Iron OOR

GRAMOPHONE DREAMS

- HERB REICHERT

I’m deep into audio power amplifiers because they remind me of race car engines. Both power sources are wildly inefficient, converting only a small percentage of their stored energy into work while dissipating the rest as heat and vibration. Mainly though, I love how race car engines sound. How they shake the air. Just like amps and speakers.

Audio-frequency power amplifiers take a small input signal-usually less than 1V-apply it to an input impedance of (typically) no less than 10k ohms, and make this tiny eyeblink of power (0.0001 W) into a waveform that's many times more powerful, capable in some cases of doing hundreds of watts of speaker-moving work. To grasp the magnitude of this chore, and what I am about to describe, it might be useful to imagine power amplifiers as energy adders.

The majority of audio amplifiers I've encountered were built-in closed metal boxes (with power cords), and every high school grad knows that energy is conserved: neither gained or lost. Therefore, if we want more energy at the output-if we want the amplifier to amplify-then we need to import energy from an outside source like our household AC line) and store it in something-capacitors-that's engineered to hold and release a rapidly varying stream of energy.

Audio frequency amplifiers are notoriously inefficient. Therefore, amplifiers of the highest fidelity must not only store (by necessity limited) volumes of stable standing energy in their capacitors; they must also have effortless access to a flow of fresh energy through their power cords (to fill and refill those capacitors) and, equally important, a direct, low-impedance path to an infinite source of free electrons from our good and gracious Mother Earth.