A few issues ago, we raved about the B.M.C. Audio BDCD 1.1 CD player/transport and DAC1 DAC/preamplifier. We liked these products because they represented some of the truest aspects of high-end audio as it used to mean; high performance sound, significant build quality, and ‘reassuringly expensive’ without being utterly financially unattainable. There is a big piece missing from this B.M.C. Audio line up, however: the power amp.
In this case, it’s not just a power amplifier. The CS2 is a cleverly configurable amplifier that can be used as an integrated, or the power amp in a pre-power system. Also, if used with B.M.C.’s own system architecture, it can easily adapt to become potentially an even higher level of amplifier, and the clever fibre-optic comms connections between DAC and amp (or amps) means installing the system is extremely easy.
Easy, that is, in terms of plugging the thing together. Things are a little different when it comes to physically lifting the CS2 into place. In today’s Class D, slimline world, this is a beastie. Behind the big front panel, large VU meters and huge volume and control knobs is an amplifier built for the big game. Open the amp up (not an easy task, it’s all vents and fins rather than a simple top-plate) and you are met with an exercise in transformer and capacitor use. It’s not weighed down by a heavy chassis; it’s rooted in place thanks to the sort of power reserves that could jump-start an Airbus. Any amplifier with 2kW of toroidal transformer in the power supply is very likely going to be dynamic, powerful, and stable… and the amp is all of those things.
However, it’s not simply a big amplifier. Instead, this uses B.M.C.’s own LEF (Load Effect Free) design. This uses a very small single-ended class-A output stage with a low-impedance voltage output. This stage, as well as the gain stages, has no feedback loop whatsoever. An independent circuit, not attached to the music signal, measures the current inside the voltage stage and keeps it constant by supplying an external phase independent current. Combined with a floating voltage cascade, the voltage stage hardly moves on its non-linear curve and thus doesn’t produce any THD. Uniquely, this is actually avoiding THD instead of correcting it by an overall loop.