Audio Research LS8 line preamplifier Page 2
The use of two gain stages in series provides correct signal polarity, while a cathode-follower output confers wide bandwidth and low output impedancein this case, a claimed 200 ohms. FETs are also used for interfacing and for constant-current duty.
In ARC's earlier preamplifier designs, the input section used a hardwired selector switch and rotary, track-type level controls. Adopting later practice from the more costly, remote-controllable Audio Research preamps, the manually operated LS8 uses a FET-switched attenuator chip for volume, hence the finite input headroom. The input selector is logic-switched, controlling an array of relays at the back of the unit.
Following the attenuator, the audio signal is DC-coupled at the differential triode input stage, the operating current set by a hand-trimmed FET source in the tail of the circuit. The output is direct-coupled to a single-ended triode voltage amplifier directly followed by the output stage cathode follower. That final capacitor to the output socket is a selected 2;uF InfiniCap, relay-muted for protection.
An onboard power transformer supplies AC to three main reservoir/regulators delivering ±5V to the ICs, 160V for the tube plates, and power for the relays and tube heaters. The main power supply includes ARC's frequency-staged filter approach, with different values and grades of reservoir capacitor, coupled with high-frequency filtering and polypropylene REL caps for final control of the voltage rail.
The unity-gain tape output is taken straight from the selected input lines via a 470 ohm buffer resistor. There is no true tape monitor loop. To get the best results from the main outputs, the tape-output sockets should not be loaded by unpowered equipment.
At the outset, I took care not to listen too carefully to the LS8, allowing it a decent running-in time of 3050 hours before doing any serious listening. But almost subconsciously, I felt that something intruded, a characteristic I wasn't able to entirely forget in later sessions. It was a feeling of boxed-in control, dryness, a rather contained sound with an inward focus.
Some aspects of the LS8's tonal character were reminiscent of the LS7. There was a pervasive neutrality in the mids that was not obviously tubelike, and was free of hardness and that feeling that a mechanical process is at work that is sometimes heard in solid-state designs. Upper-mid transients sounded suitably crisp and explicit, while the midrange focus was rated "good" to "good plus." There the similarities ended.
Where the LS7 sounded lively (for some tastes a bit too much so, verging on mild brightness), expressive, exuberant, upbeat, and involving, the LS8 sounded compressed, sat-upon, downbeat, quiet, and substantially less musically involving. Something "electronic" was getting in the way of the clarity and expressiveness of the original design.
By 1998 standards, the bass was disappointing. It didn't feel particularly extended in terms of low-range impact, while the upper bass was mildly emphasized, with a thickened, almost drawn-out character like a cat's purr. Articulation, snap, and tune-playing ability were rated as unexceptional.
Unfortunately, the LS8 fared little better in the treble. Although essentially neutral in tonal register, it possessed a noticeable degree of grainnot rough in the unpleasant sense, but the kind that masks detail, tonal differentiation, and air. A kind of grayness existed in the treble that told against natural air and sparkle in the extreme highs.
Dynamically, the LS8 sounded rather "cool"; perhaps this was associated with the feeling that musical tempos were perceptibly slowed, that the musicians were playing with less enthusiasm.
While midrange focus was undeniably good, the LS8 had unexceptional image depth. Low-level ambience cues were not properly reproduced, even at low volumesfor example, when I used the preamplifier with the Cary 300SE LX20 power amplifier. The reduced perception of recorded ambience emphasized the dryness I noticed, contributed to a sense of "containment" to the soundstage.
These are subtle but important factors. On more comfortable parameterssubjective frequency response, audible distortion, and observed system interfacingthe LS8 sounded essentially neutral, competent, and capable. There's no easy critical target here, no obvious failing that could be blamed for the overall result.
Extended trials with alternative components throughout the chain revealed the inevitable differences. For example, the Cary power amplifier and Transparent cable combination were the sweetest match for the LS8's treble. Conversely, the Krell power amplifier and Siltech cable showed it in a poorer, more etched-sounding light.
Extended use certainly allowed the LS8 to open up a little, with consequent gains in transparency and detail, but I felt that this preamplifier never really came to life.
The LS8's measurements showed very little out of place, though I would have liked some finer control settings below 20dB of attenuation, and the input overload margin could be increased. It could drive low-impedance loads, distortion was excellent, noise levels were fairly good, channel balance was superb, and frequency response was excellently uniform.
Matters were very different on the listening side. The LS8 had a dulled edge that lacked some of the lively, upbeat, engaging excitement generated by its Audio Research stablemates old and new. Its restrained dimensionality, "quiet" and near-downbeat temperament, and significantly reduced musical expression, all combined with its just-average bass and "grayed" treble, preventing the LS8 from coming alive.
Perhaps critics have become so accustomed to Audio Research pulling something impressive out of the hat every time that a preamplifier design that rates as merely "good" is a disappointment. Certainly I've heard worse in this price sector, but I think audiophiles can do better.