Integrated Amplifiers

In practice, the InPoL Legacy achieves higher than its rated 100W, offering 2x160W/8ohm before falling back to 2x105W/ 4ohm (re. 1kHz at <1% THD). Relaxing our distortion limit to 2% realises a substantially higher 2x220W/4ohm with 182W and 225W under dynamic conditions into 8 and 4ohm, respectively [see Graph 1]. Current output is limited by the InPoL inductor to just 7.5A and although this is sufficient to maintain the rated Class A power into 8ohm it’s also partially responsible for the limited 70W and 33W into 2 and 1ohm loads, respectively.

Distortion increases gently with output over the first 10W, from 0.016%/1W to 0.032%/10W, but then increases more steeply to 0.046%/20W, 0.12%/50W and 0.3% at the rated 100W (re. 1kHz/8ohm). This is all within Pathos’ published specification. Versus frequency, distortion increases at higher frequencies – a feature of the limited feedback – and at lower frequencies when also at lower level [see Graph 2]. At 1W/8ohm this is 0.009-0.05%, increasing to 0.018-0.45% at 10W and rising further to 0.20-3.4% at 100W (all re. 20Hz-20kHz).

The +32.8dB overall gain is artfully judged, noise is low and the A-wtd S/N ratio above average at 88.9dB (re. 0dBW). The output impedance is a flat 0.218-0.25ohm (20Hz-20kHz), rising to 0.74ohm/100kHz and while this is still sufficient for the amp/speaker system response to be slightly modified by swings in loudspeaker impedance, the amplifier’s ‘native’ response was largely unaffected by changes in our non-reactive test loads. Here its response reaches out from 1Hz-30kHz (–0.5dB) and to –4.9dB/100kHz into 8ohm with only a slight attenuation to –0.5dB/20kHz and –6.6dB/100kHz into 1ohm. PM