Vintage

The 'baby brother' of B&O's Beomaster 4400 [HFN Jun '12] musters a very distinctive technical performance, beyond the difference in rated power specification of 30W/8ohm vs. 50W/8ohm (2400-2 vs. 4400). In practice our venerable test sample sustained a maximum continuous output of 2x32W/

8ohm and 2x56W/4ohm with sufficient reserve to accommodate transient peaks (1kHz/10msec/<1% THD) of 42W, 72W, 36W and 17W into 8ohm, 4ohm, 2ohm and 1ohm loads, respectively [see Graph 1, below]. The 4.3A current headroom is modest, suggesting the 2400-2 is best used with speakers rated at 6ohm and above, and of generous sensitivity. However, Graph 1 also reveals another unusual 'feature' of this amplifier not seen in our review of the 4400 – the 2400-2's output stage distortion actually falls with decreasing load impedance from 0.07%/8ohm to 0.045%/4ohm to 0.035%/2ohm (re. 1kHz/10W).

Otherwise, the 2400-2's performance is more predictable, with distortion increasing linearly with output from 0.02%/1W to 0.07%/10W and 0.15% at its rated 30W/8ohm, and with frequency to 0.1%/10kHz and 0.19%/20kHz [all at 10W/8ohm – see red trace, Graph 2 below]. The amplifier's output impedance is gratifyingly flat at 0.11-0.12ohm across the 20Hz-20kHz audio range and the response sensibly tailored between –3dB points at 10Hz-80kHz. Noise is low too at –79dBV – testament not only to the design of B&O's linear power supply but also the elegant circuit layout – and ensures an overall A-wtd S/N ratio of 84.7dB (re. 0dBW). This is a match for many modern amps even if age has caused some drift in the opto-coupled volume, contributing to a 1dB channel imbalance at the reference 0dBW setting. PM