Pre/Power Amplifiers

Burmester 218

Weighing in at 42kg and very nearly a full half-metre in width, the 218 might be expected to have an equally 'massive' 8ohm power specification. However, while the 218 is rated at a relatively modest 165W/8ohm, and achieves 2x193W/8ohm in practice, the power supply regulation is sufficiently stiff to accommodate peaks at <1% THD of 221W, 419W, 738W and 1.13kW into 8, 4, 2 and 1ohm loads, respectively [see Graph 1, below]. With a current capacity of 34A, the '165W' 218 is thus very tolerant of low and difficult loudspeaker loads. The output impedance is a fairly consistent 0.014-0.019ohm (20Hz-20kHz), maintaining its +0.0dB to –0.06dB response (20Hz-20kHz) into most loads. At the extremes, the 218 dips to –0.5dB/1Hz and –1.15dB/100kHz. Gain is more than high enough at +34.3dB (balanced input) and noise very low, yielding a very wide 95dB (re. 0dBW) A-wtd S/N ratio – so the 218 is a very quiet amplifier.

Just as critical, from a subjective standpoint, is the uniformity of the 218's distortion profile, no doubt informed by Burmester's proprietary 'X-AMP technology'. Versus level, distortion remains <0.002% from 1W to 140W and only touches 0.0028% at the rated 165W (all re. 1kHz/8ohm). Versus frequency, distortion gently climbs from 0.0007%/100Hz to 0.0017%/1kHz and 0.008%/20kHz (re. 10W/8ohm), a pattern that holds true at lower and higher power outputs [see Graph 2, below]. Intermodulation distortion is <0.0003% (re. 10W). Finally, stereo separation is a wide 70dB+ (20Hz-20kHz), channel balance/matching is good to 0.01dB and any DC offset at the output is held to below ±2mV – impressive bearing in mind the 218 is a fully DC-coupled/capacitorless amplifier. PM

Burmester 077

Burmester's 60-step volume control operates with a mix of 1dB and 2dB steps (one 2dB step for every three 1dB steps) to offer a reliable 80dB range and a channel balance error of <0.1dB down to volume setting '15'. Gain is variable within either 'Low' or 'High' master modes, with the default '00' gain setting offering +3.5dB (or +6.5dB in 'High') adjustable to +15.6dB and +19.2dB (+12dB input gain setting in 'Low' and 'High' modes) and down to –2.5dB and +13.1dB (–06dB gain setting in 'Low' and 'High'). The maximum output(s) are 3.5V in 'Low' and 21.5V in 'High' M-Out modes regardless of input level 'gain' settings. Output impedance is 112ohm in 'Low' and 64ohm in 'High', and the A-wtd S/N is 99.1dB and 92.5dB, respectively, but there is no difference in the ±0.0dB response (20Hz-20kHz) which reaches +0.5dB/1Hz and –1.45dB/100kHz. Distortion is lowest in 'Low' mode at 0.00015-0.0003% [20Hz-20kHz, 0dBV; black trace, Graph 2] with 2nd-4th harmonics dominating.

Used as a DAC/preamp with upsampling enabled, the 077 delivers a 2.63V balanced output for a 0dBFs digital input (the output clips beyond volume position '55'). Distortion is a low 0.0006-0.0016% (re. 20Hz-20kHz) at this full scale input [see red trace, Graph 2] and falls to a minimum of 0.0003%/1kHz and a lower 0.00009%/20kHz over the top 30dB of its range [Graph 1]. The A-wtd S/N is a fine 109dB, linearity good to ±0.2dB over a 100dB range and channel separation is an excellent 130dB. Wolfson's WM8741 DAC [see Burmester 069, HFN Jan '12] has built-in jitter rejection (all sample rates <10psec), while the linear phase digital filter confers 99dB stopband rejection and a 'digital' response of –0.0dB/20kHz, –2.1dB/45kHz and –14.5dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. PM