Audio Gadgets: Digital Amplifiers

To understand how a digital amplifier works, it is first important to understand how a classic linear amplifier works. Basically, an audio amplifier is an electronic device that takes a small signal audio inputs, usually in millivolt range and amplifies them into several watts strong enough to drive a speaker load.

Most audiophiles and enthusiasts have grown up with at least a basic understanding of what an amplifier does. It takes a tiny alternating electrical signal that represents the moment-to-moment variations of musical frequencies and their amplitudes (volume levels), and increases their strength many times so they're powerful enough to drive the cones and domes of speakers back and forth to generate air pressure variations (waves), which replicate the original sound waves.

Musical tones vary as slowly as 16 times per second (16 Hz)--a very low pipe-organ note--to as fast as 15,000 times per second (15 kHz) or more--the highest harmonics of a cymbal or a violin, for example.

The audio amplifier was invented in 1909 by Lee De Forest when he invented the triode vacuum tube. The triode was a three terminal device with a control grid that can modulate the flow of electrons from the filament to the plate. The triode vacuum amplifier was used to make the first AM radio.

Early audio amplifiers were based on vacuum tubes (also known as valves), and some of these achieved notably high quality (e.g., the Williamson amplifier of 1947-9). Most modern audio amplifiers are based on solid state devices (transistors such as BJTs, FETs and MOSFETs), but there are still some who prefer tube-based amplifiers, due to a perceived 'warmer' valve sound. Audio amplifiers based on transistors became practical with the wide availability of inexpensive transistors.

Shown below is my QUAD II valve amplifier which I treasure so much, it's been my pleasure to own such a great amplifier.

Most modern audio amplifier components are transistor based, shown below is the Marantz PM7001 Integrated amplifier.

The true measure of amplifier output is based on its RMS power and not in PMPO, PMPO rating tends to fool consumers who doesnt know anything about electronics. I won't go into details about that, just remember that when buying amplifiers, ask for the RMS rating and not the advertised PMPO rating.

[sinusoidal signal]

Amplifiers discussed above are classified as 'analog' amplifiers, that is, they accept audio signal in sinusoidal form. The input signal is amplified at the output to produce the same signal, only amplified. Deviation of the output signal from the input signal is called distortion, most amplifier manuals specify THD on the specs measured in %THD. For high fidelity, this is usually expected to be < 1% .

In Short, What In The World Is A Digital Amplifier ?

Unlike analog amplifiers, digital amplifiers accepts digital audio signals for processing directly from the CD or DVD player's laser pick-up. Most digital amplifiers has a build in PWM decoders and digital to analog converter integrated circuits.

What's inside the Optical Disc

Optical discs contains pits and bumps representing digital signals. These signals are read by a laser beam and fed into the digital output terminals. Modern optical disc players usually has a digital output, either optical or coaxial. Coaxial digital outputs uses the standard RCA jack to connect it to a digital amplifier, whereas optical digital outputs uses S/PDIF fiber optics links, or TOSLINK.

[I'm using an Audio-Pro fiber optic cable]