April 2015

Merrill Audio Thor Monoblock Amplifiers
Nothing short of amazing!
Review By Tom Lyle

 In December of 2013 Jules Coleman reviewed the $12,000 a pair Merrill Audio VERITAS Monoblock amplifiers (a Blue Note Best Of 2014 Award winner). These 400 Watt (at 8 Ohms) amplifiers cost nearly three times as much as the subject of this review, the THOR monoblocks. The THOR's output is half of the VERITAS at 200 Watts per channel, and although not cheap, they are priced at a more affordable $4800 for the pair. Merrill Audio claims that the THORs benefit from the technology and research done for the more powerful and more expensive models that are one step higher in Merrill Audio's line. Which makes sense, as to begin R&D anew to create a lower powered smaller amplifier would make little sense given the success of their larger and more powerful sibling. Professor Coleman and I both use Sound Lab speakers in our systems, although I have a second, smaller system that uses medium-sized floorstanding dynamic speakers that are better suited for the lower output of the THOR. This enabled me to hear the them in a system that would most likely resemble one in which the majority of these amplifiers will be used in the real world.

In the THOR monoblocks Merrill Audio says they used "top notch" components such as the Hypex OEM Udc modules, which Merrill Audio modified for the THOR unit, and the chassis of the THOR is divided into two chambers to minimize interference and microphonics. When they were designing the THOR, transient detail was of paramount importance says Merrill Audio, and without any switches in the audio's signal they say that this feature help achieve this goal. The THOR is shipped to customers with their own pair of power cables, which are available for $499 each if purchased separately. These cables use terminals sourced from Cardas, and have Rhodium over silver-plated pure copper contacts with wire sourced from Furutech. The Furutech wire uses 27 strand pure-alpha copper with silver plating. Internally, the THOR has Synergistic Research fuses, uses heavy-gauge wire throughout, and the inputs are differentially balanced to ensure that again, noise is kept to a minimum. In fact, the input into each THOR is a balanced XLR. An adaptor is to be used if the preamplifier has only unbalanced RCA outputs. Merrill Audio found that the advantages of using balanced inputs far outweigh the inconvenience that some audiophiles may encounter.

The THOR monoblocks are sold factory direct, although a few "select" dealers at the time of this writing also stock them. Merrill Audio says that selling factory direct keeps the retail price an "affordable" $4800. Although, one can easily imagine that this fledgling company would jump at the chance to secure a large dealer network, it is the customers who can use this factory direct situation to their advantage. The THOR monoblocks are great looking small components. My review samples of the 9" by 9" by 2.5" (WxDxH) cabinets were finished in a glossy piano black, and when the rather large round On/Off switches under the front of the cabinet are activated a red LED glows that is bright enough to reflect off the floor beneath, but not bright enough to distract. The preamplifiers that I used for auditioning the THORs are also fully balanced designs, so they both have balanced XLR outputs to take advantage of not only THOR's XRL inputs, but the THOR's fully balanced design.

Power
I was excited. In the late 1990s and early 2000s more than a few audio manufacturers began to sell power amplifiers using Class D circuits in the output stage. Excitement turned to disappointment after a short audition of one of these amplifiers, and shortly after that, another. Both were made by a well known, medium sized high-end manufacturers. Anyone with ears could tell that this technology had not yet matured. There were quite a few other high-end manufacturers selling Class D products at this time using transistors operating as electronic switches rather than the much more common Class A/B which are linear gain devices. Word on the street was that other than a few select (and very pricey) units, these amplifiers had no business being sold to the audiophile public. Yes, the advantages of Class D were and are still obvious – they are much more efficient and because of this the majority of them are very high powered units, and at the same time they are lighter, smaller and run cooler than similar amplifiers using more traditional Class A/B circuitry. The few reviews I agreed to write of these early Class D amps stressed the advantages of Class D, and they were indeed advantages. But facts are facts: The bass was powerful and the sound was super-clean, but the upper midrange and treble of these amplifiers were so harsh sounding that even a short listening session would give me a headache. After that, listening to music was the last thing I wanted to do. Especially through these Class D amps.

That was then and this is now. Class D has come a long way. But that doesn't mean that every Class D amplifier has rid itself of all the sonic disadvantages. As in all things high-end, it takes a good designer to make a good sounding amplifier, regardless of its class. Combining a Class A/B or tube input section with a Class D output section often results in a good partnership. But often this merely masks a poorly designed output stage. Conversely, often these combinations are quite successful, such as Rogue Audio's use of a tube input stage with a Class D output stage in their Medusa and Hydra amplifiers. The combination of a Class A input stage with a Class D output stage is used successfully in the AURALiC MERAK monoblocks that I reviewed in July 2014.

Response
These days pure Class D amps don't elicit nearly the same negative response from audiophiles as they once did, and rightfully so, because Class D designs have evolved, so most of the complaints regarding their sound quality have been largely addressed. These amps might not be a perfect fit for every system out there, but there is a heck of a lot more systems that they do fit than they once did. To eliminate an amplifier from consideration solely on the basis that it is Class D is foolish. Case in point is the Merrill Audio THOR monoblock. As I said previously, the THOR might not be inexpensive, but in the past the only Class D amplifiers that were worth listening to were priced much higher than the THOR. The THOR monoblocks have all the advantages one has come to expect from a Class D amplifier: Each THOR monoblock weighs a mere 15 pounds, is about the size of a hardcover novel, puts out a healthy 200 Watts into an 8 Ohm load, and its output doubles into 4 Ohms. After playing music all day at a "normal" (for me!) listening volume the amps became only a few degrees warmer than room temperature. Merrill Audio has also designed a very good looking cabinet for the THOR. They are raised off the floor with Stillpoints Ultramini Risers that have screw-in metal cones to make them look very attractive, in a miniature sort of way.

Located
The Merrill Audio THOR monoblocks spent most of the review period in my second system, located in a common area on the first floor of our home. They drove either a pair of EgglestonWorks Isabel Signature floorstanding two-way speakers or a set of Bowers & Wilkens (B&W) CM10 S2 five-driver towers (review forthcoming). Both of these speakers are easy to drive, with a stable impedance of 8 Ohms. They are also rather revealing of upstream gear, so a power amplifier with any sonic nasties will instantly be exposed for all to hear. Plus, the Class D THORs weren't going to get off easy as far as the upper-midrange and treble is concerned, as this is a purely digital system. One source is an Oppo BDP-83 Special Edition universal disc player, and the others either an AURALiC VEGA digital audio processor or a Benchmark Media DAC1USB digital-to-analog converter. The AURALiC and Benchmark are fed by the digital output of the Oppo using an MIT digital cable and through its analog output I play discs from my growing collection of SACD and DVD-A discs. The now discontinued Logitech Squeezebox Touch reads FLAC files (many of them high-resolution) over my home network has the digital output connected to one of the DACs, and shortly into the review period AURALiC's wireless streaming bridge ARIES arrived, which was also connected to the DACs. The ARIES serves as a bridge between the FLAC files on network attached (NAS) hard-drives on my music server two floors away and plays them through either of the DACs without the any loss of data that is typical with the Squeezebox Touch.

The signal passed through one of two linestages, a vacuum-tube Balanced Audio Technology (BAT) VK-33 preamplifier I reviewed or the solid-state LKV Research Line One linestage reviewed in October 2014. Interconnects that link the preamp to each THOR monoblock and the speaker cables in this system is made by Cardas Audio. Interconnect connecting the front-end gear to the preamplifiers is a mix of MIT and DH Labs. The medium sized room that hosted this system is a touch live sounding, but it has enough furnishings and window treatments to prevent the sound from causing any offensive reflections. I never had a problem with standing waves since the room is not a perfect rectangle, and since it is an older house with plaster walls and a very sturdy floor errant vibrations have never caused much of a problem, either. The front end equipment is supported by Metro Commercial shelving, and the THORs monoblocks sat on the floor on either side of the equipment rack, their steel cones lifting the amps off the floor about 1".

Sound
I didn't notice much change in the Merrill Audio THOR monoblocks' sound between the time I unboxed them and about two months later when beginning to write this review. I suppose the amps were either used as demos before they arrived or they are simply not that susceptible to break-in. My first impressions of the THOR monoblocks were positive, and continued to be so during the audition period. Actually, I was amazed that not only were there no negative Class D traits coming forth through the speakers, but that these diminutive amps sounded freakin' great. The THORs' sound is proudly solid-state – they aren't going to fool anyone into thinking they are listening to a tube amp, but neither were they annoyingly detailed or possessed any traits that I remember from the bad old days when Class D amps were thrust upon me to review, and any unlucky consumers who bought one. It was about three weeks into the review period that I stopped thinking of the THOR monoblocks as good Class D amps and started listening to them as good amps. Period.

It was tough to ignore the positive qualities that have always been present in Class D amps, especially their deep, tight, pitch specific, extended bass. Both speaker systems that I connected to the THOR monoblocks specifications claim that they reach as low as 40 Hz, but have usable bass to the low 30's, which is more than low enough to reproduce the lowest notes of a standard bass guitar or double bass. Of course there are lower resonant frequencies that add to the sound of these instruments that all lovers of powerful music, from orchestral to metal shouldn't have to live without, and these speakers are more than sufficient to produce these deep bass frequencies in my medium sized listening room. The THOR was able to display its prowess on a host of selections that its bass is a mighty thing to behold, and it was up to the recording to provide a bass sound that was extended and flat, and did not display and peaks or valleys that would ruin this sound.

The organist of Norte Dame in Paris in the early 20th Century was Louis Verne, who wrote six symphonies (more accurately suites) for the organ between 1899 and 1930. On a CD of his 1^st and 2^nd Symphony (which is also the first three sides of the five LP set that I often spin on my main system) which was recorded on this very same organ. To say that the bass frequencies on this recording are important is quite an understatement. Vierne's compositions are very dynamic. Through the course of one short movement the organ will leap from ppp to fff dozens of times, and during the climaxes the bass pedals of the organ, especially when I had the B&W speakers in the system, was able to shake the floorboards – yet these tones coming from the speaker's woofers were hardly a "one note" bass. Even during the lowest bass tones the THORs managed to reproduce the bass pedal pedals of the organ with the pitch intact, so as I could feel the bass I could easily detect its pitch. Vierne starts off his First Symphony building to one of these fff passages almost immediately, as if he's announcing his presence, but one only has to wait a couple of minutes more before Vierne eclipses this introduction. One can take the easy route and compare his work to those who came before, a Bach fugue, or organ works by other French composers such as Charles Widor or Cesar Franck come to mind, but Louis Vierne definitely had his own voice – which is clearly displayed in this quasi-romantic suite, and it is blended with modernistic touches that make it appealing to the modern listener. There was even a European progressive-rock band that did a short "cover tune" one of his symphonies. And this led me immediately to spin the DVD-Audio of Genesis' progressive-rock masterpiece Foxtrot album released in 1972. The B&W speakers bass isn't the most subsonic. But they do reproduce the synthesizer-bass pedals without relying on a pumped up mid-bass, or any other sonic illusion. The pedals are heard through the speakers as powered by the THORs as a very stable tone that underpins the rest of the music. The pitch of these tones was never in doubt, and neither was their timbre that was chosen by Dewtron and Moog Taurus bass pedal artist Mike Rutherford.

I expected the THOR monoblocks to have excellent bass. I also expected them to have a very quick, responsive transient response, and the THORS did not disappoint me in either department. Thankfully, these traits were accompanied by a transparent, natural sounding midrange and treble. The THORS were free of any annoying artifacts in its midrange that would make me squirm in my listening seat when listening to these types of amps in the bad old days, but really, enough time has passed that one would have hoped that these things would have been worked out by now. The THORs surpassed my expectations. The midrange and treble of the THOR monoblocks not only sounded crystal clear, but also did not sound over-analytical, and relied on the recording to determine the level of detail. Even more noticeable was that the midrange and treble frequencies were just there. Despite every attempt to find fault with the sound of these frequencies, my efforts were in vain.

When sitting in the sweet spot listening to the HDTracks download of John Coltrane's My Favorite Things I felt as if I was listening to the master tape of the session. Coltrane's horn occupied a distinct space in the hard-panned man-made soundstage, and I felt as if I could reach out and draw the outline of his soprano sax in space using a grease pencil. And although this hardly is the way things sound like in real life, this is how this masterpiece was recorded, and so this is how this masterpiece was being reproduced on my system. The space between the instruments of the quartet was filled only with the sound of tape hiss, and under this tape hiss was a black background. The THOR monoblocks rival the most silent backgrounds I've ever heard from an amplifier. Even when I foolishly raised the volume of the preamplifier significantly higher than is necessary, the only way to tell that the power of the amps was in the "on" position when no program material was being played was the glow from the red LED reflecting off the floorboards. Switching out the LKV Research for the BAT VK-33 preamplifier let a little more noise seep into the background. BAT manufactures notoriously quite preamplifiers, yet with the THOR monoblocks in the system I could hear a slight hiss, definitely lower in volume than tape hiss or other noise present in the background of the recording, but still present.

Using the Oppo universal player, LKV Research Line One, and the B&W CM10 S2 speakers on a grey, rainy afternoon I played my single-layer Japanese SACD of the Rolling Stone's Beggars Banquet. Nestled in my listening seat about eight feet from the center of the two speakers I could hear the tape hiss begin a split-second before the congas and percussion broke the silence. It is a rather busy rock/pseudo-samba recorded at Olympic Studios in London in the summer of 1968, and besides guest conga player Rocky Dijon, The Stones are also joined by pianist Nicky Hopkins, and the background vocals of Marianne Faithfull and Anita Pallenberg. Some have paid big bucks to own the mono mix version of Beggar's Banquet on LP, but I think that the rather crude stereo mix helps unravel all that's been recorded without spoiling the sense of envelopment that occurs when played through a high-end system. One of the great joys I have is when I play a recording that I've heard hundreds or perhaps thousands of times through a high-end system and hear new things. This time out, with the THORs in the system I could easily hear details of the reverb and tape echo applied not only to Mick Jagger's voice, but also some other details of the other voices on the recording that I don't remember ever hearing before. No matter how dense things became I could still hear the six young men and women singing their parts, as I could picture in my mind's ear each separate track of the multi-track during play-back. The various noises as a result of the recording process – whether it is tape overload, hiss, or noises of unknown origin – didn't distract me from this work of art, but added to its authenticity. There certainly weren't any noises or other unwanted sounds coming from the THORs, no matter how high I cranked the volume.

Boasts
On their website Merrill Audio boasts that their mission includes "their endless quest for audio purity" and "to deliver audio signals with the least amount of intrusion and influence from electronics being pushed through from the source to the speakers". I'm sure the readers of Enjoy The Music.com have read plenty of manufacture's websites throughout the years with this type of swagger and hyperbole. I sure have. But my thoughts regarding the sound quality of the THOR monoblocks were exactly as Merrill Audio states on their website. The THORs will not blow away the listener with sonic fireworks, unless these sonic spectacles are present on the recording. What is on the recording is what you'll hear through the THORs. Nothing more. Nothing less. This is more difficult than one might assume, and that Merrill Audio has managed to do this with such a small, good looking component is nothing short of amazing. I unequivocally recommend the Merrill Audio THOR Monoblocks for anyone searching for an amplifier for a system that needs anywhere near 200 wpc, and can spend anywhere near their asking price.

Ratings: I tend to rate very conservatively. A five-note rating is reserved for traits of the best state-of-the-art components I've ever heard.

Specifications
Type: Solid-state mono power amplifier
Frequency Response: 10Hz-30kHz (+/-3dB)
Power: 200 Watts at 8 Ohms, 400 Watts at 4 Ohms
Input Impedance: 50 kOhms
Output Impedance: 20 mW
Damping Factor: 500 4 Ohms
THD: 0.05% at 100 Watts
Current: 18 Amperes typical maximum
Gain: 26 dB
Signal to noise ratio: 100Db
Balanced Input: Cardas XLR with silver pins, rhodium plate, gold-plated body
Remote Trigger: 12 Volt for remote turn on/off
Speaker Output: Patented Cardas rhodium over billet copper posts
IEC: Furutech gold-plated
Custom designed power cord for THOR 14AWG 27-stranded silver plated alpha pure copper wire from Furutech and pure copper contacts, rhodium over silver-plated electrical plug and IEC from Cardas
Stillpoints Ultramini Risers for footers
Warranty: hree year transferable warranty
Short circuit protection
Over-temperature protection
Auto shut-off in case of fault
Dimensions: 9" x 9" x 2.5" without footers (WxDxH)
Weight: 15 lbs.
Price: $4800

Company Information
Merrill Audio Advanced Technology Labs, LLC.
80 Morristown Rd. #275
Bernardsville, NJ 07924

Voice: (415) 562-4434
Email: Sales-123@merrillaudio.net 
Website: www.MerrillAudio.net