Positive voltage instead of ground on fx-loop shield??

[MarcoMike]

Hi, I need some advice... I built my amp with a relay-switchable fx-loop now 2 stereo and 1 mono wires come from the amp to the pedalboard:
1-input, mono, signal/ground
2-loop, stereo, send/return/ground(not connected to the pedalboard)
3-switch, stereo, +5,sw,0 (different from ground but connected by the 100ohm-100ohm heaters reference) sw means the wire that has to be connected to ground to actuate the relay. +5 used for LEDs in the footswitch and 1 other relay

ok, here is the 1st point: I would like to include a booster (or a rog-thor, still not sure) into the amp footswitch. It would be nice to use the power from the amp to power this effect, so it can be a "standalone" addon to the amp. my amp has also a regulated 30V supply for the loop circuitry (shame on me... solidstate loop )
so...
is there a chance to use the wires available to power this effect? one idea could be using the shield of the send/return cable as carrier for the positive voltage... is this bad for shielding... noise stuff and so on? the 30V PS is regulated and of course I can add a regulator and turn it into 12V/9V...

or... should I drop the +5V thing and use the "grounded" 30V/12V/9V PS for LEDs and other relays as well? would it contribute to noise?

if the thing works... would it be bad to power the whole pedalboard through this? like, the footswitch turns into a onespot adaptor? I'm not talking about massive currents, but still... more or less 10 pedals...

[GibsonGM]

Why not step up the +5 to 9V, then bring it down again inside the footswitch but also use it to power the booster?
You could get noise if you use the shield to send power, but I'm not looking at the layout so I can't tell offhand.
In pedal building, the PS for 10 pedals IS massive current, LOL....maybe 300mA there.  A dedicated power line would be best, away from signal paths. Preferably one that uses a different connector than the signal lines, so you don't accidentally plug power into an input or something. 
Sounds like a cool project! 

[MarcoMike]

thank you for the reply....+
actually it is not possible to use the 5V line to power anything, as it comes from the same supply as the tube heaters, that has its own ground, which is referenced to the signal ground.... connecting the 5V ground to anything in the signal path means shorting something somewhere... not cool!!!

now the pedals are powered by a laptop PS regulated to the correct voltages... everything works just fine... but the thing of having just a maxy-wire going from the pedal board to the amp and just one "plug to the wall" away from my feet sounds just perfect!!

[GibsonGM]

Ouch, yes, we want to leave the heaters alone ;o)
You could look into a multi cable, maybe something using RCA jacks?  That would make things easier...