Mesa Rosette 300 Two:Eight, Owner'S Manual

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QUESTION
Why is the Class D power amplifier so small and light weight?
ANSWER
A Class D amplifier operates its output stage non-linearly, meaning that the output devices are switched either
fully on or fully off at a switching frequency of about 500kHz. This “cutoff-saturation” switching minimizes waste heat by avoid-
ing operation in the wasteful “linear range”, and without the heat, there’s no need for the large, heavy aluminum heatsinks.
QUESTION
How does the Class D amplifier work?
ANSWER
In Class D amplifiers, the analog audio signal is converted into a PWM (pulse width modulated) pulse train
representation of the analog audio signal (similar to the A/D converter in a PWM digital audio recorder but at a much higher
frequency) at +5 volts conventional computer logic level. This PWM pulse train is level shifted by large solid state switching
power transistors (that operate non-linearly to avoid waste heat) to a high voltage (and current), the resulting high level PWM
signal passes through a high powered “low pass reconstruction filter” that reintegrates the original but level shifted (amplified)
audio signal from the PWM signal which feeds your speakers. Class D is neither digital or analog, but share properties of
both platforms. (Disclaimer: While this is a very simplified description, and there are many critical details omitted, the basic
operational function is correct. There are a lot of highly technical tricks used in this highly specialized area of audio that are
important to a high performance, robust, safe and reliable design.)
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