Negative feedback is one of those engineering tools that’s both brilliant and dangerous. It lowers distortion, flattens gain, extends bandwidth. It can also make things sound worse—if you use too much of it.
Imagine you’re driving a car and constantly correcting the steering. You see you’re drifting, so you turn the wheel a bit. The road curves, you adjust again. That’s feedback—looking at the output, comparing it to the input, and correcting the error.
But now imagine your steering has a delay. You turn, and the car responds 100 milliseconds later. By then, you’ve already overcorrected. Now it’s oscillating—tiny corrections chasing errors that are already gone.
That’s what happens in feedback loops with delay. When you apply negative feedback around a circuit, the correction signal is only as fast as the circuit’s bandwidth allows. In simple terms, the amp can’t “fix” the signal instantly. The higher the gain and the wider the loop, the longer it takes to respond.
This shows up in the impulse response: instead of a clean, single spike when a signal arrives, you get overshoot, ringing, or a slower rise time. That’s the amp correcting itself after the event.
But it also messes with phase—especially at high frequencies. Phase shift means the timing between harmonics starts to skew. Now that violin note isn’t just thinner—it’s spatially confused. The spatial cues encoded in time alignment get scrambled. Instruments don’t sit in a place anymore. They drift, flatten, or hover in weird ways.
It’s subtle, but your ear is hypersensitive to this. You hear it as loss of air, dimension, and that uncanny sense of “there-ness.”
That’s why we use local feedback—within a gain stage, not around the whole circuit. It stabilizes the gain where it counts, without the global time smear.
Where might we use this to our advantage? The new PMG Signature Preamplifier has zero negative feedback, and guess what? It is one of the biggest reasons this preamp will simply startle you with its openness.
You still get low distortion from the circuit's topology. But you also get music that breathes.
