G707 13 pin upgrade project using GK2A circuit board

Started by Retro-Zed, March 16, 2021, 12:09:58 PM

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Retro-Zed

Hi everyone,  I'm an aging rocker and retired electronics tech and thought that the VGuitar community might welcome some notes on upgrading a G707 to the 13 pin standard utilizing a GK2A board. My goal is to maintain as much of the original guitar as possible with one exception, noted at a later time.

Starting with the 707, taking the original board and removing the toggle switch, volume pot, tone pot, one of the 50K pots, a ribbon connector, and two capacitors' from the tone circuit (C19 0.047 uf and C20 250p).

From the GK2A, removing the selector switch, the two pushbutton switches and the mix pot (fortunately 50K).

The 50K pot from the 707 will be used for synth/guitar mix and the addition of two rotary encoders with push switch function will be used in place of the two GK push buttons. One benefit of using the encoders is that they can be connected to provide the up/down function of the GK buttons as well as adding a scroll up and scroll down feature but it must be noted that the "up" button will scroll only up when twisted either CW or CCW. The down button/encoder will do the same for the down function.

Finally the 707 toggle will be used in place of the GK selector switch.

Here's a photo of the project so far:



This setup has been tested successfully with the mounted G707 hex pickup using a Gi-10 interface.

Wish me luck!


Brent Flash


Retro-Zed

Thanks Brent I hope it's useful to the forum (and love the ordanance!).

Next step:
I tweaked a piece of plastic that can be easily mounted in the 707 cavity and superglued the ribbon connector to it. The two very smooth surfaces worked like a charm for the superglue.

Then removed the cable from hex pickup, shortened it and attached it to 707 ribbon connector.
Here's a pic:


And if anyone can use it here's a pic of the interconnection diagram:


Stay tuned,
Cheers,
Dennis

Shingles

Nice!
When I converted my (black) G707 to 13-pin system I used a GK internal kit, so the 13-pin socket is not mounted on the board and all the pots and switches can be located where I want them to be.
I used the New GK hex pickup in place of the original - I see you are using the original. I wasn't sure if that would work and besides, I had promised the complete 24-pin system to someone else.
I ended up with; one guitar volume, one guitar tone, same old pickup selector toggle, one synth volume, one S1/2 switch, one guitar/mix/synth switch. Oh, and a bright blue LED.

Very pleased with the result. For guitar to MIDI, this is the most stable tracking GK platform I have, beaten only by my Godin with piezos. That stabiliser bar is certainly not just a gimmick!
Nik
--------------------------------
Tonelab, VG99, Axon AX100, EDP, Repeater
Godin, PRS, Crafter and Roland guitars
Center Point Stereo Spacestation V3

Retro-Zed

#4
Sounds sweet, the internal kit is the preferred way to go and far less fiddly but I had the GK2A on hand after removing it from a beautiful Japanese strat. And the internal kit is 300 bucks here and well worth the price but I get a kick out of tinkering and have the time.

I'm only using the GK 13 pin socket to feed a chassis mount socket after making an adapter plate.
Here's a pic but take note this is not the correct 13 pin connector (see Gumbo's reply):


And on we go...
The volume and tone pots were wired according to the 707 schematic using the original parts.
See pics:





You'll notice a non original pot with pull switch. Rather that have a "dummy" pot I decided to make use of the extra hole by installing a 741 distortion circuit level control, and the pull switch jacks a sub-board in when yanked on. All of the original G707 knobs will be used for a function.

And back to the GK board....
The board is now mounted to the original casing - bottom with 15mm standoffs installed.
See Pic:


The standoffs allow space for the rotary encoders etc. and just got lucky that 15mm standoffs bring the top of the assembly exactly to the level of the 707 cavity cover plate. In fact it's so close you don't really need to anchor the bottom ends of the standoffs, a thin layer of non-slip would hold the unit securely.
Nother pic:


Stay tuned, I wanted to get these photos captured before the assembly stage.
Cheers,
Dennis

GuitarBuilder

Quote from: Retro-Zed on March 17, 2021, 08:54:22 AM
And the internal kit is 300 bucks here and well worth the price but I get a kick out of tinkering and have the time.

Where are you located?  I order my GK internal kits from Andertons in the UK for $127!
"There's no-one left alive, it must be a draw"  Peter Gabriel 1973

Retro-Zed

South of Ottawa in Ontario, Canada, the cheapest I could fine so far was NOS for 300 at a pawn shop, music store prices seem to all be 329.00. I've only checked online though and maybe someone out there knows a better source available here. But I'll look up Andertons, thanks.
Dennis

gumbo

..Firstly, a great job you're doing there..  !!

...Secondly, and acknowledging my obvious interests in that arena, the 13-pin chassis mount jack that you have incorporated does not have a locking facility for the 'regular' (Roland-type) jackplug, and the contact strip in the keyway slot of the jack is designed to press on the INSIDE of the shell of a non-locking jackplug.

When a locking jackplug is inserted in that particular design of jack, that contact strip aligns with and makes contact with, the underside of the locking 'pawl' component of the jackplug...

...this in turn forces the the jack's contact strip deeper into the keyway slot than was originally designed, and runs the risk of deforming it over time so that its 'spring' force may be eventually compromised...

When this happens, coupled with the jackplug's locking pawl pointy-bit being forced harder (than designed) into the inside surface of the jack's outer body, it is a recipe (once again, over time) for excessive movement to take place of the jackplug within the jack during use....     ...this can lead to intermittent connectivity of the 'Ground' circuit in particular, and associated intermittency of all signal output.

...that is just one of the reasons why these 'off the shelf' Atari-type jacks are a lot cheaper than the ones I build and sell, which have the facility to accept the locking pawl of the jackplug, while also incorporating four special embossings of the jack body to securely centre and hold the shell of the locking jackplug and maintain electrical contact when inserted.

Pedantic stuff, I know, but people who know me probably already know that I am....   ;D

...but as I said in the beginning, you have done a great job with this project and I certainly respect all the effort you have put in to get it together....congratulations are in order !   :-*

Kind regards from Oz,

Peter

Read slower!!!   ....I'm typing as fast as I can...

Retro-Zed

Thanks for the input Peter, very helpful. I was ok with the lack of the locking feature, no longer playing on stage but you raise an important issue that I was unaware of (gads I love this forum!). I'll try to source the proper connector in the nether regions of Canada. Failing that perhaps I can mod the socket to function as Roland intended, much rather find that connector. The game is afoot!
Cheers,
Dennis

chrish

Here is a good source for those jacks. I believe There is a US distributor now so that would save shipping costs from OZ.

https://www.vguitarforums.com/smf/index.php?topic=8888.0

Btw, I'm thinking of doing this mod to a G505 that I got some parts off of to feed a G303.

I purchased a GK3 internal kit from Andertons delivered for $113 to the states. Like what you did with that metal plate to mount the GK Jack.

Retro-Zed

#10
Thanks for the help Chrish, one of those would be perfect and good idea on the G505/G303, it'd be well worth it. And GuitarBuilder mentioned Andertons as well so I got me arse in gear and ordered one from them, thanks! I've another project on the go building a graphite necked unfinished Mockingbird but at Andertons price now it can be synthed! Excellent....
Cheers,
Dennis

Retro-Zed

And on we go....
At the beginning I mentioned the goal of "as original as possible with one exception". Well, here's the exception, kind of a guilty pleasure but techs salivate over real time info on the status of equipment.

The original G707 as we know had two contact "plates" but they're not very useful with today's standard, though it would be cool if someone installed some capacitive contact circuitry for a real function, who knows maybe later. For this project two power indicator leds will be installed in the bridge pickup frame, one for the GK, the other for the fuzz (battery) power.

Unfortunately the corner of my original frame was broken so a replacement was tweaked. The contact plate holes were drilled according to the Roland standard and 3mm leds fit nicely. Cut and drilled, a thin piece of plastic secures the leds.
Here's a pic:


Both leds mounted, red for GK, green for fuzz:


Top view mounted on test jig.


I'm trying to focus on the items most relevant to the forum but felt it was important to explain the exception.
Cheers,
Dennis

Retro-Zed

Ok, back at er' again
Installed a couple of screw terminals for the power indicator leds behind the bridge pickup cavity, plenty of room under the hex. You can't have things come apart when you're in the Zone.


And another in the body cavity, same reason.


End view


And lastly end view with the distortion sub-board and battery clip mounted. The upper standoffs are anchored into the body but the bottom two are only attached to the board. This arrangement facilitates the removal of the board for service/modding/replacement once the volume/tone circuit is installed.


All for now and "Keep Watching the Skies".
Cheers,
Dennis


Retro-Zed

We're getting there...
I decided to mount the current limiting resistors under the leds themselves, there's a fair amount of space in the bridge pickup cavity to accommodate the original touch plates and wiring. Not a lot of movement there plus very flexible and reliable test lead wire is used for interconnection. Final testing will tell of course.

See pic:


To match the brightness levels of the red and green leds two resistor sizes were needed. There's two power sources after all and that's the purpose of the "bling". That's not bling he says, that's a critical and necessary equipment function designed for the benefit of mankind! Ok, if you say so...

It's Alive!


Next we move to the main cavity installation where a brass standoff has been mounted to act as a common ground point. With this method all of the subsections can be removed more easily. That includes the volume/tone circuitry which will otherwise be hardwired at the pickup selector switch and bridge/trem as in normal practice.

See pic with distortion and vol/tone sections:





All for now and the snow is melting, huzzah!
Cheers,
Dennis

Retro-Zed

And on we go...

The clear plastic plate supporting the ribbon connector/Gk p/u cable and plug is finally mounted in the body cavity. It seems like overkill to mount such a large piece of plastic for this purpose but it tucks in nicely and is quite stable.

See pic:


Next a little detail and trivia on the distortion circuit. It's an off-the-shelf unit and originally had the level control pot attached to the board. The pot was removed and  a circuit board connector installed, sourced from a GR-50 that I've begun to scavenge for parts. It was toast, not worth repairing and was a slow tracker. A cable/plug also scavenged from the GR will be attached to the new distortion level pot. The connector, installed with the help of a pin vice facilitates the removal of the board. It may be replaced later with a MXR Distortion+ circuit, my favourite fuzz. Handy to have options.

See pic:


And back to the GK-2A.
A wire attached to the +7volt rail on the board will feed the front mounted red led. After scraping off the coating on the trace and buffing the copper, the wire is soldered directly to the trace near electrolytic capacitor C12. Not a great solution but seemed the best choice. The synth level pot and toggle both have approx. 5 volts riding on them and would be tidier but connection at that point would drag the synth/vol. send voltage too low. Too bad but it is what it is, so we move on.

See pic:


Lastly, a board trace connection of this type needs to be stressless and stable and a small slot was filed into the underlying plastic frame-bottom to provide an exit path that also applies a little compression on the wire to assist in stabilizing the board trace connection. In actuality that connection is quite strong but one of my least favourite jobs is to replace a broken trace, bla!

See pic:


We're getting there friends and the Spring Peepers (frogs) have begun their chorus, an early Spring, oh Ya!
Cheers,
Dennis

Retro-Zed

To improve the battery clip mounting method a small piece of ebony was cut to size and drilled out for attachment to the cavity wall. The clips hold is improved and the orientation of the battery is maintained, important for fit in relation to other components.

With clip mounted securely we move onto completion of some inter wiring details, three grounds tied to a common point (removable), send and return signal to/from the distortion board, distortion level pot to dist. board, one led feed to screw terminals, ground jumper at screw terminal and battery connector positive to dist. board and negative to the ring contact on the guitar output 1/4 jack.



It's fortunate that the original G707 was factory fitted with a TRS (stereo) jack and the ring contact unused. This helps maintain my goal of "as original as possible", otherwise a replacement would have been installed. And it's a handy way to provide battery power switching

A bit of testing follows with a 1khz tone injected into cable end that will be connected to the pickup selector toggle and the output scoped at the TRS output jack. The software generated tone from my ancient tablet is a poor signwave but it'll do for this.



And finally the same test point monitored with the distortion board switched into the circuit, maximum distortion selected (is there any other way?...to each his own). Please note, there's a 1/4 inch plug inserted into the output jack to provide power to the dist. board.



Next time I hope to finally mount the GK-2A board, it's ready to go with led feed line and common ground wire attached. I was also thinking of trying to inject a signal into the hex pickup by driving another pickup to produce a toned magnetic field, not sure how well that would work or relevant it would be but it would be nice to be able to test the GK without having to mount the neck and strings. If anyone's tried this, I'd appreciate your thoughts. Might have to take that one to Dr. Frankenstein's lab.

Cheers,
Dennis


gumtown

Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

Retro-Zed

Thank you Gumtown, retirement rocks and there's now time for details. And Lurker no more!

Today a little prelim. work necessary for the overall assembly, with luck happening tomorrow. This part took longer to produce than expected but doesn't it always? An adapter connection is necessary from the GK-2A socket to a chassis mount 13 pin socket.

Important: the chassis connector used here is a standard 13 pin din and unsuitable for the Roland 13 pin cable connections. Roland employs a different grounding method than the standard din (please see Gumbo's replay further up the chain) and the shield ground being the only ground on the guitar output connector and cable is critical for operation. It was best to ground the connector case as well as its tab. It'll work in a pinch for testing now while the correct connector wings it's way here from the land of OZ.

Here's the source used (thanks again Chrish):  https://www.vguitarforums.com/smf/index.php?topic=8888.0

And here's a pic of the adapter, let's call this one "new school meets old school".


A way to keep things flexible yet under control. Been a long, long time since doing anything like this. Heck, if it was good enough for our grandfathers...
Stay tuned
Cheers,
Dennis

Retro-Zed

And on we go...
Bringing various elements together today starting with mounting the bridge pickup and frame. First the led feeds were cut to a suitable length, the ends tinned and attached to the screw terminals. Seems to fit decently, love that test lead wire. The pickup is then mounted into the frame and attached to the G707 body. After that the bridge/trem/hex is mounted with the ribbon cable fed through the opening to the back cavity.

See pic


Turning this venerable old gal over, the clear plastic ribbon connector plate is remounted to the cavity sidewall and the ribbon cable's contact patch inserted into the connector. Gotta treat these ribbon cables gently but they achieve an excellent contact.

See pic.


Next the pushbuttons/rotary encoders, synth level pot and toggle switch are mounted to the body and the GK-2A (on its plastic base, 15mm standoffs attached) is fitted into place and the red led feed line is attached to the screw terminal. The cable from the board to the toggle switch could have been longer and fed underneath, ah well there's enough stuff under that board as it is.

See Pic.


And the opposite view.


Lastly the 13 pin adapter is plugged into the GK and fed to the back of the cavity and GK guitar input mounted. Not sure about the cable lacing whether it looks cool or is rather hokey but it certainly does the job.

See pic.


End view.


There appears to be ample space for the cabling and connectors once the back plate is mounted. Hey maybe one could install a Mr. Fusion, seen one on some movie...

Next a major test to see if anything's gone haywire while installing, there's gotta be something, the universe pretty much demands it.
Cheers,
Dennis

Retro-Zed

And finally back at er' again..

And yes the universe decided to have its due. The backplate was attached and the guitar strung with a cheap set for testing, plugged the 13 pin cable into a GI-10 and fired it up. Everything worked fine except there was absolutely no output from the hex pickup. Tore it all down and found that some of the copper traces on the flex were cracked. Probably age and handling during the rebuild, whatever it sure sucked, go figgur'.

Ok a little trace fixing time, my favourite. As I didn't want to shorten the flex the copper breaks were jumped resulting in a more delicate bond that had to be stabilized to make the pickup useful. Some small pieces of plastic were affixed to the area of the new joins with poster tape, then wrapped in clear. Sure wish that ribbon flex was available, a much nicer connection could be made.

Since the GK circuits had to be removed for the fix, a photo of the pushbutton/rotary encoders, synth level pot and toggle mounted to the body was taken.
See pic.


And finally the backplate is positioned again and the cabling and jacks mounted to it have lots of room.
See pic.


Fired up into the GI-10 and a little pushbutton/program change scrolling function testing is performed and works great.
See pic.


The G707 still needs to be restrung so the test phase can continue, unfortunately no time left for it today. Plus the bridge and neck pickups still need to be wired to the selector toggle but that can't happen until the Gk function is confirmed good. That would certainly be asking for it.
Cheers,

Retro-Zed

And forever forward..

First a picture.


Restrung the G707, tuned, adjusted hex pickup height, jacked er' into the GI-10, fired it up and as Magnus Pyke used to say, "Bejoing!".

First things first, red power indicator:on, pushbutton/program scroll function:good. Gi-10 parameter 7, pickup sensitivity next. The 6 "channels" had been maxed previously using a Roland ready strat (and found the up/down buttons on the strat intermittent..so it goes). All pickups received and then adjusted down with the 10's value controls as needed for each pickup. All good. Switched to parameter 9, tuning. Each string tunes well with the GI-10.

See pic, I wasn't coordinated enough at plucking and snapping to catch the far right led in parameter 7 for strings 4 and 6 but they're all good and here's some pictures.


Only the synth volume control remains untested until it's all connected to a sound module but it measures good at the 13 pin output socket. It'll be connected shortly to my fancy sound module in a PMA-5 if you can believe it. Or if someone takes pity and sends me a spare JV-1080? Ah well.

And the correct Roland compatible 13 pin socket sent from OZ (thanks Peter) should be installed in the near future as the package cleared Canadian Customs earlier today. A few more posts yet to come but we're getting close to a wrap on this project.
Cheers,
Dennis

gumtown

Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

Retro-Zed

#22
My pleasure gumtown, it's a blast and I hope some it may be useful to others planning their own projects in the future. This forum is an excellent source of specialized information with a real community spirit. I love it and appreciate the help other members have kindly given to me.

Gotta warm up that old PMA-5 and get crankin'.
Cheers,
Dennis

admin

Quote
Gotta warm up that old PMA-5 and get crankin'.
Cheers,

I gotta find my PMA-5 as well , battery power GM /Sound Canvas module is handy for busking with MIDI guitars

https://www.yumpu.com/en/document/read/10886372/roland-resource-book
https://www.squest.com/Products/MidiQuest12/Instruments/RolandPMA-5

Retro-Zed

That would definitely wow 'em out there. I find the PMA-5 handy for testing, small, portable, prop it up anywhere, no wall wart needed and a good selection of instruments that also sound decent. Roland knew what they were doing and still do. But I miss my GR-50, looks like it might be time to upgrade to the 90's.
Cheers,
Dennis