12
dm78 Inputs
The dm78 has three switch selectable inputs,
each having an associated input socket. Both
the input sockets and switch are mounted on
the top rear panel, and the switch must be
operator set to indicate which input is
required. The table below lists the properties
of these three inputs.
The balanced voltage input or current-mode
input are most desirable for minimizing earth
loop generated mains hum and ripple, or high
frequency interference. Earth loop generated
mains hum and ripple, or high frequency
interference should not be a problem unless
the source equipment is poorly designed.
Sources with current-mode outputs are rare
and are most likely to have an RCA output
socket. The advantages of this source are
that:
Earth loop generated mains hum and ripple
are minimized, and cable, plug and socket
generated interference is minimized (from
poor connections which may be affected by
sound vibration for example).
The unbalanced input is quite satisfactory so
long as earth loop generated mains hum and
ripple are not a problem.
The input sockets may have active sources
simultaneously connected to them. The
selector switch selects the input to be
amplified.
Input styles
Required output source
impedance
Input
socket
Input impedance
Balanced voltage input
Low impedance. Standard
preamplifier or CD player for
example.
XLR
100 kohms + 100 kohms
Unbalanced voltage
input
Low impedance. Standard
preamplifier or CD player for
example.
RCA 100
kohms
Current-mode input
Very high impedance; “infinite.”
RCA
60 ohms
