NAD C 298

POWER AMPLIFIER

- KALMAN RUBINSON

Power amplifiers should be boring. They have a single, well-defined function: Make the input signal large enough to run a loudspeaker so that it makes sound at levels suitable for listening to music. Generally, controls and features are few or none. Peter Walker of Quad famously defined the ideal amplifier as a “straight wire with gain.” That’s just one feature: gain.

That ideal is not easy to achieve, for many reasons. Even a straight wire of any practical length and structure has properties (resistance, capacitance, inductance) that can affect how the signal is transferred to it on one end and how the signal is transferred from it on the other. These effects can be within the audible range depending on what device is at each end. Insert a complex device like a real-world amplifier (with different wires in and out) and Walker’s ideal starts to seem unrealistic, although it should be possible to get close.

Walker further stated that an “audio power amplifier is required to produce an output signal that differs from the input signal in magnitude only.”1 In attempting to realize that goal, he tried both tubed and transistor designs (although he averred that the latter were superior). Today, with the availability of tube amps and an expanding range of solid state designs, we have a broad range of options but no better standard than Walker’s.