Integrated Amplifiers

There is seemingly a lot of amplifier under the Model 404 Reference's bonnet, including a substantial power supply and very impressive (optional) MM/MC phono card. However, rather than use discrete output transistors, Moonriver has opted for a pair of TI's Overture-series 11-pin power amp modules. The LM3886 was introduced some 23 years ago and is rated at 38W/8ohm, or 50W/8ohm with ±35V PSU rails. This is the specification adopted by Moonriver for this 'Reference' version of the Model 404 integrated amplifier although, on test, the output is closer to 2x46W/8ohm and 2x72W/4ohm (re. 1kHz at <1% THD) with a little extra headroom to accommodate 51W, 92W, 146W and 178W into 8, 4, 2 and 1ohm loads under dynamic conditions [see Graph 1, below].

Moonriver has modified its expectations for the amplifier's S/N, as its flyer claims '95dB (line)' while the website says '85dB (line)'. In practice the A-wtd figure is closer to 81dB (re. line in/0dBW out) while the overall gain is a very high +46.1dB. As this requires just 95mV from your (2V) digital player to reach full output, it's arguable that the 'Blue' ALPS volume control is not being optimally employed here. Distortion increases gently with output level from 0.003-0.014%/1W to 0.009-0.024%/10W and 0.03-0.06%/30W [all 20Hz-20kHz, see Graph 2], broadly in line with the 0.03% specification of TI's amp-on-a-chip. The ~0.14ohm output impedance is defined by Moonriver's choice of external components and while not low it is usefully constant from 20Hz-100kHz. The response is less 'flat' however, showing a gentle treble roll-off with a –0.8dB drop at 20kHz and an arguably (again) sensible –7.7dB at 100kHz. PM