A six coil pickup and on board electronics for individual string distortion.

[Mike Sulzer]

Hello Mike,

Sounds like a feasible explanation of the physics. You are right, I measured the unloaded, resonance frequency and it is somewhere in the order of 44KHz. The Strat pickup was just over 5KHz. Only time and experimentation with EQ will tell whether the sound of this pickup will work for me.

Thanks for your feedback.

JB.

Start by putting a few thousand pf across the pickup to bring down the resonant frequency. When you get it to about 5 KHz, you can adjust the resistive load across it to get the Q that sounds best.

[harvey_tbee]

The idea of this six-coil pickup with six individual distortion units has been going through my head for decades. I was simply called stupid by people I told it to. Nice to see someone actually began to build it! Main question now: has the project been finished, does it work and how does it sound? Is there a complete plan somewhere (or a commercial product that I can buy)?

[Mike Sulzer]

The idea of this six-coil pickup with six individual distortion units has been going through my head for decades. I was simply called stupid by people I told it to. Nice to see someone actually began to build it! Main question now: has the project been finished, does it work and how does it sound? Is there a complete plan somewhere (or a commercial product that I can buy)?

The project is continuing; it is now in a two-pickup guitar with a single knob for controlling the whole range of distortion and FET switches for changing pickups, both of which I will describe on this forum eventually. The project is not complete until I find a way to control the nature of the distortion as well as its intensity. This would be something like a symmetry control; it is not easy to control this on six devices together over a wide range of distortion intensity.

[Rick Turner]

Mike, this would be interesting using parallel processing on each string. Split the signal and EQ one "track" to taste for best distortion, then use the other split clean and mix it back in after the distortion for more clarity.

[CRU JONES]

Mike!

Nice work! This is very ambitious! Have you heard the distortion of your preamp/distortion circuit? The waveforms are interesting!

I really like how you are putting a neo mag on the top of a high perm slug. Is there a reason to put it on top, not on the bottom?

I used to be obsessed with the hex coil... Or Rather the Sex coil as I was winding for a seven string. I wrote about it on Ampage in the nineties under the user name "Eth". But I didn't own any test equipment at the time and my main stumbling block was using Alnico cores. The permeability was so low, they never sounded the way I wanted. I only realized that later.

Your core looks good, and I would like to try it! I connected all my coils in series and used diff amps between each node. At the time I was strictly against IC's (religious reasons). So the diff amps were discrete. Adjusting the bias current would control gain and thus distortion(VC idea). The benefit of having the coils all in series, you can plug a mono cable into it and jam passively in mono, for instance if your batteries die.

At the time I was stoked on the sex coil, Ken Gilbert pointed out that IM distortion is very important to tone. I found that he was right. The sound of two strings modulating each other is amazing, though I agree, the next level of complex chords, in saturation, is yet to have been heard. I encourage you to go there!

Keep up the good work, and thanks for sharing!
Eth

[Mike Sulzer]

Mike!

Have you heard the distortion of your preamp/distortion circuit? The waveforms are interesting!

Sure, that waveform is the result of a lot of listening.

Why put the magnet on top? Why on the bottom? If the magents are weak, they have to be big and need to be put out of the way, but once you have very strong inexpensive magnetic material that holds it magnetization in very small pieces, why not just put a very small piece near the string? The pole piece is high permeability and amplifies the field a lot. I would prefer slightly smaller magnets, but I have not got around to looking for them.

If you need more IM than this circuit gives alone, you just get it the old fashioned way: with the amp.

[Corvus]

Mike,

Your hex pickup is very impressive. I will suggest another way to feed the individual string channels.

Consider that each string to be the dynamic element such as in a ribbon microphone. You can do a quick experiment by measuring the impedance of each individual string. They vary from a fraction or an ohm to over 1 ohm depending on its diameter for solid strings and the core size for wound strings.
Just use a miniature ourput transformer across a string with a 4 or 8 ohm side and a 20K to 100K side for a high turns ratio. Alligator clips will work for a quick experiment on one string. Generally, you want the transformer input impedance to be 10 times the individual string impedances for the maximum voltage transfer. By using an input transformer with a cente tap, you can optimize the balance between wound and solid strings a little better. You can even use a 70V speaker line matching transformer to try this out.

The laws of physics dictate that the amount of voltage induced into the string is higher when the length of the magnetic field under the string is increased. I use a .5" wide X .125" thick X 7" long rubberized/flexible magnets under the strings from the neck to the bridge. This ensures that a full range of harmonics are being induced into the string.

With this type of pickup, each string is fully isolated from each other. On one of my early prototypes, that I made about 25 years ago, I took an old Applause guitar, removed the fingerboard and placed a copper strip over the truss rod and extended the end into the guitar body in the heel of the neck as a ground return. I used a brass nut and soldered the copper strip to make the connection behind the brass nut.

Each string had the common ground at the nut end of the string and the six hot connections behind the bridge. The Applause guitar had the strring ball ends secured behind the bridge rather than inside the body. I just put a copper rivet in the bridge for each string to go through and soldered a wire to each rivet. I routed a hot wire from each rivet to the low impedance side of an 8 ohm to 50K ohm transformer. I enclosed all six transformers in coper foil and mounted it on the heel of the neck. By alternating the phase of each alternate string I was able to minimize hum similar to a humbucking pickup. I routed a common ground from each transformer and one hot connnection from each transformer to an eight pin microphone connector (using only 7 pins, one for ground and one hot for each string). I made breakout cable with six 1/4" plugs that I fed into a six channel Radio Shack Mixer. I had individual string level, EQ, and L-R panning control. At that time I mounted a large ceramic magnet on a wood block that I suspended in the sound hole. But, longer magnets, putting more string length in a magnetic field, work better as it produces a higher output and produces a greater amount of higher harmonics. Just put the long magnet closer to the string near the bridge where the string motion is less. I believe you will get an invividual string output very close to your reported 0.2V P-P output.

So what is the point to all of this? This design produced a wide bandwidth pickup that sounded more acoustic than electric with a greater amount of higher harmonics, as I did not loose all the upper harmonics beyond the resonant point as would happen in high impedance pickups. In your case, I believe you mentioned that each string coil has a 5KHz resonant point.

Since you are going to the effort to add active EQ and distortion in your design, I thought that you might want to see what happens when you have more upper harmonics on each string to play with. You can even produce many common electric guitar sounds (both single coil and humbuching) by active EQ shaping.

Since it only takes two alligator clip wires and a junk box transformer, I thought you might want to quickly try this. I believe this method has some potential that might contribute to the next generation of guitar pickups.

If you try it, let us know what happens?

Joseph Rogowski

PS. Here is an additional thought. I even had success by using a 3000 turn, low frequency torroid current transformer by wrapping a different amount of low impedance turns through the torroid ring from each string. This is a simple way to make combined output with a single transformer.

Joseph do you have any more details or pics of your implementations this design?

I've built myself single-string humbuckers for multi-channel output but I'm finding that string cross-talk between channels is good in some situations (bending strings) and problematic in others (more noise when switching strings with lots of distortion.)

I'm intrigued by your description of this design and how it could fully isolate each string from the others.

I hope to try your design myself as soon as I can.

[bbsailor]

Joseph do you have any more details or pics of your implementations this design?

I've built myself single-string humbuckers for multi-channel output but I'm finding that string cross-talk between channels is good in some situations (bending strings) and problematic in others (more noise when switching strings with lots of distortion.)

I'm intrigued by your description of this design and how it could fully isolate each string from the others.


Corvus,

I hope to try your design myself as soon as I can.

See this forum link for more information. http://music-electronics-forum.com/t4881-2/

To obtain independent outputs from each string you need to use the truss rod as a common ground return or find some other creative way to put a low resistance wire that returns the common ground point at a brass nut or electrically connected machine heads back to the guitar body. Since the string impedance is low, you want the ground return to be as low of a resistance as practical so as not to introduce too much loss in the primary string loop side of each transformer.

You should play with this idea by doing the following:
1. Place an oscilloscope across each string attached behind the nut and bridge. Ensure that no other strings are electrically shorting out the individual string chosen for this test.
2. Place your magnets under the string with double face tape.
3. Observe the peak voltage induced in each moving string.
4. Multiply the peak voltage by the turns ratio of the individual string transformers to obtain an approximate output voltage from the individual string transformer.
5. Connect the individual string transformer high impedance output to an amp input and listen for tonal changes when you move the magnets closer/farther from strings or lengthen/shorten the length of the magnetic field.
6. Measure the output from each string so you know the range needed to balance the outputs.

Since the ear is the final arbitrator of pickup quality, I recommend that you do above test first to better understand the individual design choices you will face and do some intelligent planning.

Read the Clevenger patents from the mid 1980's: 4408513 and 4499809.

Post your findings to continue this discussion.

Go to www.tamuracorp.com and look for some miniature audio transformers that have a low secondary 4 to 8 ohms and high secondary resulting in a high turns ratio. Search the web for small audio transformers usually about 0.75 cubic inches in size. Audio output transformers can work backwards with the 4 or 8 ohm output side being used as the input side or as the new primary. I have had a workable output by using a miniature toroid current transformer (CT) with several thousand turns and simply passing the output from the individual string through the CT and looping this wire back to the common ground return point. Search the web for "miniature current transformer". Look at the "yuanxing electronics transformers" web site for the smallest CTs with the highest turns (5000 turn secondary toroid). To balance the output you can use individual string volume controls or active mixing with a six-channel mixer on-board with a gain of between 10 and 20 depending of the CT output and the gain you need to drive you off-guitar circuits.

I hope this helps?

Joseph Rogowski

[Corvus]

Thanks very much for your reply Joseph

I should have mentioned that my design requirement is that I'm taking the output from each string and plugging into the mic preamps on my computer audio interface. All my panning, EQ, amp simulation and effects are done in software using Logic and MainStage.

Does routing each string into a mic preamp rather than a guitar amp input change any of the transformer values in your guidelines?

Also did you mean to say low primary below?

Go to www.tamuracorp.com and look for some miniature audio transformers that have a low secondary 4 to 8 ohms and high secondary resulting in a high turns ratio

I really appreciate the help.

Leo Pedersen

[bbsailor]

Thanks very much for your reply Joseph

I should have mentioned that my design requirement is that I'm taking the output from each string and plugging into the mic preamps on my computer audio interface. All my panning, EQ, amp simulation and effects are done in software using Logic and MainStage.

Does routing each string into a mic preamp rather than a guitar amp input change any of the transformer values in your guidelines?

Also did you mean to say low primary below?



I really appreciate the help.

Leo Pedersen

Leo,

The rule of thumb for using transformers is to have the input circuit impedance of each channel/string be in the range of 5 to 10 times higher than the output impedance of what is feeding it. This keeps the transformer output level from being loaded down too much by the mixer input impedance. If the input impedance is 2000 ohms (typical for XLR type mic inputs) then you want a string transformer output impedance to be between 200 and 400 ohms, with a low of 3.2 ohms or 4 ohms. You can probably go as high as about 500 ohms and have it still work OK. This will be an approximate turns ratio of 8 for 200 ohms and 11 for 400 ohms. Typically we call the input of a transformer the primary as it is the side that is being feed the signal. The load is the output or secondary side. Transformers work wither way. Typically, the only common transformers that work well on the low impedance of a guitar string is a miniature speaker driver transformer with a 3.2, 4 or 8 ohm impedance side. Look for a transformer that has about a 1 ohm to 1.5 secondary DC resistance and use this side as the primary to be fed by the voltage induced on the string.

To calculate the turns ratio, divide the transformer input impedance into the output impedance and then take the square root of this number.

Remember that the ground return from the nut side of the string is the common string ground and should be grounded to the output of the guitar to minimize noise. Try alternating the transformer phase of adjacent strings to help reduce induced noise on the strings. This is a crude way of humbucking direct string low impedance pickups.

I hope this helps.

This is fun stuff to play with. It wil be very educational as well.

Post your results.

Joseph Rogowski

[Corvus]

Thanks very much for your patient help Joseph, it's much appreciated.


I'll definitely post my results and probably think of a couple more questions to ask along the way.

[Mark Hammer]

Harry Bissell (well-respected among the DIY synth community) brought his guitar synth over to my house about 8 years ago. He used a G-Vox pickup (a GK-1 or GK-2 work-alike, readily available on e-bay for peanuts at the time) mounted on on his Ibanez solidbody.

He used it to drive what were essentially - in his words - a sextet of Big Muffs (though looking at it, not really), coupled to VCFs driven by his excellent envelope follower design. Somewhere in there he had co-opted a 360-systems Slave Driver, though I'm not exactly sure how. As you can see here, it was a pretty complicated design: Larry’s DIY synthesizer module page But man oh man, what a responsive system. A sheer delight to play. The speediness of it was largely attributable to the complete absence of any P-2-V conversion.