Vintage Electronics

How Small Can They Get? – A Look At Super-Miniature Audio Power Amplifiers

New generation super-miniature amplifiers are a result of the same miniaturization that has caused computers and cell phones to shrink. Products are shrinking at a rapid tempo. At the same time, vendors are packing in more and more features. The majority of audio amplifiers would be tube amps in the past. Even though a large number of fanatics still is fond of tube amplifiers, they have been replace by solid state amps for the most part.

Today’s amps combine traditional pre-amps and power amps and arrange everything neatly in a single box no larger than a VCR. New developments in audio technology in regard to power efficiency of have permitted the development of a new generation of super-miniature audio amplifiers, such as Amphony’s microFidelity Model 100. Even though these amps are as small as a deck of cards, they are capable to deliver up to 50 Watts power and easily drive a speaker to full volume.

“Class-A” and “Class-AB” amplifier topologies were the two primary amplifier architectures of previous audio amplifiers. These technologies have rather low power efficiency. Analog audio amplifiers will only convert between 20% to 30% of the consumed energy into audio while the remaining portion is radiated as heat. Analog amplifiers hence require substantial cooling which is done by heat sinks that are often bulky and prevent the amplifier from being made very small.

Digital “Class-D” amplifiers offer higher power efficiency than analog amplifiers – usually around 80% to 95% – and thus can be miniaturized. One major difficulty which has slowed the growth of “Class-D” amplifiers is audio distortion which is caused by nonlinearities of the switching output stage.

Some new amplifier technologies have emerged. Among those are “Class-T” and newer generation “Class-D” architectures. These types of new architectures, such as the technology used in Amphony’s Model 100 use a feedback mechanism. The output signal is fed back to the amplifier input. By using this feedback, the amplifier can compensate for nonlinearities of the output stage. This enables the distortion to be reduced to levels similar to analog audio amplifiers. At the same time the amplifier offers the high power efficiency of digital amplifiers.

These new generation miniature audio amplifiers open up applications where traditional amplifiers would fail, such as speaker installations where space is premium, including in-ceiling speakers and applications that connect speakers to a cable box or DVD/MP3 player.