. Imagine that the acoustic sound is better with these holes open. Imagine a loop in shape of a humbucker mounting frame, and hence pretty far away from the strings. Will it be possible to get a sufficient singal from such a setting?[/QUOTE]

Bea,

Yes, adding two or more primary string loops in parallel is the same as using heavier wire. Go to a wire table to see the effect of using multiple parallel wires to calculate the effect on the current transformer output impedance based on my previous posts.

What does CGB mean?
Have you obtained any CSE187L current transformers yet?

The acoustic sound of your archtop with the pickups removed is an acoustic issue and not related to what a pickup sees. This current transformer low impedance pickup will respond to string distance from the coil the same way that a traditional high Z pickup will respond with different distance settings. The real issue is signal to noise ratio, as lower noise can support higher amplifier or mixer gain and farther pickup distances to the string generator source. You need to experiment with CSE187L (or similar) current transformer pickups to hear what sounds good to you. Let us know what you find.

Joseph Rogowski