Avid Sigsum Integrated Amplifier Lab Report

Lab Report

With so many tube, hybrid and variations on the Class D theme populating the ranks of hi-fi amplifiers these days, AVID's Sigsum is about as close to the 'textbook' Class A/B amplifier as you'll find. However, with no fewer than four pairs of Sanken A1294/C3263 power devices per side, plus that huge ~1kVA mains transformer in tow, the rated 110W/8ohm power output looks fairly modest. In practice the Sigsum will deliver a continuous 2x128W/8ohm and 2x225W/4ohm with sufficient headroom for 142W, 265W, 459W and 535W into 8, 4, 2 and 1ohm loads [see Graph 1, below] – powerful, certainly, but there's possibly some untapped reserve under the bonnet should AVID's engineers choose to open the throttle. As it stands, the Sigsum offers a sensibly moderate +38.6dB overall gain (balanced in) and an above-average – low noise – 89.3dB A-wtd S/N ratio (re. 0dBW). The response is flat and extended with a –3dB/1Hz DC filter and a HF reach of –0.14dB/20kHz to –0.67dB/100kHz, although there's some progressive loss of extreme top-end into lower impedances, reaching –0.83dB/20kHz and –4.0dB/100kHz into the toughest 1ohm loads.

The parallel/complementary design of the Sigsum's output stage confers an impressively consistent trend of distortion versus output, holding to within 0.004%/1W to 0.006%/10W and 0.0085%/100W (all 1kHz/8ohm). Versus frequency, however, distortion does not simply increase at HF in the fashion of most solid-state designs but gently trends upward from the lowest bass through midrange and treble – specifically 0.0009%/20Hz to 0.006%/1kHz and 0.028%/20kHz (all re. 10W/8ohm). Both these features are clearly illustrated in Graph 2, below. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 23.1A


Distortion vs. frequency at 1W/8ohm (black, 5Hz-40kHz), 10W (blue) and 70W (red, 20Hz-20kHz)

Continuous power (<1% THD, 8/4ohm) 128W / 225W
Dynamic power (<1% THD, 8/4/2/1ohm) 142W / 265W / 459W / 535W
Output imp. (20Hz–20kHz/100kHz) 0.024–0.090ohm / 0.66ohm
Freq. resp. (20Hz–20kHz/100kHz) –0.02dB to –0.14dB / –0.67dB
Input sensitivity (for 0dBW/110W) 33mV / 355mV
A-wtd S/N ratio (re. 0dBW/110W) 89.3dB / 109.7dB
Distortion (20Hz-20kHz, 1W/10W) 0.0004–0.017%/0.0009–0.028%
Power consumption (idle/rated o/p) 56W / 372W (1W standby)
Dimensions (WHD) / Weight 471x190x500mm / 31kg
Price £14,995

AVID Hi-Fi Ltd
Kimbolton, Cambs
Supplied by: AVID Hi-Fi Ltd
01480 869900