Single Cable for Multi Output Guitar

MARVlN · July 2023

I'm planning the next guitar build (even though I was warned, it's an addiction...), which is fairly ambitious for me, with a reasonable amount of on-board electronics (LED fret markers, Graph-Tech Ghost piezo and a pre-amp for the magnetic pickups).

My plan is to have two outputs - one for the magnetic pickups and one for the piezo, and I'd also like to feed 9V DC in from the pedalboard (where I'll have an enclosure splitting the signal into two standard mono outputs, and with 9V DC in). Ideally I'd like to do this in one cable. TRRS would have worked, but I've not found any 6.3mm ones, so I started looking at 4 pin XLR.

First, am I being electrically sensible? Common ground (which will be the outer cable shield), then a pin each for magnetic signal, piezo signal and +9V supply? Or should I separate the grounds? I keep going over this in my head, but have now got a bit confused...

Second, is this sensible from a noise perspective? I don't see why it wouldn't be...

Third, is XLR a reasonable choice of connector? Seems good on the surface, go up to 7 pin, good size/strength. Are they happy being unplugged/plugged in a lot? I use them for monitors/DI/audio interface etc, but they're all low-removal applications.

Sporky · July 2023

I think you could do it TRS, like phantom power. Bias one pin to 9v, and remove the bias inside the guitar.

I think @Danny1969 has done something along these lines.

4-pin XLR would work, or 3-pin with the shield and XLR case as ground, leaving you the pins for piezo, mag, and 9v.

ICBM · July 2023

XLRs are excellent, robust and reliable connectors widely used in the professional audio industry. The only issue with using one for what you want is creating a non-standard cable, so for professional use you will need at least one spare.

I don't think a common ground is an issue as long as the power supply is well-filtered so noise from the probably fairly unshielded LED system doesn't get into the audio.

Sporky's idea of using 3-pin XLR is neat, but means that you will have to be careful with what you use for pin 1 - otherwise a standard microphone cable used by mistake will short out the 9V supply if you have that as pin 1 (or at best not work, if the plug casings aren't connected to pin 1).

Sporky · July 2023

ICBM said:

Sporky's idea of using 3-pin XLR is neat, but means that you will have to be careful with what you use for pin 1 - otherwise a standard microphone cable used by mistake will short out the 9V supply if you have that as pin 1 (or at best not work, if the plug casings aren't connected to pin 1).

That is an excellent point. I don't like connectors that are easily confused, so 4-pin XLR sounds a better idea.

It might be worth going for a non-locking one, so that if you run off to the end of the cable it doesn't tear a chunk out of the guitar (or pull the amp over, or other fine comedy outcomes exist).

Danny1969 · July 2023

One easier way would be use dual VD blue cable which is 2 x balanced mic lines in one jacket. Use one set and a mono jack for the guitar, so ground and hot and ignore the spare conductor.
Then one hot, one ground and the other conductor can carry the 9V DC with a TRS jack for the Piezo.

Roland · July 2023

ICBM said:

... The only issue with using one for what you want is creating a non-standard cable, so for professional use you will need at least one spare...

It’s worth using different coloured cable for non-standard leads.

MARVlN · July 2023

Thanks all +Wis all round.

On board electronics are:

Magnetic pickup preamp (3 band EQ) powered by 18V, for which I'll use a charge pump/voltage doubler
RGB LEDs, using an Arduino micro-controller to select which to switch on and colours. These are 5V, controlled via PWM, and there will be a step-down regulator that will supply power to the whole system
Graphtech Ghost piezo preamp, powered by 9V

You can see why I'd rather power from the pedalboard! I have a good power supply (Voodoo Pedal Power 3), but essentially I guess this is basically daisy-chaining. Bit worried about the microcontroller dumping noise.

I could just run two TRS cables with a bit of heatshrink at regular intervals to make 'one' cable as @Danny1969 suggests, but I just quite liked the idea of keeping the look minimalist (although I guess with all those electronics and inevitable knobs etc, 'minimalist' is probably out of reach...)...

This is only for home use for the foreseeable, so happy to make something custom.

Danny1969 · July 2023

I didn't mean lash 2 cables together, I meant you can buy a cable that's essentially 2 mic cables in a single jacket. So looks like one cable but gives you a total of 6 conductors. The type I tend to use is Van Damme blue series.

Here's one of my IEM cables with integral headphone amplifier powered by the pedal board. This use's the same type of cable but you would be using the extra conductors for the piezo rather than running a headphone amp.

Image: https://thesuperheroesonline.co.uk/ha1.jpeg

If you go XLR multi pin then I suggest 5 pin XLR as that is more common, being used for DMX as well as audio. I have used used a lot of these in various products I sell and it's a good robust connecter if you stick to Neutrik versions.

MARVlN · July 2023

Danny1969 said:

I didn't mean lash 2 cables together, I meant you can buy a cable that's essentially 2 mic cables in a single jacket. So looks like one cable but gives you a total of 6 conductors. The type I tend to use is Van Damme blue series.

Here's one of my IEM cables with integral headphone amplifier powered by the pedal board. This use's the same type of cable but you would be using the extra conductors for the piezo rather than running a headphone amp.
...
If you go XLR multi pin then I suggest 5 pin XLR as that is more common, being used for DMX as well as audio. I have used used a lot of these in various products I sell and it's a good robust connecter if you stick to Neutrik versions.

Ah, that's what I initially thought, then I struggled to find Van Damme blue in the configuration you described. I've now looked again and it was obvious - I think the part number is 268-202-060?

I was reading about DMX, will do as you suggest with 5 pin XLR.

Roland · July 2023

It’s worth getting a right angled XLR plug long the guitar end

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Single Cable for Multi Output Guitar

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