GS-500 sustainer / hex pickup

[AJDbass]

Hi,

I know this is not a stompbox, but being a long time lurker I found out there's a lot of knowledge in understanding circuits here. Please bear with my limited English language.

I am trying to understand the circuitry of the Yamaha GS-500 guitar (a seventies guitar/synth controller). The part  I am particularly interested in is hex pickup, sustainer circuit and hex signal out. The problem is, this is quit an old design and I am fairly new to electronics. I have build a few pedals / amplifiers.  I would like to experiment with hex signal modulation (like hex fuzz, trem etc.), but more on that later.

I would like to recreate a hex sustainer based of the concept of the Yamaha GS-500 guitar. It works kind of like an inverted ebow. Instead of sending the amplified signal through an electromagnetic pickup (like an ebow), the amplified signal is send through the strings, which will then vibrate because they are in a magnetic field (iron plate with 2 strong magnets attached at the neckpickup position). There is a circuit for each string. All frets are grounded, and the circuit closes when a string is fretted.

I have found this schematic, which covers the sustainer and signal splitter circuit for hex output:
http://www.joness.com/gr300/service/GS-500_SCHEMATIC.jpg

It is not much, but this is what I found out yet. Please correct me if I'm wrong;

The hex pickup look very similar to tape heads. I found tapeheads can have a impedance in the range of 30 – 300 ohms. The first stage is a 4558 dual opamp. I think it works as a buffer and a signal splitter. I guess the signal is amplified as well? The next stage is a TC5012 non inverting buffer. I think the last stages amplifies the signal; a C945 NPN transistor (low power signal amplifier?) and at last an 2SC2120 NPN transistor.

I would love to try out this system, but would be really glad to know what's going on in the circuit before I start experimenting. I can source tape heads from cheap cassette adapters (with the little jack cable attached) on the fleebay, or I could wind my own. I also have some pc speakers lying around, with an impedance of 50 ohms. After removing the diapraghm this could be ideal pickup coils. The circuit is from the seventies, so I was wondering about more convenient ways to get a useable amplified signal to move the strings. I guess power consumption is not really a problem if I use phantom power? If possible I would like to use a more convenient power supply instead of the bipolar (-15 / + 15) psu.

Any hints, tips and info on recreating this system would be highly appreciated.

[pinkjimiphoton]

cool idea, gonna be difficult to implement tho.

if ya need a cheap hex pickup, get one of them plastic guitar controllers on ebay... not the urock, the earlier thing. i can't think of the name right now, bugger!!! but it has a combo humbucker/hex on it. begging to be extracted and messed with.

when i was on enforced recreation, live in cage 30 some years ago, we built a pickup out of them cheezy ass little earplugs... the plastic mono ones that used to come with am radios and stuff... each one has a coil and magnet, and the pickup we made from them worked out to be really cool, i wish i still had it. that may be worth investigating too.

[nate77]

On a slight tangent, it's amazing what we can come up with when forced to. I may have been in a similar situation for quite some time and very few things stir up the ingenuity like being held in a box. I used to refer to it as "backpacking through Europe". Few more ingenuitive  than us musicians/tinkerers.

[J0K3RX]

Have you seen this?

https://www.tindie.com/products/Cycfiresearch/neo-6-hex-active-polyphonic-pickup/

[AJDbass]

Wow, those active polyphonic pickups do seem nice! They even sell them as single units.

@ Jimi: I think I remeber someone mention toy guitar controllers as a source for hex pickups. I will investigate those a little more, sounds interesting and probably cheap.

I remember trying to fix a little earplugs when the cable broke at the driver part, but it was way above my skill to solder those tiny wires. Cool that you managed to build a pickup out of those!

[soggybag]

Here's another one. These are hexaphonic, but are traditional passive style pickups.

http://www.ubertar.com/hexaphonic/

[Mark Hammer]

Note that almost ALL guitar synthesizers use some form of string-sensing built into the bridge, or installed very close to the bridge.  The reason is that as you move farther away from the bridge (or the fret/nut), the wider the deviations the string makes from its resting position.  So, if you want to benefit from separate sensing elements for each string, you need to either pick VERY softly (so that the string doesn't move very much) or else sense the string at a point where it doesn't move to the side no matter how hard you pick.  If not, you get bleedthrough from adjacent strings into the coil.  This is why all Roland, and other synths, after the GS-500, that used magnetic pickups, would use a very slender pickup, jammed as close to the bridge as possible.

Another way of doing this is to use individual piezo saddles that fit onto a standard bridge, like these ones: http://www.graphtech.com/products/brands/ghost

[soggybag]

I should have thought of that, those bridge saddle piezos have been around for a while. The bridge saddles might be an easier route to installing a hexaphonic pick up on some guitars.

That said, for some purposes, bleed through might not be a problem, and hex humbucker, or single coil might be a easier to work with. If you're feeding the single to six outputs into six different processing chains a little bleed through might not matter.

[AJDbass]

Yeah I thought of piezo saddles and even infrared sensors (like lightwave) for pure single string sensing, but a little bleedthrough wouldn't matter too much indeed because I don't wan't to use it for midi. Piezo saddles do have my interest because I think it could be hard to get a good sound of a magnetic pickup very close to the bridge, and those graphtec ghosts seem to sound rather nice. I will have to experiment a bit. Thanks for the insight.