FTP - DIY adapter to use GK 13 Pin Guitars with Tripleplay

Started by utensil, April 21, 2013, 01:29:52 PM

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gumbo

"Aha...So a six channel pot would be great  ;D or a six channel volume chip controlled by one DC level (one knob), or a six-channel chip controlled by a tiny PIC. Stop! Now we're getting into work mode again :P.



...just keep taking the tablets, ok?    :-*
Read slower!!!   ....I'm typing as fast as I can...

CodeSmart

Quote from: gumbo on September 28, 2015, 04:52:17 PM
...just keep taking the tablets, ok?    :-*
You're right. Elantric can do the PCB tonight, I should really get some sleep now.
But I got more gear than I need...and I like it!

Elantric


Piplodocus

Great, thanks for the circuit diagram, especially with the 13-pin pinout. It'll be a massive help once I get that one going.

I gather the 9V is needed to power some of the Graphtech Hexaphonic then, even though there's already a 9V in mine for the Acoustiphonic bit?

On a related note I've already built an FTP into my Parker MIDI fly. It works, but it's a different kettle of fish as there's no 13-pin in it anywhere and it's all wired off the piezo buffer. It's currently a bit jumpy and has a habit of playing a note up sometimes or occasionally jumping an octave (even though the guitar's in tune). I used 50k pots though so I'm wondering if I use a 10k if the extra loading might help it a bit, although my gut instinct is it'd roll off the fundamental more if there's a later in-line decoupling cap (would form a HPF - but this is guess work and anything could be happening tbh). Anyone have a particular reasoning for 10k, or did it just seem a nice not-too-high, not too-low value? It might be that I have bad MIDI guitar technique though as I haven't played much MIDI guitar before, so maybe I'm being heavy handed, even though I'm trying not to be.

Elantric

#104
QuoteI gather the 9V is needed to power some of the Graphtech Hexaphonic then, even though there's already a 9V in mine for the Acoustiphonic bit?

Actually most GK13 pin preamps require DC power from the Host GK processor ( GR-55, GP-10, VG-99, etc) and in this setup feeding the FTP Controller's hex Mag Input connection- that  power is missing

On the GK13 pin connection:
pin #12  must have +7VDC
pin #13  must have -7VDC

this is true for Roland , Axon, Yamaha, Godin /RMC Piezo, Carvin Ghost Piezos = all are powered from the GK13 pin cable

Internal Batteries on those instruments are for the separate 1/4" mono Piezo Output   

Elantric

#105
10K Pot is suitable because the hex preamp Opamp buffer output signal fed to the GK-13 Instrument Output on GK-2A, GK-3, RMC , Ghost, etc, -  is typically 100 ohms (or less) impedance 



more here:

https://www.vguitarforums.com/smf/index.php?topic=73.0

https://www.vguitarforums.com/smf/index.php?topic=2500.0

QuoteIt's currently a bit jumpy and has a habit of playing a note up sometimes or occasionally jumping an octave (even though the guitar's in tune).

Sounds like you may be over driving the FTP preamp with too hot signal

be sure to check and reset the FTP String gain sensitivity in the FTP Control Panel 

Piplodocus

Cool. Cheers. :)

I'm not sure if swapping from 50k to 10k will make much difference in the one I already tried. I might give it a go though. I figure if I get the new one working far better with this 13-pin adapter I might try adding some caps to the other one I've made since there's no filtering before the FTP in that, just straight off a unity gain piezo buffer, whereas I believe a standard 13-pin out is filtered to some extent?

Any idea what the Graphtech's "Traktion" switch does other than Graphtech's rather non-technical "make the Roland or Axon systems track better" depending on switch position?

Piplodocus

#107
BTW, I checked the FTP levels and it didn't make much difference if I set the trim pots to give anywhere loud being from quite low up to the hot. Hence why I might need some caps for filtering since that's a bit of a different beast.  :-\

Thanks for that GK schematic too. I'll look at the cap/resitor values and see if I can derive some useful filtering ideas at some point when I get chance.

Elantric

QuoteAny idea what the Graphtech's "Traktion" switch does other than Graphtech's rather non-technical "make the Roland or Axon systems track better" depending on switch position?

I understand its Gain Boost - use the position that works best for you.

utensil

#109
FWIW, when I get a chance to redo mine I was planning on using these http://www.ebay.com/itm/201403106341?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

as they have the added advantage of being hand adjustable.  If planning on using it consistently with the same guitar then you wouldn't have to adjust it much as once set it's fine but I've found that the outputs are slightly different between my 3 Graphtech hexpanded guitars (2 even have the exact same bridge). The balance between the 6 strings is also variable hence needing separate adjustments for each string. On one of my guitars, I barely need to trim the high e but on others I need to set the trim pot about half way. In Nutshell , each guitar needs a distinct unique setting that remains consistent for that guitar.

Possibly would be cool to use a teensy, digital pots and be able to save settings to "presets" selectable with a rotary knob or something.

Coincidently just came across a tutorial on using a 6 channel digital pot (http://datasheet.octopart.com/AD5206BRU10-Analog-Devices-datasheet-8405.pdf)

with arduino based boards.  https://www.arduino.cc/en/Tutorial/DigitalPotControl





Elantric

The trick would be have a stored memory setting  with MIDI control

- or even be able to change the gain on the fly

Why stop at feeding the FTP ?

Could feed Antares ATG DSP for a "RackVax" type experience


or install a Gk-13 Out put too  - and be able to dynamically change the gain for GR-300 vs Guitar to MIDI  - or add an LFO with waveform selection on one or two strings 

But this gets into Spicetone 6APPEAL territory


CodeSmart

#111
Quote from: utensil on September 28, 2015, 07:29:24 PM
Coincidently just came across a tutorial on using a 6 channel digital pot (http://datasheet.octopart.com/AD5206BRU10-Analog-Devices-datasheet-8405.pdf)

A very poor choice. The pot suggested cannot run on +/- 7 Volt. Only +/- 2.7V. That voltage swing will clip you GK signal. Need at least headroom for +/- 5V with GK. I've been down this road with my GKMX-33. Really recommend using the digital pot suggested by Elantric.

Note also: placing a any computer near these lines and especially if powered from the same power source may introduce noise on the GK signal. GK is very sensitive on voltage fluctuations of the +/-7V, any change is audible.

Another non-computerized way is using a rotary switch on the outside and internally there's 2, 3 or 4 banks/sets of 6x trimmer pots. Simple 40XX CMOS switches connects one of the trim pot banks center pins to the hex output.
But I got more gear than I need...and I like it!

utensil

Quote from: CodeSmart on September 28, 2015, 10:34:44 PM
A very poor choice. The pot suggested cannot run on +/- 7 Volt. Only +/- 2.7V. That voltage swing will clip you GK signal. Need at least headroom for +/- 5V with GK. I've been down this road with my GKMX-33. Really recommend using the digital pot suggested by Elantric.

Note also: placing a any computer near these lines and especially if powered from the same power source may introduce noise on the GK signal. GK is very sensitive on voltage fluctuations of the +/-7V, any change is audible.

Another non-computerized way is using a rotary switch on the outside and internally there's 2, 3 or 4 banks/sets of 6x trimmer pots. Simple 40XX CMOS switches connects one of the trim pot banks center pins to the hex output.

Good to know. I had assumed that the wipers and pot pins were isolated from the rest of the circuit, i.e I thought it works just like an analog pot but instead of mechanically turning the pot it could be digitally controlled.

neshel

I'm not understanding why you want to do this.....just so everything on your guitar is wireless through the TP?.....

susbemol

Quote from: Elantric on November 26, 2014, 04:05:22 PM
For those of us with multiple 13 pin guitars - its more attractive to place the FTP Controller down on the floor, and use a US-20 A/B/Y 13 selector for control

This is exactly what I would like to achieve, only using one of @CodeSmart's GKPX-14 boxes instead of a US-20. I will probably be giving this a go myself.

To be honest, I am quite surprised that nobody has produced a product for this purpose. The mod described here sounds good but obviously not for everyone.

susbemol

Could I just ask you clever people to clarify whether this mod would be wired exactly the same as previously described here if I'd like to use it with a internal GK3 kit and GKPX-14 box (similar to a US-20 in functionality)? I assume that I wouldn't need to wire a battery to mine but I would love to hear your comments.

CodeSmart

#116
Quote from: susbemol on January 01, 2016, 05:27:29 PM
I'd like to use it with a internal GK3 kit and GKPX-14 box (similar to a US-20 in functionality)? I assume that I wouldn't need to wire a battery to mine but I would love to hear your comments.

If you connect GKA to Roland synth unit it will provide power to the GK equipped guitar and the GKPX-14 unit itself. However on GKB there will be no +7 and -7 volts available. On GKB, GKC and GKD the power terminals (pin 12, 13) are connected via a a large resistor to ground.

If GKA is not connected to a synth unit, instead consider getting two pcs cheap stepwise adjustable DC wall units 5,7,9,12V and a 13-pin male plug connector to provide +/-7V power to the GKA connector of the GKPX-14.

The outlined FTP mod with pots and FTP etc could be implemented as described earlier on any of the GKA-GKD outputs.

Batteries sucks...
But I got more gear than I need...and I like it!

susbemol

That's great, thanks for confirming that. I plan on using the GKA output with a GP-10, GKB with a GI-20 and GKC with the TriplePlay so no need for the battery which is excellent news.

CodeSmart

Quote from: susbemol on January 02, 2016, 02:05:42 PM
That's great, thanks for confirming that. I plan on using the GKA output with a GP-10, GKB with a GI-20 and GKC with the TriplePlay so no need for the battery which is excellent news.
You'll be doing just fine  ;D
But I got more gear than I need...and I like it!

susbemol

By the way, I haven't seen any values suggested for the coupling capacitors... have I missed that?

CodeSmart

Quote from: susbemol on January 02, 2016, 04:06:51 PM
By the way, I haven't seen any values suggested for the coupling capacitors... have I missed that?
I wonder if they are needed at all....the GK-3 will swing the hex voltages around +/- 0V, with virtually no DC offset. If,...of some reason needed, probably 470nF -> 4.7uF (plastic film or bipolar electrolytic cap) is ok enough for guitar frequencies when input impedance > 50K ohms.
But I got more gear than I need...and I like it!

gitarrensalat

Hi,

I just ordered the FTP, can't wait to test it with my Strat.

I also would like to connect my Godin Multiac Nylon via 13 pin, but don't want to take the FTP apart. I'm  looking for a non-destructive method.

My idea was to use 6 coils to feed the FTP hex pickup inductively. Layout like a pickup, but sending instead of receiving. Will this fail due to crosstalk? If not, what coil would be the best?

I'm skilled to build such a thing, but I don't have any experience with electromagnetic stuff. I will probably get uncontrolled oscillations with a regular OpAmp, when I try to drive an inductive load like this. Is there a simple one chip solution for this?

Chris

utensil

While I don't know if that would work but if you get this connector

http://www.ebay.com/itm/Micro-JST-1-5-ZH-8-Pin-Connector-Plug-with-Wire-x-10-sets-/111380528002?hash=item19eecbfb82

And make your adapter with it , you can easily disconnect the triple magnetic pickup and plug this is by only removing 3 screws . It would be completely reversible (non destructive) though technically voiding your warranty. If something goes wrong with the adapter you can abandon it and go back to the original pickup.


gitarrensalat

Thank you for the link! Maybe I will follow your proposal, when I'm confident that I want to keep the FTP.

I want to avoid breaking any warranty seal. I did this once and was regretting it afterwards.

Another point is: I could leave the hex pickup attached and quickly switch between my inductive adapter and the Strat.

drbill

GP-10, KPA
BM i2.13p, '76 Les Paul Deluxe w/GK-3, MiM RRS, Ibanez RG420GK, Charvel strat copy w/GK-2a, FTP