Brilliant Corners

In a scene from The Silence of the Lambs—a film that for all of its camp happens to be nearly perfect—FBI cadet Clarice Starling asks caged psychopath Hannibal Lecter for help in figuring out a serial killer's motives. "Do we seek out things to covet?" Lecter responds, following Starling with his eyes as though she were his next meal. "No," he continues, "we begin by coveting what we see every day." Lecter's astute observation applies equally well to audiophilia. Much of this hobby consists of coveting: before we own a component, we usually spend a long while imagining all the ways it will improve our lives.

To misquote Morrissey, some knobs are better than others. The Manley Neo-Classic 300B amplifiers that I've been listening to, for example, have a knob marked "feedback" that goes from 0 to 10. I've learned so much from using it that I've come to believe that if your amp doesn't have such a knob, it should. You see, the higher you set this control, the better the amp will measure. Applying more global negative feedback to these amps lowers their nonlinear distortion and noisefloor, increases their bandwidth, renders them less sensitive to the speaker's impedance variations and otherwise makes them more stable and efficient. In fact, by applying lots of feedback to an amplifier, it's possible to reduce distortion to barely measurable levels.

So what's the problem? Well, a few turns of the knob suggest that negative feedback isn't as useful as it appears on paper.