Negative Feedback
Negative feedback returns part of an amplifier's output in opposition to its input to correct deviations in the signal.
Global feedback surrounds the amplifier; local feedback acts within stages. A feedback-free design omits negative feedback, while switchable designs allow the user to change its use or amount. These describe circuit arrangements rather than a quality ranking.
Negative Feedback — Headphone Amp
Feedback can influence gain, distortion and output impedance, affecting how the amplifier behaves with a headphone load. The result depends on circuit implementation and operating conditions. A switchable arrangement may change these properties between settings, so the mode used matters when reading measurements.
Compare the stated scope of the feedback and measured performance at the same setting. 'No global feedback' does not establish that stages lack local feedback. A bare reference to voltage or current feedback does not identify the loop's extent. Worldwide mains-voltage support has no connection with global feedback in the audio circuit.