Integrated Amplifiers

Hi-Fi News has been at the forefront of the 'energy debate' for many years [see HFN Apr '08], publishing power consumption figures for every product tested. Integrated and power amplifiers typically soak up more AC power than source components and preamplifiers, and tube amplifiers are the least efficient of the lot. In order of efficiency (AC mains power in vs. amplifier power out) Class D amplifiers are the 'greenest'. At 2x100W/8ohm output, the best Class D amplifiers will be drawing just 230W from the wall, or <10W when idling [green trace, Inset Graph] while a Class A/B transistor amp of similar specification will draw 400W or more [see red trace].

Icon Audio is well aware of this and has made steady improvements over the years. For example, its Stereo 40 MkIIIm [HFN Mar '13] drew 222W at idle (switched on but no signal) and 320W at the rated 2x40W while the ST40 MkIV [HFN May '19] drew a reduced 198W when idle and 289W at the rated 2x50W output. The stripped-down ST40 we have here is some 5kg lighter, mainly due to the smaller iron transformer cores, while the reduced 0.9A filament current and ~20W dissipation of each 6L6/KT66 pentode results in a further reduction in idle consumption to 153W or 209W at the (reduced) 2x28W power output. While Icon Audio should be congratulated for addressing the consumption/cost equation for tube-focused audiophiles, in practice the efficiency of even this amplifier is still <30% over its full dynamic range [black trace, inset Graph]. PM