Solid State Power Amp Reviews

Lindell Audio, a Swedish professional-audio company, was founded in 2010 by recording engineer Tobias Lindell, and claims to offer equipment "by engineers, for engineers." Tobias Lindell specifies the features and functions that he wants each product to incorporate; the actual circuit designs are by others. Although Lindell's corporate headquarters are in Sweden, the products are manufactured in China, and are competitively priced.

Lindell makes rack-mount and "lunchbox" compressors, limiters, and microphone preamplifiers. They also make a 32-bit/192kHz digital-to-analog converter, as well as a power amplifier intended to drive passive monitoring loudspeakers such as Yamaha's NS-10 and ProAc's Studio 100.

I became aware of Lindell Audio when I saw a photograph of their handsome AMPX dual-mono, class-A–only power amplifier in an e-newsletter from New York City retailer B&H Photo, which also has a pro-audio division. I was intrigued by the amp's appearance, but I fairly goggled at its suggested US retail price of $1599. I got in touch with Lindell's US importer, RAD Distribution, who agreed to send me a review sample as soon as one was available.

The AMPX arrived in sturdy double boxing—prudent, given that it weighs about 42 lbs. The loaner obviously had been around the block a few times. It showed some signs of wear, and its footers' rubber inserts were missing, along with its power cord and manual. No big deal on any count. Anyway, I'd rather have an experienced review sample than one that someone might later claim to have needed 500 hours of break-in.

RAD sent me a new set of footers, and Tobias Lindell told me that new amps come with all of the aforementioned items, plus a cloth bag and a pair of cotton gloves. So much for the oft-heard claim that reviewers get special treatment.

At 18.8" (483mm) W by 3.5" (90mm) H by 17.4" (445mm) D, the AMPX is one rack unit wide. Its faceplate, machined for rack mounting, is heavy, about 3/8" thick, and dominated by two large, blue power meters (wonder where they got that idea from?), calibrated to show watts into 8 ohms. The stated power output is 20Wpc, which, after extensive listening, strikes me as a conservative claim. Centered between the power meters is a round black pushbutton for On/Off—apparently just that, not standby. There are front-panel legends with the maker's logos, model name, and descriptions in script. On startup, the meters blink for about five seconds; perhaps some diagnostic function is going on. I downloaded the owner's manual from Lindell's website, but it was silent on that issue.

The sides of the AMPX are occupied by thick-finned modular heatsinks, considerately designed with slightly chamfered edges to reduce the risk of cut fingers—this is one dense amp. For some reason, however, it looks lighter than it is. The heatsinks got so hot that placing the AMPX in the bottom of a rack full of equipment would probably be unwise. I estimated the temperature of the heatsinks to max out at about 124°F.

The rear-panel layout is mirror-imaged, reflecting the AMPX's dual-mono construction. Lindell claims that the right and left power supplies are completely isolated from each other. An IEC power-cord inlet is in the middle; to either side of it are the speaker binding posts, then the input jacks. The connection hardware is respectable but not ne plus ultra. Input is by XLR connectors only; RCA input is not an option. The circuit design itself is single-ended, so the balanced inputs are unbalanced by op-amps.

One unusual and potentially useful feature is that both channels' female XLR inputs are mirrored by a corresponding male XLR output (or, rather, throughput). If your speakers are biampable, you could vertically biamp them with two AMPXes. In that scenario, the input signal would go into one channel, then an XLR jumper cable would connect that channel's throughput jack to the other channel's input, giving you a biamped total of 40Wpc.

Tobias Lindell describes his circuit design as being "rather simple." He arrived at the decision to offer an energy-inefficient class-A–only design entirely through listening tests—nothing else sounded as good. To reach an output of 20Wpc, each channel uses four pairs of complementary Sanken 2SA1695 PNP and 2SC4468 NPN output transistors.

Lindell claims for the AMPX a frequency response of 10Hz–100kHz, ±1.5dB, a signal/noise ratio greater than 100dB, and the virtues of "high resolution, high headroom, accurate, easy-to-mix sound at an affordable price."

Listening
I cued up the "Channel Identification" and "Channel Phasing" tracks from Stereophile's Test CD 2 (Stereophile STPH004-2). Compared to the voiced-by-ear, somewhat euphonic Unison Research S6 tubed integrated amplifier, the AMPX definitely had a more present, "modern" sound. Its treble was surprisingly delicate and sweet for an amp that had just come off a UPS truck. The sibilance of Richard Lehnert's somewhat closely miked speaking voice slating the tests on these tracks were more apparent than through the S6, and John Atkinson's Fender bass sounded surprisingly more dynamic.

I was not surprised that a solid-state amp would go deeper in the bass than a tube amp, but I was surprised that a 20Wpc solid-state amp would sound more dynamic than a 45Wpc tube amp. So far, so good, and even at that very early point, I was ready to declare the AMPX not only to be excellent value for money, but also that it met a need I'd been trying to fill for 10 years now.

For the last decade I've regarded Grace Design's 901, m902, and m903 headphone amplifier–DACs as being among the greatest bargains in audio. What I've searched for by fits and starts and not come up with is a power amplifier to partner with an m903 that is, in its own way, as good as the $1995 Grace but costs no more. That's why I requested the loan of Lindell's AMPX. And until something even better comes along, as far as I'm concerned, the Lindell AMPX is it as the affordable amplification partner for the Grace m903.

I then ran Ayre's Irrational, But Efficacious! System Enhancement Disc's "Full Glide Tone" track, and followed with a quick assortment of favorite music tracks. To assess the AMPX's ability to drive the Opera Callas's 4-ohm/86dB load, I cranked up the title track of Al Stewart's Year of the Cat (CD, Arista ARCD 8229) so that the Bricasti's volume control was set to "–0dB." Very respectable; I'd characterize the impact as satisfying but by no means overwhelming. That said, we should keep in mind the AMPX's intended use with monitoring speakers, which often sit only an arm's length away from the listener, atop a mixing console's meter bridge, and which—in sanely run studios—are rarely played louder than 85dBA over the long haul.

Ella Fitzgerald's landmark recording of "Easy to Love," from her The Cole Porter Songbook, Volume Two (CD, Verve 821 990-2), was also very satisfying, but the Lindell's upper-bass drive might have excited a bit of string-bass room boom from the Opera Callases that the Unison Research S6 did not. I didn't move the speakers—the Callases were on their way out anyway.

Time for Love: The Best of Julie London (CD, Rhino R2 70737) did show that the AMPX had superb resolving power. At times I felt uncomfortably close to London's tonsils—but my discomfort was more a matter of my social space being invaded than of a tipped-up tonal balance. Quite enrapturing were the Cypress String Quartet's recordings of Dvor†k's Cypresses and String Quartet 13 (CD, Avie AV2275), which I raved about in the August issue; and the Lendvai String Trio's Destination Paris (CD, Stone 80079) and Alan Feinberg's Basically Bull (CD, Steinway & Sons 30019), which I raved about in October.

Early on, my friend Bob Saglio took exception to what he perceived as excessive sibilance in "Honeysuckle Rose," from Jane Monheit's Taking a Chance on Love (CD, Sony Classical SK 92495). Perhaps Bob is overly sensitive to sibilance. Anyway, I do think that some tracks of that CD are a bit too closely miked. I also think that, as I put more time on the AMPX, the sibilance excess in "Honeysuckle Rose" dissipated somewhat—but the AMPX always had more energy in that region than the Unison S6. The solo electric bass that kicks off the track was very satisfying.

Summing Up
The AMPX was unfailingly musical, sounding both powerful and revealing. Some aspects of its performance reminded me of Plinius's 8150 integrated amplifier: a liveliness that was never undisciplined or "electronic," and its top-to-bottom coherence.

I believe that the Lindell AMPX, despite its lowish nominal power, belongs in Class B of "Recommended Components." And remember, to be listed in Class B is not a slight, but high praise. Class A is reserved for "the best of the best, regardless of price or practicality." In my book, Class A is the province of the darTZeel NHB-108 and other amplifiers every bit as good; as nice as the AMPX is, it is not a drop-in replacement for the darTZeel. Class B is supposed to be the "next best thing [to Class A]," and I think that that is where the AMPX belongs. A great amp and an amazing bargain. I've shipped it to JA for measurement. Highest recommendation.