[sdiy] +/-12v from a single +12v psu - possible?

[Julian]

Hello,

I dont know much about power supplies at all.  I have a +12v linear supply, 3.4A, with sense terminals (this meens its regulated,
right?)

I want a +/- 12v supply, which can happily be some ammount under the 3.4A.

Now someones informed me that i can just run it through somthing like a 7912 regulator / invertor, but i thought these needed some
ammount of headroom?  The data sheet for the 7912 certainly lists the min voltage at somthing arround +15v.

In short, is there a simple way to get a negative rail from this supply?

I know i could take it all appart and just use the transformer, etc. but theres a lot of circitary on there allready, which, i
assume (like i said - i dont know a lot about psus) is giving it a good stable output, and it seems somewhat of a shame to junk all
that.

The psu is an advance-power unit, for which the manual is online here: http://www.farnell.com/datasheets/21071.pdf

(not that its very informative at all, in fact, so i wouldnt actually bother looking ; )

Any suggestions?

Or just give up and build / buy a differnt psu?

Cheers, Julian