Integrated Amplifiers

Pegaso's specification for its one-and-only product is very limited. The P50A is rated at 50W without reference to load, distortion or frequency just as the single set of speaker outputs are not referenced to any particular transformer secondary. I discuss the description of 'Class A' in my boxout, otherwise the achievable power output is largely determined by speaker load and the tolerable limit for distortion. Like many limited-feedback tube amps, the P50A's distortion increases progressively with output rather than slamming into the endstops with a hard clip, so while 2x25W is achievable into 8ohm between 1-3% THD it's possible to squeeze more into 4ohm – 2x27W/1%, 2x33W/2% and 2x38W/3%. There's more still under dynamic conditions at 28W, 55W and 82W into 8, 4 and 2ohm before falling back to 28W/1ohm [see Graph 1]. Distortion otherwise increases at bass frequencies (core saturation) from ~0.12% midband to 1.4%/20Hz at 10W/8ohm and at HF to 1.2%/20kHz [see Graph 2] while the A-wtd S/N ratio is about 'average' at 85dB (re. 0dBW).

The output impedance is high at 1-1.9ohm (20Hz-20kHz) but not as high as we've seen with many other recently-tested tube amps [see HFN Mar & Apr '21], which means the P50A's system response is less influenced by peaks and dips in the attached speaker's impedance trend. In fact, into a non-reactive 8ohm load, the response is uncommonly flat and extended to within ±0.2dB (20Hz-20kHz) and just –1.6dB/100kHz. And this trend simply gets flatter and more extended still into lower 4, 2 and 1ohm loads. There is, however, a subsonic 'bump' of +5.5dB/3Hz so the P50A is absolutely not suited to life with a vinyl-playing front-end and big, reflex-loaded loudspeakers. PM