Phaux 'Phantom' Power por Preamps - Is this a bad idea?

[phaeton]

Hey kids,

I've got another one of my trademark half-cooked ideas. I did some searches here about phantom power, but everything that came up seemed to apply to microphones and mic preamps with XLR connectors.  What *I* want to do, is power preamps and/or stompboxes from a power amp using the signal cable.  Allow me to demonstrate with this highly technical illustration:



On the right is a chipamp power amp (specifically the ~8W Craig Anderton TDA2003/383T setup, but it could be anything).  The amp is to be built into its own housing, and will be powered by a 12V regulated wall wart.  The power amp has two inputs, where the upper one connects the tip of the cable to +9V (voltage divided from the +12V power amp supply).  Thus, the power is fed across the cable into the preamp on the left, which has the tip of the signal cable connected to its own power rail.  Both sides have DC blocking caps to keep the 9V out of sensitive areas, and if all is dandy the power amp will power the pre-amp, and the signal will ride atop the DC.

* Obviously, anything that I plug into that upper 'powered' input on the power amp would have to be made for this or the likely result is wreckage and ruin. I would use something different than a regular 1/4" connector (like maybe a 1/8" jack) to prevent any accidental connections.  This illustration is a top-shelf 'deluxe' version where there are non-powered jacks below, and hopefully those jacks would allow either component to play nicely with normal equipment. I would only use preamps and non-bypass stompboxes that I've built myself for this purpose in those powered jacks. I have no intention of modifying commercial stompboxes for this use, and those would just get plugged into the normal jacks. 

* The wall wart I have is made to be super quiet, and hopefully it (or either circuit) won't inject any ripple into the signal but I don't have a scope to look. It is 12V and is rated to push up to 1A.  The chipamp on my breadboard draws about 38mA at 12V (idle), and the Runoff Groove Eighteen I had build was pulling about 2mA at 9.8V (idle), so I think I'll have enough power with just the two.  (I know this isn't really "phantom power" per se, but I don't know what else to call it).

* The cable connecting these is going to be really short, like 1 foot maximum.  They'll probably just sit on top of a table or speaker cabinet right next to each other.

* This will be all about bedroom-level practice and tinkering more than anything else.  Beauty is in the ear of the beholder.

[markusw]

Why not just use a stereo cable (TRS)  and put the 9V to the "ring"?
Check out EBS bass amps. They have exactly this option.

[PRR]

The "9VDC" is essentially a short-circuit to Audio. So any way you look at your plan, the audio is shorted out.

As said, TRS connectors are one solution.

[phaeton]

Why not just use a stereo cable (TRS)  and put the 9V to the "ring"?
Check out EBS bass amps. They have exactly this option.

Well now... that makes all kinds of sense now, doesn't it?  I don't know why I didn't think of that one myself.

Thanks for the solution!

[duck_arse]

I know this isn't really "phantom power" per se, but I don't know what else to call it.

why wouldn't you call it "phaeton power"?

[midwayfair]

There's a company that makes amps that power pedal chains through a TRS cable. It works fine but you have to convert your entire setup to use it -- and as everything's daisy chained, if you have any digital or high-current needs, you are probably going to need a separate power supply anyway. My El Capistan, for instance, won't be happy with any power supply except the one it came with.