Headphones

Adding to the permutations on offer here – the various gain, push-pull or single-ended configurations – Manley also includes a rotary that governs the level of global feedback (NF) applied. Counter-intuitively, perhaps, turning the control fully clockwise yields minimum feedback, and a maximum overall gain of +19dB in 'Low'/push-pull mode, while fully anticlockwise delivers maximum feedback and a reduced +10dB gain. In practice the level of feedback applied is roughly 'maximum' right up to 12 o'clock on the rotary, falling thereafter, also determining frequency response extension and distortion.

Ordinarily, output impedance would also increase with decreasing feedback, but the 'L/M/H' gain settings have the biggest influence here. Distortion is not especially low anyway, but ranges from 0.016% at 1kHz/1V output to 0.7%/20Hz (low bass) with maximum feedback [black trace, inset Graph] up to 0.042%–2% with minimum feedback applied [red trace]. Distortion in triode (SE) mode is typically 5-8x higher still, regardless of the NF applied. PM