Both the 201 and 302 use the B&O PowerHouse modules. The differences are in the module used and its implementation.
The 201 (and 501) use the ASP modules which feature built-in SMPS power supplies. The amplifier is rather simple, consisting of the module itself plus the chassis and connectors for AC power, XLR input, and one pair of binding posts for speaker cable.
The 300 series use the A modules which require an outboard power supply. If you open the gorgeous anti-resonant chassis here is what you will find, beyond the ICEpower500A modules:
Lundahl input transformers. These transformers enable the input section to accomplish a number of unique goals, including insensitivity to unbalanced source impedances, high common-mode rejection extending to well beyond the audio bandwidth, immunity from RF contamination and system ground loops, and the same input impedance and gain regardless of whether the input signal is truly balanced or unbalanced.coupled inputs.
Plitron toroidal power transformer between the AC mains and the OPS power supply. This transformer interface increases the AC line voltage, which improves overall power supply efficiency, adds another stage of solation and AC mains filtering in both common and differential modes, and significantly reduces stray leakage currents throughout the entire audio system. Since the transformer is operating under ideal conditions due to the benefits offered by PFC, it does not exhibit common transformer problems such as hum and stray field radiation. This yields an even lower total system noise floor.
Dual
OPS 700w PFC switch-mode power supplies drive the output section. These are extremely expensive, retailing at around $1250 each, and aren't found in any other audio equipment to my knowledge. OPS supplies are used mainly in medical, defense, telecommuncations, and industrial control equipment.
I have a lot more information on the power supplies, as well as the ICEpower modules, if anyone is interested...
