Loudspeakers

Chicken or egg, which came first? In practice ATC's MOSFET power amplifiers were initially developed for its professional (active) loudspeakers before being refined into the 'domestic' 100W P1 [HFN Mar '10] and 300W P2 [HFN Mar '17] models. Naturally there's been some to-ing and fro-ing between the design of the active speaker power packs and its hi-fi stereo amplifiers, so the three-channel system fitted inside the SCM100SE is its most elegant yet, with fully discrete op-amps used in the balanced line input and active filter stages. The crossovers are set at 380Hz and 3.5kHz and employ 2nd-order Butterworth all-pass filters. These offer a flat magnitude/variable phase response – the implementation claimed to offer an improved phase coherence through the crossover regions that could not be achieved with a conventional passive crossover design.

Finally there are the amplifiers themselves, a combination of 50W (treble), 100W (mid) and 200W (bass) Class A/B MOSFET stages with their own rugged power supplies. Separate PSUs, with localised regulation, are employed for the active line and filter circuits, the ensemble adding a full 5kg to each speaker's weight. PM