c421™
v1.00
Headphone
Amplifier
Operating
Instructions
General
Use
Battery
must
be
fully
charged
prior
to
first
use.
See
reverse
side.
1.
Connect
an
audio
player
to
the
Source
jack
using
a
Line
Output
Adapter
or
3.5mm
interconnect
cable.
2.
Connect
headphones
to
the
Output
jack.
3.
Upon
first
use,
set
bass
to
Flat
,
gain
to
Low
,
and
turn
the
Volume
knob
to
its
minimum
position.
4.
Turn
the
rear
Power
switch
on
(see
reverse
side).
5.
Slowly
raise
the
Volume
knob
to
an
appropriate
level.
See
Listening
Tips
below.
Bass
boost
can
be
turned
on
or
off
by
moving
the
toggle
up
or
down,
respectively.
Reduce
volume
before
switching
bass
boost
on.
This
feature
boosts
low
frequencies
by
+8dB,
which
can
overdrive
the
headphones
and/or
opamp
at
especially
high
listening
levels.
You
should
hear
no
noise
or
whining
with
your
audio
player
connected
and
paused/muted.
Every
amplifier
is
hand
tested
to
ensure
proper
operation.
If
noise
is
present
or
audio
is
significantly
distorted
at
all
volumes,
try
a
different
input
cable.
Listening
Tips
Use
Low
gain
unless
volume
cannot
be
further
increased
with
your
source
and
headphones.
For
maximum
sound
quality,
use
a
line
‐
output
adapter
(LOD).
If
using
a
3.5mm
interconnect
cable,
set
a
high
source
volume
(60
‐
80%)
and
only
use
the
amplifier's
volume
control.
c421
can
produce
dangerously
loud
music.
Be
sensible
and
listen
safely:
www.hearingloss.org
Thank
you
for
purchasing
c421.
If
you
have
additional
questions
or
comments,
please
contact
us
at:
JDSLabs
.com
