Усилители мощности моно — Audio Research Reference 750SEL

The Reference 750 SEL is a monaural valve amplifier made by Audio Research, built at the company's headquarters in Maple Grove, Minnesota. It is the final iteration of the 750 series and was offered as a limited production run of ten pairs. Each unit is sold singly at a list price of USD 42,500, so a stereo system calls for two chassis.

Key specs that matter

Each chassis is specified for 750 W continuous from 20 Hz to 20 kHz, with roughly 850 W available at clipping measured at 1 kHz. Output stays above 750 W into speaker loads between 4 and 16 ohm, and separate 4, 8 and 16 ohm taps sit on the back panel. Total harmonic distortion at 1 kHz is typically 0.5 percent at full rated power and below 0.04 percent at 1 W. The signal enters through a balanced XLR connector only, and mains power arrives through a 20 A IEC socket. Each chassis measures 343 x 584 x 528 mm and weighs 77.2 kg.

Engineering and use context

Every channel's output stage uses sixteen KT150 tubes. Two further KT150 tubes each drive a bank of eight output tubes, which is how the amplifier handles bias control across such a large complement. Power supply regulation relies on 6550WE and 6H30 tubes rather than solid-state parts, and a massive custom-built power transformer works alongside an equally large custom output transformer. Compared with the earlier SE version, the SEL update brings 23 new wires and 26 new capacitors. Before shipping, every unit goes through 48 hours of burn-in, followed by testing and careful matching of tubes. The front panel carries twin analogue meters - one monitors power output and is also used for bias adjustment, while the second displays line voltage. A meter on the rear panel tracks accumulated tube hours, which helps plan tube replacement over the life of the amplifier.

Pairing

Because the only input is balanced, the preamplifier feeding this monoblock must provide XLR outputs. The choice of taps lets the owner match the transformer secondary to what the connected speaker presents, and the 20 A mains connector means the supply circuit and power cord should be rated accordingly. With two heavy chassis, a sturdy floor-level platform close to each speaker is the practical placement.

Alternatives

The Audio Research Reference 160M is a far smaller mono tube amplifier with four KT150 output tubes, rated at 140 W in ultralinear mode or 70 W in triode mode.