Pre/Power Amplifiers

With its analogue line stage based on the Director Mk2 (minus the DAC here), the Elector is essentially a buffered, unity gain volume control. At maximum volume the (balanced) output shows a mere –0.18dB loss while, courtesy of those VOLTAiR op-amps, the output peaks at a high 32.5V. This is also the Elector's maximum input level, a figure achieved by very few DAC/line sources aside from one or two similarly 'high voltage' and typically tube-based components, including the 92V-capable REF Phono 3SE from Audio Research [HFN Apr '22].

The output impedance [red trace, Graph 1 below] is a uniform 36ohm from 100Hz-20kHz, increasing very slightly to 38.5ohm at lower bass frequencies. This slight variation is not reflected in any significant low bass or high treble roll-off [black trace, Graph] – in fact the Elector has wide ±0.5dB response limits of 2Hz-50kHz, rolling away to just –1.8dB/100kHz (SPL quotes a –3dB/300kHz bandwidth). SPL also offers a very precise THD+N specification of '0.000992%' for the Elector although it references neither the test frequency or output level.

Leaving aside the fact that 'real world' production variations would make such a target impossible to guarantee, in practice the Elector preamp does rather better, incurring a mere 0.0001-0.0008% THD from 20Hz-20kHz at a standard 0dBV output [see Graph 2, below]. Better, perhaps, for SPL to specify its Elector preamplifier at <0.001% distortion (20Hz-20kHz, re. 0dBV). Finally, the A-wtd S/N is a respectable 93.8dB (re. 0dBV), residual noise a low –100dBV while the motorised 'Big Blue' Alps RK27 potentiometer offers a channel balance that's good to ±0.04dB at 0dB and ±1dB at –60dB. PM

Lab Report Power Amp

While SPL's quest for low distortion performance is firmly anchored with its line/preamp products, including the Phonitor xe [HFN Jul '21], the partnering s1200 stereo power amp is simply listed at <0.04% THD (re. 1kHz/8ohm). In practice, the s1200 meets this specification with distortion falling from 0.02%/1W to 0.01%/10W and a minimum of 0.003%/100W beyond which it increases again to 0.0055%/200W and 0.01% at the rated 300W/8ohm. At higher frequencies, particularly above 10kHz, distortion increases more markedly, although as its ~0.3-1% THD/20kHz increases only marginally with output level [see Graph 2, below] this suggests it's as much a function of the input buffer/voltage gain stage as the final power amp. Which, it must be said, is a very powerful 'engine' for the modest proportions of the SPL s1200's fan-cooled enclosure.

Rated at 2x300W/8ohm and 2x520W/4ohm it actually achieves 2x345W/8ohm and 2x630W/4ohm, increasing still further to 405W, 765W, 1.30kW and 1.59kW under dynamic conditions into 8, 4, 2 and 1ohm loads, respectively [see Graph 1, below]. Note also from this Graph that distortion under dynamic conditions is higher than with the same power under continuous conditions (0.028% versus 0.01% re. 10W/8ohm). The output impedance also follows this same 'flat' trend seen with the THD profile through bass and midrange (0.024-0.045ohm from 20Hz-6kHz) but then kicks up to 0.12ohm/20kHz and 1.30ohm/100kHz. Similarly with the frequency response: flat to within ±0.05dB from 2Hz-6kHz but then –0.55dB/20kHz and –6.9dB/100kHz. Finally, gain is +26.4dB (balanced in) and the A-wtd S/N ratio a little above 'average' at 86.7dB (re. 0dBW). PM