Pre/Power Amplifiers

With a host of power MOSFETs, and a PSU to match, each BHK M600 boasts over 600W/8ohm on tap, and some 25A in reserve to support over 1kW into low 2ohm loads. Each mono chassis pulls 277W from the wall at idle, a portion of this soaked up by the triode tube stage but most is absorbed in the generous biasing of the bridged, quasi-complementary MOSFET power amp. These devices are mounted on two very substantial side-mounted heatsinks so, in practice, the M600 takes a few hours to reach thermal equilibrium at a toasty 50oC. Its designer, the late Bascom H King, typically took a relaxed approach to the application of corrective feedback – often good for sound but, in this case, only after a protracted warm-up.

When first switched on (beware, 'standby' still pulls 114W), a 'cold' M600 already shows a low 0.0055-0.006% distortion [re. 1kHz/10W/8ohm; black infill, inset Graph] but after several hours of running this reduces still further to 0.00095% [red trace] as the thermal latency of this metal mass and multiple parallel power MOSFETs is resolved. PM