The 1/55 takes advantages of new features and advancements from the 1/70 to create a worthy successor to the 1/50.
1/55 imports all of the functionality of the 1/70 into a chassis that maintains the look and power output of the 1/50.
The foundation is an all-tube amplification circuit using two matched sets of 6550 power tubes, fed by 6922 input tubes. The traditional combination of power and grace for which Audio Research is renowned is instantly recognizable even in this compact model. Challenge the 1/55 and be surprised by its depth of bass and dynamic expression. Two Lexie TubesⓇ provide display information for input selection and volume.
Chief among the improvements from 1/50 to 1/55 is the addition of auto-bias. This keeps the output tubes in their optimal operating range for the life of the tubes.
The 1/55 integrated amp has independent tube preamplifier and tube amplifier sections, providing flexibility with a set of stereo preamplifier outputs. While we suspect very few listeners will pair it with an external power amp, many will need this feature to feed powered subwoofers that offer only low-level inputs.
The active preamplifier also offers a much wider range of gain setting compared to the passive preamp on board the 1/50. This is especially helpful with recordings that are cut at a low gain setting for wide dynamic range. Despite its identical power rating to the 1/50, the 1/55 will offer additional output due to both additional gain and higher headroom in its preamplifier section.
The headphone output is driven by the 6550 output tubes. It was designed for high quality headphones, able to provide the best possible personal listening experience.
The DAC card’s AKM Velvet Sound DAC chip provides high resolution formats over USB, Optical, Coax, and Bluetooth. All are upsampled. The result is fine resolution, great transparency, and tonal purity that is rarely heard outside of the finest separate DACs.
There are three sets of single-ended inputs and one set of Balanced XLR inputs. The optional phono card has both MC and MM gain settings, controlled via the I/55 remote. MC loading is also adjustable, from 50 to 1k ohms.
TECHNICAL SPECIFICATIONS
| Power Output | 50 watts continuous from 20Hz to 20kHz. 1kHz total harmonic distortion typically 1% per channel, below 0.1% at 1 watt (Note that actual power output is dependent upon both line voltage and “condition” i.e.: if power line has high distortion, maximum power will be affected adversely, although from a listening standpoint this is not critical) |
| Power Bandwidth | (-3dB points) 10Hz to 22kHz |
| Frequency Response | (-3dB points at 1 watt) 7Hz to 30kHz |
| Input Sensitivity | 1.25V RMS for rated output |
| Input Impedance | 100K ohms Balanced, 48K ohms Single Ended |
| Output Polarity | Non-inverting. Balanced input pin 2+ (IEC-268) |
| Input Impedance | 100K ohms Balanced, 50K ohms SE 8 Inputs – 4 balanced, 4 single-ended |
| Output Taps | 8 ohms, 4 ohms |
| Power Requirements | 105-130VAC 60Hz (210-250VAC 50Hz) 252 watts at rated output |
| Tube Required | 2 matched pairs 6550WE; 3 x 6922 (1 input, 2 driver) |
| Dimensions | Width 16.5” (42 cm) Height 7.25” (18 cm) Depth 13.5” (34 cm) Weight: 40 lbs (18.1 kg); 51 lbs (23.1kg) shipping weight |
