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Positive Feedback ISSUE 40
november/december 2008


clayton audio

M-300 amplifiers

as reviewed by Mike Wechsberg






Wilson Cubs

Audible Illusions Modulus III preamp and a Krell KAV-250 amplifier.

VPI Scout turntable. and a Sumiko Blue Point Special cartridge. Music Hall Maverick CD player.

Cables are a combination of Nordost Blue Heaven and MIT Terminator series.


This review completes my first year anniversary as a PFO contributor. It is both a pleasure and a challenge to describe the sound of today's audio components and how well they communicate the music. I hope my contributions to PFO have made a difference to some of you out there. This time around I have the pleasant chore of writing about the Clayton M-300 Class A Monoblock solid-state amplifiers. PFO has devoted quite a bit of editorial space to the Clayton Audio line of Class-A amplifiers with reviews of the M-70, S-40, M-200 amplifiers and most of these reviews have been gushingly positive. I'm about to add to those superlatives with this review of the M-300 monoblocks. These amplifiers have a definite "WOW!" factor that you need to listen to if you can. Although relatively expensive at $13,500 per pair, I think you will find they compare very well with some of the most expensive amplifiers, tube and solid-state, from all around the world. And, they are designed, developed and manufactured right here in the US of A. Their build quality is terrific, with a conservative electrical design that should be reliable for decades, and they have a minimum of frills so the dollars you spend go into making music and not raising your social status.


The M-300's are rated at 300-watts per channel into 8 ohms and 600-watts into 4 ohms. Like other Class A amplifiers there is no power rating for 2 ohms which hints they might not like very unusual speaker loads, something to keep in mind before you buy but not an issue in most cases today. The input impedance is 100K ohms and the Claytons accept balanced inputs only (other models have both balanced and unbalanced inputs, but designer Wilson Shen believes the additional circuitry—to accommodate both inputs—to have a sonic impact). All the Clayton amplifiers operate in Class A with virtually no negative feedback. Most PFO readers know that Class A is the "purest" amplifier configuration where each transistor handles the entire audio signal instead of half the signal as in class B or class AB designs. In Class A the transistors are biased to be on at all times, which means such amplifiers draw more current and release more heat than their more common class AB brethren.  The entire top surface of the M-300 is a heat sink to keep the amplifier relatively cool. According to the manual the power supply uses a 2 kVA transformer with 200,000 microfarads of capacitance (that's a lot), although there are no capacitors in the signal path. There are separate power sources for the driver and power stages. These features account for why the amplifiers weigh 70 lbs. each. Designer Wilson Shen worked for IBM for a number of years, where he learned about designing and building reliable power supplies and circuits for continuous and heavy duty operation. He has brought these design principles into his amplifiers.

The Claytons have a two-position bias switch that offers some mercy to the user's pocket book. In the low bias position the power consumption at idle to 300-watts instead of 800-watts at full bias (that's for each amplifier). The lower bias point also limits the heat released into the room to only 40 degrees F above ambient instead of 55 degrees. Clayton says the lower bias point is suitable for less critical listening and I used this switch position while breaking in the amplifiers, but the power consumption is still mighty high to allow leaving the amplifiers on at all times. I turned the Claytons off between listening sessions.


The Claytons are not real beauties unless you like the black industrial look, but they do exude quality. Physically they are deeper (20 inches) than they are wide (11 inches) and they are 11.5 inches high. Clayton uses this same chassis for some of their other amplifiers (notably the recently introduced S-100), which is a smart way to reduce parts cost (the fancy chassis on some competing products can account for 20% or more of the parts cost). The front panel has only the name "Clayton Audio" in a soft typeface and two indicator lamps. No model number and no power switch on the front. In fact the power switch is not on the back either, which is the second logical place to look for it. Instead the power switch is on the bottom front and it's right next to the bias mode switch. This makes for a clean look but it also means one has to consult the manual to figure out how to turn the amplifier on (most reviewers hate to read manuals). In my case there was no manual packaged with the amplifier so I had to get on the Internet to download one. Switching the amplifier on and off is easy once you know what to do. Although the top heat sink gets quite warm to the touch, the front panel and bottom plate remain cool, so no danger there. One of the front panel LEDs indicates power and comes on as soon as the power switch is turned on. The second light comes on a few seconds later and indicates the bias mode. When this LED is just as bright as the power light then the amplifier is in high bias mode. When half-lit the low bias mode is indicated.

The rear panel of the Clayton is much more imposing. It contains a pair of WBT speaker posts and a WBT balanced input connector. There are four Clayton Audio Safety Bumpers™ that prevent cables from being stressed when the amplifier is placed close to a wall or solid object. Also present are terminals for a remote control and two fuses, plus a ground terminal and the AC input connector. There is also a handy indicator lamp on the rear panel that duplicates the power LED on the front. Check this lamp if working on the rear of the amplifier before changing any cables. This is a good safety feature that other manufacturers should adopt. The black color and relatively small 11 x 11.5 inch front face help the Claytons disappear in the listening room. With the lights low all you see is the two LEDs.


I installed the Claytons in my listening room on two Target amplifier stands. Clayton notes that the supplied feet are machined to be taller than usual so the amplifiers can be set directly on most carpet with still enough ventilation underneath for the required convective air flow. The M-300s have several power cord options (consult Clayton or distributor TRI Audio Marketing for details ( I was supplied with a pair of DH Labs Power Plus AC cords for use in the review. These are very nice cords, relatively inexpensive, and they served the amplifiers well. Per Clayton's recommendation, the AC cords were plugged directly into the wall outlet instead of into a power conditioner that might restrict dynamics.  

The Claytons accept balanced inputs only, but my preamp is single ended (Audible Illusions IIIA). My plan was to use some RCA to XLR cable adapters so I could retain my reference single-ended interconnects for the review without introducing an additional variable, but when I tried these adapters I experienced significant hum problems. It took quite an effort for me to achieve a noise-free installation between my single-ended preamp and the balanced Claytons. The issues were specific to my system so I don't want to make a big deal about it, but I do recommend caution if you are buying the Claytons to use in an unbalanced system. With helpful advice from Terry Rossen at TRI Audio Marketing I eventually reached a splendid configuration. TRI supplied me with pairs of both single ended and balanced DH Labs Silver Sonic interconnects and I purchased an ISOMAX™ stereo line isolator from Jensen Transformers Inc. in Chatsworth, CA. (A relatively inexpensive accessory that I should be able to use in future reviews—it probably isn't required for most users). While I was trying to resolve my hum problems I ran the amplifiers at low bias for several hours per day to get them broken in. During this period I traveled to Denver for the Rocky Mountain Audio Fest where I got to meet Clayton designer Wilson Shen and distributor Terry Rossen. I returned home with a cold that affected my hearing (among other things) and made it hard for me to determine whether the sound from the Claytons was improving during the break in period. But, a week or so later, once my hearing was back to normal, the Claytons began to really sing in my system. So I cranked the bias mode up to high and began some serious listening that quickly turned into just plain fun.


"These amplifiers made my speakers disappear!" That was my first impression of the Claytons. All audiophiles aspire to a system that transports us to the recording space, but most of us are lucky if we hear this from our systems 20 or 30% of the time. Often the sound seems to get trapped in the speaker box (this even happens with planar and electrostatic systems). I always believed this problem was due to speaker frequency, phase or resonance issues or, alternatively, due to room effects. However, as soon as I began listening to familiar recordings on the Clayton M-300s these distractions virtually disappeared!  All I heard were voices and instruments suspended in the space behind the speakers with rock-solid positioning. Even some early stereo recordings that had voices or instruments panned to one side or the other imaged as sources slightly behind the speaker and with palpable air around them rather than sounds trapped in the speaker box as they had before. So, I learned that some of the distractions I had become accustomed to in my system were, in fact, electronic artifacts and not speaker problems. The Claytons did such a good job of capturing the soundstage and placing realistic images in that space that any other component problems took second place. This was a revelation to me, and one that transformed my listening experience.

As I listened further my appreciation for the imaging capabilities of the Claytons grew and grew. Depth went wayyyyy back when it was in the recording and the sound stage, which formerly had 2 or 3 layers of depth, now seemed to have many more tiers. I have always experienced a wide soundstage with my reference system and this continued with the Clayton's, but now the details of the soundstage were thoroughly filled out. The same was true for both CD and vinyl sources. I've had other good electronics in my system during my year of reviewing for PFO, but nothing nailed the soundstage better than the Clayton M-300s and nothing transformed my box speakers into veritable electrostatics.

So the imaging and soundstaging of the Claytons is state-of-the-art, now let me describe how the Claytons sound in the different frequency bands. The low frequency portions of the spectrum sound dynamic, firm and tight with the Claytons. My Wilson Cub speakers are only good down to around 50Hz so I really can't comment on the extreme low frequency performance of the amplifiers. However, I did about one-third of my listening without a subwoofer and the Claytons seemed to push the Cubs another 10Hz lower than usual. When I did hook up the subwoofer using my normal settings I thought the bass was a little too strong and loose. I reduced the subwoofer level a tad and lowered the crossover point a bit as well and this restored the tightness I was hearing without the sub, but gave me the lower octave to enjoy as well.

The midrange with the Claytons is spectacular. It's dynamic and full with loads of detail. There might be a few tube amplifiers and an occasional solid state amp with a better midrange but the Claytons are pretty good.  Voices, which I enjoy listening to the most, are just beautiful and, with the right recordings, sound almost real. For example I tried Aaron Neville on the "Warm Your Heart" XRCD and Johnny Cash on a couple of his American Recordings LPs and they never sounded better. Rickie Lee Jones on her debut LP was terrific, Eva Cassidy in "Live at Blues Alley" sounded in the room and Christina Aguilera singing "Walk Away" from her "Stripped" album was wonderful and heartfelt. I also tried several jazz and classical recordings to get a feel for the midrange performance and everything I tried was spectacular through the Claytons. I enjoy a dynamic sound and the combination of tight low frequencies and full and detailed midrange gave me all that I ever wanted out of my stereo. The midrange dynamics were also very nuanced, whether the sound was soft or loud.

The highs on the Claytons are clean, detailed and extended, though perhaps not as lush or sweet as realized from some tube gear. The amplifiers at times gave the impression of being slightly rolled off at the extreme top end, but when the music called for high frequency energy or detail it was right there. The sound I normally get with my tube preamp and solid-state power amp is a little on the dark sound, however the Clayton amp banished the darkness and provided much more clarity, smoothness and openness. Upper string harmonics were terrific and cymbals and bells sounded as good as I have ever heard them in my system.

The high resolution and detail present with the Clayton amplifiers made system adjustments much easier. For example, I have always had trouble optimizing vertical tracking angle on my Scout turntable, but with the Claytons I had no trouble at all. I would not say the Claytons have a very analytical sound, but just a very clean audio signature that communicates the music as well as any thing else going on in the sound system or recording.

With its full dynamics, limitless power, extended frequency response at both ends, full midrange, detailed and transparent sound and spectacular soundstaging the Claytons are first rate at drawing you into the music and communicating its message. In the two months or so I had the Claytons I enjoyed every single recording I played through them often finding new insights and emotional connections. And as I said, they elevated the overall performance of my system by preserving the stereo illusion despite known shortcomings in other parts of my rig.


One thing that concerned me in writing this review was that I was forced to use new cables (supplied by DH Labs) while listening to an unfamiliar amplifier in my reference system. So my review is really one of the combination of the DH Labs cables and Clayton amplifiers. This was necessary because of the hum problems I experienced when using my stock single-ended cables with the Claytons. Fortunately, my Krell KAV-250 also accepts balanced inputs (in addition to single ended), so I was able to compare the sound of the Krell with the Claytons with identical interconnects. For this comparison I also used the DH Labs Power Plus AC cord for the Krell and plugged it directly into the wall outlet. It did not take long to notice the collapse in the sound stage and the return of the slightly dark frequency signature of my reference. I concluded that at least 90% of the enjoyment I was experiencing with the Claytons was due to the amplifiers and not the interconnects. The Krell did a little better when I plugged it into the PS Audio Power Plant Premier (I normally run it this way), but it was still distinctly different than the Clayton.

So that is one comparison, the $3000 (when new) Krell stereo amplifier, an example of the common class AB type of amplifier, compared to the $13,500 Class A Clayton (two monoblocks). These two amplifiers match up pretty closely in wattage (500-watts per channel into 4 ohms for the Krell vs. 600-watts for the Clayton), but one wouldn't expect the Krell to represent the best in class given its price. The Krell held its own in low frequency punch and midrange fullness and was close in portraying macro and micro dynamics, but the Clayton was far superior in transparency, imaging, detail, and smoothness in the highs.

The only other Class A amplifier I've had in my system recently is the Luxman M-600A (reviewed in PFO issue 36) that offers 30-watts per channel into 8 ohms and 60-watts per channel into 4 ohms. The Luxman costs around $8000 for a 2-channel amplifier last time we checked. Although much lower in power, the Luxman drove my 89 dB efficient Wilson Cubs to satisfactory levels in my medium size room for all types of music, although the bar-type power display got pretty close to the top a number of times. Maybe it was the visual image of the power display, but I did reach a point where I didn't want to push the Luxman any higher in volume than I did, whereas with the Clayton running out of power was never an issue (the Clayton does not have a visual power display). As for sound, the Luxman had a sweeter high end than the Claytons and sounded more tube-like, but I could never get the Luxman to image as well in my room and with the cables I had available (including some pretty good ones from Shunyata Research). If 30 to 60-watts is enough for your system then the Luxman is worth checking out. The Clayton M-300 gives you 10 times more power for less than twice the price.

Another interesting comparison is with the Audio Crafters Guild ACG 1000 Control Amplifier (reviewed in PFO issue 37), which runs $3750 plus another $995 for the additional energy storage unit.  The ACG can deliver up to 1000-watts per channel into 4 ohms. This amplifier uses the B&O ICE™ power modules being an example of a class D switching amplifier. The ACG 1000 was a very dynamic amplifier that I thought was a little juiced in the low end. It had a great midrange that allowed me to connect with the music in a very special way, but was not nearly as refined in the high end as the Clayton's. They also did not present the level of 3D soundstaging that the Claytons delivered. The ACG 1000 is a good amplifier, especially for the money, but not in the same class as the Claytons.


The Clayton M-300 monoblocks have made me a believer in Class A operation. They sound wonderful with spectacular dynamics, a nice full midrange, virtually limitless power, and just about the best soundstaging I've ever heard. I would keep them and make them my reference if I could afford them. Let's talk a bit about value. There are many high power solid-state power amplifiers out there that cost as much or more than the Claytons. For example, using the October 2008 issue of Stereophile Recommended Components as a reference, there is the Ayre MX-R 300-watts monoblocks at $18,500 per pair, the 1000-watts Bryston 28B-SST monoblocks at $16,000 per pair, the 180-watts Halcro dm38 Stereo amp at $22,900, and the Krell Evolution 600 monoblocks at $33,000 per pair, just to name just a few. I haven't heard all these amplifiers under controlled conditions, but the ones I have heard at audio shows were great, yet I don't believe the Claytons would be embarrassed in their company. You can also find 200 to 300-watts amplifiers for less than half the price of the Claytons. I have more experience down in this price range and I haven't heard one yet that could equal the Clayton M-300s. If you can afford the $13,500 price and you need this much power I strongly encourage you to find a place to give the Claytons a listen. Mike Wechsberg

M300 amplifiers
Retail: $13.500 a pair

Clayton Audio
8151 Stratford Ave.
Clayton, MO 63105
TEL: 314. 862. 6017
email address: [email protected]

Dealer Sales, Marketing, Technical Support:

TRI Audio Marketing
13604 Hartsbourne Drive,
Germantown, MD 20874-2828
email address: [email protected]
TEL: 301. 540. 1156