This amp is the swankiest integrated around. It matches the AR-XA turntable (featured below), and would fit perfectly in Don Draper's Manhattan apartment (last season included AR-3 speakers in his sunken living room). Now for the tech stuff. Some people will find this next section deathly boring, but we've been receiving requests to break down exactly what we do when we restore an amplifier. So here goes... enjoy.
On this amp we replaced the electrolytic capacitors (E. Caps) on the phono stage (C1, 2, 7, 8, 9, 11, 12). Other non-electrolytics were checked and were within tolerance. E Caps were replaced on the tone Control Board (C18, 19, 20, 29, 30). E. Caps were replaced on Power Supply (+/- 39 vdc, C49 & 50, 20vdc C51 -three section can replaced by individual caps). Added extra capacitance (2200 uF) to C51C as suggested by AR service notes to reduce initial turn on noise. 20vdc electrolytic, C43 (two section can) replaced with individual caps. Other work done includes: connected signal wiring to volume control. Found that the Tone Control board was inop due to 20vdc PPS ground was not connected. Dressed and reconnected. Heat shrinked loose ends of signal grounds to prevent ground loops and shorts. AR used this rather unorthodox method of not grounding all signal return grounds as a means of reducing inducted noise: unusual in HiFi but common in guitar amps. Cleaned and lubed jacks, pots and switches. Replaced 20vdc PPS Q28 (shunt regulator). This transistor had essentially become a fixed resistor and was responsible for high noise induced into the circuitry. Also replaced D16. This power supply is always on when the amp is plugged in. Its purpose is to reduce clicks, pops and noise when initially powering up after the unit is turned on. Cleaned knobs and front panel, repainted cage. It was burned in for 12 hours and the amp remained cool and quiet. There. Was that so bad?
Acoustic Research was a Cambridge, Massachusetts company that produced high-end audio products including this amplifier, the XA suspension turntable, and the AR3 loudspeaker. The company was founded in 1952 by Edgar Villchur and Henry Kloss. For nearly ten years after its introduction, the AR-3 speaker was widely regarded as the most accurate loudspeaker available at any cost, and was used in countless professional installations, recording studios, and concert halls. Many well-known professional musicians used AR-3 loudspeakers because of their excellent sound reproduction. In the early 1960s, AR conducted a series of over 75 live vs. recorded demonstrations throughout the United States in which the sound of a live string quartet was alternated with echo-free recorded music played through a pair of AR-3s. In this “ultimate” subjective test of audio quality, the listeners were largely unable to detect the switch from live to recorded, a strong testament to Acoustic Research's audio quality.