McIntosh MA 230 - SERVICS BULLETINS, Руководство пользователя

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couples the output tube cathodes into the
transformer. Six db of negative feedback is
produced in the output stage with this circuit.
Twenty db of negative feedback around
the entire power amplifier circuit is achieved
by coupling a special secondary winding on
the output transformer back to the first stage
12AX7 cathode.
The fixed bias on the 7591 output tubes
is adjustable over a small range with indi-
vidual controls. These adjustments are fac-
tory set to 0.7 volts DC at the test points.
Convenient test point jacks are provided next
to each output tube. The setting of these con-
trols is not critical and need not be touched
in normal use. To assure best possible per-
formance of the MA230 over long periods of
operation, or whenever output tubes are
changed, the bias can be checked and reset
if necessary.
A pair of stereo headphone jacks is pro-
vided on the front panel. The jacks are con-
nected to the amplifier outputs through 100
ohm resistors for low impedance head phones.
The speaker switch turns off the speakers
for headphone listening.
POWER SUPPLY
A silicon rectifier voltage doubler power
supply assures stable voltages and cool oper-
ation. A zener diode holds the transistor pre-
amplifier operating voltages at exact values
and eliminates all traces of hum.
A thermistor is used in the primary AC
circuit of the power transformer to protect
against line voltage surges and extend tube
and transistor life. The thermistor places
slightly more than 25 ohms in the AC circuit
when cold. As the amplifier warms up the
thermistor also warms and its resistance
then drops to less than 0.7 ohm. The ampli-
fier then operates at normal line voltages but
is protected during the initial warmup period.
Again, Mclntosh care in engineering protects
your investment in listening pleasure.
The combination of these features results
in performance available only from a Mc-
lntosh amplifier. The MA230 delivers 30
watts RMS continuous power from both
channels at the same time, 20 cycles through
20,000 cycles with harmonic distortion less
than ½ of 1%. This superior level of per-
formance is unequaled by any other preamp-
amplifier. A listening test quickly proves the
superiority of the Mclntosh MA230.
MECHANICAL SPECIFICATIONS
Size
Front panel, 16 inches wide by 5
7
/
16
inches
high; chassis, 15 inches wide by 4½ inches
high by 14½ inches deep, including connec-
tors. Clearance in front of mounting panel
including knobs, 1½ inches.
Weight
43 pounds net, 57 pounds in shipping carton.
Finish
Anodized gold and black (Front Panel).
ELECTRICAL SPECIFICATIONS
Power Output
30 watts continuous per channel with both
channels operating simultaneously. 60 watts
continuous, monophonic.
Harmonic Distortion
Less than 0.5% at 30 watts output, 20 cycles
through 20,000 cycles. Distortion decreases
as power output is reduced.
Intermodulation Distortion
Less than 0.5% for any combination of fre-
quencies from 20 cycles through 20,000
cycles if instantaneous peak power is 60
watts per channel or less.
Phase Shift, Power Amplifier-
Less than ± 5° 20 to 20,000 cycles.
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