Balanced power devices use a transformer to convert the 120V wall power into balanced 60-0-60 volts. In doing so the
neutral line is isolated from ground which reduces common-mode interference which may be on the powerline. They can
also help to eliminate ground loops.
For a discussion of the construction of these devices, check out
Jon Risch's web site. In his notes, Jon calls out
Signal DU-2 and SU-2 transformers which are high quality and available in quantities of one from the manufacturer. These quality units are not cheap.
I have found suitable substitutes on EBay in the form of outdoor industrial control transformers. These units are made by
Magnetek/Jefferson, Acme and Hevi-Duty and have their coils potted in resin and encased in a metal cabinet.
When purchasing these transformers, you want to get one with an
electrostatic shield and most of these manufacturers
make their transformers in shielded and unshielded versions. If you can't tell if a particluar transformer is shielded or
not
don't buy it! since an unshielded transformer will not be as effective at noise reduction. Below are picture
of shielded transformers from various manufacturers in various sizes that I've seen on EBay. Notice that most of them are
marked "shielded" on the case. Since the unshielded versions look identical, you must either see this designation on the case
or read in the ad that a particular transformer is shielded
