DIY 13 pin GK to jack converter

Started by gumtown, June 15, 2016, 08:48:18 PM

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gumtown

Just purchased a new bass yesterday and don't have a spare GK-3B to install for it yet,
.... and I want to try the bass out at a gig this weekend,
so I made this adapter to plug into my GR-55, letting me use a regular jack input and also let me use the GR-55 as a mono synth/modeller.
This should work fine for guitar too..

The 6 DIP switches let me choose which GK string input the normal pickup is routed to.
It would be cool if the DIP switches could be replaced with 6 bandpass filters.





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

sixeight

Cool. Nice work.

Do you get a good sound on the GK patches without the filter? I guess playing PCM sounds on the GR55 will be tricky...

gumbo

LOVE IT, Colin!!   ;D

I've got a bunch of breadboards glued together to get a similar background for playing with 13-pin ideas and came close to that one a while back but went off at a tangent (again..  !)  ...sigh!   ::)

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

gumtown

#3
After a bit of tweaking to get more gain, it is working quite well.
I need to get a better opamp, only had a LM301 in the parts bin on hand, the external frequency compensation capacitor is killing the top end frequency response at the trade off for no hiss.

PCM and modelling tones work great, but very mono. The more DIP switch closed, the louder it gets.
I was surprised that any one GK string input is very wide range, I thought there would have been band-pass filtering in the GR-55, but it appears not.
I also noticed that frequency response vastly affects the PCM triggering, if the signal is too bright tone, it kills the PCM triggering to the point of false triggering,
perhaps if someone is having triggering problems with their GK setup, some tone caps added to each 6 GK inputs might help.
Also had to add a resistor divider to reduce the opamp output level to the GK inputs to even out the "normal pickup vs modelling/PCM" levels.

EDIT NOTE: the schematic drawing has now been updated with the tweaks added.
Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

gumbo

"I also noticed that frequency response vastly affects the PCM triggering, if the signal is too bright tone, it kills the PCM triggering to the point of false triggering,
perhaps if someone is having triggering problems with their GK setup, some tone caps added to each 6 GK inputs might help."

Hmmm...Now that IS interesting...might have to dig out the breadboards again...  ;)

Please let us know how it all goes..

Cheers,
Peter



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

mbenigni

Cool project!

Quote from: gumtown on June 16, 2016, 04:13:53 AM
I was surprised that any one GK string input is very wide range, I thought there would have been band-pass filtering in the GR-55, but it appears not.
I also noticed that frequency response vastly affects the PCM triggering, if the signal is too bright tone, it kills the PCM triggering to the point of false triggering,
perhaps if someone is having triggering problems with their GK setup, some tone caps added to each 6 GK inputs might help.

This was a massive oversight on Roland's part IMO.  What you recommend here makes a lot of sense.  It would be ideal if there were somewhere in the circuit where you could apply the filtering to affect the audio-to-MIDI/PCM path but not the COSM instrument modeling, etc. path, but I imagine that's unlikely.  Next best compromise would be to make this filtering switchable, so you could turn it on as needed for specific patches (e.g. PCM pianos!)  MIDI-switchable would be even better!

Elantric

#6
Quote"I also noticed that frequency response vastly affects the PCM triggering, if the signal is too bright tone, it kills the PCM triggering to the point of false triggering,
perhaps if someone is having triggering problems with their GK setup, some tone caps added to each 6 GK inputs might help."

QuoteThis was a massive oversight on Roland's part IMO.  What you recommend here makes a lot of sense.  It would be ideal if there were somewhere in the circuit where you could apply the filtering to affect the audio-to-MIDI/PCM path but not the COSM instrument modeling, etc. path, but I imagine that's unlikely.  Next best compromise would be to make this filtering switchable, so you could turn it on as needed for specific patches (e.g. PCM pianos!)  MIDI-switchable would be even better!

I have experienced the same phenomena,
A 6 channel EQ (one per string) with MIDI control could be implemented, for when you want full range for COSM modeling, but require the "Band Pass Filter " for improved Guitar to PCM tracking on the fly


like this old Akai PEQ-6 channel MIDI Rack EQ
   Akai PEQ-6



Add a pair of DB25 connectors  to a future US -20 /fanout box clone for interfacing separate string external "Side chain" signal processors before the GK 13 pin signal can hit the input on the VG_99 / GR-55/GP-10 -  using off the shelf Hosa Tascam DA-88 DB25 to TRS breakout cables

explains why flat wound strings track better for Guitar to PCM or Guitar to MIDI with fewer glitches.

like - D'Addario ECG23 Chromes Flatwound Extra Light Electric Strings
http://www.sweetwater.com/store/detail/ECG23


HoosierMan

Quoteand also let me use the GR-55 as a mono synth/modeller...

Musically, how are you making use of 1 string as mono synth during your playing? 

gumtown

#8
Quote from: chartzog on June 16, 2016, 12:13:16 PM
Musically, how are you making use of 1 string as mono synth during your playing?
I'm using it for a bass,
but it will still affect some songs which I play when 2 notes or chords are required, so the GK-3B equipped bass (Fender Am jazz deluxe 5) will be coming along to the next gig as well.
Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

gumtown

#9
Another item of interest I might note is the DIN 13 plugs,
I wired my own plug using 24 wire + Earth cable I cut from an old D25 parallel printer cable.
EDIT NOTE: if wiring your own cable, only connect the screen/shield wire at one end only, and use the remaining unused conductors for the ground wiring, or else you project audio will be as noisy as...

The DIN 13 plug back shell is in 2 pieces, the bottom half is where the shield solders onto, but in the GK 13 pin socket of the GR-55, and presumably other GK 13 equipment, the outer shell/shield connection is on the top half of the plug's outer shell.
My project was plagued with bad connections as I wiggled the GK plug, then I realised that the floating top half of the outer shell is where the ground connection is made, so I fixed that by soldering the two halves of the plug outer shell together.... solved !!, no more problems..  ;)


As you see from the picture, the bottom half shell is where the ground connection and cable anchor is made, but the GK socket ground connection uses the top half only - hence the need to solder both halves together for good connectivity..

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

gumbo

Yep...that was something I worked out a long time ago, but obviously forgot to pass on.. ::)

...when I have built installations that include the plug, I solder the screen directly to the 'other side' of the plug shell...

..that way the lead will work in a Roland jack.....

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

mbenigni

Quote from: Elantric on June 16, 2016, 06:47:56 AM
A 6 channel EQ (one per string) with MIDI control could be implemented, for when you want full range for COSM modeling, but require the "Band Pass Filter " for improved Guitar to PCM tracking on the fly

like this old Akai PEQ-6 channel MIDI Rack EQ

That is a pretty incredible piece of hardware - I've never seen one before!  I wonder if there's some 21st century equivalent, roughly the size of your thumbnail.  :)

HoosierMan

Do you have a photo of the inside to show how you wired it?

mmmmgtr

Quote from: mbenigni on June 16, 2016, 06:15:01 AM
Next best compromise would be to make this filtering switchable, so you could turn it on as needed for specific patches (e.g. PCM pianos!)

We need a GKFX-31 - a GKFX-21 with added foot switchable low pass filters.  Maybe a pot or switch to select target frequency.

::)

gumbo

Quote from: chartzog on June 17, 2016, 08:10:41 AM
Do you have a photo of the inside to show how you wired it?

The first post includes a wiring diagram...

HTH

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

GuitarBuilder

This thread is taking me back to the late 70s!  When the ARP Avatar first came out, it attempted to do what is suggested here with 6 filters to "isolate" the individual guitar strings.  It met with only partial success.  I built my own Avatar clone in 1978 and discovered massive string crosstalk, no matter what bandpass filter design was used.  Roland quickly realized that the isolation had to be at the pickup and the hex pickup concept was introduced.  This discussion is following that exact same line of thinking and I'll bet the conclusion will be the same: nothing beats the divided pickup for guitar synth applications.

The culprit is the design of the guitar itself.  There is massive frequency overlap between strings:



Unless you're willing to play cowboy chords only, filtering will not get you clean enough signals to isolate the strings.  This is also why higher harmonics wreak havoc in the system.  You can still get nice effects, like the Avatar or hex fuzz pedals, etc.
"There's no-one left alive, it must be a draw"  Peter Gabriel 1973

aliensporebomb

Well the Avatar did have a hex pickup as well but I've only ever seen one of the Avatar units and it didn't have the pickup - someone lost it.  So I never go to try one out. 

I listened to the late Ned Liben's demo record over and over though back in the day.
My music projects online at http://www.aliensporebomb.com/

GK Devices:  Roland VG-99, Boss GP-10, Boss SY-1000.

whippinpost91850

ASB , I have a case that looks just like that that I keep my GR55 in :)

HoosierMan

QuoteI need to get a better opamp, only had a LM301 in the parts bin on hand

Gumtown:

Do you have a recommendation and a source for a better opamp than the LM301? 

Also, there is a section in your schematic that has +7 and -7 with a 33uF cap in between.  Does this indicate that the 33uF cap is added between pins 12 and 13 of the GK plug?

vanceg

Quote from: gumbo on June 16, 2016, 06:06:18 AM
"I also noticed that frequency response vastly affects the PCM triggering, if the signal is too bright tone, it kills the PCM triggering to the point of false triggering,
perhaps if someone is having triggering problems with their GK setup, some tone caps added to each 6 GK inputs might help."

Hmmm...Now that IS interesting...might have to dig out the breadboards again...  ;)

Please let us know how it all goes..

Cheers,
Peter


In using the VG-99 with the VO96 sustainer/harmonic controller, I have noticed a similar situation.  The VO96 is capable of enhancing the upper harmonics and diminishing the lower harmonics of any note played.  If I turn the VO96 system all the way to this extreme, the PCM sounds will completely stop triggering and the pitch tracking goes totally out the window. This includes the Harmonizer portion of the VG-99 as well as effects which track pitch like the Intelligent Ring Modulator.  They all fail when the VO96 system is set to emphasize higher harmonics.  I'm hoping to start trying some band pass filters on the outputs of the CycFi pickups I'm using as a GK-3 replacement now and see if I can enhance the VG-99's sound some by doing some creative limiting of the levels of some harmonics.

GuitarBuilder

#20
Quote from: chartzog on June 18, 2016, 03:30:25 PM
Gumtown:

Do you have a recommendation and a source for a better opamp than the LM301? 

Also, there is a section in your schematic that has +7 and -7 with a 33uF cap in between.  Does this indicate that the 33uF cap is added between pins 12 and 13 of the GK plug?

The Linear Technology LT1115 is the best low noise audio op amp today.  The old standby is Texas Instruments' TL072A.

I would not recommend a capacitor across the positive and negative supply as indicated in the schematic.  A better deign is two capacitors, from each supply to ground.

"There's no-one left alive, it must be a draw"  Peter Gabriel 1973

gumtown

Quote from: GuitarBuilder on June 19, 2016, 09:00:45 AM
The Linear Technology LT1115 is the best low noise audio op amp today.  The old standby is Texas Instruments' TL072A.

I would not recommend a capacitor across the positive and negative supply as indicated in the schematic.  A better deign is two capacitors, from each supply to ground.
That is correct, the TL072 is my first recommendation, as it is easily available, and the 33uF cap is too big also, two 10uF caps  (+ to ground, - to ground) would be better.
I have yet to make more adjustments and fine tuning, after trying it at a gig the other night, the schematic will get updated too, it should have an input low-pass filter cap to block any induced R.F. interference.
Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

vtgearhead

Quote from: aliensporebomb on June 18, 2016, 03:11:06 PM
Well the Avatar did have a hex pickup as well but I've only ever seen one of the Avatar units and it didn't have the pickup - someone lost it 

A guitar player I knew in the 70s had an Avatar w/ hex pickup.  It had little mu-Metal rings around each string to keep crosstalk down.  Very effective, but probably expensive to build.

gumtown

#23
Here is the latest updated schematic, using the TL072 opamp.
This works great..
I have observed that the DIP switch will generally select the lowest range/note, and from that string, you will get around a 26~28 note range upwards, being the band-pass range for the selected string.
So if I select string 2 (E) it will give me a range of (-)D to (+2)B
Select more GK strings in parallel (with the DIP switches) and the GK tone increases about +3dB each extra string.
It works well on both PCM synth and Modelling. But remember it is only monophonic, play more than on concurrent note and it all turns to custard (PCM tones).

Also noticed the 13 pin DIN solder plugs will fit into my GR-55 GK socket upside-down too, need to watch out for that, or it doesn't work.
Something to do with not enough indent on the plug.




So why do this?
Because I can,
it is a handy box for using with a non GK fitted Bass.

QuoteDo you have a photo of the inside to show how you wired it?
Not very elegant, but it is practical.
stripboard (veroboard) with a few components, a lightswitch mounting block for a box with a cutout bit of plastic cover, a bit of soft foam to hold the board up, and a GK cable made from an off cut from a printer cable and a 13 pin DIN plug, and finally a jack socket for the guitar in.




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

gumbo

Love it!
..would be interesting to hear it too, if you ever get hold of a postable sound file.. ;D

The non-locking 13-pin jackplugs can have that 'reversible' function..  it's sometimes a pain.. 
...I guess that's yet another thing I should have posted about...dang!

Lemme know if you need me to post you a couple of locking ones for MK II... ;)

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