Pre/Power Amplifiers

Of all the features on offer in this innovative pre/power combo – including the L1’s input DC offset calibration – the ability to adapt the M1.1’s applied feedback on the fly is arguably the most useful for optimising your system’s performance. While a range of 100% to 0% feedback is offered, the latter does not really mean ‘zero compensation’. In practice there is always sufficient nested feedback to manage the bandwidth, gain and stability of the M1.1’s input and output stages. Nevertheless the notional ‘100%’ global feedback setting necessarily delivers the lowest distortion versus frequency [black trace, inset Graph], the lowest output impedance (0.012-0.035ohm, 20kHz-20kHz) and the least variation in frequency response against big swings in loudspeaker load.

Switching to 80% feedback [cyan] increases distortion from 0.0003-0.015% to 0.0017-0.028% (20Hz-20kHz/10W) and the output impedance to 0.03-0.055ohm while 60% [orange] gives 0.003-0.05% and 0.05-0.072ohm, respectively. Note that the Graph has a logarithmic Y axis so the differences in distortion appear less significant with the lowest levels of feedback. In fact there is a regular increase in THD with each 20% reduction in feedback. So at 40% [green] the M1.1 incurs 0.005-0.075% distortion, 20% [purple] has 0.006-0.09% and 0% global feedback [red] brings 0.0075-0.12% (all re 20Hz-20kHz, 10W/8ohm). ‘0%’ feedback also sees the M1.1’s output impedance increase to 0.11-0.126ohm, offering ~10x less damping than at 100% feedback. All this feeds into the overall system sound. PM