Music and Recording Reviews

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.