McIntosh MC7106 Owner's Manual page 18

DIRECT CURRENT FAILURE PROTECTION
TECHNICAL
A protection circuit is provided that turns off the speakers if for any reason a DC voltage
DESCRIPTION
should appear at the output terminals of any one of the six channels. The speakers will turn
off only for the pair of channels that are affected. This safeguard prevents possible speaker
damage.
POWER GUARD*
The MC7106 amplifier includes the unique patented Mclntosh POWER GUARD circuit.
POWER GUARD eliminates the possibility of ever overdriving the amplifier into clipping.
Clipping occurs when an amplifier is overdriven past its output design capabilities. An over-
driven amplifier can produce both audible and ultrasonic distortion levels approaching 40%.
The audible distortion is unpleasant to hear, but the ultrasonic distortion is also undesirable,
since it can damage tweeter loudspeakers.
The POWER GUARD circuit acts as a waveform comparator, monitoring both the input and
output waveforms. Under normal operating conditions there are no differences between these
waveforms. If an amplifier channel is overdriven beyond its maximum distortion free output,
there will be a difference between the two signal waveforms. When the difference exceeds
0.3% (equivalent to 0.3% harmonic distortion), the amber POWER GUARD indicator will light.
If the difference continues to increase, the POWER GUARD circuit will control an electronic
attenuator at the amplifier channel input to reduce the gain just enough to prevent any fur-
ther increase in distortion. Distortion will not exceed 2% with as much as 14dB overdrive
at 1000Hz.
A Mclntosh power amplifier with POWER GUARD will always deliver its maximum distor-
tion free output. This power is always well above its rated power due to the Mclntosh philosophy
of conservative design. You will never experience the harsh and damaging distortion due to
clipping when using a Mclntosh amplifier with POWER GUARD.
POWER GUARD is protected by U.S. Patent No. 4048573.
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