Усилители мощности моно — Audio Note Neiro

Audio Note (UK) supplies the Neiro monoblock as a pair of separate chassis, one for each loudspeaker channel. Inside each box two 2A3 directly heated triodes share a pure Class A output stage wired in parallel single-ended form. In the current mono range it sits in the 2A3 parallel single-ended section, alongside the Empress and the Kageki, and the company offers it in three forms, the standard Neiro, a Neiro Low Gain and a Neiro Balanced.

Key specs that matter

Maximum output is 8 W RMS per channel into 4 or 8 ohm loads. The input presents 100 kOhm and reaches full power with a 250 mV signal. Level matching between the units is specified at plus or minus 0.3 dB. For the pair, the tube list is two 5U4GB rectifiers, four 2A3 output triodes and two 6SN7 double triodes, which means one rectifier, two output valves and one 6SN7 per chassis. Each amplifier weighs 20 kg and measures 195 mm high, 205 mm wide and 506 mm deep. The mains input accepts 100-120 V or 220-240 V at 50 or 60 Hz, and maximum consumption is 200 W.

Engineering and use context

Two 2A3 valves are paralleled within a single-ended output stage, so the pair shares the load while the circuit keeps the single-ended form, and the triodes run with direct heating. The amplifier uses zero negative feedback and a valve rectified supply. In the Level Four build the power supply is choke coupled with Cerafine filter capacitors. The output transformer uses a UHiB double C-core, wound with a copper primary and Audio Note silver secondary windings. Rather than plain film parts, signal coupling uses Audio Note copper foil capacitors, the resistors are 1 W tantalum types, and the internal wiring is Audio Note silver throughout, so the whole circuit is silver wired rather than copper wired. The narrow chassis is laid out in depth, with the valves and transformers placed one behind another.

Pairing

With its input sensitivity the standard version suits line level preamplifiers of ordinary output, while the Low Gain variant exists for sources and preamplifiers with higher output and the Balanced variant for preamplifiers with XLR outputs. With its low power, the Neiro is meant for loudspeakers of high sensitivity, and each speaker gets its own chassis.

Alternatives

The Audio Note Kageki is another mono power amplifier that uses paralleled 2A3 triodes.