Rear Panel Information
LEFT and RIGHT OUTPUT
For stereo operation, output impedances of 2, 4, 8 and
16 ohms have been provided on a secure, screw type bar-
rier strip. For monophonic operation proper interconnection
provides, 1, 2, 4 and 8 ohms from the same barrier strips.
POWER GUARD
Amplifiers are capable of delivering large quantities of
power when they are driven to clipping. Clipping is
caused when the amplifier is asked to produce more power
output than it can deliver with low distortion. A clipped
amplifier can have more than 40% harmonic distortion.
The extra energy content of the clipped signal will dam-
age most speakers. A new Mclntosh advancement helps
to protect your speaker from this kind of damage. The
MC 2120 has a built in "waveform comparator" that com-
pares the wave shape of the input signal with the output
signal. If the non-linearity between the two signals exceeds
0.5% a front panel signal illuminates in red (LIMIT). With
the POWER GUARD switch in the NORMAL position, 1.0%
distortion will cause the POWER GUARD circuit to operate.
The POWER GUARD circuit limits the input dynamically so
that the amplifier cannot be overdriven. This eliminates
amplifier output clipping. Recommended operations is with
the POWER GUARD switch in the NORMAL position at all
times.
MODE SWITCH
The MC 2120 can be used in these different manners:
stereo (or as a twin amplifier) and mono. Because of the
excellent channel separation of the MC 2120, it can
all of these functions. When the instrument is properly con-
nected the MODE switch is used to select the method of
operation desired.
INPUT
In the stereo or twin amplifier mode of operation both
input jacks accept signal. In the mono mode of operation
the Left channel input jack is disconnected and only the
Right (MONO) channel input jack accepts signal.
INPUT LEVEL
The input sensitivity of the MC 2120 is 0.75 volts or
2.5 V depending on the position of the INPUT LEVEL switch.
With indicated voltage applied and the GAIN control clock-
wise, the amplifier will deliver its rated power. All Mclntosh
preamplifiers have been designed to deliver 2.5 volts out-
put with rated input. For the best signal to noise ratio when
using Mclntosh source equipment, always have the INPUT
LEVEL switch in the 2.5 V position and the front panel LEFT
and RIGHT/MONO GAIN controls in the fully clockwise posi-
tion. If more gain is desired the 0.75 V position may be
used. For source equipment other than Mclntosh set the
switch in the position nearest to the stated output rating of
the source equipment.
AC POWER
The MC 2120 is rated for 120 volts, 50/60 hertz. It uses
50 watts when there is no signal output and 460 watts
with both channels delivering rated power. An 8 ampere
fuse protects the MC 2120 electrically. An auxiliary AC
power outlet has been provided. The auxiliary outlet is
neither fused nor switched.
10
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