Krell KSL line preamplifier

The KSL ($1800, $2100 with phono section) is a one-box line controller/preamplifier, just 2.25" high, with a nominal voltage gain of 10dB, or 3x. Despite its moderate price, the KSL is distinguished by having balanced outputs (via industry-standard XLR connectors), as well as two balanced inputs. Conventional single-ended, unbalanced outputs are also available via a pair of gold-plated phono sockets. Two unbalanced inputs are provided, plus a third via the tape monitor switch. The tape output is unbalanced, derived from the selector switch setting, while the main outputs may be used independently or simultaneously. A medium-impedance, four-wire–lead headphone could be wired to a pair of XLR plugs and be fed directly from the balanced outputs, since these can provide up to 9.5V RMS from a low source impedance.

Though this option wasn't available at time of review, the KSL will also accept a sophisticated card for pickup cartridges, this broadly based on the sonically successful circuit used in Krell's KSP-7B. This card merely plugs inside, together with some locking screws, and accepts both moving-coil and moving-magnet types, with variable gain and input loading. This card's price has been provisionally set at $350.

AC connection for the KSL is via an IEC socket with an adjacent fuse, the remainder of the rear panel being well-packed with audio connections. Front-panel controls include, from left to right, the input selector, followed by the tape monitor, a switched-position balance control, and the unstepped volume pot, this said to have a custom taper. Finish is to Krell's usual excellent standard.

Design Notes
While the main chassis is of steel, the top cover is of aluminum-alloy. Related to the power-amplifier circuitry, the KSL's line amplifiers are also all-discrete, using cascode pairs of differential FET and bipolar stages. Top-quality components are used throughout, though I thought the long track routing to the selector switch more a concession to layout style than to sonic fidelity.

Though located inboard, the power supply is quite substantial, in the KSP league, and separated discrete double regulation is used for each channel. All in all, the KSL has an impressive build quality. Krell has not compromised their high standards to achieve this design's price.

At last we have a solid-state match for the delightful Audio Research LS1. The KSL made no excuses, sailing directly into the top control preamp group. When the KSA-80/160 power amp series was introduced, I said that the situation was embarrassing because far too few preamps were up to the task of driving them, regardless of cost. Now in the years of the Krell KSA-150 and KSA-250, there are certainly better preamps available.

Despite its comparatively moderate cost, the KSL really delivered at the top level. Its general performance level was amazingly close to the costly two-box Krell KBL, and even reached beyond the established and still highly rated KSP-7B.

Much of my description of the Krell KST-100's sound is closely paralleled by that of the KSL, indicative of great component matching. The notes include such comments as "a crisp clean bass, devoid of any emphasis or restriction." Krell has managed to make the KSL's bass sound open and deep, but always completely in control.

The KSL's midrange was of very good quality, encompassing clarity and lack of grain, free from hardness or edge-type colorations, and with lively, explicit delivery. The mid was judged to be a shade lean or cool in tonal balance, a small shift to the blue end of the spectrum. Conversely, this was sufficiently mild so as not to significantly disturb tonality or perspective on orchestral strings or brass.

By preamp standards the treble was very good, little removed from a good-quality passive controller—that's praise indeed. Its active electronic origins were just perceptible in a tinge of "haze" and zing high in the treble register, audible when less than tidy program was played. However, in context, its magnitude was significantly less than that noticed with the KST-100.

However, it was in the area of dynamics and rhythmic drive that the KSL left much of the competition behind. It was subjectively more articulate, involving, and rhythmically coherent in the true sense of a musical performance, and capable of stretching the best digital replay in this area.

The KSL proved capable of generating a large-scale soundstage with top-class depth and perspective. High transparency is essential for such a performance, and the quality and consistency of stereo focus were also much admired.

Thus the KSL finds itself up with the best available, with a balanced input and output capability to match.

Here Krell has addressed the need for a high-performance line-control amplifier, with balanced and unbalanced working, at a realistic price. The surprise is that the acknowledged performance of the upmarket KBL preamplifier has not suffered unduly in the exercise, and that the KSL is worthy to drive not only the KST-100 but also the KSA-150, and any other products of comparable merit. As a line amplifier, the KSL is close to the state of the art, not far removed from the concept of a perfect potentiometer with gain. As well as gain, the advantage it presents over a passive control is its powerful cable-driving ability, even over long runs, and the addition of a balanced interfacing which can result in lower noise floors in difficult AC-supply situations.

One note of criticism concerns the poor channel balance at low volume settings. While the gain provided is fine for normal volume settings with CD-level sources, check your other possible signal sources for sufficient output. Ultimately, what matters is sound quality: here Krell delivers a very fine standard for the price, a worthy equivalent of the Audio Research LS1, but with balanced facilities if these are required.

I suggest the KSL will begin to supplant Krell's own KSP-7B. In any case, it significantly brings down the cost of a top-line Krell system—for example, a KSL plus a KSA-150 costs $5750.

Krell Industries, LLC
45 Connair Road
Orange, CT 06477-3650
(203) 799-9954

Axiom05's picture

Love these old reviews, brings back a lot of memories of reading Stereophile and trying to figure out how I could buy some of this stuff. It doesn't seem that long ago. Seems there were a lot more reviews per issue back then too.

jmsent's picture

would not be acceptable in a $500 preamp, much less one that sold for 2 grand. Odd that Krell didn't have a manufacturer's comment addressing this. High quality controls with near perfect tracking were certainly available in the early '90s. Most Japanese receivers did far better than this.

tonykaz's picture

You make a valid observation but it probably wouldn't bother me if I owned the piece, which, I did just look up on eBay to find one for under $1,000.

I was selling Audible Illusions PreAmps that had separate volume knobs for each channel, I felt it was a good design.

Krell is good gear, I could live with it.

Tony in Michigan