Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

The problem with feedback

PS engineer Darren Myers and I were enjoying lunch together at a new Thai food restaurant. The food was lousy but the conversation was stimulating when the subject turned to feedback.

Darren knows my distaste for too much feedback in a piece of stereo electronics and he wanted to wrangle me in a different direction.

What he pointed out to me made perfect sense. That when feedback is used to correct a problem, it doesn’t sound good and the more you rely upon it the worse it sounds. That much we could certainly agree on. This is the reason so many off-the-shelf op-amps sound dreadful. Their open loop (without feedback) bandwidth rolls off within the low audio band. They need feedback to even work.

Compare that with the opposite: a properly designed audio circuit whose open-loop bandwidth extends well beyond 50kHz and whose distortion products are below 0.1%. Used on its own that’d be a nice sounding circuit. Add feedback and wowsers!

The point is that when we use feedback to fix something that is broken—as opposed to fixing the problem itself—sound quality always suffers.

Used as a Band Aid we’re all the worse for it in the circuit.

Used as an enhancement the purity of music is honored and we all benefit.

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