13
How to Operate
How to Operate
is at the 2 O’Clock setting. If the Preamplifier or A/V
Control Center has an Electronic Volume Display,
adjust the Volume Display for an indication of 70% or
0dB.
This will help to assure the widest useful range of
volume control settings especially when listening to
music at lower levels. Refer to figure 9.
Standby/Protection Indicator
The MC75 Sentry Monitor Tube Protection Circuitry
provides protection to the Power Amplifier in the
event of an impedance mismatch
1
between the MC75
and the Loudspeaker. It will also activate if there is
a short circuit at the MC75 Output Terminals (or the
Loudspeaker Terminals) or if a MC75 Power Output
Tube should fail. During normal operation the Sentry
Monitor Tube Protection Circuitry has no effect on the
performance of the Power Amplifier.
In the event a problem occurs, the MC75 Sentry
Monitor Tube Protection Circuitry will activate to
prevent potentially destructive high levels of current
from flowing in the amplifier. The Front Panel Stand-
by LED will start flashing indicating the
Protection Circuitry has activated and the
AC Power to the MC75 is halted. Refer to
figure 10.
To reset the Sentry Monitor Tube Pro-
tection Circuitry first note the position of the POWER
Switch. If the POWER Switch is set to the OFF/STBY
position, switch Off the Preamplifier or A/V Control
Center for approximately one minute and then switch
the Preamplifier or A/V Control Center On. When
the POWER Switch set to the ON position, place the
POWER Switch to the OFF/STBY for approximately
one minute, then place the POWER Switch to the ON
position.
Power On
To have the MC75 automatically turn On or Off when
a Preamplifier or A/V Control Center turns on or off,
place the Power Switch to OFF/STBY(Standby) posi
-
tion. For manual operation, place the
Power Switch to the ON position as
desired. Refer to figure 7.
Note: There must be a power
control connection between the MC75 and the
Preamplifier/A/V Control Center, in order for the
remote power turn-on to function.
Input Mode Switch
The Input Mode Switch, which is located
on the Left Side Panel of the MC75, al-
lows you to select either the BAL (Bal-
anced) or UNBAL (Unbalanced) Input.
Refer to figure 8.
Input Sensitivity Switch
The Input Sensitivity Switch, which is located on
the Left Side Panel of the MC75, allows
matching the Preamplifier or A/V Control
Center output voltage capability so the
MC75 Power Amplifier can be driven to
full power output. Refer to figure 9.
With the MC75 is connected to most McIntosh
Preamplifiers or A/V Control Centers the correct set-
ting of the Input Sensitivity Switch would be the 1.7V
position.
While listening to a recording with a wide dynamic
range, adjust the volume control on the Preamplifier or
A/V Control Center so during the loud passages of the
recording of the approximate rotational position of the
Preamplifier or A/V Control Center Volume
Control
1
The impedance of a Loudspeaker actually varies as the
Loudspeaker reproduces different frequencies. As a result,
the nominal impedance rating of the Loudspeaker (usually
measured at a midrange frequency) might not always agree
with the impedance of the Loudspeaker at low frequencies
where the greatest amount of power is required. Contact the
Loudspeaker Manufacturer for additional information about
the actual impedance of the Loudspeaker before connecting
it to the McIntosh MC75.
Figure 7
Figure 9
Figure 8
Figure 10
