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directly to the volume control. A loudness circuit is con-
nected to a tap on the volume control to provide loudness
compensation. Compensation can be switched in or out.
The high level signal then feeds to a pair of transistors
connected as high gain amplifiers. Negative feedback is
used around this pair of transistors to reduce noise and
distortion. The negative feedback provides the low imped-
ance needed to drive the highly selective filter networks
which follow.
In the left channel the second transistor is connected
in a balanced output arrangement. This circuit provides
equal amplitude signals but of opposite phase for the phase
switch.
The filter networks can be switched in or out. The high-
frequency filter network reduces treble response above
5,000 Hz. The low-frequency filter reduces bass response
below 50 Hz. The slope of the filters is selected for maxi-
mum rejection of commonly encountered noise. Careful
design keeps the loss of useable program material to a
minimum.
The output from the filter circuits is fed to the balance
control. The output of the balance control drives the first
stage of the tone control section. The remaining two tran-
sistors are connected as a high-gain amplifier stage. The
high-gain of this stage is used to advantage for the tone
control negative feedback circuits. Negative feedback in
the tone control circuits assures low distortion and accurate
shape of the tone-control response curves. Negative feed-
back is maintained at all frequencies, even with tone con-
trols turned to full boost. Overall distortion is low at all
frequencies including frequenices where maximum boost
occurs. The negative feedback also provides the low im-
pedance output required for the main preamplifier outputs.
L + R AMPLIFIER
The L + R amplifier consists of a single transistor con-
nected as a voltage amplifier. Negative feedback is used
around the summing amplifier to maintain low distortion
and provide a low impedance for the center channel output.
POWER SUPPLY
The power supply of the MX 113 has received very spe-
cial attention.
Three separate rectifier circuits are used. First, a full-
wave rectifier supplies DC to all audio circuits. The second
full-wave rectifier supplied DC to all tuner and multiplex-
decoder circuits. The third supply provides DC to the AM
circuit.
The power supplies are elaborate in design. They use
electronic filtering to insure the lowest possible back-
ground hum level, maximum stability, and extremely good
regulation.
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