Интегральные усилители — Audio Research I/55

Audio Research introduced the I/55 as the successor to the I/50 integrated amplifier. It keeps the same output rating and tube line-up but adds automatic bias, an active tube preamplifier stage in place of the earlier passive design, a wider gain range and a tube driven headphone output. Prices start at USD 6,950 in the US, and six finishes are listed - black, silver, red, blue, gold and white.

Key specs that matter

Output is 50 W per channel continuous from 20 Hz to 20 kHz. Two matched pairs of 6550WE tubes form the output stage, and three 6922 tubes handle input and driver duties. Frequency response measured at 1 W is 7 Hz to 30 kHz at -3 dB, with a power bandwidth of 10 Hz to 22 kHz. THD at 1 kHz is typically 1% per channel and falls below 0.1% at 1 W. Sensitivity is 1.25 V RMS for rated output, and input impedance is 100 kOhm on the balanced input and 48 kOhm on the single ended inputs. The chassis is 42 cm wide, 18 cm tall and 34 cm deep and weighs 18.1 kg.

Engineering and use context

Four line inputs are fitted, three on RCA sockets and one on XLR. Auto-bias adjusts the output tubes on its own, so an owner no longer needs a technician visit to rebias after a tube change. The headphone output is powered by the 6550 tubes rather than a separate solid state circuit. Two LexieTubes display the active input and volume, and a remote control is supplied. Speaker connections are made to 8 ohm and 4 ohm output transformer taps. Optional cards add a DAC based on an AKM Velvet Sound chip with USB, optical, coaxial and Bluetooth inputs and upsampling, and a phono board covering MM as well as MC cartridges, with MC loading adjustable from 50 to 1,000 ohm. The mains draw at rated output is 252 W, from a supply of 105 to 130 V at 60 Hz or 210 to 250 V at 50 Hz. Compared with the I/70, the I/55 keeps a smaller chassis.

Pairing

Stereo preamplifier outputs allow one or two subwoofers or a further power amplifier to join the system. With the phono card installed, a turntable connects directly, and the MC load can be matched to the cartridge from the remote. The Bluetooth input on the DAC card gives phones and tablets a wireless route into the amplifier without a separate receiver. Speakers of moderate to high efficiency suit its moderate tube power, and the separate taps accept both common nominal loads.

Alternatives

The Audio Research I/70 is the next integrated amplifier up, delivering 70 W per channel from KT120 tubes through Reference 75SE output transformers.