Challenging and exciting new design needs a guru !

[David King]

Wait

Now thinking about this further, do we care that notes are going to be fretted and that our primary coil DCR is going to be jumping all over the place? Seems like that change in resistance could also be used to determine the note's pitch to some extent and perhaps help eliminate the dreaded midi lag/latency.

[bbsailor]

Thanks, Joe.

I was hoping you'd join in since I wasn't entirely clear on the moving coil concept.
The current mode pickups are easy to prototype, too.

Dan and others,

Here is a quick experiment that you can do on any acoustic guitar or electric guitar. You will need a 2" long neo magnet or ceramic magnet, a metal reflective plate, one long alligator clip test lead and an oscilloscope set on the 5mv or lower scale.

1. Attach the alligator clip on the low E string behind the nut.
2. Clip the oscilloscope test probe to the low E string behind the bridge and the probe ground to the long test lead. This measures the voltage being generated across the low impedance of the guitar string.
3. Pluck the low E string and hand hold or duct tape the neo magnet about .25" below the string running lengthwise so there is a wide magnetic window.
4. Note the output on the Oscilloscope should be a few milli volts (mv).
5. Add the metal reflective plate and measure again. It should be about 20% higher.
6. Turn the magnet 90 degrees so it is perpendicular to the string with a narrow magnetic window. The output will be lower.
7. Try the same test on the high E string. You must move the alligator clip lead to go across the string you are measuring.
8. Obtain a few SPCT-251 2000 turn current transformers (CT) from Prem Magnetics. These have a nickel alloy laminated core and are slightly more sensitive then the SPCT-250 which has a steel laminated core.
9. Remove one clip from the test lead so you can loop the test lead through the open primary of the SPCT-251 E-I core. Connect the test lead to the same string behind the nut and bridge so current is going through the CT.
8. Measure the output voltage which should be in the 100mv to 150 mv P-P range with one CT.
9. Add an additional CT in series with the first CT and put the secondaries in series (watch the phase) and measure the voltage. It should be about twice your previous measurements on the oscilloscope.
10. Controlling the reflected impedance of the string to the single and multiple CT outputs allows you to match the input impedance of a microphone matching transformer which is about 3K ohms at 1 Khz. Playing with putting the CTs in series or parallel allows you to have some tonal variation. Hint: a 2000 turn CT reflects the 3K ohm load back to the primary to a low resistance of 3,000/4,000,000 or .00075 ohms. Here is where some lab work and string impedance modeling will help you obtain CTs with the right turns ratios to achieve a variety of passive outputs, active amplification and tonal variations.

I have had good luck with using two SPCT-251 CTs on each end of a 4" wide string loop made of AWG 6 square enameled copper wire (surplus sales of nebraska) with a single neo magnet (.25" wide X 2" long X .125" thick) in the center
of the string low impedance (measured in a few hundred micro ohms) loop perpendicular to the strings mounted in my acoustic guitar. By putting outputs from each CT in parallel helps to match the input of a mic matching transformer and puts the final output of the microphone matching transformer in the 200mv to 250mv range depending on magnet type, reflective plate and distance from strings. The mic matching transformer is located at the amplifier end. If you hear noise when you take you hand off the strings, simply put a "Plate Mate" (available at www.stewmac.com) under the bridge, ground it and the primary loop to the ground lead of the XLR connection prior to going to the microphone trannsformer. When thinking in terms of current-bases transducers, a low impedance loop is necessary. Since strings have an impedance range of from .5 ohms to near 2 ohms, having a ground return that is at least 10 times less than the lowest string resistance will help minimize series resistance which will limit the string loop current and not optimize the voltage output from the CT or string transformer.

Note: you can also use toroid CTs but look for some that have a high turns ratio (1000 to 5000 turns) and are rated to operate in the 50 to 400 HZ range. The Zettler ACST 260 series has a variety of E-I models that have a prewired single turn "U-shaped" AWG 16 loop with secondary turns that range from 50 turns up to 1500 turns. Order a few of each and play with the effects of changing the transformers. Using thin copper tubing makes experimenting much easier. The 300 turn, 500 turn and the 1000 turn models work nicely into a microphone matching transformer wired in parallel. Use your Extech LCR meter to see the effects of using various gauge wires on the primary low impedance string loop.

These tips should get the technically curious moving in the right direction.

Joseph Rogowski

[Mike Sulzer]

Hi Joseph,

This is an interesting application of your idea.

As a moving coil pickup with the string as part of the coil, then it should be the conductivity of the string that matters. So the string does not need to be made from magnetic material; is this true? If so, then that raises the question of how to orient the magnet. You need to cut across lines of flux when the string vibrates, and maximize the number of cut lines to get the highest voltage. So if the field is perpendicular to the top if the guitar body, then you sense horizontal vibration from the string. If you made the field parallel to the top of the body and perpendicular to the string, then you should get vertical vibrations, I think. ( I hope the directions are correct.) Similarly, you could get any angle. Does this agree with your experiments?

[salvarsan]

I don't guess I get it!
Why do you keep saying it has to fit in a 1/4" tube?
I thought the whole idea was to come up with a new improved P/U.
I would throw the 1/4 out the window and comes up with something that works, then make a suitable cover to go with it. But then again I don't get the whole concept to start with.
Terry

Hi, Terry.

The Gittler is an Art Guitar and that's why some people want it.
You can't change its appearance without its market disappearing.

So, we make suggestions about thin-walled pickup tubes to fit a bigger pickup,
or bbsailor's moving coil design that requires electrically isolating a string from the bridge and the tuner.

[bbsailor]

Hi Joseph,

This is an interesting application of your idea.

As a moving coil pickup with the string as part of the coil, then it should be the conductivity of the string that matters. So the string does not need to be made from magnetic material; is this true? If so, then that raises the question of how to orient the magnet. You need to cut across lines of flux when the string vibrates, and maximize the number of cut lines to get the highest voltage. So if the field is perpendicular to the top if the guitar body, then you sense horizontal vibration from the string. If you made the field parallel to the top of the body and perpendicular to the string, then you should get vertical vibrations, I think. ( I hope the directions are correct.) Similarly, you could get any angle. Does this agree with your experiments?

Mike,

Ribbon microphones use a thin non-magnetic ribbon made of an alumium-like material with a resistance in the range of .05 ohms for a 2" length. The magnetic field in the ribbon microphone runs paraellel to each side of the ribbon width, about .25" with a very small gap on each side to ensure that the magnetic field through the ribbon is strong. The magnet under the guitar string provides a highly asymmetrical signal espicially if the magnet is moved near the neck where the string motion is greater. This also has the effect of possibly dampening the ferrous strings vibrations in an attempt to obtain a high output. A .375" OD ring magnet with a .25" ID allows the magnet to be mounted to the bridge and allows the string to pass therough the ring magnet, providing a very strong magnetic field, but for a short distance. Ribbon microphones typically transform the very low impedance of .05 ohms to a typical output impedance of between 150 to 250 ohms. The typical guitar string impedance is an order of magnitude higher and scales a little differently because of the added ground return resistance which is in series with the string. The ribbon microphone typically has about a 50 to 70 turns ratio to match the desired input impedance into an XLR input typically in the 2K to 3K ohms range. The primary of a ribbon transformer looks like a shorted primary and results in the seeing the secondary impedance as leakage inductance as measured by the Extech LCR meter and thus the secondary impedance is very sensitive to the high turns ratios of current transformers and the resistance of the total primary loop.

Placing the magnetic field in parallel with the strings results in a higher output, typically a few mv. Observe it on an oscilloscope to see first hand what challenges we are dealing with while trying to fit magnets inside about a .25" tube. Since the strings on the Gittler do not arch like on a traditional electric guitar, rather they lay flat, allowing the placement of another magnet over the top of the strings to intensify the magnetic field, and makes the output more symmetrical. This seems more practical from a technical point of view but may not be visually acceptable. So the challenge is how to stuff the right magnets, coils, transformers, active electronics and other parts inside the available space makes this a very challenging while attempting to obtain an output level compatable with guitar amplifier expected input ranges.

Magnets placed in one location, typically under a moving string mostly pickup the vertical motion of the string. Ring magnets with the string passing through the center operate like early phono cartridges with different vertical and horizontal motion being responsible for right and left channel separation of 16db to 20db.

It would be desireable to know all the design constraints in advance. But here are a few questions that can be explored in advance of obtaining firm insight into the design constraints.

Could a copper wire such as an AWG 10 to 6 gauge be used inside the main tube to help lower the ground return resistance?
Would different string brands work better that have higher steel (ferrous) content?
How does the resistance of each string scale to building the best matching transformer across each string?
What length of magnetic field produces the most desireable audio tone output?
Is a passive output required or can an active circuit be used to electronically (vice mechanically) adjust the individual string and/or midi output volume?
How could the six under-string tubes be used creativly to form a new type of transducer?
Could over and under magnets be used or cylinder magnets with the string passing through?

The answer to many of these questions comes from lab work, measurements, note taking and doing a set of tradeoff analysis to see what is gained or lost with each technical capability examined. This is where design engineers earn their keep!

Joseph Rogowski

[bbsailor]

If you play a Gittler, it's not enough to look goofy,
you must also be able to sound goofy.

That means a synthesizer and a signal that is facilely sampled by MIDI, which means
6 pickups having minimal crosstalk.

let's assume that an improved hum-cancelling pickup is possible for the Gittler.

Because of crosstalk from conducted vibration in a stainless steel guitar,
a pickup potting requirement is absolute.

One design: a small two-blade geometry like the Roland and Gibson hex sensors.

The 2-blade pickup would be small and with a squared aspect ratio.
The square aspect that fits in a circle is .707 * ID, or .176" at the corners for a .25" bore.

That's an onerous size constraint.

If the 304 stainless steel (3/8" OD, 1/4" ID) was replaced with an alloy at least 4x stronger,
(which is easy enough to find, these days) then the tube wall thickness (1/16") could be cut in half.
NB, there are nickel-chromium and copper-chromium alloys that fit the bill, but you can go crazy and get superalloys, too.

A 1/32" wall thickness mean a 5/16" ID = .3125".
The hypothetical pickup is then .22" at the corners, less onerous, but tolerable.

The magnets would necessarily be neodymium since Alnico that small won't hold magnetization.

Dan,

Can you make your matal restivity calaculator available so the resiatance of all the metals used on the Gittler can be measured or calculated to see the effect on moving string pickup performance?
Example: titanium has and IACS rating of about 2 compared to 100 for copper.

It would also be helpful if you could locate an eddy current calculator so pickup designers can see the effect of using various metal alloys in unconventional ways.

Thanks

Joseph Rogowski

[salvarsan]

Can you make your metal resistivity calaculator available so the resistance of all the metals used on the Gittler can be measured or calculated to see the effect on moving string pickup performance?

It's there at Resistance Calculator. I haven't added any other alloys, although 304 is in there too.

[jason lollar]

it has to fit in a 1/4" tube because its an art guitar and its part of the design- not only does it have to fit in the tube but the tube is oriented in a particular way to the strings and is quite far from the strings for a conventional design pickup to work.
rick turner has it in a nutshell "well, there is a challenge to being given the packaging first and being told to make something work well in that visual form!"
I have run into that wall probably more than half the time when I make one of a kind pickups- they have to fit in a particular size hole and often have height restrictions so often you wind up with a coil shape that you wind up with therefore you wind up with a tone you wind up with and you also wind up with limitations that are given to you. I have made at least a thousand if not 2 of one of a kind pickups to fit in something either already routed or to fit some visual ideal so when Turner says itsd a challenge its a challenge I am all too familiar with- its funny how simple Rick put that together- I am going to use that exact phrase in the future- thanks Rick.

[martin manning]

Or, stated a little more concisely, a case of function following form.

MPM

[J M Fahey]

So, in a nutshell, Mr Sashua/Russ has the rights (we'll have to assume so, have not seen proof of it) to build/market a gorgeous and revolutionary guitar, which unfortunately comes attached to a very poor pickup design.
And he needs a bright designer who pulls him out of the pit where he's now.
Is that so?
Nothing against that, but trying to get it for free, counting only on the typical ego of bright people, specially a newcomer, is expecting a little too much.
And that approach won't cut too much ice in this Forum full of hardened combat veterans.
I say: it's his business, the risk is his (after all, it's him who will profit if this succeeds), he's the one who must pay for consultation no matter what it leads to.
If it ends up in nothing, it's his problem, it's his risk, that's the way this game is played.
I find this akin to going to s Doctor, telling him: "Hey Doc, I have a deal for you. Check me up, treat me for what you find, I warn you I'm not paying"
"The next time I need Medical assistance, I'll consider calling you again and maybe paying, what say?"
Anyway he has already gotten 1000 times what he bargained for, high level magnetic analysis, sound estimation and tweaking, different approaches, lots of ideas, the full Monty.
I guess I'll market some pickup designed using this pool of knowledge and experience, thanks guys !!
Or somebody might post some blueprints here, or CAD files for CNC machines.
If possible, already in Simplified Chinese, to save one step.
he he.

[salvarsan]

So, in a nutshell, Mr Sashua/Russ has the rights (we'll have to assume so, have not seen proof of it) to build/market a gorgeous and revolutionary guitar, which unfortunately comes attached to a very poor pickup design.

My understanding is that the patent without trademark lapsed in the 1990's, and that the guitar was not built after 1983.

This makes it an orphan and fair game for replication as long as the saleable goods are not called Gittler or Bar Rishi.

And he needs a bright designer who pulls him out of the pit where he's now.
Is that so?

He's got one, but it looks like the guy has a day job.

Anyway he has already gotten 1000 times what he bargained for, high level magnetic analysis, sound estimation and tweaking, different approaches, lots of ideas, the full Monty.

Bullshit. We've discussed what we would do with an antique design constraint, but have made no prototypes and done no testing.

At best, we've made reasoned guesses to fit the old design rather than the one that the manufacturor is working with.

I guess I'll market some pickup designed using this pool of knowledge and experience, thanks guys !!
Or somebody might post some blueprints here, or CAD files for CNC machines.
If possible, already in Simplified Chinese, to save one step.
he he.

There are differences between a written idea and a blueprint, a blueprint and a product and, a product and a business model. You can execute this chain from beginning to end with strong and persistent effort, but having only one link in the chain doesn't mean you have the payoff.

To think so is like confusing television drama with reality.

[J M Fahey]

Dear salvarsan, maybe you missed my "" and "he he" ; the bright LEDs that indicate that my processor is in the "irony/tongue_in_cheek" mode. he he oops!, I said it again !!
As of the *tons* of insightful technical info and ideas which has been posted above, I consider them of the highest value.
No, no blueprints, no prototypes, no testing so far, but I still stick to considering this "much more than what the OP bargained for".
Maybe I value what I read here more than you do. Oh well.
Have a good day <--- no, I'm not in irony mode here.
PS: worst case: none of the ideas posted above is useful to make a new, marketable design?, at least it lets him *not* waste time, money and frustration on a challenged design.
That alone is worth a lot.

[Steve Conner]

There are differences between a written idea and a blueprint, a blueprint and a product and, a product and a business model. You can execute this chain from beginning to end with strong and persistent effort, but having only one link in the chain doesn't mean you have the payoff.

I +1 on this. Even if you have all but one of the links it won't fly. Goodness knows I've worked on enough projects that failed because they had one of them missing.

(Product to business model is the most common one in the hi-tech industry. Engineers love to build cool gadgets just because they can, and then try to think up a way of selling them afterwards. Yet, Apple does that all the time and it works beautifully for them.)

[salvarsan]

Dear salvarsan, maybe you missed my "" and "he he" ; the bright LEDs that indicate that my processor is in the "irony/tongue_in_cheek" mode. he he oops!, I said it again !!
As of the *tons* of insightful technical info and ideas which has been posted above, I consider them of the highest value.
No, no blueprints, no prototypes, no testing so far, but I still stick to considering this "much more than what the OP bargained for".
Maybe I value what I read here more than you do. Oh well.
Have a good day <--- no, I'm not in irony mode here.
PS: worst case: none of the ideas posted above is useful to make a new, marketable design?, at least it lets him *not* waste time, money and frustration on a challenged design.
That alone is worth a lot.

Couple things here.

ONE
They don't need us.
Because of some of their added constraints, our ideas are inapplicable.

I've spoken at length to the CEO and lead engineer.
They have things well in hand and needed only a few small nudges.
Otherwise, they are rather ahead of the curve for a high-impedance pickup design.

What they really need is a build technician for the lead engineer
since his time is so precious.

TWO
Damn, but this kind of gedanken experiment is fun!

This pickup design problem for a difficult form factor was so interesting,
some of us couldn't put it down. We kicked some terrific ideas around,
learned a bit more about why metal shields around pickups are bad,
and so forth.

That is one of the best parts of this forum -- a good exchange on the science of pickups.

[David King]

+ we can all come away from it feeling like "gurus" and maybe even adding it to our resumés.