GK install with Variax 500 brains

Started by erikbojerik, June 22, 2014, 09:19:23 PM

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erikbojerik

So I have all the boards, knobs and switches laid out for installing a GK-3 internal kit and a Variax 500 in the same cavity (custom guitar).  As I see it my options for signal routing are:

#1 solder the Variax output to the input for magnetic pickups on the GK board, but I am not sure what will happen since the impedance will not be that of a magnetic pickup.  But if this works then I can power the Variax from batteries and send all signals out on the 13 pin cable.  Right?

#2 keep the signals separate and gang the 2 cables (13 pin and TRS) together.

Am I right that with #1 I'll need a dummy TRS plug to inser into the Vax 1/4" jack to switch in the battery for the Variax?  Or install a separate switch?

I searched and found a bit of discussion but no one here who actually pulled this off.  What might I be missing?


Elantric


erikbojerik

#2
Yep thanks Elantric, I had already found that and read through it but was left guessing as to how he actually soldered up the signal leads.  I did notice that as the build went on, the number of mini-switches went from 4 to 5 to 6.

This morning now I am thinking about bringing in 9V phantom power for the Variax on pin 9 and either building a breakout box or adding a DC-in jack to my VG-99 to connect a 9V wall wart...anyone tried this?

Edit: I just found out the Variax board needs +7V (it will obviously still run with +9V), any chance pin 12 provides enough current to drive both the GK and the Variax boards?  Or maybe there is somewhere inside the VG-99 I can find +7V with enough current?

Edit 2: the Variax draws ~350 mA of +7V, for anyone interested in the Variax service manual: http://www.epanorama.net/sff/Audio/Musical/Products/Line_6/Variax%20Service%20Manual.pdf

erikbojerik

OK so my experiment on this has finally drawn to a conclusion, and I've decided to go with Option #1 above and use an Energizer Ultimate Lithium 9V.  This works great, very low noise levels and good signal from both the GK and the Variax board.

I tried repurposing the unused pin 9 on the 13-pin cable to power the Variax motherboard; I was able to find clean sources of +7V and +9V inside the VG-99 and I jumpered them both to pin 9 on the VG-99's GK jack (one at a time), and they both worked in the sense that I got sound out and all the functions of the GK pickup and VG-99 continued to work fine on the single 13-pin cable.  But there was a whole lot of high-freq noise on the GK signal that I could not filter out in the usual ways (Noise Gate etc); I connected the +7V and +9V it to various places on the Variax board all to no avail, so the noise must be coming from the pin 9 lead inside the cable causing some interference with the GK signals that are sent to the VG-99.

The battery option was the most quiet so I am currently going with that.  But it works equally well powering the Variax board using the Variax power supply that sends +7V up a TRS cable into the Variax 1/4" jack, very low noise and good Variax signal - and also works if you use a 1/8" TRS along with the proper 1/8" to 1/4" TRS adapters.  So one could bundle a 1/8" cable along with the 13-pin cable (shielded separately) and go without a battery.  And while you're at it, you could bundle another 1/8" TRS (shielded separately) for in-ear monitors if you wanted.  Which I might, someday - and might be worth a custom cable.

Anyway, the guitar is below.  Buckeye burl on black limba (bloodwood accent between), 5-piece maple-walnut laminated neck, birdseye maple fretboard.  I sacrificed the Variax tone control (too many knobs for the space), otherwise everything works great, sounds great, plays great.