Integrated Amplifiers

Slimline chassis rated at 130W/4ohm? It might be tempting to think the Attessa SA is another 'off the shelf' Class D amplifier, but it's not... In practice this is a very capable Class AB amp that meets its specification at 2x88W/8ohm and 2x145W/4ohm with sufficient headroom to accommodate 105W, 195W and 330W into 8, 4 and 2ohm under dynamic conditions at <1% THD. However, there's a current limit of 16.7A that trips the electronic protection at 280W/1ohm [see Graph 1, below]. Midband distortion is held in check at ~0.0035% from 1-80W (~0.0085% via the left channel), increasing very slightly at low and high frequencies – 0.006%/20Hz and 0.007%/20kHz. The response shows a slight HF roll-off amounting to –0.6dB/20kHz (to –10dB/100kHz) but the most unusual feature is a +9.2dB boost at 3Hz suggesting care with big, reflex-loaded loudspeakers. Otherwise gain ('Low' sensitivity) is a sensibly limited +35dB and the A-wtd S/N ratio about average for the class at 85.2dB (re. 0dBW).

The performance of the Attessa's DAC stage is determined, in part, by Roksan's choice of the TI PCM5242's slow roll-off (low latency) minimum phase filter. Reduced time domain distortion (no pre-echo/limited post-echo) is traded for a minimal 5.5dB stopband rejection and early treble roll-off of –2.1dB/20kHz with 44.1kHz and 48kHz sample rates. Higher sample rates fare better with responses of –1.35dB/20kHz to –7.6dB/40kHz (96kHz) and –15.7dB/90kHz (192kHz) while distortion falls as low as 0.0005-0.0008% at –10dBFs from 20Hz-20kHz [see Graph 2]. The preamp's A-wtd S/N ratio is a creditable 107dB via the coaxial input while jitter is suppressed to 220psec (48kHz) and 320psec (96kHz). I discuss the BluOS performance in our boxout [p71]. PM