Article VI- Power Amplifiers
We’ve developed a line of three power amps for our Desktop Audiophile System: a Stereo Amp, a Monoblock, and a Bi-Amp. All three amps are based on the latest generation Bang & Olufsen ICEpower class-D amplifier modules. These amps are perfect for a desktop application: highly efficient; small size; low heat output; and terrific sound. Frankly, we’re amazed and extremely pleased with the excellent price-to-performance ratios of these amps.
The Desktop Stero Amp is simplest and least expensive way to fire up your desktop is to get on of these 47 Watt/Channel (into 4 Ohms) amps. Take the left and right volume controlled outputs from the back of the Desktop Headphone Amp and put it into the left and right inputs of this amp, then wire up your speakers from the two pairs of binding posts on rear of the amp.
Looking for that liquid ease that comes from a little well placed overkill? Buy a pair of 170 Watt, balanced drive, Monoblock Amplifiers (one for each speaker), and prepare to be astonished. Improved channel separation and headroom (no pun intended) delivers holographic imaging and organically natural articulation with jaw dropping ease.
The Desktop Bi-Amp is designed to use with speakers (like the Harbeth HL-P3ES-) that are bi-amp capable. Bi-ampable speakers have two binding posts on the back of each speaker, you can remove the jumper straps and drive the tweeter and woofer with separate amps. The Desktop Bi-Amps are sold as a pair; each has one input and two outputs for use with speakers of this type.
How Class-D Amps work
Class-D amplification is a little tricky to understand. Class-D does not mean digital, it’s just the letter after ‘C’, and when the new class of amplifiers was born, it was D’s turn. A class-D amplifier can also be called a ‘pulse width modulation’ amplifier.
A class-D amplifier has two inputs: the audio signal; and a high speed (about 200kHz to 500 kHz) precision triangle wave. These two signals are compared, and a series of pulses are created at the triangle-wave generator rate; when the triange-wave is higher than the audio signal, the output from the comparator is low; when the triangle-wave is lower than the audio signal the output pulse is high.
The result is a train of pulses in which the average value of the pulses is directly proportional to the amplitude of the incoming audio waveform. This stream of pulses is then amplified and put through a filter which removes the high frequency component of the signal, leaving only the average power level which represents the amplified audio signal.
The most important characteristic of this type of amplifier is that the output devices are either completely on or completely off. This means that the output devices are never in a condition where they are dissipating any heat. (When fully on they have virtually zero resistance and therefore do not dissipate power; when they are fully off they have no current flowing through them and again do not dissipate energy.)
Class-D amps do have potential troubles, however, high-frequency noise radiation, control of the signal during the dead time, and effective output filter changes due to the instantaneous apparent speaker impedance are among the problems that this typwe of design has to contend with. Fortunately, Bang & Olefson in the ICEpower class-D amplifier module development and manufacture have been able to largely overcome these problems and produce amplifiers that are extremely competitive, efficient and cool running.
For further, more technically complete explanations of class-D amplifiers check here and here.
http://www.audiodesignline.com/howto/177102531
http://sound.westhost.com/articles/pwm.htm
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