Ayre Acoustics KX-5 Twenty line preamplifier

The hoary question of tubes vs transistors, once certain and clear, is made ambiguous by recent products from a few solid-state specialists, not the least being Ayre Acoustics—the company that endures in the wake of the passing of its founder, the widely admired Charley Hansen. In their solid-state preamplifiers and amplifiers of the past decade in particular, Ayre has enshrined a number of technologies that are more than just variations on the audio-engineering status quo, and that appear to pay real sonic dividends.

Consider Ayre's Variable-Gain Transconductance (VGT) circuit, introduced in 2008 in their then-new KX-R preamplifier ($18,500 at the time). Instead of adjusting volume in the traditional manner—with a potentiometer that discards varying amounts of the product's signal gain—each phase of each stereo channel of the VGT contains 46 discrete resistors that, selected with a rotary switch, create 46 distinct variations on the preamp's voltage-gain stage, for a range of 46 volume levels. Thus there are fewer parts than usual in the signal path, and the preamplifier as a whole, from signal inputs through output buffer, is always maintaining an optimal S/N ratio.

In 2013, that and other Ayre technologies trickled down to their then-new KX-5 preamplifier, which since then has been rethought, redesigned, and, in 2015, recast as the KX-5 Twenty ($9950). "Twenty" refers to the number of years Ayre had been in business. In fact, they've now been in business for 24 years—but it's taking a while for Ayre's engineers to revamp everything in the line. And besides, who's counting?

The KX-5 Twenty is a solid-state, line-level preamplifier with six inputs—four balanced (XLR), two single-ended (RCA)—as well as balanced and single-ended outputs. Charley Hansen thought that balanced audio circuitry isn't superior in and of itself, but rather that the technology's advantages stem from its relative immunity to power-supply noise; in any event, Ayre has long offered adapters for converting their products' unused balanced inputs to single-ended use.

Like the original KX-5, the KX-5 Twenty has a single gain stage, built with complementary pairs of J-FETs and incorporating the above-described VGT. Downstream from that stage is an active output buffer, each of its channels based on four bipolar transistors that comprise what Hansen described as the diamond circuit, named for its shape when drawn in schematic fashion (no precious gems were destroyed in the making of this preamp). Ayre's take on the diamond circuit, which has historical precedent, provides current gain but not voltage gain; it bowed in their AX-5 integrated amplifier of 2012, in the role of the output stage.

Asked what distinguishes the KX-5 Twenty from the original KX-5, Ayre's manager of sales and marketing, Brent Hefley, points to the Twenty's AyreLock technology: an approach to power-supply design that uses discrete regulation devices instead of chips to create what Hefley describes as "a push-pull power supply—this one can pull voltage back down." The power supply is also fully linear—at its heart is a hefty EI—as opposed to toroidal—transformer, which Ayre considers more suitable than toroidal types—and it also uses the proprietary AyreConditioner RFI filters on the incoming power line.

All of this is built into an aluminum enclosure 17.25" wide by 4" high by 12.25" deep, with a brushed finish in silver or black. (My review sample was silver.) The KX-5 Twenty weighs a manageable 23 lbs, and is supported on four nonadjustable hard-polymer feet.

The interior is tidy and evidently well laid out. Setting aside the large power transformer—which is encased in a polished stainless steel wrap, the finish of which rivaled that of the preamp itself—I would estimate that the mechanical and electromechanical elements of the VGT system occupy as much interior space as the actual circuitry, most of the latter occupying a single 14" by 3" main circuit board, with two daughter boards, a front-panel logic board, and a dual-mono pair of boards fastened to the inside of the rear panel.

Also included is a slim, curvy, easy-to-hold remote-control handset with two separate banks of buttons, labeled Digital and Analog—this is a multiple-product control. The handset offers controls for volume, source selection, muting, and display brightness, but can't be used for basic setup or advanced configuration chores. (The latter include the ability to tailor the gain of each input to match the source component connected to it.) The KX-5 Twenty has neither balance control nor mono switch.

Installation and Setup
Installation was easy: I plunked the KX-5 Twenty atop my Box Furniture rack, used its RCA jacks to make single-ended connections to my sources and amps—I don't do balanced—and plugged its power cord into my AV Options power strip, using the outlet nearest the strip's own AC cord.

Setup was less easy, especially inasmuch as the KX-5 Twenty, like the AX-5 integrated amplifier, is supplied with all its inputs deactivated: Until the preamp is configured, operating its left-hand control knob, which is designated for source selection—the right-hand knob is the volume control—has no effect, and no inputs are identified, by number or name, on the display that's located between those knobs. Apparently this is so the user won't have to activate any more inputs than he or she actually needs, meaning that, for those who have fewer sources, browsing the inputs will take less time.

But Ayre's regimen for configuring and activating inputs is less than intuitive, a shortcoming made worse by an unclear owner's manual that devotes page after page to secondary matters while giving short shrift to essentials—something I believe I have noted in past Ayre reviews. The manual is reasonably clear on how to enter the preamp's setup mode—this and other procedures involves the use of one of two front-panel buttons, full descriptions of which are beyond the purview of a product review—in which the six inputs and their naming possibilities are easy to call up, yet the manual gives not a hint as to how, precisely, one selects the desired name. (It turns out that, during scrolling, to simply leave a name onscreen for a certain amount of time before proceeding to the next step is to select it.)

In my opinion, the Ayre newbie who wants to use their new $10,000 preamp to listen to music right away, or even soon, would be better served by having all inputs preconfigured and numbered 1 through 6. That eager user can then ditch unneeded inputs and change to fancier, more germane names later. Perhaps, then, the Quick Start portion of the KX-5 Twenty owner's manual, which presently numbers 14 of a total of 36 pages, could be whacked down a mite. Also, though the manual instructs the user how to put the KX-5 into Sleep mode, it offers no clue about how to wake it. Turns out that one quick press of the same button does that. Ayre perhaps considered this sufficiently intuitive—it was, I admit, the first thing I tried—but its omission from the manual seems glaring.

Ayre Acoustics, Inc.
2300-B Central Avenue
Boulder, CO 80301
(303) 442-7300

mrkaic's picture

...what this means: "Instead of adjusting volume in the traditional manner—with a potentiometer that discards varying amounts of the product's signal gain—each phase of each stereo channel of the VGT contains 46 discrete resistors that, selected with a rotary switch, create 46 distinct variations on the preamp's voltage-gain stage, for a range of 46 volume levels. Thus there are fewer parts than usual in the signal path, and the preamplifier as a whole, from signal inputs through output buffer, is always maintaining an optimal S/N ratio."

I am especially intrigued by the optimal(sic) S/N ratio. How does one determine this optimality?

Axiom05's picture

The volume is controlled by changing the gain of the preamp. Changing the volume changes the resistor value in the signal path. This is not a passive preamp, every volume step has a specific amount of gain. Despite being conditioned to think that a passive preamp should sound best, this preamp sounds absolutely amazing: extremely quiet and smooth. The drawback to this approach is that you need a lot of resistors to effect the volume changes, the smaller the steps, the more resistors, the higher the parts cost. This is why the KX-5 Twenty has about 1.5 dB volume change for each "click" of the control vs 1 dB for the KX-R Twenty. The optimal S/N ratio can be maintained by choosing parts with close tolerances. You have more control over part values. Typical volume potentiometers are not accurate over their entire range often resulting in an increase in noise and/or channel imbalance.

mrkaic's picture

Thank you for an exhaustive and informative answer. So, if I understand you correctly, the bank of 46 resistors essentially selects the closed loop gain -- like the resistors in an op amp circuit?

Could this work with a digital potentiometer? Those can give very close tolerances and even more choices that a bank of resistors.

Indydan's picture

Would it not have been better to test the preamp with an Ayre power amplifier? Of course the Shindo preamp will sound better with a Shindo power amp, DOH!

Can generalizations be made when the Ayre was tested with 50 year old speakers?

I wish Mr. Hansen was still around. He would have surely commented on the review.

johnnythunder's picture

As much as I love Art's writing and reviews, I agree with Indydan about this somewhat flawed approach to reviewing these state of the art components in a "vintage" reference system. I think it's an interesting angle to hear how these components blend together but it's sort of a tangental idea not one for a comprehensive review. It should be classified as a separate type of review - this mix of old and new. How do AR or KLH bookshelf speakers stack up against today's ELACs or KEFs or NOLAs or JOSEPHS? that would be interesting to read...but speakers designed to be used with low powered tube amps powered by a new amp is not the same thing...

mrkaic's picture

Johnny, what is your problem?

Mr. Dudley writes SUBJECTIVE reviews, so he can pair any components he wants and evaluate them by LISTENING. [Gee, I wonder where the master title of his editorials comes from? :)] His approach is not scientific.

If you want rigor, read JS'a measurements.

johnnythunder's picture

and especially not attacking Art D. who is a national treasure and who's ears and musical taste are impeccable. He's one of my favorite magazine writers. My issue was the odd mismatch of amp and speakers as the only point of comparison in the review of the amp. I am not in the double blind comparison camp or a skeptic about tweaks, cables or AC power enhancements. I simply felt that the Ayre should ALSO best be paired with a modern state of the art speaker that it was obviously designed for. I wouldn't be stating any of this if the review was of a modern state of the art push pull or single ended tube amp used w his Altecs. So this has nothing to do with science or rigor but of what is in my opinion a slightly incomplete way of assessing this particular piece of equipment. It's just my opinion in this instance.

mrkaic's picture

You see, I'm a passionate objectivist and rely on measurements first and foremost. However, if the genre of a piece is subjectivist, then anything goes. Including pairing amps and speakers that are not from same period of audio development.

So, I guess we see this issue somewhat differently.

villager56's picture

Hi John,
The measurements reported for this unit appear very similar to the measurements that you reported for the K-5xeMP in 2011. Would you kindly add a few words comparing the measurements of these two units and how the new technologies are reflected in the measurements of the latest model? Thanks!