I’m in the process of building a GK-3 breakout cable.
I’m posting this to share ideas with others that might be interested in building their own.
I do NOT intend to sell these so please don’t ask.
I am trying to build the best possible cable for studio use, so top notch materials and each channel will have it’s own shield for optimal channel separation.
So lets start.
The cable I choose was Mogami w2368 and some heat shrink.
Good start ElectroFuzz.
I am up for helping anyone build a breakout cable, though soldering an in-line 13-pin socket requires advanced construction and cable management skills.
I would suggest DIY enthusiasts go with a small diecast box, a 13-pin panel mount socket for GK IN, and a d-sub 9-way cable for strings out. A d-sub is easy to solder and available cheaply. Finally, a +7/-7 VDC supply is needed for GK3. A v-guitar unit power supply is the obvious choice, though a dual-battery 9V +/- will do. A second 13-pin panel socket for v-guitar/GK3 power is an option.
Mission creep…arghh
It’s starting to sound like minimum breakout box:( A better choice is to get a well-researched and proven separate strings breakout cable at £90.00GBP / $117.00USD. The next choice is a minimum GKP-1 breakout box priced £160.00GBP / $207.00USD. As already mentioned, if anyone needs help on a DIY breakout cable or box, please feel free to ask. Thanks, Bill
Hi anjo,
Here’s a basic dual battery +/-9VDC supply for GK3. I recommend adding two LEDs for +/- voltage status and as a precaution, two protect 1N4148 diodes - forward and reverse diodes. Two PP3 9V battery will only last about nine hours with GK3 use, or two heavy recording sessions. Finally, GK3 battery power needs care, as some op-amps can be be damaged with one voltage-rail dipping below op-amp minimum operating voltage. Best go for a v-guitar power supply instead, or use a dual-battery setup with great care.
Two GK battery adapters: Both offer the same specifications, though the boxed unit is easily modified and does not need diode polarity protection.
Thank you Bill for your information so far. Do you know of a circuit that allows these -7V and +7V for the GK3 from 24V or 48 phantom power?
This could be handy as many audio interfaces have a 48 volt phantom power supply that could possibly be used. Or is this not possible due to the specification of the GK3 and phantom power?
In any case, at best it would save an additional power supply unit or additional batteries.
Hi anjo, I don’t know of a 48V/24V working voltage step-down circuit. However, I know of a very quiet variable 0-13VDC dual-rail power supply (audio grade), and the circuit will easily power a GK3. I like the idea of using 48V stepped down, and the only problem might be lack of phantom power current to drive a GK3. Most v-guitar units supply at least 100mA per rail.
For phantom power you will need a dual DC to DC converter and that might introduce noise in the circuit. Personally I will use two 1 Spot power supplies wired in a +9v / -9v configuration. It works very well, the 1 Spot is a good power supply, I tried others and they introduced all kind of noises in the circuit.
What would a circuit look like that only takes the GK pickup (without the associated electronics) and turns it into a circuit that only works with phantom power and can feed 6x the audio interface?
It is absolutely possible to run the Hex PU in passive mode with no power supplied to the op-amps. If you use a good audio interface with decent pre-apms you can use MG3Hex without feeding any power to the PU. I made a cable/box device like that and it works fine.
Using XLR here for bipolar -7+7 power looks kinda dangerous. I think that it could be better to choose a plug that would not be confused with a regular XLR and accidentally plugged somewhere where it would fry stuff.
Maybe you are super organized, but still human factor exists, and best practice is to exclude the very possibility of connecting things that should not be connected.
Or at least I would suggest marking these special XLR connections with a poisionous frog color coding, so it could not be mixed even by a suddently woken up drunken man in 5.am.
Hi anjo, Dutti67 has an idea, as you can access separate strings directly from a GK3 sensor. The only problem is the need for a hi-pass filter, removing most of unneeded low-frequency (below 80Hz). Another issue is DAW input gain to 0dB, and the need for at least 25dB from the GK3 sensor mags. Mic preamps are best, but then you will need phantom power protection 10uF/50V caps inside six XLR plugs. My XLR breakout cable has protection caps fitted.
I might build something similar but with rechargeable batteries.
Old idea I got from Mission Preamps from the 90’s.
There will be a big on/off switch on it.
When you are done playing you shut OFF the power switch and that will disconnect the batteries from the circuit and automatically connect them to the charger.
Next time you are ready to play you will turn ON the switch and that will automatically disconnect the batteries from the charger and connect them the GK-3 circuit.
This can be achieved with a simple double throw triple pole power switch.
The battery box photo shows rechargeables. A more simple idea is to have four 9V PP3 batteries, with two in use and two on charge. Over the years I sold about 30+ battery adapter units, but most users didn’t like it and asked for a wallwart/mains power supply. Obviously I could not provide a mains unit due to public liability issues. That said, there are a few mains powered variable and regulated supply projects available for quiet GK3 operation.
Here’s one I throughly checked out and works extremely well.
PCB overlay. Component count is a quite high but that’s offset by battery like performance with ultra low mains ripple and overall noise. The custom psu unit replaced my Roland R8MK2 psu and is used in a custom headphone amp. Noise-floor is improved by 3dB compared to Roland’s power supply BTW. The schematic and PCB design is available. Parts costs are around £30.00GBP. Finally, the custom psu is a major audio improvement over a standard v-guitar to GK3 supply.
I received Bill’s breakout cable last week and it works great. He is very thorough and makes sure you order exactly what you need. It is great to be part of the MG3 Hex crowd!
thank you for sharing your knowledge and the expertise you’ve acquired over years and years of work with hex interfaces.
the gkp-1 you sold me works great. unlike a few other pieces of gear which have been fiddly lately, it just keeps doing its thing without the need for any attention.
