B&O Beomaster 6000 4Ch Lab Report

Lab Report

A generous proportion of the Beomaster 6000 4Channel's 16kg weight is given over to its substantial PSU transformer and this, in turn, helps support an equally generous 4x35W/8ohm and 4x60W/4ohm power output in SQ/quad mode. B&O rated this 670mm-wide behemoth of a receiver at just 4x30W/8ohm and 4x40W/4ohm but we discover in practice that it is considerably more powerful and load tolerant, maintaining a full 2x44W/8ohm and 2x72W/4ohm at <1% THD with sufficient in reserve to support 46W, 85W, 130W and 115W into 8, 4, 2 and 1ohm loads under dynamic conditions [see Graph 1, below]. The Beomaster 6000 4Ch even includes sophisticated over-current protection that lifts and resets a series of output relays in the event of overload – so no crude in-line fuses for this elegant 1970s creation. Distortion is lowest at 2-300Hz (0.006%/1W), increasing gently with frequency (0.017%/1kHz to 0.11%/20kHz) and with level [0.025%/1kHz to 0.17%/20kHz at 10W; Graph 2].

Gain is a sensibly modest +34.6dB ('70s receivers typ. offered 40dB+), noise is impressively low and the A-wtd S/N ratio up with the 'average' amplifiers of today at 85dB (re. 0dBW), though channel separation (just 40dB) and balance (1.1dB re. 0dBW) are somewhat weaker. With all tone controls in their defeat position, the 6000 4Ch's response shows a sweetening presence/treble roll-off of –0.35dB/10kHz, –0.9dB/20kHz to –5.2dB/100kHz. This trend is emphasised into lower impedances (output impedance is 0.5ohm) while the 'LO' filter extends the pre-existing –1.7dB/20Hz bass roll-off to a steep –3dB/58Hz and –26dB/20Hz. The latter is ideal should your big, reflex-loaded woofers of the day be flapping in the wind of a warped LP and too-low arm/MM resonance. PM


Dynamic power output vs. distortion up to 1% THD into 8ohm (black trace), 4ohm (red), 2ohm (cyan) and 1ohm (green) speaker loads. Max current is 10.7A


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

Power output (<1% THD, 8/4ohm) 44W / 72W (4x35W/4x60W)
Dynamic power (<1% THD, 8/4/2/1ohm) 46W / 85W / 130W / 115W
Output imp. (20Hz–20kHz/60kHz) 0.42–0.56ohm / 0.75ohm
Freq. resp. (20Hz–20kHz/100kHz, 0dBW) –1.7dB to +0.85dB/–5.2dB
Input sensitivity (for 0dBW/30W) 53mV / 365mV
A-wtd S/N ratio (re. 0dBW/30W) 84.8dB / 99.6dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.013–0.17%
Power consumption (Idle/rated output) 41W / 136W
Dimensions (WHD) / Weight 670x80x320mm / 16kg