Amplifiers come in all shapes and sizes, from the de-facto stereo amplifier to luxurious A/V receivers offering up to 7-channels and a plethora of features. Obviously there are also amplifiers that don’t come fully assembled but can be bought in kit-form and hence can be constructed tailored to your exacting needs. Hypex is a Dutch manufacturer of amplifier kits that are distributed worldwide by a network of dealers that also supply the do-it-yourselfer with loudspeakers, filter components and similar products.
Although Hypex is known for their subwoofer plate-amps they’ve recently endeavored to offer kits that allow you to construct your own full-range amplifier. What’s interesting about the kits that Hypex offers, however, is the fact that these are not your run-of-the-mill amplifier kits. They’re based on a whole new amplifier technology called ‘class-D’. Conventional kits regularly use amplifier technology dubbed ‘class-AB’, which has powered the majority of amplifiers over the past four decades and has basically reached a point where further improvements are unlikely.
Enter class-D, which sets a new standard. Although class-D is often referred to as being a ‘digital amplifier’ that’s not an accurate statement at all. There’s nothing digital about these amplifiers, so the ‘D’ in class-D has no relevance to the word digital. In essence the amplifier works much like an AM-radio. The amplifier oscillates at a given frequency, usually around 400KHz, which is called the carrier-frequency. The audio-signal is then mixed in with this carrier-frequency, so the carrier-frequency becomes amplitude modulated (AM) by the audio-signal, similar to AM-radio signals.
This mixed signal is then amplified and fed through an output filter. This output-filter, which is a classical 12dB/oct. low-pass L/C filter, will filter out the carrier-frequency; hence the net result available at the amplifier’s output will be the amplified audio-signal. Class-D offers a number of advantages over the established amplifier technologies such as class-AB. A distinct advantage of this technology is the fact that distortion is kept at a set level across all frequencies. Another advantage is the high efficiency (~90%) requiring less cooling, less stringent power-supply constraints and enabling smaller amplifiers to be built.
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