Specifications

l1
Operation
Each
channel
of
your
Plw/F,hzn
amplifier
has
a
nominal
balanced
input
impedance
of
3OkOhms
(@1kHz)
and
should
not
present
a
diffiq.rlt
load
for
any
signal
source.
Your
signal source (i.e.
the
equipment
feeding
the
amplifier)
should
have
an
output
impedance
of
600
Ohms or lower
to avoid urnvanted
h
i
gh
freq
uency
loss
in the
cabling.
lnput
overload
occurs
at
+20.5d8u
(8.25
volts).
See the
specification
section
for
more
detailed
infor-
mation.
Hum
Problems
Most
equipment
is
designed
for minimum
hum
when
used
under
ideal
conditions.
When
connected
to
other
equipm€nt,
and to
safety
earth
in an electrically
noisy
environment
however,
problems
wi ll
often
ocanr.
The
three "E"s
of
hum
and hum
related
noise
which
can
plague
your
audio
system
are:
a)
Electrostatic
radiation,
b)
Electromagnetic
radiation,
and
c)
Earth loops
Electrostatic
radiation
capacitively
couples
to
sys-
tem
elements
causing
an interference
voltage
that
mainly
affects
higher
impedance
paths,
such
as
amplifier
inputs.
The
source
is
generally
a nearby
high
voltage such
as
a
mains lead
or
a speaker
lead.
The
problem
can usually
be
reduced
by
moving
the
offending
lead
away,
or
by
providing
additional
electrostatic
shielding
(i.e.
an earthed
conductor
wfrich
forms
a
banier
to the
field).
Electromagnetic
radiation
induces
interference
cur-
rents
into
system
elements
that
mainly effect
lower
impedance
paths.
Rqdio transmitters
or stray
mag-
netic
fields from
mains
transformers
are often
the
cause
of
this
problem.
lt is
generally
more
difficult
to
elirninate
this
kind of
interference,
but again,
moving
the source
away or
providing
a
magnetic
shield
(i.e.
a steel
shield)
should
help.
I
Earth
loops
can arise
from
the
interfacing
of
the
various
pieces
of equipment
and
theirconnections
to
safety
earth.
This
is byfarthe
most
common
cause of
hum,
and it
occurswhen
source
equipment
and the
amplifierare
plugged
into difierent
points
along
the safety
earth
where
the safety
earth
wiring
has
a cunentflowing
in
il
The
cunent
flowing
through
the
wire
produces
a
voltage
drop
due
to the
wire's
resistance.
This voltage
difference
between
the
amp earth and
source equip-
ment
earth
appears
to the amplifief s input
as a signal
and
is
amplified
as hum.
There
are three
things
you
can
do to avoid earth
loop
problems:
1.
Ensure
your
mains
powerforthe
audio system
is
"quiet"
i.e.
without
equipment
on it
suclr as
air-
conditioning,
refrigeration
or lighting
whicfr
may
generate
noise in
the
earth circuit.
2.
Ensure
all
equipment
within the
system shares
a
common
ground/
safety
earth
point.
This
will
reducethe
possibility
of
circulating
earth
currents
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-Lift
Switch
When
proper
system
hook-up
has
been carried
out,
you
may
still have
some
hum
or
hum
related
noise.
This
may
be due to
any of
the
previously
mentioned
gremlins.
Y our
PtfutPltmampl
ifi
er has
a
"
S
ignal
Ground Liff
switch
which
disconnects
the input
ground
wiring
from
the
amplifier.
A substantial
drop in hum
and
or
hum
related
noise
can
result
from
judicious
use
of
this switch.
NOTE
lf the input
ground
lift
switch
is used
you
must ensure
adequate
shielding
of the
input wiring.
lf
the signal
source
equipment
does
not
provide
adequate
shielding
(i.e.
a definitive
connection
to
ground) you
must disconnect
the
shield
from
the input connector's
ground
pin
(Pin-1)
and
re-connect
it to the
"drbin"
contact
on
the input
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
DIRECTLY
TO THE
DRAIN
CONNECTION.
You
will
defeat the
amplifiers
intemal
grounding
scheme
and
possibily
cause
instabilitytothe
amplifi
er.
Always
ensure that
your
amplifier
is off
and the
attenuators
are down
when
you
engage this
switch.
This switcfr
should
only be
used
when the amplifier
is
operated
from a
balanced
signalsource.
NOTE:
Be
wary
of
quasi{calanced
outputs, these
are often
no more thanfloating
unbalanced
outputs.
ltu