Audio Engineering

392 Chapter 13

topology is very resistant to ground loops, even with an unbalanced input; the limitation
on system performance in the presence of a ground loop is now determined by the voltage
drop in the input cable ground, which is outside the control of the amplifi er designer.
A balanced input could, in theory, cancel out this voltage drop completely.

Figure 13.1 also shows how the other grounding requirements are met. The reservoir
charging pulses are confi ned to the connection D–E and do not fl ow E–F, as there is no
other circuit path. E–F–H carries ripple, etc., from the local HT decouplers, but likewise
cannot contaminate the crucial audio ground A–G.





Screened input cable

Amplifier

A

Input

connector

Output

terminals

Local HT

decouple

Feedback network

Mains

earth

Protected

chassis

earth

0 V connection

to transformer

centre-tap only

Star

point

Main PSU

reservoir

capacitors 0 V returnfor relays, etc.

C B

E F

D

G

H

Figure 13.1 : A grounding system for a typical power amplifi er.