B&O Beogram 1800 turntable Lab Report

Lab Report

B&O provides a strobe pattern to assist in the manual fine-tuning of the Beogram 1800's speed although, with the strobe 'stripes' stationary, its absolute accuracy was a mere +0.3% adrift. Further fine-tuning using a spectrum analyser (not an everyday audiophile accessory, I know...) brought the speed bang-on 33.33rpm [see Graph 1, below] and revealed both the low peak wow (0.05% at ±2.8Hz) and, especially, very low peak flutter (0.03%). This is far better than many of today's new decks riding the wave of the vinyl revival. Rumble was slightly less impressive at –67.3dB (DIN-B wtd, re. 1kHz/5cm/sec) through the bearing where discrete resonances at 10Hz, 14Hz and 44Hz were detected, although the through-groove figure improves by about 1dB to –68.2dB thanks, in all likelihood, to the rubber mat.

The fitted tonearm is more complex than it looks – the pivot resting and swinging on three small steel ball-bearings while stylus pressure is adjustable over a 3.5g range via a threaded, cylindrical counterweight built into the rear of the tube. The thin-walled alloy tube and lack of any conventional headshell confers a low 8g effective mass that's purpose-designed for the moderate 25cu of the partnering SP10 pick-up, the latter tracking securely at just 1g. Friction is higher at ~40mg laterally than vertically and this, along with the tube's internal damping, results in a primary low-Q bending mode at 130Hz [see Graph 2, below]. The sequence of other peaks at 260Hz, 280Hz, 345Hz, 400Hz, 550Hz, 680Hz, etc, are probably related to the cartridge mounting, the fingerlift, the bearing and auto-lift/lower mechanism under the arm, but despite their complexity are relatively low in amplitude. PM


Wow and flutter re. 3150Hz tone at 5cm/sec (plotted ±150Hz, 5Hz per minor division)


Cumulative tonearm resonant decay spectrum, illustrating various bearing, pillar and 'tube' vibration modes spanning 100Hz-10kHz over 40msec

Turntable speed error at 33.33rpm 33.43rpm (+0.3%)
Time to audible stabilisation 6sec
Peak Wow/Flutter 0.05% / 0.03%
Rumble (silent groove, DIN B wtd) –68.2dB
Rumble (through bearing, DIN B wtd) –67.3dB
Hum & Noise (unwtd, rel. to 5cm/sec) –55.0dB
Power Consumption 12W
Dimensions (WHD) / Weight 438x160x324mm / 7.8kg