Power amplifers take a line level signal -- like the one that comes out of a preamplifier or processor -- and add power to it so that it can drive speakers. While most power amplifiers are built into receivers or otherwise have multiple channels, such as a stereo amplifier that works with both the left and right channel signal, some are one channel only. These "mono block" amplifiers offer significant benefits over traditional multichannel amplifiers.
Class AB Monoblocks
Most high-quality amplifiers use a Class AB design. In these amplifiers, the line level input signal serves as a trigger. When the amplifier senses a signal, it lets power from the power supply pass through. AB amplifiers always keep a little bit of power flowing to the switching device, even when there is no signal passing through it. This design combines the potentially cleaner sound of a power-hungry Class A amplifier with the potentially less accurate, but much more energy-efficient sound of a Class B amplifier. In a mono block amplifier, there is one input, one power supply and one amplifier circuit that feeds one amplifier.
Class D "Digital" Mono Blocks
Class D mono blocks also have a single channel, but operate very differently from Class AB amplifiers. Instead of having an always-on power supply, they switch the power supply on and off very quickly to simulate the waveform of the input signal. This rapid switching makes them extremely efficient, and allows class D mono blocks to be much smaller and much less power hungry than traditional AB amplifier designs. On the other hand, according to Home Theater Review Magazine, some audiophiles feel that their sound quality is lacking.
Mono block amplifiers have two key benefits over traditional multichannel amps. Because they only handle one channel of sound, there is no risk of multiple channels bleeding together and muddying the sound; and because they have a dedicated power supply, they deliver all of the power that the channel they are amplifying requires, without having it split with other channels.
Because each mono block amplifier is a separate unit, it is usually much more expensive to set up a system with mono blocks than with comparable multichannel amplifiers. A multichannel system also usually takes up more space, and presents a wire-routing challenge because each amplifier has its own power cord.
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