McIntosh MCC602TM - Manual (Page 17)

17
Technical Description, con’t
Power Supply
Figure 16
Figure 14
Without Power Guard
Figure 15
With Power Guard
Figure 13
Input Test Signal
engineers know how to do it right.
Protection Circuits
The MCC602TM incorporates it’s version of the McIntosh
Sentry Monitor output transistor protec-
tion circuit. Refer to figure 12. There is
absolutely no compromise in sonic per-
formance with this circuit, and it ensures
safe operation of the amplifier under
even the most extreme operating condi-
tions. The different types of protection
circuits incorporated in the MCC602TM
insure a long and safe operating life.
This is just one of the many characteris-
tics of McIntosh Power Amplifiers that
make them world famous.
The MCC602TM also includes the
unique patented McIntosh POWER
GUARD circuit. Power Guard elimi-
nates the possibility of ever overdriving
the amplifier into clipping. Refer to fig-
ures 13, 14 and 15. An overdriven am-
plifier can produce both audible and in-
audible distortion levels exceeding
40%. The audible distortion is unpleas-
ant to hear, but the inaudible ultrasonic
distortion is also undesirable, since it
can damage valuable loudspeaker sys-
tem tweeters. You will never experience
the harsh and damaging distortion due to
clipping.
The POWER GUARD circuit is a
waveform comparator, monitoring both
the input and output waveforms. Under
normal operating conditions, there are no differences be-
tween the shape of these waveforms. If an amplifier chan-
nel is overdriven, there will be a difference between the
two signal waveforms. When the difference exceeds 0.3%
(equivalent to 0.3% harmonic distortion), the POWER
GUARD activates the PG light and a dynamic electronic
attenuator at the amplifier input reduces the input volume
just enough to prevent any further increase in distortion.
The POWER GUARD circuit acts so fast that there are ab-
solutely no audible side effects and the sonic purity of the
music reproduction is perfectly preserved. The
MCC602TM Power Amplifier with POWER GUARD is
not limited to just the rated power output, but will actually
produce distortion free output well above its rated power
due to the McIntosh philosophy of conservative design.
Power Supply
The high efficiency Pulse Width Modulation Regulated
Power Supply operates with 85% efficiency and features
MOSFET power transistors switching at 40KHz. Refer to
figure 16. The power supplies are independent for each
channel. Regulation is maintained from 12 to 16 volts at
the battery input. The turn-on inrush current is cushioned,
by a soft start circuit in the power supply which eliminates
component stress during turn-on.
Accidental blockage of the cooling intake port or some
other fault condition could cause the amplifier temperature
to continue to rise, even with the fan at full speed. A tem-
perature sensing circuit in the power supply will reduce
heat dissipation by lowering the voltage to the amplifier. If
cooling is still not sufficient, additional heating will shut
down the power supply completely. The fan will continue
to run and once normal temperatures are restored, opera-
tion will resume.