Pre/Power Amplifiers

Variable (user-adjustable) negative feedback is a core feature of this triode tube amp and may prove invaluable in ‘fine-tuning’ its sound with your personal choice of loudspeaker. Feedback defines the gain bandwidth of the amplifier, and also its distortion and output impedance. Manley offers 11 steps from ‘0dB’ to ‘10dB’ although the former will still invoke some residual nested feedback to ensure stability.

Overall gain reduces from a high +31.8dB at ‘0dB’ feedback to just +19.6dB at ‘10dB’ feedback with steps of 30.5dB, 29.4dB, 28.0dB, 27.0dB, 25.8dB, 24.5dB, 23.4dB, 22.4dB and 21.2dB in between. So you must also account for the increase in sensitivity (loudness) when auditioning lower feedback settings. The 8ohm response also changes from +0.4dB/20kHz (10dB feedback) to –3.0dB/20kHz (0dB feedback) – see Graph above [10dB feedback, black; 8dB, blue; 6dB, green; 4dB, orange; 2dB, grey; 0dB, red].

There will be further deviations in amp/speaker response as the output impedance increases from a low ~0.65ohm with 10dB feedback to a significant 3.2-3.7ohm with 0dB feedback. Finally, distortion increases from 0.08-5.0% (10dB feedback) to 0.26-4.1% (0dB feedback, all re. 10W/ 20Hz-20kHz) – see Graph above. PM