Solid State Preamp Reviews

This may seem a pain in the you know what, but good XLRs offer at least three advantages over RCA connectors: they make the ground connection before the hot, thus avoiding the possibility of blowing up loudspeakers and amplifiers; they lock, providing a mechanically secure connection; and the contacts are both gas-tight and self-wiping, ensuring a consistent contact. It is not surprising that they have become the connector of choice for all pro-audio work where people's livelihoods depend on their connectors. If you are worried about soldering your own plugs and cables to use with the LK1, isn't that what dealers are for? In any case, Audiophile Systems can supply adaptor cables to enable the LK1 to be used with source components and power amplifiers fitted with RCA sockets.

The LK1 is exquisitely made, though my sample did feature a couple of electronic afterthoughts in the form of extra resistors soldered on the top of the main board and a little piggyback board on top of one of the chips. The case gets quite warm, apparently due more to the power transformer than to hot-running circuitry, so plenty of ventilation should be arranged. My only quibbles concern the number of line-level inputs (too few), the volume control—there is no visible feedback of selected volume to aid resetting to an exact level (though the memory does help here, if you remember to use it)—and the buttons on the remote are undifferentiated, making it hard to use the thing intuitively. It also took me quite a while to realize that locking out the controls using the remote only affects the remote, leaving the front-panel switches operative, although locking the controls with the front-panel switches does also shut out the remote.

The LK280
The LK280 is a more powerful development of Linn's original LK2 power amplifier. Of similar height and depth to the LK1, it is wider. The only control is a power on/off switch on the right of the front panel. Construction is totally dual-mono, apart from the centrally sited toroidal power transformer, and even that has dual secondaries, one for each channel. Complete left and right channels of the amplifier—diode bridge, twin reservoir capacitors, voltage regulators, output transistors, heatsink, and input circuitry (everything except the output sockets)—are each carried on an individual vertically mounted pcb running the full depth of the chassis. The rear panel carries a 3-pin male XLR socket at each end, these the same as featured in the LK1 and mounted directly on the pcb. One has pin 2 connected to define that channel as "left," the other pin 3 connected for "right." Two input leads are therefore required. The outputs are taken from 4mm sockets, these taking only banana plugs—they are spaced too close to take dual bananas—and are very tight-fitting with conventional plugs. A heavy internal wire connects the negative terminal to the junction of the two reservoir caps, while the positive terminal is connected to the two flat-pack output transistors with another heavy piece of wire. The series-pass voltage-regulator transistors appear identical to the output transistors and are in intimate thermal contact with them.

As with the LK1, the '280's modular construction means that assembly can be quick and testing automated. According to their literature, Linn's Quality Control procedure involves testing every LK280 board with a Hewlett-Packard computer that measures the value of every component and checks it against specified tolerances. The computer then powers up the board and runs a full function test. The boards are soak-tested at high power for two days (!), then retested. Additional tests not featured on the production line include thermally cycling the amplifier from –20°C to 80°C (–4°F to 176°F) while operating; storing the '280 at temperatures of 100°C to 180°C (212°F to 356°F!) for up to two weeks (at the higher temperature, the amplifiers apparently look like they have been in a fire but still work); overloading the amplifiers into all manner of impedances, from a short circuit to a purely reactive load; and, toughest of all, being used on Linn's loudspeaker production line!

Unusually, the voltage supplies to the output stages are fully regulated. (The only other domestic power amplifiers currently available in the US that I am aware of that use full output-stage regulation such as this are the Mark Levinson No.20.5 and the top Naim and Exposure designs.) Full protection is provided by a custom thick-film hybrid circuit that monitors the current in the voltage regulators, shutting them down if it appears that the amp is about to be overloaded. To reset the protection, the LK280 must be turned off and left for about five minutes.

The Sound of the LK1
The LK1 and LK280 were used on and off for everyday listening over a period of six months, with formal auditioning of both pre- and power amplifiers divided into four distinct sessions. First, the LK1 was used as a phono preamplifier, then as a line preamplifier; third, the LK280 was substituted for my regular amplification; finally, the combination was assessed as a whole.

Comparing the LK1 with the Vendetta Research SCP-2, it was apparent that the latter was in a different class from the Scottish preamp, both in the delicacy with which it presented the music and the overall soundstage and in the manner in which it presented detail within that soundstage. This is rather an unfair comparison as the Vendetta now costs some $2250 and is dedicated to MC-cartridge replay.

More relevant is the comparison with the PS 4.6/M500 combination, which competes in the same approximate price region as the Linn. The initial auditioning involved comparing the PS with its active line section in-circuit. There was no question that the Linn LK1 bested the Californian preamplifier in this condition. Listening to the Arturo Delmoni solo violin recording that Kavi Alexander produced for Apogee, for example, revealed that the PS sound was fizzier than the LK1, with less body and more of a rosiny edge to the sound of the violin. However, I have never been that impressed with the sound of the PS 4.6's line section, and continued the auditioning with the PS set to its "Straightwire" setting, where the output is taken from the wiper of its volume control, bypassing the active line circuitry.

Now the sound from LP was slightly better through the PS. Both preamps presented an excellent sense of space, but the PS had just that more "palpable presence" (to borrow a cliché from Sam Tellig, the Audio Anarchist). Whether vocalist or instrumentalist, they sounded just that bit more "human" through the 4.6 when compared with the LK1. Listening to the excellent collection of songs by Noel Coward and Flanders & Swann from the King's Singers (EMI EMC 3196), the LK1 could be heard to dilute the individual identity of the different voices a little, as though a slight layer of thin gauze was being interposed between image and listener.

Moving on to the 1979 Proprius recording of Bach's "Wachet Auf" cantata (released on Meridian E77016)—a beautifully natural sound—confirmed the impression that voices had a rather lighter tonal balance through the LK1 than the PS in "Straightwire" mode, but that the sound was less open overall. Similarly, the individual tonalities of violin and oboe on this recording were rendered more alike through the Linn than through the PS Audio.

The low-frequency performance of the Linn preamp, however, was excellent. Despite lacking a little weight in absolute terms, the bass was beautifully defined. I slapped the MFSL re-release of Emmylou Harris's Quarter Moon in a Ten Cent Town (MFSL 1-015) on to the LP12, specifically the Jesse Winchester song "Defying Gravity." It's probably because this album was half-speed mastered, but the lows have always had a flabby quality to them. Via the LK1, the bass guitar and bass drum were, relatively speaking, as tight as a nut, with considerably less overhang to the sound when compared with the PS 4.6. Dynamics, too, were excellent, there being a good feeling of "slam" to the sound of rock recordings in general.

To sum up my impressions of the sound of the LK1's phono section, the complete preamp from MC input to line-stage output has a less HF-prominent nature than the complete PS Audio 4.6, and gives a better sense of space. Its bass is a little lightweight, but is very well defined, and rock program reproduces with a good sense of pace and dynamics. Using the PS preamp in its optimum configuration, however, reverses this ranking order, and reveals that the LK1, while extremely detailed, is a little thin in the presence region, accentuating the throat character of female voice. Recorded tape hiss, too, came over as a little "whiter." The highs, however, were not as dry as the Hafler, which also presented less of a sense of space than the Linn.

Bypass testing on a preamp's line stage is a particularly revealing, even cruel, way of assessing overall quality. The LK1, however, did quite well on this test. (Its inverting nature meant that I had to reverse the speaker connections when it was in the loop, a most awkward procedure.) Yes, it did have an identifiable character, but it modified the nature of the sound to a relatively small extent (though it did have more of an editorial nature than the tubed Conrad-Johnson PV9 that I reviewed in the May issue). Specifically, the LK1's line section appeared both to reduce the size of the performing space a little and to bring forward individual images within that image. The Michael Tilson Thomas CD of Gershwin piano works, for example, (CBS MK 39699), though mainly featuring the Rhapsody in Blue and Second Rhapsody, also includes a number of solo piano works. The sleeve is ambiguous about where these were recorded, either the Dorothy Chandler Pavilion in LA or RCA's Studio A in New York. If the latter, then artificial reverberation must have been used as the piano seems to be in a large hall, particularly via the Line Drive. With the LK1's line section in circuit, the hall noticeably becomes smaller, particularly on the first Prelude, which has a number of percussive climaxes where the ambient die-away is clearly audible.

This was just as apparent on my own recording of Anna Maria Stanczyk playing Chopin on the HFN/RR Test CD. The CD, made from a digital tape, even under the best circumstances always sounds a little drier, a little closer, than the analog tape I ran at the same time. The LK1 takes the sound slightly further in the same direction, as well as reducing the image depth.

The piano recordings also hinted of a slight degree of added warmth in the lower midrange, which was confirmed with tracks from Linda Ronstadt's What's New album, recorded with the late, great Nelson Riddle (Asylum 9 60260-2). I love the songs on this album so much that I can almost forgive Ms. Ronstadt for the fact that no one ever taught her how to breathe, how to effortlessly float a melody. But I can't forgive engineer George Massenburg for the "swallowing the microphone" perspective he chose for her voice, which adds a phlegmy edge to the sound. This edge is accentuated via the LK1, but only to a moderate degree, and the lower mids are definitely warmed up a little. There was also a slight loss of top-octave "air" with the LK1 in-circuit.