Technics ST-K808/SE-A808 'preceiver'/power amplifier Lab Report

Lab Report

Vintage it may be, but the performance of Technics' ST-K808 'preceiver' could teach more than a few modern preamps a thing or two! Gain is a very sensible +9.8dB and distortion is not only vanishingly low but also wonderfully uninfluenced by frequency – just 0.0005-0.0006% from 100Hz-10kHz at 0dBV output [black trace, Graph 2]. Maximum output is 9V and the input overload threshold is at least 7V, so the ST-K808 is perfectly compatible with all modern sources and power amps. Similarly, the 98.5dB A-wtd S/N ratio (re. 0dBV) is as 'digital ready' as any preamp from 2018 while the response with its gently tailored ultrasonic response (–0.4dB/20kHz to –3.4dB/100kHz) is arguably very well suited to contemporary DSD64 downloads!


Dynamic power output versus distortion (up to 1% THD) into 8ohm (black trace), 4ohm (red), 2ohm (cyan) and 1ohm (green) speaker loads


Distortion vs. extended frequency – preamp (black, 0dBV) versus power amp (red, 10W/8ohm)

The partnering SE-A808 power amp proved similarly impressive although Sanyo's thick film hybrid Darlington 'power packs' were seemingly more robust and lower in distortion on the right channel here than the left. On test, the best figures suggest that Technics' original specification was very conservative indeed at 2x45/8ohm, with 2x65W/8ohm and 2x90W/4ohm being achieved in practice. (Sanyo's STK1050 module was rated at a 'minimum of 50W' with a tolerance for 18A peak current.) Within the SE-A808, and under dynamic conditions, the PSU regulation is sufficiently 'relaxed' to allow 101W, 152W and 165W into 8, 4 and 2ohm with 118W/1ohm or 10.9A for 10msec at <1% THD [see Graph 1]. Distortion increases with level from 0.0024% at 1W/8ohm to 0.0078%/10W and 0.01%/40W (all 1kHz) and with frequency [red trace, Graph 2] from 0.00075% in the bass to 0.0125%/3kHz (all 10W/8ohm). Noise is low and the A-wtd S/N good at 83.2dB (re. 0dBW). PM

Power output (<1% THD, 8/4ohm): 65W / 90W
Dynamic power (<1% THD, 8/4/2/1ohm): 101W / 152W / 165W / 118W
Output imp. (20Hz–20kHz, pre/power): 370–425ohm / 0.05ohm
Freq. resp. (20Hz–100kHz, pre/power): +0.0dB to –3.4dB / –3.7dB
Input sensitivity (for 0dBV/0dBW): 329mV / 73mV
A-wtd S/N ratio (re. 0dBV/0dBW): 98.5dB / 83.2dB
Distortion (20Hz-20kHz, 0dBV/0dBW): 0.0005-0.0006% / 0.008-0.013%
Power consump. (Pre/idle/rated output:) 8W / 29W / 193W
Dimensions (WHD, Pre/Power) / Weight: 430x75x310 (280)mm / 11.6kg