Integrated Amplifiers

The PA 1100 E's Class D amplifier bests its rated 140W with 2x160W/8ohm and 2x265W/4ohm while, under dynamic conditions, there's headroom to service peaks of 215W, 415W and 720W into 8, 4 and 2ohm loads with protection limiting output to 405W into 1ohm [see Graph 1, below]. Otherwise performance is influenced by the Class D architecture, including its slightly below-average 78dB A-wtd S/N ratio (re. 0dBW) that would be closer to 73dB if various ~18-22kHz spuriae were included. The reactive output impedance climbs from 0.040.05ohm/20Hz-1kHz to 1.1ohm/20kHz, peaking at 18ohm/52kHz, and influencing the amp/speaker response accordingly. Distortion also rises with frequency from <0.0035% through bass and midrange to 0.05%/20kHz and 0.1%/40kHz, but is typically 10x higher under dynamic conditions over the first few watts. This is clearly illustrated in Graph 1 while, under continuous output conditions, distortion increases more linearly with output from 0.001%/1W to 0.004%/10W, 0.014%/100W and 0.019% at the rated 140W/8ohm (all at 1kHz).

The PCM1795-based DAC stage offers a 104dB A-wtd S/N ratio from a 1.2V preamp output. Good jitter rejection is achieved at ~80psec (all sample rates, all inputs) while distortion falls to a minimum of 0.0009%/1kHz and 0.0022%/20kHz over the top 20dB of its dynamic range [see Graph 2]. The default FIR digital filter offers responses of –0.3dB/20kHz, –1.6dB/45kHz and –3.9dB/90kHz with 48kHz, 96kHz and 192kHz files, respectively. T+A's own Bezier IIR filter eliminates any pre/post ringing in the time domain but alias rejection is poorer and the responses are –4.6dB/20kHz, –5.7dB/45kHz and –7.6dB/90kHz. PM