Putting XLR connectors on the back of keyboards for power and sound

[HobitLight]

Hi!

 

If I were to put a 4 pin XLR connector on the back of my keyboard (two pins for power, two for sound, and a 6 pin XLR for stereo keys), would the power affect the sound quality?

 

The reason for this is for when use two or three keyboards in a stack. If I had a box on stage that had a couple of 4 pins and a 6 pin (or whatever is needed for the keyboards) and inside the box I could have the transformers out of the way with the power direct into the connectors. I could also have DI boxes inside with 3 pin XLR connectors on the front (with line out jacks, too) and a 16A connector on the side for tidyness.

 

It'd be so that there is one cable to each keyboard and all the mess inside on central unit, so there doesn't need to be several DI boxes, fourways to power the keyboards, etc on stage.

 

Is the above idea feasible? Note, that I would on run the 12v or so DC down the XLR cable. My synth which is sadly on 230 AC in will have to be powered seperatly. Also, this is only an idea at the moment but I would like to do this as a project at some point in the future :D

 

Many thanks in advanced.

[paulears]

There is a convention for using 4 pin XLRs for 12V volt power - and video equipment has worked this way for years. Assuming your soldering skills are good, and you take steps to prevent the DC and audio 'meeting' then there's no reason why you cannot do this. People like Canford and others do quad mic cable, that has extra cores that can be pressed into providing the DC circuit - as long as the current demand and cable length isn't too high. There are a couple of snags I found when doing something similar in the past. I found that some power supplies are not as noise free as I expected, and as you're dealing with unbalanced audio, squeezing them down one cable with a shared screen did produce some odd noise - it was a Roland PSU - and swapping it for another improved things.

 

The other snag I had was mechanical. The case is quite thin and I pop rivetted the XLR onto the back. The weight of the cable put quite a strain on the panel, and it started to crack. I reinforced it with fibreglass and it lasted. The mod does make a mess of the keyboards value - I got very little for it when I sold it. Everyone spotted the 'bodge' - and it didn't make what it should have.

 

I'm assuming the 4 pin version is for a mono source and you want to use the 6 for stereo? For simplicity, if one k/b needs the extra pins, put that type on everything so you can make up identical cable systems. Then they can be swapped without having to worry.

[drsound]

As you've probably sussed out it's best to run a 2 pair rather than 4 core cable so that your audio and DC are separately screened. Get Mr Faraday to help you out with caging those nasty noises.

 

Beware of your DC - it's probably nowhere near on anything but a very expensive power supply so expect it to be full of horrible noise that will gladly couple to anything nearby. Try to screen the individual pairs as closely as possible to the point of termination in a manner that surrounds the cores as near 360 degrees as you can. Heatshrink will help here as well as preventing you sticking 12v DC into your mixer if a wire breaks. You can undo the benefits of very good cable with careless connections - it only needs a small gap in your screening to allow significant noise to evolve.