Hexaphonic pickups for synthesizer output

[chad h]

In my family, we believe in specialization. I make the pickups; my son plays the guitars.

For better or worse, my son has developed a serious fascination with Pat Metheny, and consequently has obtained a Roland GR-55 guitar synthesizer. Currently he uses it with Roland's GK-3 pickup, which has the advantage that it can be attached to just about any guitar. It also has the disadvantage of being highly inelegant.

So I've been kicking around some ideas about alternatives.

One option is to build a GK-3 (or equivalent) into a guitar. The GK-3 is a low-impedance, hexaphonic pickup. It feeds six separate signals into a pre-amp, that is then fed to 13-pin connector. The other 7 pins from the connector feed signals from on-guitar controls to the synthesizer (two of them carry +7v and -7v power; two of them allow "up" and "down" signals to be sent, allowing the player to scroll through the list of synth voices; one of them carries the normal output from the guitar's magnetic pickups; one of them carries a signal that tells the synth whether or not to blend the output from the standard pickups and the output from the synth; and one attaches to the volume on the pre-amp.

Roland themselves make a GK-Kit available that allows you to do all of this.

RMC Pickups has a completely different pickup arrangement, built into saddles in the bridge. They also offer on-board pre-amps. So they have a solution that is equivalent to the Roland's GK-Kit.

But maybe I can cobble together something just as functional.

The first question I have is what the advantage is using low-impedance pickups with on-board pre-amplification in this application? It wouldn't be all that hard to build a hexaphonic, high-impedance pickup that might sit in the standard bridge position on the guitar. In fact, this is the kind of solution that the guy at Ubertar (http://www.ubertar.com/hexaphonic/ uses. He sends six signals to a break-out box, where potentially you can do all sorts of things with the signals. But, notionally, you could add some additional circuitry in the guitar to allow the full functionality associated with Roland's GK-3 without having to bother with pre-amplification, and just run a 13-pin cable from guitar to the synth.

We all like the sound of high-impedance pickups, so I don't see any reason why a six-coil, high-impedance pickup couldn't sound great even without putting the signal through a synthesizer. So my second question is, if one has six separate signals coming from six coils, is there a clearly superior way to wire the outputs into a mono signal? Series or Parallel? For hum rejection should one pair RWRP coils? Or should one put three like coils in series, and then put them in parallel with the RWRP coils?

Any ideas would be appreciated.

Chad

[Leo_Gnardo]

For hum rejection should one pair RWRP coils? Or should one put three like coils in series, and then put them in parallel with the RWRP coils?

Any ideas would be appreciated.

Chad

One notable feature you may want to borrow from the RMC pickup, each one of the individual pickups is reverse-polarity to its neighbors. The six pickups are brought separately to a preamp board for signal boost, conditioning & mixing for the audio output. How they're handled for the synth drive function, I don't know. Hope this is of some help. Looks like you're onto a very interesting project!

[big_teee]

This thread will be better supported in the main pickup forum, rather than the B/H forum.
T

[Lollar Jason]

I have made lots of that type of pickup over the last 20+ years. There are several problems; one being to isolate each coil from the other to minimise bleed through- that can be big problem, having the adjacent strings bleed into adjacent coils if you are trying to have each coil discreet. Another problem is the inductance of a single pole pickup with a small diameter coil is completely different than a typical guitar pickup so they don't sound as loud or as full- they will sound better with a pre amp but if you dont isolate the coils- the more you preamp the more bleed through you'll get. Not much help to offer but there are a few things to consider once you get farther along.

[bbsailor]

On this MEF post I described how I used six transformers to treat each string as an independent moving coil transducer. https://music-electronics-forum.com/...ically+curious

Basically it treats each string like the ribbon in a ribbon microphone. After trying many small audio transformers I came to the conclusion that a small 20K to 8 ohm transformer will provide a 1 to 50 voltage boost when the 8 ohm side is used as the primary and mounted across each string. The longer the magnetic field is for each string, the higher the output will be.

The problem is obtaining a common ground connection from the nut end of the string with the hot side attached from behind the non conducting bridge. I did this by removing the fingerboard using heat. Then, I put a long strip of copper over the truss rod location connected to a brass nut and into the acoustic guitar body. The copper strip should have a resistance 10X lower than the lowest resistance string to minimize input losses. Since the 8 ohm impedance of the transformer input is about 10X higher than the DCR of the strings, it acts like a good bridging impedance to optimize the transformer output level from each string.

On the heel of the neck I mounted six miniature audio transformers with each 8 ohm side connected to the common ground and the hot side of each transformer going to the individual string connection. I placed a small copper rivet in the pull through tail piece to pull the string through and attach a wire to each string and rout that string wire to the hot side of each transformer. The magnet mounting can be as simple as using a wood tongue depressor or ice cream stick to mount the magnet or distribute smaller magnets along the strings to optimize the output or tone from each string. With this setup there is no bleed through of adjacent strings as each string operates totally independent of its neighbor.

Anyone who builds guitars could try this little trick to try this concept with little consequences if you want to go back to traditional pickups. Make a nut end truss rod washer with a tab that would electrically connect to a metal nut. Extend the heel end of the truss rod with a way to bring the common ground nut end into the guitar body where the transformers would be mounted.

I used a common male and female 8-pin microphone connector on the guitar body and 6 conductor shielded wire. When I built a breakout cable with a .25 inch plug for each string, I could set the volume, tone and pan left or right each string independently. It also allowed me to feed my Roland midi guitar synthesizer.

These are just some thoughts for those who like to tinker.

Joseph J. Rogowski

[Mark Hammer]

The use of low-impedance coils in such applications is much more a function of the sheer difficulty of winding anything involving more wire, than of any deliberate attempt to use low-impedance coils.

Divided pickups can have several goals. On is certainly to provide a "bigger" sound, by sending different strings to different channels. The old Kramer Ripley guitar that Eddie Van Halen would do ads for on the back of Guitar Player magazine are an example of that. In that sort of application, there is some concern for bleedthrough of adjacent strings, but it's not a dealbreaker since the goal is "space".

In the case of guitar synthesis, or at least individual string processing, the challenge is preventing ALL crosstalk/bleedthrough from adjacent strings. And one does that by snuggling the pickup as close to the bridge as feasible, where the string "wiggles" less. But of course, to situate it close to the saddle, that coil has to be small, or risk crosstalk. I own a bizarre unit called the Guild Tri-Oct, produced around 1971 or so, that used a proprietary hex pickup to trigger 6 octave dividers - one-per-string. Unfortunately the insights about pickup form-factor hadn't been well-understood yet, so that pickup was about the same footprint as a P90. You could only put it close to the bridge if you didn't already have a bridge pickup, and placing it between the neck and bridge pickups yielded constant mistriggering by adjacent strings. Remember that reliable triggering is absolutely fundamental to guitar synthesis. The circuitry only knows that a note is produced at this moment from this string if that coil is detecting a signal above some critical level. But the coil doesn't really "care" what produced that supra-threshold signal.

Now, If you were able to wind several thousand turns of #46 wire on a 1" tall 1/16" diameter alnico rod, I suppose a high-impedance hex pickup, close enough to the bridge to avoid problematic crosstalk, would be a reality. But, since hex pickups have pretty much always been an add-on that would avoid routing a cavity, inductive hex pickups have always been low-impedance.

Is there an advantage to use of low-impedance, beyond being able to fit six coils into a slender confined space? Sure, greater (though not complete) immunity to EMI hum.
Do they sound "worse", and do we care? Well, the objective is not for them to have a "sound", but rather to be used to trigger sound-generating devices. At the same time, about 16 years back, Harry Bissell came up to my town for a bunch of us synth and effect folks to get together, and brought his guitar synth over to my place. He used a thin Ibanez solid body guitar with a divided pickup similar to a GK-1 or GK-2, and used it to drive a fully analog six-voice unit he had designed, that fuzzed up each string and triggered hex filtering and envelope/transient generators for each string. It was an extremely responsive setup, whose easy playability lingers with me still. So a hex pickup doesn't have to be turned into something to drive one or more oscillators. But neither does it need to have some sort of "sound" or tone of its own.

The use of individual piezo saddles has provided an elegant solution, since the string sits in the same place and doesn't bleed into adjacent pickups; though I imagine one still needs to be concerned about any unwanted and conflicting resonances vibrating up.

[galaxiex]

I don't know if these would help you...

Just throwing it out there...

https://www.cycfi.com/projects/nu-series-v2/

[Lollar Jason]

HA! Yes of course the point i overlooked- they only need to serve as a trigger- not to also function as a passive pickup which is an entirely different scenario.

[Helmholtz]

Is there an advantage to use of low-impedance, beyond being able to fit six coils into a slender confined space? Sure, greater (though not complete) immunity to EMI hum.

How this?
If a low and a high impedance coil occupy the same space and use the same core/magnet assy, I would expect them to have the same S/N ratio.

[Mark Hammer]

If I had the money to spend on them, yes they would help. Nice idea/product, though. For myself, I have a GK-1, and also have some Graph-Tech piezo saddles for a Strat bridge, sitting around awaiting installation. And, um, I do not plan to adapt the pickup from the Tri-Oct to drive a synth.

[Mark Hammer]

Well, they could serve both functions if one wanted to, I suppose. But they don't have to, much to our benefit.