Heathkit AA-1214 User Manual

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CIRCUIT DESCRIPTION
Refer to the Schematic Diagram (fold-out
from Page 65) while you read this
Circuit Description.
Numbers for resistors, capacitors and
transistors on the Schematic are in the
following groups:
101-199 Parts on the amplifier circuit
board.
201-299 Parts on the tone circuit
board.
Resistor and capacitor numbers are
further divided so the odd numbers are in
the left channel circuits and the even
numbers are in the right channel circuits.
Transistors and diodes are designated L
(left) and R (right). For example, Q201L
in the left channel is identical to Q201R
in the right channel.
Since the left and right channel circuits
are identical in operation, only the left
channel circuits will be described.
PHONO AMPLIFIER
The input signal is connected to the
Left Phono socket. From here it is
coupled through capacitor ClOl to pin 9
on IC-101. IC-101 , with its associated
circuitry, makes up a low-noise
amplifier which amplifies the signal
and couples it to pin 13 of IC-101.
The signal is then coupled through
capacitor Clll, Phono Level control
Rl23, and resistor Rlll to the Phono
pushbutton switch.
Capacitors Cl03, Cll3, and Cll5, and
resistors Rl03, Rl05, Rll3 and Rll5
provide the proper amount of feedback to
give RIAA (Record Industry Association
of America) equalisation. Resistor Rl07
and capacitors Cl05 and Cl07 form a
frequency compensation circuit.
INPUT PREAMPLIFIER
The input signals are coupled to their
respective pushbutton switch. When the
pushbutton switch is pushed in, the
signal is coupled through the switch
and through capacitor Cl21 to the base
of transistor Ql03L. Transistors Ql03L
and Ql04L are connected as a complemen-
tary amplifier with feedback. This
results in high input impedance, low
output impedance, good DC stability,
c onstant gain, good linearity at high
signal levels, and good signal-to-noise
performance. The output from the
collector of transistor Ql04L is then
coupled through capacitor Cl25 to the
tone circuit.
The signal from the pushbutton switch is
also coupled through capacitor Cll7 to
the base of transistor QlOlL. Transistors
QlOlL and Ql02L are also connected as
complementary amplifiers and operate in
the same manner as Ql03L and Ql04L. The
signal from the collector of Ql02L is
coupled through capacitor Cl23 to the
Tape Out phono socket.
When the Tape Monitor pushbutton is in,
the amplifier circuit consisting of
transistors Ql03L and Ql04L is switched
to the Tape Monitor input.

Heathkit AA-1214 Specifications

General

Brand	Heathkit
Model	AA-1214
Category	Amplifier
Language	English