conditions. To further insure reliability a special
power output SENTRY MONITORING CIRCUIT
prevents failure of the power amplifier transistors
due to excessive mismatch or shorting of the output.
When the MA 6200 operates normally the SENTRY
MONITORING CIRCUIT has no effect on signals
passing through the power amplifier. If the power
dissipation in the output transistors should rise
above normal design limits the SENTRY MONITOR-
ING CIRCUIT restricts the drive to the output stage
which reduces the dissipation in the output tran-
sistors. The SENTRY MONITORING CIRCUIT acts in-
stantaneously for any input signal or load combina-
tion. This arrangement assures circuit reliability. On-
ly Mclntosh gives you this degree of protection.
The direct coupled complementary amplifier cir-
cuit holds the output at DC ground potential when
there is no signal input which eliminates the need
for a coupling capacitor in the output. The MA 6200
power amplifier is all direct coupled to insure max-
imum low frequency performance. In most direct
coupled circuits, failure of any transistor in the
power amplifier will cause a DC potential to appear
in the output. To assure that no damaging or interfer-
ing DC appears across the output terminals, a
special, very fast acting protector circuit constantly
monitors the output circuit for DC. If, at any time, a
constant DC level appears, the speakers are discon-
nected. The protective circuit reacts in milliseconds.
Speakers remain disconnected until the cause has
been fixed. Under normal operating conditions the
protective circuit has no affect on the operation of
the output circuit. This is another example of Mcln-
tosh continuous protection.
occurs when an amplifier is asked to exceed its
design limits and the capacity of the power supply.
Since POWER GUARD does not begin to work until
this point is reached, the power capability of the
amplifier is never affected.
TURN ON DELAY
The MA 6200 has transient-free turn on and turn
off characteristics. A heavy duty relay, time-
controlled by a transistor switch, connects the out-
put to the speakers. The control to the transistor
switch is derived from a long time constant
capacitor charging network that turns the relay on
approximately two seconds after the power switch
is turned on. The same circuit has a short turnoff
time constant and the relay drops out before the
amplifier's main power supply has a chance to
discharge.
POWER SUPPLY
Two high current power supplies - a positive 48
volt and a negative 48 volt DC - are used to drive the
output power amplifier. Very large filter capacitors,
12,000 microfarads each, are used to store a large
amount of energy to provide good filtering and ex-
cellent voltage regulation. Good low frequency
response and negligible low frequency distortion in
the power amplifier stages depends on the regula-
tion of the power supply. Two additional elec-
tronically regulated power supplies are used in the
MA 6200. A + 18 volt and a - 18 volt line supply all
operational amplifiers.
POWER GUARD
Amplifiers are capable of delivering large quan-
tities of power when they are driven to clipping. Clip-
ping is caused when the amplifier is asked to pro-
duce 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 damage most loud-
speakers, particularly delicate high frequency
tweeters. A new Mclntosh advancement helps pro-
tect your speakers from this kind of damage. The MA
6200 has a built-in waveform comparator which com-
pares the wave shape of the input signal with the
output signal. If the disparity between the two
signals exceeds 0.5% [equivalent to 0.5% total har-
monic distortion] a red limit indicator illuminates.
With any further increase in distortion the POWER
GUARD circuit will operate. This circuit limits the in-
put dynamically so that the amplifier can not be over-
driven. POWER GUARD eliminates amplifier output
clipping.
POWER GUARD does not limit the dynamic range
or the power output of the power amplifier. Clipping
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