Power Amplifier Reviews

The frequency response of the Theta Dreadnaught II measured –0.08dB at 10Hz, –0.03dB at 20Hz, –0.12dB at 20kHz, and –0.74dB at 50kHz. The amplifier's gain measured 25dB. Its signal/noise ratio at 1W into 8ohms (10Hz–24kHz) was –112.5dB, A-weighted. All of the above apply to balanced operation, but the single-ended results were only marginally different. The balanced THD+noise at 1W into 8ohms measured 0.038% (0.112% at 2W into 4ohms) at 20Hz, 0.035% (0.097% at 2W into 4ohms) at 1kHz, and 0.003% (0.006% at 2W into 4ohms) at 20kHz.

Into an 8ohms load, with five channels driven, the Dreadnaught II clipped (1% THD+noise) at 192W per channel at 20Hz and at 189Wpc at 1kHz (215Wpc with two channels driven at 1kHz into 8ohms). Into a 4ohms load, five channels driven, clipping occurred at 228Wpc at 20Hz and at 227Wpc at 1kHz (255Wpc with two channels driven at 1kHz into 4ohms).

With most solid-state amplifiers, particularly those with conventional feedback, distortion is low up to the point of clipping, but increases so rapidly after that point that the amp has, for all practical purposes, run out of steam. With the Theta, however, the distortion increases gradually as power increases. At 2% distortion, for example, the Dreadnaught II will put out 257Wpc into 8ohms and 341W at 4ohms (two channels driven at 1kHz). The amplifier is able to double its 8ohms rated power when the load drops to 4ohms, but at a distortion level of 7.4% (450Wpc, two channels driven at 1kHz). It should also be noted that the distortion in the Dreadnaught II at very high power levels is higher than we measured for the original Dreadnaught.

Theta would no doubt argue that the Dreadnaught II's distortion characteristics, most certainly due to the low feedback design, pays dividends in better sound at normal listening levels—levels that draw only a fraction of the amp's rated power. Judging from the listening results, it would be hard to challenge this position.—TJN