Предусилители — Audio Research Reference 6SE Line-Stage

The Reference 6SE Line-Stage is a remote-controlled, fully balanced valve preamplifier from Audio Research, built in a single chassis without a phono section. The company calls it the highest performance it has offered in a one-box preamplifier and says the circuit draws on research carried out for the Reference 160-series and 750SEL power amplifiers.

Key specs that matter

Four balanced inputs at 120k ohm and four single-ended inputs at 60k ohm are joined by an assignable processor passthrough. Two main outputs and one record output are each provided on both XLR and RCA, with output impedance of 600 ohm balanced and 300 ohm single-ended. Main-output gain is 12 dB balanced and 6 dB single-ended, while the record output runs at 0 dB. Frequency response is 0.4 Hz to 200 kHz, +0 and -3 dB at rated output into a 200k ohm balanced load, and distortion stays under 0.01% at 2 V RMS balanced. Residual noise is 1.7 uV RMS, IHF weighted, which Audio Research equates to 109 dB below 2 V output, and crosstalk measures -88 dB or better at 1 kHz and 10 kHz. The case is 480 mm wide, 198 mm high and 419 mm deep, with handles extending about 41 mm forward, and the net weight is 17 kg.

Engineering and use context

The audio path is a Class A design with zero feedback and a single gain stage, using six 6H30P dual triodes. A further 6H30P and a 6550WE work in the power supply as vacuum-tube regulation, and the electronically regulated supplies hold line regulation better than 0.01%. Volume is set by rotary encoders in 103 steps. At switch-on and after a brown-out the unit mutes its outputs for 45 seconds while the valves stabilise. Front push buttons cover Power, Menu, Enter, Mono, Invert and Mute, with settings reached through a menu. The mains inlet is a 20 A receptacle, consumption is 130 W in operation and 2 W in standby, and versions exist for 100-135 VAC at 60 Hz and 200-250 VAC at 50 or 60 Hz.

Pairing

Audio Research specifies a load of at least 10k ohm and no more than 2000 pF, so the power amplifier input and the interconnect run should respect both limits, which favours short cables and amplifiers with moderate or high input impedance. Because gain is doubled on the XLR side, a balanced power amplifier takes full advantage of the circuit, and the assignable passthrough input allows a home cinema processor to drive the front channels through this preamplifier.

Alternatives

The Audio Research Reference 20 is a newer line-stage preamplifier with dual-differential all-tube balanced circuitry, using two 6H30P triodes for signal gain plus a 6550 and a 6H30P in its supply.