REVISED POST.
I am now working on a smaller cheaper solution and have changed the 3D printed box but I'm leaving the wiring diagram up in the meantime. You will need a "noiseless" power supply to be 100% sure of eliminating background noise. The power board screens noise on some power supplies but not others. I think I got lucky with the supplies I used. The link to the Sweetwater XPS is appreciated for non-techie people but I'm sure it just uses a cheap buck convertor like my solution.
Parts -
the power board (it is supplied with supports which can be glued into the box).
a box
a mono and a stereo 1/4" socket (I used 2 stereo sockets which were cheaper to buy on ebay)
a socket to match your DC power supply.
some wire.
.
Schematic below. Tested 100% working with a Variax 600 & 700. Definitely not advised for use with any of the later, standard, JTV or Shuriken models. Just to be 100% safe, plug in the power supply after the guitar leads. I've forgotten to do this a couple of times and nothing bad happened but you never know.
