increase in temperature will result in a reduced life expectancy for the amplifier.
The Autoformer creates an ideal match between the Power Amplifier Output Circuitry and the Loudspeaker. There is absolutely no performance limitation with an Autoformer. Its frequency response from below 20Hz to well beyond 20,000Hz exceeds the Power Output Circuitry Frequency Response, and extends well beyond the audible range. Its distortion level is so low it is virtually impossible 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 Loud- speakers.
Protection Circuits
The different types of protection circuits incorporated in the MC303 insure a long and safe operating life.
The MC303 incorporates the McIntosh Sentry Monitor output transistor protection circuit. Refer to figure 16. There is absolutely no
compromise in sonic performance with this
circuit, and it ensures safe operation of the
amplifier under even the most extreme op-
the shape of these waveforms. If an amplifier channel is overdriven, there will be a dif- ference between the two signal waveforms. When the differ- ence exceeds 0.3% the Power Guard activates the PG light and a dynamic electronic at- tenuator 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 absolutely no audible side effects and the sonic purity of the music reproduction is perfectly preserved. The MC303 Power Amplifier with Power Guard is not limited to just the rated power output, but will actu- ally produce distortion free output well above its rated power due to the McIntosh philosophy of conservative design.
Without Power Guard
Figure 18
With Power Guard
Figure 19
erating conditions. The MC303 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 inaudible 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 system tweeters. You will never experience the harsh and damaging distortion due to clipping.
The Power Guard circuit is a waveform comparator, moni- toring both the input and out- put waveforms. Under normal operating conditions, there are no differences between
Power Supply Circuits
To compliment the design of the MC303 Power Amplifier Circuitry, there is a high current high voltage power supply for the three channels. Refer to figure 20 on page 15. The power amplifiers draw high current from the AC power line. Therefore, it is important that they plug directly into the wall outlet.
The MC303 incorporates a very large high current Main Power Transformer. Refer to figure 21. It is enclosed in the legendary McIntosh Potted Enclosures and weighs 38 lbs. The super size multiple large main filter capacitors
Figure 21
14
