Specifications

premise that all speakers have a fixed impedance
regardless of frequency In fact, the impedance of
many poor speakers designs varies by as much as 4
to 1 For a specific output voltage the current varies
inversely to the speaker impedance So if the speaker
impedance is lower, the output current and power are
higher Since Mclntosh can not control other
manufacturers speakers, we decided to provide extra
output current to drive these mismatched low imped-
ances and to indicate the REAL output power required
to drive them Therefore the meter circuit in the
MC7300 electronically measures both voltage and
current, multiplies them and displays the REAL
OUTPUT POWER IN WATTS
Another important feature of these output
wattmeters is their ability to respond 95% full scale
to a single cycle tone burst at 2kHz After voltage
and current are measured and multiplied, the product
is fed to a special circuit that accelerates the meter
pointer in the upward direction When it reaches its
peak, it pauses only long enough for the human eye
to perceive its position then returns to 0 Response
is almost 10 times faster than a professional VU me-
ter
A front panel switch is provided to change the
meters to the WATTS HOLD mode of operation fast
upward movement of the pointer but greatly
increased HOLD time at the peak of its travel The
highest power output of the source material is thus
recorded
OUTPUT AUTOFORMERS
The unequaled expertise of Mclntosh in the
design and manufacture of output transformers is leg-
endary in the Hi FI industry. In the MC7300 they
provide proper matching for 2, 4 and 8 ohm loads in
stereo and 1, 2, 4, 8 and 18 ohms in mono They
protect your speakers from damage in the event of an
output transistor failure provide low distortion power
transfer at frequencies well beyond human hearing
and deliver peak output currents in excess of 85
amperes
PROTECTION CIRCUITS
Some manufacturers of power amplifiers
advertised that their products do not require or use
protection circuits and that such circuits compromise
performance Mclntosh Laboratory agrees that
diligent measures are required to allow unrestricted
performance, but we also insist that protection
circuits are desirable and necessary to prevent
amplifier or loudspeaker damage due to abnormal
circumstance and that they actually enhance
performance The MC7300 incorporates seven
protection circuits to enhance its performance, assure
its reliability and to protect loudspeakers
POWER GUARD
Power Guard, a unique feature of Mclntosh
amplifiers, assures that each channel of the MC7300
will deliver full power free of clipping distortion
Clipping is caused when an amplifier is asked to
produce more power output than its design is capable
of delivering with low distortion Amplifiers that are
overdriven may deliver large quantities of power
when they are clipping but they have more than 40%
harmonic distortion. In this mode, the sound is
grossly distorted and the extra energy content of the
clipped signal will damage most loudspeakers The
Mclntosh Power Guard circuit protects your ears and
your speakers from this kind of damage
The Power Guard circuit consists of a
waveform comparator which monitors the wave
shape of the amplifier input and output signals
Normally there is no disparity between these signals
and the comparator produces no output When the
amplifier is driven beyond its maximum power
capacity a difference will develop If the disparity
exceeds 0 3% (equivalent to 0 3% total harmonic
distortion) the comparator output causes the amber
power guard indicator to light. If there is a further
increase in the disparity the comparator output
controls an electronic attenuator at the amplifier input
to reduce the amplifier gain, thus holding the amplifier
output to a low distortion value. Overdrive by 14dB
is possible before the output distortion exceeds 2%
SENTRY MONITOR
All power transistors have limits for the
maximum amount of power they can handle The
MC7300 output transistors and power supply have
been designed to allow very high current flow into
properly matched load impedances If, however, a
short circuit or very low value of load impedance is
applied to the output of the MC7300, destructive
current levels could be reached if it was not control-
led by the Sentry Monitor circuit. This circuit senses
the dynamic operating time, voltage, and current of
the amplifier output stage and controls the current
flow confining it to nondestructive limits Sentry
Monitor does not limit the power output available
MC7300 Product Preview/Page 6
MclNTOSH LABORATORY INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903