Unless otherwise noted, all measurements were made on the left channel using the balanced inputs.

The frequency response of the Parasound Halo A 51 was –0.04dB at 10Hz, –0.01dB at 20Hz, –0.08dB at 20kHz, and –0.47dB at 50kHz, and essentially the same single-ended. The gain was 28.6dB balanced, 28.8dB single-ended. The A-weighted signal/noise ratio (10Hz–24kHz) mea-sured 98.5dB. The THD+noise at 1W into 8ohms was 0.013% at 20Hz, 0.014% at 1kHz, and 0.013% at 20kHz into 8ohms (0.015% at 20Hz, 0.015% at 1kHz, and 0.014% at 20kHz, into 4ohms).

Into an 8ohms load, the Parasound clipped (1% THD+noise) at 287W at 20Hz and 317W at 1kHz, all channels driven. Into 4ohms, clipping occurred at 379W at 20Hz and 382W at 1kHz, all channels driven. With two channels driven, the amplifier clipped at 332W at 1kHz into 8ohm and at 584W into 4ohm. The line voltage for all measurements was 120V, but the 5-channel, 4ohms readings shown here may be slightly low because they severely strained the voltage-control devices on our test bench! The Halo A 51 is a genuine powerhouse.—Thomas J. Norton