Network Audio Players/Servers

When designing a complex/comprehensively equipped amplifier at an attractive target price, choices have to be made in the BOM (bill of materials). In this case, Leak has fitted an MM phono stage and specified a very flexible USB/HDMI digital section while retaining a relatively hefty linear PSU for the power amplifier. However, rather than use discrete, complementary power transistors, the output stage uses capable, monolithic TDA7293 Class AB DMOS modules from STMicroelectronics. These are variously rated at 100W or 75W (10% and 1% THD, respectively) so Leak is – sensibly – employing a pair of the modules per side, sufficient to realise a generous 2x92W/8ohm and 2x140W/4ohm with enough in reserve to support 120W, 215W, 345W and 365W (19A) into 8, 4, 2 and 1ohm loads, respectively, under dynamic conditions [1kHz/10msec to 1% THD, see Graph 1].

Overall gain is a sensible +33dB, noise is low and the A-wtd S/N ratio a wide 92dB (re. 0dBW) while the fairly ‘flat’ 0.010-0.015ohm output impedance holds the frequency response to ±0.1dB (20Hz-20kHz) and –1.2dB/100kHz (all re. 10W/8ohm). Very low bass looks to be AC-coupled, rolling away to –1dB/4Hz and –4dB/2Hz. Distortion clearly increases with diminishing speaker load impedance [again, see Graph 1] but, into 8ohm, remains <0.002% from 1-40W, rising to 0.005% at the rated 75W (all re. 1kHz). Versus frequency [see Graph 2, below], distortion is typically lowest through the midrange and increases at HF from 0.001-0.04% (1kHz-20kHz, re. 10W) and from 0.003-0.12% (1kHz-20kHz, re. 50W). In similar fashion, CCIR (19/20kHz) intermodulation distortion is largely second-order at 0.015% (re. 10W/8ohm). Overall, this is a well-judged little amp. PM