58
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HEATHKIT
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ihltMM9N9
When
the
Tape
Monitor pushbutton
is
"in"
and
a tape recorder with tape monitoring
capabilities
is
connected to the
Tape
Out
and
Tape
Monitor sockets, the signal
from
the
collector
of
transistor
Ql02L
is
recorded
on
tape
and
immediately
played
back
through the
Tape
Monitor
pushbutton switch, capacitor Cl21,
and
the
rest
of
the amplifier
circuits.
Thus
you
can
hear the actual recorded
signal
right
after
it
has
been
recorded.
This
is
not
to
be
confused with tape
playback
which
would
be
connected to
the tape socket.
When
the
Mono
pushbutton
is
"in",
signals
from
either
the
left
or
the
right
input socket are channelled to both
left
and
right
input
amplifiers.
In
this
way,
a
single
channel input
can
be
amplified
by
both channels.
TONE
CIRCUIT
From
the input amplifier
circuit,
the
signal
is
coupled to lug 1 of Treble .
control
R211
and
through
resistor
R201
to lug 1 of
Bass
control
R203.
The
bass
circuit
consists
of
resistors
R201, R213,
and
R205,
control
R203
and
capacitors
C201
and
C203.
The
treble
circuit
consists
of
resistor
R207,
control
R211
and
capacitor
C207.
The
outp~t
from
these
two
circuits
is
coupled through
capacitor
C205
to the base
of
transistor
Q201L.
The
signal
is
amplified
by
transistor
Q201L
and
fed
back
to lug 3
of
the
Bass
control
and
lug 3 of the Treble
control.
This feedback signal
is
out of phase
with
the signal
at
the base of
Q201L.
With
the input signal
at
lug 1
and
the
out-of-phase signal
at
lug 3 of the
controls,
there
will
be
a point near
the centre
of
the control
where
the
response will
be
essentially
the
same
as
the input
signal.
As
the
arm
of the
control
is
moved
counterclockwise,
more
out-of-phase signal will
be
applied to
the base
of
Q201L
and
a cut
in
a
response
results.
As
the
arm
of
the
control
is
moved
clockwise,
more
of
the
input signal
is
applied to the base
of
Q201L
and
a boost in response
results.
Both
the bass
and
treble
circuits
use
the
same
principle
of
operation.
How-
ever, capacitors
C201
and
C203
in the
bass
circuit
by-pass higher frequencies
and
prevent the control
from
affecting
them.
Treble coupling capacitor
C207
has
a
low
value to block
low
frequencies
while p~ssing the
high
frequencies.
The
amplified signal
from
the
collector
of
Q201L
is
also coupled through
capacitor
C211
to the Balance
control.
As
the Balance control
is
moved
clock-
wise
from
centre,
the
left
channel signal
is
reduced without
affecting
the
right
channel
signal.
As
the Balance control
is
moved
counterclockwise
from
centre,
the
right
channel signal
is
reduced
without
affecting
the
left
channel
signal.
From
lug 2 of the Balance
control,
the
signal
is
coupled through the
Volume
control to the output amplifier
circuit.
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