lower than optimum, causes more output current to flow, which results in extra heat being generated in the power output stage. This increase in temperature will result in a reduced life expectancy for the amplifier.
The Autoformer creates an ideal match between the power amplifier output stage and the loudspeaker. Refer to figure 15. There is absolutely no performance limitation
Figure 15
with an Autoformer. Its frequency response exceeds that of the output circuit itself, and extends well beyond the au- dible range. Its distortion level is so low it is virtually im- possible to measure. In the rare event of a power amplifier output circuit failure, the McIntosh Autoformer provides absolute protection from possible damage to your valuable loudspeakers.
Protection Circuits
The MC252 incorporates its version of the McIntosh Sen- try Monitor out-
put transistor protection cir- cuit. Refer to figure 16. There is absolutely no
compromise in sonic perfor-
mance with this circuit, and it ensures safe op- eration of the
Figure 16
amplifier under even the most extreme operating condi- tions. The different types of protection circuits incorpo- rated in the MC252 insure a long and safe operating life.
The MC252 also includes the unique patented McIntosh Power Guard circuit. Power Guard elimi- nates the possibility of ever overdriving the amplifier into clipping. Refer to figures 17, 18 and 19. An overdriven amplifier can produce both audible and inau- dible distortion levels exceeding 40%. The audible distortion is unpleasant to hear, but the inaudible ultra- sonic distortion is also undesirable, since it can damage valuable loudspeaker system tweeters. You will never experience the harsh and damaging distortion due to clip- ping.
The Power Guard circuit is a waveform comparator, monitor- ing both the input and output waveforms.
Under normal operat- ing conditions, there are no differences between the shape of these waveforms. If an amplifier channel is overdriven, there will be a difference between the two sig- nal waveforms. When the difference exceeds 0.3% (equivalent to 0.3% harmonic distortion), the Power Guard ac- tivates the PG light and a dynamic elec-
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