Интегральные усилители — Audio Note OTO Line SE

The OTO Line SE is a valve integrated amplifier from Audio Note of the UK, the line-only version of the OTO SE, which Andy Grove and Peter Qvortrup first designed in 1991 as a single-ended pentode development of the original OTO. Operation is pure Class A, using EL84 output valves in parallel single-ended configuration. For the 35th anniversary edition Audio Note reworked the design with a new output transformer made for this amplifier and wound in-house, and a power supply using a custom-designed choke. A sister model, the OTO Phono SE, adds an onboard valve MM RIAA stage, and both versions come in Line, Signature and Silver Signature build levels.

Key specs that matter

The current edition is rated at 8 W RMS per channel into either 4 or 8 ohm loads. The valve complement is four EL84 output valves and two ECC83 drivers. Line input sensitivity is 200 mV and input impedance is 100 kohm. Channel balance is held within plus or minus 0.3 dB. The chassis measures 140 mm high, 440 mm wide and 410 mm deep, and weighs 17 kg. Maximum power consumption is 125 W, from mains at 100 to 120 V or 220 to 240 V, 50 or 60 Hz. Earlier versions were rated at a maximum of 10 W in Class A, with four ECC83 valves and 350 mV line sensitivity, plus CD1, CD2, tuner and tape inputs plus tape and pre-amp outputs.

Engineering and use context

Every version uses a mains transformer with a C core, designed and wound by Audio Note, feeding a choke-filtered power supply, plus custom output transformers. The Signature build adds improved selector switches, copper foil signal capacitors and output transformers with I HiB cores. The Silver Signature goes further with Kaisei capacitors, non-magnetic tantalum and silver niobium resistors and S HiB core output transformers. Parallel single-ended operation pairs two EL84s per channel, which raises the available power while keeping the circuit in single-ended Class A. The front plate is made from black acrylic or from anodised aluminium, and Audio Note can supply custom colours.

Pairing

With its modest output, the OTO Line SE suits efficient loudspeakers and moderate listening levels in rooms of around 20 m2 rather than low-sensitivity designs. Audio Note's own speakers are the obvious system match. There is no phono input on this version, so a turntable needs an outboard MM stage or the OTO Phono SE.

Alternatives

The Audio Note Meishu is another single-ended integrated from Audio Note, built around a pair of 300B direct heated triodes.