Audio Engineering

Noise and Grounding 399

It has been suggested that balanced mains has miraculous effects on sound quality, makes
the sound stage ten dimensional, etc. This is obviously nonsense. If a piece of gear is that
fussy about its mains (and I do not believe any such gear exists) then dispose of it.

If there is severe radio frequency interference (RFI) on the mains, an extra transformer in
the path may tend to fi lter it out. However, a proper mains RFI fi lter will almost certainly be
more effective—it is designed for the job, after all—and will defi nitely be less expensive.

Where you might gain a real benefi t is in a Class II (i.e., double-insulated) system with
very feeble ground connections. Balanced mains would tend to cancel out the ground
currents caused by transformer capacitance (see Figure 13.4 and previous discussion
for more details on this) and so reduce hum. The effectiveness of this will depend on
C 1 being equal to C 2 in Figure 13.7 , which is determined by the details of transformer
construction in the unit being powered. I think that the effect would be small with well-
designed equipment and reasonably heavy ground conductors in interconnects. Balanced
audio connections are a much less expensive and better way of handling this problem,
but if none of the equipment has them then beefi ng up the ground conductors should give
an improvement. If the results are not good enough, then, as a last resort, balanced mains
may be worth considering.

Finally, bear in mind that any transformer you add must be able to handle the maximum
power drawn by the audio system at full throttle. This can mean a large and expensive
component.

L

N

E

230 V 115 V

C Unit 1

1

C 2

0V 115V

Chassis

Audio out

Ground

Figure 13.7 : Use of a balanced mains supply to cancel ground currents stemming from

interwinding capacitance in the mains transformer. This is an expensive solution.