Specifications

l4
Operation
Each channel of
your
amplifier has a nominal
balanced input impedance of 2SkOhms
(@1kHz)
and should not
present
a difficult load forany signal
source.
Yoursignal source
(i.e.
the equipment feeding the
amplifier) should have an output impedance of
600 Ohms orlowerto avoid unwanted high frequency
loss in the cabling.
lnput
overload occurs at
+20.5d8u
(8.25
volts).
See
lhe specification section for more detailed
information.
Hum Problems
Most equipment
is designed forminimum hum when
used under ideal conditions. When connecled to
other equipment, and to safety
earth
in
an electrically
noisy
environment however,
problems
will often
occur.
Thethree
"E"sof
hum
and
hum
related noisewhich
can
plague your
audio syslem are:
a) Electrostatic radiation,
b) Electromagnelic radiation, and
c) Earth loops.
Electrostatic radiation capacitively couples to
system elements causing an
interference vollage
lhat mainly
affects higher impedance
paths,
such
as
amplifierinputs. The sou rce is
generally
a nearby
high voltage such as a mains lead ora speaker lead.
The
problem
can usually be
reduced by movingthe
offending
lead away, or by
providing
additional
eleclroslatic
shielding
(i.e.
an earthed conductor
which forms
a barriertothe field).
Electromagnetic radiation
induces interference
currents into
system elements that mainly effect
lower
impedance
paths.
Radio
transmitters orstray
magnetic
fields from mains transformers are often
the cause of
this
problem.
lt is
generally
more
difficult to eliminate this kind
of interference, but
again, moving lhe source away or
providing
a
magnetic
shield
(i.e.
a steel shield) should help.
Earth loops
can arise from the interfacing of the
various
pieces
of equipment
and their connections
to safety earth.
produces
a voltage drop due to thewire's
resistance.
This
voltage difference between the amp earth and
source equipment
earth
appears
to the amplifier's
input as a signal and is amplified as hum.
There arethree things
you
can
do to avoid earth loop
problems:
1 .
Ensure
your
mains
powerforthe
audio system
is
"quiet"
i.e. without equipment
on it such as air-
conditioning, refrigeration or lighting
which may
generate
noise in the earth circuit.
2. Ensure all equipment within the
system shares
a common
ground/
safety earth
point.
This will
reduce the
possibility
ofcirculating
earth cunents
as the equipment
will be referenced to the same
ground potential.
3. Ensure that balanced
signal leads
going
to the
amplifier
are connected to earth at one
end only.
Signal Ground
Lifting
When
propersystem
hook-up has
been carried oul,
you
may still have
some hum or hum related noise.
Thismaybeduetoanyofthe
previouslymentioned
gremlins.
One ofthe most
effective waysto reduce earth loop
or eleclromagnetically induced hum isto disconnect
input signal
ground
at the input
connector of
your
amplifier.
This effeclively breaksthe earth loop
path
or open circuits the inpul
ground path
so no
electromagnetically
induced currenls can flow
through the amplifier.
NOTE: lf the input signal
ground
is lifted
you
must
ensure adequate shielding
ofthe input wiring. lfthe
signal source
equipment does not
provide
adequate
shielding
(i.e.
a definitive
connection to
ground) you
must disconnectthe
shield from lhe input
connectois
ground
pin
(Pin-l)
and
reconnect it to the "drain"
coniact
on the inpul connector. This
will ensure the
shield on
your
input wiring actually
goes
to the
amplifier chassis
and subsequently to earth.
DO NOT CONNECT PIN-1 DIRECTLYTO
THE
DRAINCONNECTION.
You will defeat
the amplifiers internal
grounding
scheme
and
possibly
cause
instability within the
amplifier.
This is by farthe
most common cause of hum, and
it occurs when source equipment
and the amplifier
This should only
be done when the amplifier
is
are
plugged
into different
poinls
along the
safety
operated from a balanced
signal source.
earth where the safety earth wiring
has a current
NOTE: Be wary of
quasi-balanced
outputs,
these
flowing in it.
The current flowing through the wire
are often
no morethan floating unbalanced
outputs.
/tu