Audio Research VS110 power amplifier & SP16L line preamplifier Page 2

SP16L: If Audio Research's VS55 and VS110 amplifiers have the prototypical "tube amp" look, their companion SP16L line-stage preamp hardly looks like a preamp at all, and certainly not like one from Audio Research. Unlike the traditional AR preamps, this one has no knobs, just six soft-touch buttons for Power, Input selection, Processor Bypass, Volume up/down, and Mute. A set of green LEDs indicate status, including the level selected. (I half-expected the LEDs to flash up and down with the volume of music.) All of these functions, plus Mono/Stereo, are available on the remote control. There is also a 12V trigger output to turn on power amplifiers, including the VS55 and VS110.

The look may be different, but the SP16L's design and construction quality are pure Audio Research. Gain is provided by three 12AX7EH tubes from Electro Harmonix. There are eight high- and low-voltage regulators, a high-energy storage plate supply, patented DEC filter-cap decoupling, high-performance input-selection relays for short signal paths, and a 70-step, digitally controlled, analog-switch stepped attenuator with 0.5dB steps and typical 0.25dB tracking. (The SP16L has no balance control, so the accuracy of L/R tracking is particularly important.) When the power is off, microprocessor memory retains the input last selected.

Dual low-impedance cathode-follower outputs permit driving two power amplifiers simultaneously. Like the VS55 and VS110, the SP16L is single-ended only. The preamp is also available in a version with an integral phono stage as the SP16, for $2495. The phono stage is suitable only for moving-magnet or high-output moving-coil cartridges, not low-output MCs such as my AudioQuest 7000nsx, which is why AR sent me the line-stage version for review. Construction quality is up to the usual high AR standard, with expensive board material, extra-thick circuit traces, and machined RCA jacks.

Some amplifiers are highly sensitive to tweaks of various sorts, their performance changing significantly with small changes in setup. Although the VS110 was not immune to tweaks, their effects were much more subtle than I've found with other amps. I placed the VS110 on the PolyCrystal amplifier stand that I normally use, and it looked immediately at home. Placing three Aurios MSB Pro component supports under the amplifier resulted in the sound becoming a bit more open, but only by a very small amount—much less than I've found with the Audiopax Eighty-Eight or the Air Tight ATM-211.

The VS110's small tubes come with damper rings already installed, so there was no chance for me to try the Duende Criature tube dampers, which I've found effective with other amplifiers. (I was not about to remove AR's rings to try a different set!) Even the VS110's stock AC cord seemed to work just about as well as my aftermarket cords from TARA Labs and PS Audio. I routinely use a PS Audio High Current Ultimate Outlet to supply AC power to amplifiers, and this worked well in the VS110's case, with some small—that word again—improvement in signal/noise ratio, and no apparent restriction of dynamics.

When it came to setting up the SP16L, I must admit that I did not go through a careful comparison of various AC cables, supports, and power-line conditioners. Instead, I decided to keep these contextual variables constant by using the TARA Labs Decade AC cable, placing the SP16L on the Aurios MSB 1.0 support, and plugging it into the PS Audio P300 Power Plant set at the P2 Multiwave setting—all the same accessories and settings as I normally use with my reference Convergent Audio Technology (CAT) SL-1 Ultimate preamp. A brief listen to the SP16L without any of these tweaks (stock cable, no component supports, plugged into the wall) showed that the tweaks did improve the sound, but, as with the VS110, the tweaks weren't in the category of "must use if you want to know what this product is capable of."

Trouble is my middle name
Regular readers of Stereophile might think that reviewers are engaged in some sort of a contest to determine who has the highest percentage of malfunctioning review equipment. In fact, there is no such contest, but if there were, the last few amplifiers I've had for review might very well put me in first place. But since the VS110 has such "battleship" construction, and worked flawlessly for several weeks, I thought that maybe the jinx was broken.

Not so. One morning, I turned on the system and the right channel had a much higher level of noise than the left, a difference that had not been there before. Reversing the inputs made no difference, so I knew I was dealing with an amplifier problem. I checked the output tubes' bias settings, and found that the bias voltage for one of the tubes in the right channel read "0." Something was clearly amiss. (Interestingly enough, the right channel sounded otherwise okay, just more noisy.)

I called Terry Dorn at Audio Research, who consulted with their technical staff, and reported back that the problem was probably a tube that had arced and taken the cathode resistor with it. "We check our tubes thoroughly, but tubes are still tubes, and this can happen." Rather than send the amplifier back to the factory, Dorn suggested that I take it to a nearby AR dealer, American Sound of Richmond Hill, Ontario. AR would send them the parts needed to effect the repair.

That's how it worked out. According to Michael Thompson, American Sound's ace service technician, the problem was, as suspected, a tube and a blown resistor; once those had been replaced, everything was fine. To make sure that the arcing would not recur and that all the tubes in that channel would be matched, Audio Research sent an entire set of replacement output tubes for the right channel.

Audio Research
3900 Annapolis Lane North
Plymouth, MN 55447-5447
(763) 577-9700