Linn LK1/Linn LK280 Preamplifier and Power amplifier Review

Linn Products, headquartered in Glasgow, Scotland, is probably best known for its record-playing components, including turntables, tone-arms, and cartridges, and—more recently—a line of high-quality loudspeakers. Less familiar to American audiophiles are Linn’s electronic components, the LK1 preamplifier and the LK280 power amplifier (which has replaced the LK2). Like the other Linn components, they are constructed with exceptional care and attention to quality control, and they embody design features not often encountered in consumer audio products. Although the amplifier and preamplifier are physically and electrically independent, and each is electrically compatible with any standard audio component, connecting them to another company’s electronic components would be difficult without special cables. Therefore, we tested the combination as we would an integrated amplifier.

The black-finished LK1 and LK280 are substantially smaller than other preamplifiers and power amplifiers of similar output ratings. The LK1 measures 10-1/4 inches wide, 3 inches high, and 10-1/2 inches deep, and it weighs 10 pounds. Except for the prominent power button, its front panel is unlike that of a typical preamplifier. A 2-1/2-inch square section at its left end contains all the operating controls and a display that shows which input source is being heard and which is being recorded (the two functions are entirely separate). Two volume-control buttons raise and lower the listening level smoothly in 256 steps, which cannot be heard as discrete level changes, and two other buttons perform a similar function for the left/right channel balance.

The program-input buttons select from two high-level sources (tuner and auxiliary) and either a moving-magnet (mm) or moving-coil (mc) phono cartridge. The LK1 can also handle two tape decks, providing full monitoring and dubbing capabilities. A green light appears in the window next to the name of the source being heard, and a red light shows which source has been selected for recording. The control identification markings are large and exceptionally clear.

The rear apron of the Linn LK1 is as distinctive as its front panel. Except for the gold-plated RCA-type jacks for the phono inputs, all connectors are professional cannon-type XLR jacks. Each carries the signals for both channels and has a separate ground line that minimizes the possibility of hum or noise pickup from ground loops between the preamplifier and power amplifier. Markings above the jacks show the assignment of each pin. The input jacks are three-pin types; the five-pin tape-deck jacks carry both recording (output) and playback (input) signals. There are two identical preamplifier outputs, simplifying the LK1’s use in a bi-amplified music system. Output cables fitted with high-quality XLR connectors are supplied, and accessory cables for input components and tape decks are available.

Internally, the LK1 is as unconventional as its exterior suggests. It uses modular construction, with one large board carrying all signal circuits and a separate board containing the digital control circuits. There are no mechanical switches or controls in the signal path, and solid-state analog switches are located at the points in the circuit where they are required. These switches are operated by a DC control voltage; the front-panel buttons (which actually operate membrane switches on the control board behind them) never handle audio signals. Volume and balance adjustments are done through banks of precision fixed resistors switched by solid-state devices so as to provide stable gain settings without introducing noise or distortion.

A microprocessor on the LK1’s digital board controls all the switching functions and also provides memory and remote-control capability. Using the control buttons, level and balance settings for each of the input sources can be memorized, to be called up each time that source is selected. The buttons can also instantly shift the balance to either side or to the center, mute the audio completely, recall the memorized settings, or lock out the preamplifier controls to prevent undesired changes.

A compact optional wireless remote control duplicates all of the LK1’s controls, though its lock-out function disables only the remote, leaving the front-panel controls fully operational. In addition to the red and green indicators in the preamplifier’s window, a red light flashes whenever a signal is received from the controller. The controller also contains a number of additional, unmarked buttons intended for use with future Linn products.

The third module of the LK1 is its power supply, based on a shielded toroidal transformer. The supply delivers a lightly regulated ±15 volts to noncritical circuits and to the individual regulators associated with every circuit block. A highly stable ±11 -volt source serves as a reference for all of the local regulators, which enable each stage to be highly isolated from the others. The power supply also has a protection circuit that senses any sudden change in the output (or a loss of AC line input) and mutes the preamplifier. This muting action not only prevents undesirable line-voltage transients from reaching the power amplifier or speakers but completely eliminates any turn-on thumps from the preamplifier.

The Linn LK280 power amplifier, rated for 80 watts per channel into 8-ohm loads, or 160 watts into 4 ohms, is styled like the LK1, although its front panel has no controls other than a power button (with a barely visible green pilot light next to it). It also matches the LK1 in depth (10-1/2 inches) and height (3 inches), although the heatsink fins on its sides increase the total width to 12-5/8 inches. Naturally, its power supply is huskier and heavier than that of the preamplifier, giving the LK280 a total weight of 20 pounds, which feels surprisingly heavy in view of its compact dimensions.

The Linn LK280 is effectively a dual-mono amplifier, with only the power cord and primary transformer winding common to the two channels. The shielded power transformer occupies most of the interior volume; the two modular amplifier channels are mounted vertically along the sides, close to their heat sinks. Each channel module has its own power supply (except for the common transformer) and is easily replaceable as a unit if service is required. The rear apron contains the two XLR input jacks and the corresponding speaker-output jacks. The speaker outputs, though conceptually similar to banana-plug jacks, are not usable with conventional banana plugs. The supplied plugs fit so tightly into the jacks that removing them by hand can sometimes be difficult.

The overall quality of construction and the materials used in the LK280 are similar to those of the LK1. According to Linn, the LK280 has no circuitry for sensing the out-put-device temperature, and its design eliminates any need for adjusting the quiescent current in the output stages. It also does not have any conventional current-limiting circuits, being protected against catastrophic failure by a line fuse and against all forms of overload or operating abuse by a unique sensing circuit that responds to any source of potential damage by instantly shutting down the affected channel. Typically, an excessive static current drain, or a larger transient drain lasting more than a few milliseconds, will trigger the shutdown. Power can be restored only by switching the amplifier off for at least 5 minutes and then turning it on again. Other than this instantaneous shutoff action, there is nothing in the amplifier to impede its delivery of power to the load.

The suggested list price of the Linn LK1 preamplifier is $1,050; the LK280 power amplifier is $1,495. Accessory prices: remote control for the LK1, $110; tuner/auxiliary input cable with XLR connectors, $35; tape-recorder input/output cable with XLR connectors, $45.

Lab Tests

During the preconditioning period, the exterior of the LK280 became fairly warm, though not uncomfortable to the touch. Even in normal operation both it and the LK1 preamplifier were noticeably warmer than most amplifiers. For most of our tests, the LK1’s gain was set so that an input of 0.5 volt produced a 1-watt output from the LK280.

The amplifier’s 1,000-Hz output (into 8 ohms) clipped at 89 watts per channel, for a clipping headroom of 0.46 dB, and with 4-ohm loads the output was 174 watts (headroom of 0.36 dB). When it was driving 2 ohms, the amplifier’s protection system shut it off at 356 watts. The 8-ohm dynamic output was slightly less than the steady-state clipping power, although the measurement of a tone-burst signal is inherently less accurate than a steady-state measurement and the differences were minor. The 8-ohm dynamic power was 85.5 watts, increasing to 166 watts into 4 ohms and an impressive 410 watts into 2 ohms.

At 80 watts into 8 ohms, the total harmonic distortion (THD) plus noise at 1,000 Hz was about 0.15 percent from 50 to 3,000 Hz, increasing to 0.23 percent at 20,000 Hz. At lower power levels the distortion was slightly less, but it was typically between 0.1 and 0.2 percent over the range of 20 to 20,000 Hz. By limiting the measurement bandwidth to 22,000 Hz to exclude ultrasonic noise, we were able to make a 4-ohm measurement of 1,000-Hz distortion over the full power range. From 0.3 percent at 0.5 watt, it decreased linearly to 0.07 percent at 8 watts and 0.025 percent at about 175 watts, just before the waveform clipped.

The RIAA phono-equalization error (measured at a tape output of the preamplifier) was less than 0.5 dB from 50 to 20,000 Hz and reached —2.5 dB at 20 Hz. The mm phono-input termination was inexplicably different from the manufacturer’s specification of 47,000 ohms and 69 picofarads; we measured it as 90,000 ohms in parallel with 88 picofarads. The phono-overload input was acceptable, with readings from 85 millivolts (mv) at 20 Hz to 64 mv at 1,000 Hz, but the 20,000-hz overload point of only 24 mv was undesirably low. With cartridges of moderate output, most records would be unlikely to overload the phono stage, but the safety margin is less than it should be in a preamplifier of this quality.

Comments

The Linn LK1 and LK280 represent an unusual blend of digital and analog technology. Although their audio functions are purely analog, the effectiveness of the LK1’s digital circuits in controlling and protecting the amplifier was impressive. The LK1’s pushbutton controls may seem a bit strange at first, but it takes only a few minutes to appreciate their logical design.

The considerable combined cost of the two Linn units is not difficult to justify, especially when you look inside and see their gemlike construction. In our case, a mishap on the test bench that could (and should) have destroyed both output stages did no more than shut off the amplifier totally—which gave us some bad moments until we turned it on the following day, and everything functioned normally! Heartened by that recovery, we fearlessly went ahead with 2-ohm clipping-power tests, which have been the nemesis of quite a few amplifiers— or their fuses, at least. The results show that the LK280 is a powerhouse far surpassing its modest 80-watt rating and would seem to justify Linn’s claim that it can drive any speaker without risk of damaging it. We got the impression that the amplifier itself was quite bulletproof as well.

Apart from the skimpy phono-overload margin, we found only one respect in which the Linn preamplifier fell short of ideal performance. Its digital control circuits radiated enough radio-frequency “hash” to degrade the performance of an fm tuner placed near the preamplifier. This effect was exacerbated (and possibly caused) by the fact that the antenna of the tuner was within a couple of feet of the LK1; it would almost certainly not have been detected if a good external antenna had been used.

Even if these beautiful products are not quite perfect (what is?), they are among the most satisfying audio components we have seen in some time, and worth every cent of their price.

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