Engström ERIC Encore Mono Power Amplifers Lab Report

Lab Report

This fabulous example of 'audio architecture' is ordered with either 8ohm or 4ohm output transformer secondaries – our sample, judging by the 72W/4ohm power delivery, was configured with the latter. Into 8ohm, the ERIC Encore delivered 56W with 56W, 72W, 78W and 83W achieved under dynamic conditions into 8, 4, 2 and 1ohm [see Graph 1, below]. This equates to a maximum current of 9.1A which is not unreasonable for a pair of 845 tubes operating with a 1000V plate voltage. These tubes are running as close to Class A as practical – the power consumption at idle and full 70W output unchanged at 430W while the 185oC triode temperature cools under load. Anyway, all my power figures were obtained with a slightly relaxed 2% THD limit although, as Graph 1 also illustrates, the amp is clearly optimised for 8-4ohm loads with distortion increasing markedly into 2 and 1ohm. At 1W/8ohm distortion is as low as 0.04% through the midband, increasing to 0.09% at 10W/8ohm, but jumps up at HF to reach 1.2%/10kHz and 9.1%/20kHz/10W [see Graph 2, below].

The 1.45-1.26ohm (20Hz-20kHz) source impedance of the '4ohm tap' will have some impact on damping and system freq. response, depending on choice of speaker, but the bandwidth of the amplifier – flat to within ±0.5dB from 48Hz-45kHz and –10.5dB/60kHz – is otherwise set by one of the interstage coupling transformers. Overall gain is a sensibly modest +26.3dB (balanced XLR input), requiring an 810mV input to raise the rated 70W/4ohm output. However, a moderate (rectifier) noise of –51dBV pulls the A-wtd S/N down to 76.2dB (re. 0dBW) – comparable with a vinyl rather than 'digital' system. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max current is 9.1A


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

Power output (<2% THD, 8/4ohm) 56W / 72W
Dynamic power (<2% THD, 8/4/2/1ohm) 56W / 72W / 78W / 83W
Output impedance (20Hz–20kHz) 1.45-1.26ohm
Freq. response (20Hz–20kHz/100kHz) –0.85dB to –0.1dB / –9.8dB
Input sensitivity (for 0dBW/70W) 140mV / 1100mV (balanced)
A-wtd S/N ratio (re. 0dBW/70W) 76.2dB / 95.0dB
Distortion (20Hz-20kHz, 10W) 0.085–9.1%
Power consumption (Idle/Rated o/p) 430W / 430W
Dimensions (WHD, each) / Weight 360x480x750mm / 65kg (each)
Price £136,950 (pair)

Supplied by: Boyer Audio Ltd, UK
0330 223 3769