Can't find a GK-2a Schematic

Started by steadystate, November 20, 2023, 06:36:30 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

steadystate

I'm trying to find a schematic for the GK-2a that specifically shows the 7 and 8 pin connectors leading to the 13-pin jack.  I've searched the site, but every instance seems to have been removed.  Can anyone direct me to this info?  Thanks in advance.

Elantric

#1
Quote from: steadystate on November 20, 2023, 06:36:30 PMI'm trying to find a schematic for the GK-2a that specifically shows the 7 and 8 pin connectors leading to the 13-pin jack.  I've searched the site, but every instance seems to have been removed.  Can anyone direct me to this info?  Thanks in advance.





The schematic describing the pinout of the interboard connectors you seek are here


Look here
https://www.joness.com/gr300/13-pin.htm





gumbo

In case you're still trying to work out which pin goes where in a 13-pin jack when it is connected to the GK2A mainboard, the following page out of the Synth-Linx Installation Instructions PDF is attached...

NOTE:
While the connections pin-for-pin are the same GK3 vs GK2A from the actual jack pins to the mainboard circuits themselves, in reality with the original Roland jack-plus-attached-circuit-board, there ARE differences in the way that these are laid out on that little PCB.

This is principally to take into account the DIFFERENT layout in the 7 & 8 pin headers on the GK3 and GK2A mainboards themselves (Differing pinouts to the configurations of Ground circuits, as Pin 9 was NOT utilised in the GK2A 13-pin Roland jack).

In short, original ROLAND GK2A jacks WILL NOT INTERCHANGE with original ROLAND GK3 jacks, as the circuit layouts of their attached small PCBs DO DIFFER.....although the two 7 & 8 conductor connection looms between the jacks and their respective mainboards ARE IDENTICAL and CAN BE INTERCHANGED.   ;)

HTH ...PM me if this needs further explanation...

Cheers,
Peter
Read slower!!!   ....I'm typing as fast as I can...

steadystate

#3
Thanks for the replies.  I made my own 13-pin jack/pcb replacement boards using EasyEDA/JLCPCB, one version for the GK-3 and another for the GK-2a.  The boards for the GK-3 work, but the ones for the GK-2a don't.  The schematic for the GK-2a version is attached.  I apparently made an error on the pcb layout.  But it seems to match the above diagrams (but not the conductor colors on the SYNTH-LINX chart).  I think I need another pair of eyes.

steadystate

For comparison, here is the schematic for the GK-3 board I built that works.

Elantric

#5
Quote from: steadystate on November 20, 2023, 11:11:40 PMThanks for the replies.  I made my own 13-pin jack/pcb replacement boards using EasyEDA/JLCPCB, one version for the GK-3 and another for the GK-2a.  The boards for the GK-3 work, but the ones for the GK-2a don't.  The schematic for the GK-2a version is attached.  I apparently made an error on the pcb layout.  But it seems to match the above diagrams (but not the conductor colors on the SYNTH-LINX chart).  I think I need another pair of eyes.


For clarity- these 7 and 8 pin wire harness cables are only used on the "internal Kit" version, like the 1997 Fender "Roland Ready" Strat
https://support.fender.com/en-us/knowledgebase/article/KA-01602



For new installations, many here elect to use the more compact Synthlynx 13 Pin jack assemblies which mate to the internal Roland opamp GK preamp board


Contact member "Gumbo"

https://www.vguitarforums.com/smf/index.php?topic=8888.25

gumbo

Yes...that is the only place the ribbon cables are used.   

Your pinouts for the 7 & 8-pin connectors on the GK2A and GK3 (internal) mainboards are both correct, and identical to those used in the 7 & 8-pin multiplugs that I fit to the end of the 13-core screened cable that is soldered to the back of Synth-Linx Jack models designed for those particular situations.

There are MANY of those Synth-Linx Jack models in use all over the World, and they all work in the way in which they were intended..  ;)

I believe therefore that if you are sure that you have connected the conductors around the correct way in the 7 & 8-pin multiplugs, then yes, you DO have a problem with whatever is going on at the 13-pin jack end of things..I presume you have a multimeter so that you can check the continuity of all the circuits.

If that all checks out, you may have a problem with the GK2A mainboard itself...what is the known history of that?   
Is this all emanating from a home-brew External-to-Internal conversion exercise using old parts? 

Also, are you aware that the GK2A system uses a completely different system-of-operation when it comes to the operation of the "Mix" Switch....the 'unwanted' signal (GK vs Mag) is simply shunted to Ground (without the use of Pin-9)...if you are mixing-and-matching bits of hardware (LIKE THE MIX SWITCH LOOM from a GK3!), you are going to experience funny stuff...     ...just saying...

Plenty of traps for new players in (what is now) old Roland stuff.. :-X

Cheers,
Peter
Read slower!!!   ....I'm typing as fast as I can...

steadystate

Those schematics are for the little 13-pin pcb's I made, and the first thing I did was check them with a multimeter.  I'm beginning to suspect that my GK-2 preamp board is dead.  I can't think of another explanation at this point.

BTW, this isn't an external to internal conversion.  I have internal kits in all of my guitars, mainly GK-3, but a single remaining GK-2a.  The problem is that the 13-pin jacks wear out, so I made replacements.  The hard part was sourcing 13-pin jacks with the screw-mount wings on them, which I finally found.

My next project is to make my own preamp boards, considering Roland internal kits are over $400 in the US (four times the price as overseas), and Roland no longer allows overseas vendors to sell to the US.  F#CK THAT.  I can't see myself ever buying a new Roland product after that.  It's actually cheaper to make them myself.

gumbo

Quote from: steadystate on November 21, 2023, 10:21:07 AMThose schematics are for the little 13-pin pcb's I made, and the first thing I did was check them with a multimeter.  I'm beginning to suspect that my GK-2 preamp board is dead.  I can't think of another explanation at this point.

BTW, this isn't an external to internal conversion.  I have internal kits in all of my guitars, mainly GK-3, but a single remaining GK-2a.  The problem is that the 13-pin jacks wear out, so I made replacements.  The hard part was sourcing 13-pin jacks with the screw-mount wings on them, which I finally found.

My next project is to make my own preamp boards, considering Roland internal kits are over $400 in the US (four times the price as overseas), and Roland no longer allows overseas vendors to sell to the US.  F#CK THAT.  I can't see myself ever buying a new Roland product after that.  It's actually cheaper to make them myself.

No offense meant...just pointing out a few things that I have come across in almost 30 years of playing about with this stuff.

I know the original Roland jacks wear out, that's exactly why I have been making alternative assemblies for over ten years that overcome the problem.   
BTW, the 'ears' on Synth-Linx Jacks use the same mounting bolt centers and diameters as those on the original Roland jacks, and in that way, suit straight forward retrofitting as well as making for much easier fitting in completely new installations.  :)


As I said earlier, check also what is going on in the Mix Switch circuit...you could be inadvertently dumping all your signals to Ground instead of getting anything out of your 13-pin jack...find out what is happening to your Mag Pickup signal as well, that could possibly be a clue to the problem.

Check the integrity of your Ground connection to your hex pickup as well...

Again, what is the known past history of your GK2A mainboard assembly?


Yes, some Roland stuff is cheaper to make oneself, let alone the fact that some of the shortcomings of the original designs can be improved upon with a little fore-thought.....that's what I do.

But be aware that if you think you can just clone some part of a registered Roland design and get away with mass-production of your copy for retail sale, they will probably come looking for you....it's their way..

Peace,

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

steadystate

Quote from: gumbo on November 21, 2023, 01:13:58 PMNo offense meant...just pointing out a few things that I have come across in almost 30 years of playing about with this stuff.

None taken.  I appreciate the response.

Quote from: gumbo on November 21, 2023, 01:13:58 PMAs I said earlier, check also what is going on in the Mix Switch circuit...you could be inadvertently dumping all your signals to Ground instead of getting anything out of your 13-pin jack...find out what is happening to your Mag Pickup signal as well, that could possibly be a clue to the problem.

I'll check it out.  Thanks.

Quote from: gumbo on November 21, 2023, 01:13:58 PMI know the original Roland jacks wear out, that's exactly why I have been making alternative assemblies for over ten years that overcome the problem. 
BTW, the 'ears' on Synth-Linx Jacks use the same mounting bolt centers and diameters as those on the original Roland jacks, and in that way, suit straight forward retrofitting as well as making for much easier fitting in completely new installations.  :)

Interesting.  Is the Synth-Linx something that is currently available for sale?

Quote from: gumbo on November 21, 2023, 01:13:58 PMAgain, what is the known past history of your GK2A mainboard assembly?

It  came from a new internal kit.  I am the original owner.  I haven't used the guitar since the jack wore out several years ago.  When I tried my new connector...no dice.

Quote from: gumbo on November 21, 2023, 01:13:58 PMBut be aware that if you think you can just clone some part of a registered Roland design and get away with mass-production of your copy for retail sale, they will probably come looking for you....it's their way..

I'm not interested in selling anything, or stepping on anyone's toes who may be.  Everything I make is for my personal use.  I simply refuse to pay $410 for a part I can make myself for far less.  Roland's US-only price hikes along with their new overseas sales ban seal the deal.  Since every guitar I own (or will own) has an internal GK, the US price is simply not something I can afford.  One run of custom boards will set me for life.

I'm also interested in the shortcomings you mentioned.  I have sub-sonic filters in the design, but I'm curious as to other improvements that can be made.

Bluesbird

Gear: Yamaha Revstar RSS20, Squier Tele Deluxe 70s Fishman Tripleplay Controller, D'Adarrio EXL130 Strings, Novation Launchkey 49, Jam Origin Midi Guitar 2, Line 6 Helix Native, NDSP Tone King Imperial, Focusrite Saffire Pro 14, Dell Inspiron 5676, and tons of audio effect and synthesizer plug-ins.

steadystate

Quote from: Bluesbird on November 21, 2023, 03:21:02 PMOverseas sellers on Reverb often sell the kits at a cheaper price. 

https://reverb.com/item/32674207-roland-gk-kit-gt3-exp-divided-pickup-kit



That's still double the UK price.  US retailers charge $410 for the same product that goes for $109 in other countries.  I find it more than coincidental that the price hike came simultaneously with Roland's recent policy that prohibits US customers from purchasing overseas.  I've also found no other country where the kits are this expensive.  I've written Roland and asked them why this is so.  No response.  I'm highly motivated to make my own components under the circumstances.  The only part I can't make is the pickup, and I can buy one used from a cheap external kit if I ever need one.

gumbo

Yeah ...Roland does what Roland wants...

As far as Synth-Linx Jacks go, Elantric's post above

https://www.vguitarforums.com/smf/index.php?topic=36504.msg267985#msg267985

has the link to the Sub-forum where the products were launched in 2013...they have been continually produced (and the range of models vastly increased) ever since.

There are a few threads there that have talked about various applications that have been addressed over the years, and the standard range of products now are supplied to mainland USA customers via my Distributor in Arizona...custom units are supplied direct from Australia to order.

Thank for your interest - more information can be made available via email on request to:

info@synth-linx.com

Regards,
Peter
Read slower!!!   ....I'm typing as fast as I can...

steadystate

Quote from: gumbo on November 22, 2023, 12:44:12 AMYeah ...Roland does what Roland wants...

As far as Synth-Linx Jacks go, Elantric's post above

https://www.vguitarforums.com/smf/index.php?topic=36504.msg267985#msg267985

has the link to the Sub-forum where the products were launched in 2013...they have been continually produced (and the range of models vastly increased) ever since.

There are a few threads there that have talked about various applications that have been addressed over the years, and the standard range of products now are supplied to mainland USA customers via my Distributor in Arizona...custom units are supplied direct from Australia to order.

Thank for your interest - more information can be made available via email on request to:

info@synth-linx.com

Regards,
Peter

That's a great product to offer the community.  No way could Roland hassle you over it either.

I'm curious about the "shortcomings" you mentioned concerning the preamp board (or other aspects).  I'm done with the clone design of the preamp board, but I'd like to consider mods before I send it off for production.

gumbo

Thanks for your comments.

The main thing about the GK3 mainboard is the selection of Opamps..

Have a look at this from BillBax...

https://www.vguitarforums.com/smf/index.php?topic=20038.0

Some good information there.


The other thing that occurs to me regarding your original question (and pardon me if I am being basic here  ;) ) is that we haven't discussed what you are plugging this GK2A 'output' into exactly, and therefore what piece of kit is telling you that there nothing coming out...

For example, is that synth unit (?) by any chance set to 'GK3' instead of GK2A ??

That could be the cause of your problem..if it is expecting a Control Voltage down Pin-9 to tell it to make a decision about the position of the Mix Switch...

....and BTW exactly what signal is coming down Pin-8 to tell it where the GK Volume control is positioned.

Just a few thoughts before a decent breakfast here, so they may be off the Planet, but...  ;D

Cheers,
Peter
Read slower!!!   ....I'm typing as fast as I can...

steadystate

Interesting project.  He's taken it to the extreme.  Very cool.  I can totally see how an 18 volt battery supply and the other techniques used would collectively improve the specs.  But I have to wonder about the opamps alone.

He mentions the OPA2134 (not sure if he used this), but based on this...

http://nwavguy.blogspot.com/2011/08/op-amp-measurements.html

...I have a hard time believing that my old ears could hear a significant difference between it and the NJM2068 used by Roland, all other things being equal.  In any case, the NJM2068 is the best surface-mount opamp offered by the board manufacturer, so I'm stuck with it.  I'm not soldering surface-mount by hand.  Plus, I only use the GK for live performances.  SNR, distortion, etc. aren't really an issue.

My final device is the VG-99.  I've used it for many years without a problem with the GK-2a, and now it just makes a horrible noise with it, no matter the GK 2a/3 setting.  I'm pretty sure the board went bad.  All of my GK-3's still work fine.  I'm just going to build a bunch of GK-3 compatible preamp boards, use them with my homemade GK-3 connectors, and forget about the 2a entirely.  I can build more boards than I'll ever need for far less than the cost of one kit.

billbax

I have a GK2A with the opa2134 opamp replacement (mod 2004), and the 33k +10dB output mod. Both mods make a measurable improvement to GK2A audio. Today I would choose opa1656 opamp with its improved -3dB noise-floor. https://www.ti.com/product/OPA1656