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

[Mike Sulzer]

Maybe it was already mentioned, but there are two distinct kinds of hex pickups. One is the kind like what was used in the Ripley guitar, or the Bartolini type, where the intent is to provide for a more interesting stereo image. here, the coils don't have to sense ONLY one string, but simply have to sense that string more than the others.

The other type of hex pickup is that used for guitar synthesis, where the purpose of the individual coils is to make sure that the sensing circuitry receives no information from "irrelevant" strings, such that it can generate a trigger, gate, and proportional control voltage for only the note being played on that string at that time.

The second kind imposes more stringent constraints than the first.

Maybe it would be useful to think of this pickup as a third type, where the stringency of the constraints is between the other two.

[Zhangliqun]

I remember reading in the 80's about some guy by the name of Steve Ripley or something like that who came up with a similar concept, individually distorted strings which sounded like a synth, or a real double lead when playing chords.

[Mike Sulzer]

I remember reading in the 80's about some guy by the name of Steve Ripley or something like that who came up with a similar concept, individually distorted strings which sounded like a synth, or a real double lead when playing chords.

This certainly is not a new idea; it has been discussed on this forum at least once. I bet it has been done several times. The difference today is that it is easier to build high quality low power complex electronics.

My goal is not a sound like a synth, but rather to reduce the IM enough to allow a greater variety of chords to be played.

[Mike Sulzer]

The summer and the filter

Summing the outputs of the six amplifiers is easy. This inverting op amp circuit also has variable gain implemented in the feedback loop to balance the levels in the five switch positions.

The filter is a Sallen-Key second order low pass section with some additions. The resonance of these coils is way above the audio range and damped out. Therefore, if one wants the traditional electric guitar sound, it has to be added back in at the right frequency. A resonance just below 5 KHz gives the brightest sound. The circuit is designed to have a Q somewhat higher than necessary; then a pot and capacitor are added across the capacitor to ground, just like a guitar tone circuit. A non-mathematical way to think of this circuit is that the capacitor from the amp input to ground in the Sallen-key circuit is analogous to the pickup and cable capacitance in a guitar. The resistors and feedback capacitor replace the pickup inductance. So a guitar-type tone circuit should work in this circuit, and it does. But in this case we make the effective value of the impedance variable by switching in different amounts of feedback. This is useful to reduce the high frequencies when switching to the positions with more distortion.

[David Schwab]

The Ripley guitar was stereo. It used a hexaphonic Bartolini pickup with each string going to a built in mixer channel, so you could pan the strings. I don't think it had distortion though. Steve Ripley is a member of the band The Tractors.

ARP had a guitar synth with a hex fuzz back in the 70's. It was a really cheesy sounding fuzz, but allowed you to play chords without the usual intermodulation distortion. The fuzz made up for the lack of more than two note polyphony from the synth, but allowed you to run the fuzz through the filter.

[Possum]

....

I don't know if they were hum cancelling or not, they easily could have been, one set N up the other S up and thats all it would take. turns out VH isn't selling those, probably no one bought them, stereo guitars aren't exactly big sellers...

[David Schwab]

I think those old Bart Hi-A pickups were six single coils, alternating N-S. The Bart single coils are pretty quiet though.

Yeah, EVH had one of them, and a bass version, when Kramer was making them.

It might be interesting in the studio, but that's about it.

[Mike Sulzer]

I don't know if they were hum cancelling or not, they easily could have been, one set N up the other S up and thats all it would take. turns out VH isn't selling those, probably no one bought them, stereo guitars aren't exactly big sellers...

If the set of three coils for the left channel and that for the right channel had opposite electrical polarity with respect to hum pickup, and if they were played through different amplifiers as one expects for "stereo", the hum could cancel for a listener in just the right place. But in general, no.

[MCK]

Very interesting thread. Any updates?

On a related note, have you considered using the Roland GK series pickups? These are normally wired to a 13pin DIN connector and drive guitar synth type platforms that require Hex signal. However, fundemantally, they are made of 6 miniature humbuckers. You could potentially rework the cable connector and gain access to the signal from the individual humbuckers.

Take a look at the following site & thread for a close look. Hope this helps.

Inside a Roland Ready Strat GK-2A

Regards

[David Schwab]

Take a look at the following site & thread for a close look. Hope this helps.

Inside a Roland Ready Strat GK-2A

Regards

Nice link! Man those are small coils!

Yeah, I guess buying one of those is the easiest way to do it. But where's the fun in that?

[Mike Sulzer]

Very interesting thread. Any updates?

Yes, I have made another pickup with slightly smaller coils and steel between them to improve the isolation, and a few other details. I will be writing this up in the next few weeks.

On a related note, have you considered using the Roland GK series pickups? These are normally wired to a 13pin DIN connector and drive guitar synth type platforms that require Hex signal. However, fundemantally, they are made of 6 miniature humbuckers. You could potentially rework the cable connector and gain access to the signal from the individual humbuckers.

Take a look at the following site & thread for a close look. Hope this helps.


Regards

Interesting, thanks. No, never thought about using them. Wow, they are small as David said.

[RedHouse]

...I will be writing this up in the next few weeks...

Writing it up? ...for who, is it a school project or something?
(BTW; no offense intended)

[jbforrer]

Greetings,

Interesting project and discussion. Some neat ideas, thanks for sharing this..

I have been toying with something similar. My objective is to maintain the beloved SC character/voicing with good noise reduction.

A picture of my prototype: http://www.johanforrer.net/Guitars/E...talPickup1.jpg

My prototype follows along the lines of a P-Bass split pickup with each side using opposing magnetic polarity and coils wired out of phase in order to get the noise reduction benefit. To implement the offset poles, the coils are relatively small, only occupy about half the width of a SC. About 500 Ohm of very fine wire per coil. Each coil uses a 1/8" Neodymium rod. The assembly fits into a SC housing.

I was curious what the prototype sounded like compared to a standard SC and made a little experimental recording. For this experiment I fabricated a jig to hold the pickup in place above the strings of my Strat --- the distance from the poles to the strings as like for the regular neck pickup of the guitar.

In the sample clip below, you'll first hear the standard SC, followed by the experimental prototype. Each sound segment consists of a quiet period to sample the noise followed by a strum on the open strings to sample the harmonic content. Hopefully, that will give you some idea of the noise cancellation and PU voice properties.

Here's the sound sample: http://www.johanforrer.net/Guitars/E...ntalPickup.mp3

Still work (a lot) in progress.

Regards.

JB.

[Mike Sulzer]

It is very interesting that you used three individual coils for each half rather than winding around all three polepieces. I think the result is somewhat lower resistance. The indutance is probably lower as well since the total area enclosed by the windings is smaller than if you wound around all three. (Neo has a permeability near that of a vacuum, and so the pole peices contribute little more than empty space. Therefore it is the total area that counts.)

Also the fact that the the coils are small means that there are not so many turns, and this also lowers the inductance. I would expect that the resonant frequency with a standard guitar cable would be quite high.

This agrees with what I hear from your clip. The standard SC has a bright sound from the resonance, which typically might be at about 5KHz with a cable. Your pickup sounds very neutral; this probably means that the resonance is so high that it does not affect the sound.

[jbforrer]

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.