Audio Research LS3B in Silver with QSA Yellow Fuse

Details

• Condition 8.5/10
• Non Smoking Environment
• Original owner's manual
• Thoroughly cleaned, tested and inspected
• QSA Yellow fuse included ($213 value)

Link to Owner's Manual (PDF)

• The circuit board in the LS3 incorporates extra wide traces and a minimum of point-to-point wiring to minimize crosstalk and keep the signal path as short and pure as possible.
• Massive, tightly regulated power supply
• All inputs are D.C. coupled, long-tail pair topology.
• The "Direct" and "Tape" inputs are selected via relays
• Balance control and mono/stereo switching.

The front panel of the LS3 offers a useful range of controls and switching functions without extraneous "bells and whistles." Included are Gain, Balance, Mode and Input Selectors. Muting is automatic at turn-on and in brown-out conditions, as well as manually switchable. In addition, the LS3 includes an important new signal route called the Direct Gain Path. This set of inputs offers the user a high purity signal path for audiophile-quality program sources (CD players, DAC processors, etc.)-a route which bypasses all controls and switching functions except for Gain. The Direct Gain Path is selectable from a front panel toggle switch, while other inputs are chosen through the Input Selector. 

Also included on the LS3 are two sets of main outputs for use with bi-wired systems, surround-sound or other signal processors. The optional LS3-B offers balanced XLR outputs as well.

The rated frequency response is a wide 2 Hz to 100 kHz, ±0.5 dB. Gain is 18 dB, with an optional reduction of 10 dB. There is no gain at the tape output and 24-dB gain at the balanced output. Noise is rated at more than 100 dB below a 2-V output signal with regular outputs and 4 V with the balanced outputs.

Input impedance is 50,000 ohms for most inputs, with 100,000 ohms for the direct input. Output impedance is 250 ohms, allowing the use of long interconnects.

The basic circuit is pure Class A, with a high-voltage supply. No push-pull circuits are used. There are three sections to the active gain stage. The first is a differential input using I-FETs. The feedback drives the negative input of the differential pair, which allows the feedback to include the output capacitor and improves the sound quality. The second stage has a J-FET follower driving a MOS-FET in a common gate, with feedback to limit its gain to 14 dB. The third stage is a source follower with a constant source load. The gain is limited by feedback, and the output capacitor is again included in the feedback loop.

The circuit design emphasizes short, simple signal paths and has d.c.-coupled inputs and a tightly regulated power supply. The circuit hoard uses relay switching and has board-mounted switches. The input-selector knob on the front panel is actually connected, by a long shaft, to a switch at the rear of the circuit hoard, near the input jacks. This input switch configuration, and the fact that other front-panel switches actually control internal relays, allow the LS3 B to eliminate any wires in the signal path except for the oxygen-free copper jumpers from the connectors to the circuit board.

Audio Research emphasizes the quality of the power supply and claims that the electronic line regulation is better than 0.01%. Construction, the layout of the p.c. board, and component quality of this unit are excellent.