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April 2017
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Aries Cerat Diana Forte Stereo Power Amplifier
Aries Cerat's Diana Forte is a magical sounding, and substantial, 250 pound amplifier.
Review By Tom Lyle


Aries Cerat Diana Forte Stereo Power Amplifier Review


  It obvious that one must consider many things before deciding upon which power amplifier to use for one's system. The Aries Cerat Diana Forte is a unique amplifier, to say the least. It very well could be considered the epitome of an amplifier that must be paired not only with an appropriate system, but especially the right audiophile. But if one's system meets a system's requirements; the Diana Forte power amp has the potential to transport the owner of this system to sonic nirvana.


The Diana Forte amplifier arrived by truck in a large crate, its shipping weight specified at 300 pounds. Removing the amp from its crate was a challenge, as was transporting the amp to my listening room. Luckily, I know someone who owns a landscaping company, and two of his most brawny employees were nice enough to help carry it upstairs. I'm lying. I wasn't much help. I watched them bring it up the flight of stairs. I'm lucky, because if these guys weren't around it would have taken at least three men of average build to perform this task. The Diana Forte power amplifier weighs a substantial 250 pounds and measures 22.5" x 23.25" x 13.75" (WxDxH). The photos of this amplifier might be a little misleading, as there are no other objects in the pictures to judge perspective. It is the largest amplifier I've ever had in my listening room. It is by far the heaviest.

One look at the Aries Cerat website will make it clear that Aries Cerat's owner and chief engineer Stravos Danos has a one-track mind to design and build the best audio equipment possible, with little consideration for price and user convenience. To him, the best audio equipment does only one thing sound great. He said that when designing the Diana Forte, he based the circuits on his Diane integrated amp's output and driver stages. This integrated amp's output power is only 25 Watts per channel, yet it tips the scales at well over 200 pounds, and its dimensions are similar to the Diana Forte reviewed here. The Diana Forte, at 60Wpc has an output stage that provides more than twice the power of the Diana integrated amp. And get this the Diana Forte is a parallel SET amplifier, and so Aries Cerat claims that it will deliver that "SET magic" despite it not having a typical single-ended circuit.


Aries Cerat Diana Forte Stereo Power Amplifier Review


Stavros can make this claim because the parallel SET output stage he designed is built around the 813 DHT big bottle tube. This huge vacuum tube drives an oversized core output transformer which he constructed using "special winding techniques" which can deliver wide bandwidth when at full power. The Diana Forte's driver stage uses another huge vacuum tube, the 814 DHT (Directly Heated Triode), which in Aries Cerat's website says is "loaded with a double-C core bifilar wound inter-stage transformer", which means that they use the best transformers possible in this amplifier. The output stage's power supply has a separate set of choke-filtered capacitor banks that use Aries Cerat's own Super-Capacitors.

The driver stage also uses choke filtered capacitor banks with their own power transformer to avoid power supply cross-talk. All the tubes in this amplifier can be easily biased and monitored on the fly using the two meters located on the top of the amp, and can be matched using the Diana Forte as a stripped-down tube tester.

When speaking to Aries Cerat's US distributor, he told me that what sets this amp's design apart from others is that most tube amplifiers designs, even those that use excellent output tubes are that they under-driven in their input stage. The necessity of the amp's over-built power supply and super high-quality capacitors are to drive the output stage with much less effort, and therefore with plenty of reserves for transient musical passages. Their choices in this amp are based on the highest bandwidth and performance than the standard 211, 300, and 845 vacuum tube that are used in most single-ended amplifiers. One may ask why are there not a larger selection of tube amplifiers using the 813/814 combination as in this power amp? They told me that designing a circuit from scratch is a costly and labor intensive affair without any guarantees to the desired end result. So, it is easier to use an off the shelf circuit design and one's own twist to it. Aries Cerat claims they designed this amp using no compromises or shortcuts.

The amp can be connected to other Aries Cerat components, such as the Diana Mezzo preamp, using their proprietary AC Link. But they say that their proprietary AC link method of component and inter-stage coupling is something new in audio and very much different than the signal transmission methods that are popular. Any single ended or balanced audio connection consists of the signal line (or two of opposite phase signal lines for balanced) accompanied with a ground connection. The Aries Cerat AC link doesn't carry a common ground. This type of system is comprised by a floating secondary winding. So, the output section of the source stage such as one like the Incito preamp with an AC Link is connected through a two-wire interface connection.


Aries Cerat Diana Forte Stereo Power Amplifier Review


This connection goes directly to special biasing circuits of the proceeding stage (such as in the Diana Forte amplifier) which directly modulates the biasing circuits. No common ground is present and the signal is not referenced to any of the two device's grounds. This method of signal transmission, when combined with Aries Cerat's tube stage's biasing circuits, present a much more robust way of driving the tube. Signal bandwidth is superior (when all aspects are kept the same), transient response is cleaner, and overload recovery behavior is much faster and artifact free. Therefore, the AC Link signal transmission comes with a very nice "side effect" of superior sound quality as a bonus.


When I reviewed the Aries Cerat's remote controlled Incito preamplifier about a year and a half ago, the speakers it was paired with didn't matter that much. The Incito preamp is an amazing example of fine high-end electronic craftsmanship, with excellent sound quality to match. Ever since that review I've been longing to review another Aries Cerat component. When discussing this with Aries Cerat's US distributor, Believe High Fidelity's Joshua Masongsong, he suggested I review the Diana Forte power amp. If one has read my reviews, it's clear that I'm not much of a low-powered-amp paired-with-sensitive-speakers kind of guy. At least not when I audition equipment in my main listening room, as my reference speakers are rather large electrostatic panels. For quite a long time the speakers I used were the Sound Lab hybrid DynaStat, and as of a short time ago the Sound Lab Majestic 545.

Mr. Masongsong insisted that the Diana Forte would be able to drive my Sound Labs. I told him that my reference power amp puts out 350 Watts per channel; and that when I try to drive my speakers with anything less than 200 Wpc the treble is very weak and the listening volume can't be raised to a level that I consider "normal". Joshua persisted. He said because of the Diana Forte's top-notch innards, which includes its extremely powerful transformers and capacitor banks, the amp would not only be able to drive my speakers to a satisfying volume, but will sound amazing. I reminded him that the Sound Lab speakers' impedance levels drop below 1 Ohm, and that might cause problems. Joshua said it wouldn't. We continued this back-and-forth until I finally agreed to audition the Diana Forte, telling him I'd not only write a review, but if it sounded as good as he said it would I'd nominate him and Aries Cerat owner/engineer Stravos Danos for a Nobel Prize.


Big Deal
Connecting the Diana Forte to my speakers wasn't a big deal, as the amp's large speaker posts are spaced far apart on the rear of the amp. I used Westlake bi-wire speaker cable, but when I changed over to the newer Sound Lab Majestic 545 speakers they only have one pair of inputs, so I simply connected both runs of the speaker cables to each post. At first I was amazed that there was even any sound coming from the speakers. I don't know why, it's just that I was doubtful that this amp would work at all with these speakers. After a while I cranked the volume on the Luxman D-700u preamplifier. The sound got louder and louder. I then settled on a volume I was comfortable with. I listened.

My first impressions of this amplifier were good. Very good. I heard a very lifelike, palpable representation of what was on the recording, a sort of 3D sonic hologram of what was on the source. It drew me in. I started to forget to take notes. I was mesmerized. I shook my head to waken myself from this trance, and wished that the treble was a bit higher in amplitude, yet there was no doubt in my mind that as long as I didn't push the volume too high, or play any music that was too complex, this was one of the best sounding amplifiers I've ever had in my listening room. But I'm getting ahead of myself.

One of the reasons I probably thought the treble was a bit attenuated was because I was using speakers that when listening at even "normal" volumes has an impedance that might drop as low as 1 Ohm. The Diana Forte is not designed for this type of speaker, but rather those with a 4 to 8 Ohm nominal rating. My speakers also might not have this much treble attenuation if I had used one of Aries Cerat's preamps, or one with very high gain. Aries Cerat told me that they do offer an optional impedance selector on the Diana Forte, but given that their typical customer would not even think of using electrostatic speakers, they didn't have samples of a Diana Forte with an impedance selector for me to audition.

The bass, too, was lower in amplitude than I wished for. In fact, some of the lowest bass was barely audible. So, I hooked up my Velodyne 15" 2500 Watt subwoofer by connecting it's an output of my preamplifier to the sub, that way the Diana Forte wouldn't be responsible for driving it. The sub has an internal crossover, which after a bit of testing I ended up with it set fairly low, its low-pass crossover at f about 50Hz. The overall sound was much better. The bass wasn't as good sounding as when using a high-powered solid-state amplifier to power the Sound Labs, that's for sure. But I'm picking nits here. The system sounded great using this setup. I left the subwoofer in the system for the rest of the review period.


Aries Cerat Diana Forte Stereo Power Amplifier Review


One might doubt me and think it hyperbole, but during the first half of the review period I started taking notes, but the majority of the time I unable to put into words the sound of the midrange that was reproduced by the Aries Cerat Diana Forte power amplifier. Even though the frequency extremes were not being reproduced to their fullest potential, it was as if I was having a midrange epiphany, thinking to myself, "So this is what the midrange on my records is supposed to sound like!" I quickly became addicted to the sound I was hearing. Addicted because the midrange was not only the best I've ever heard through my speakers, but because it was one of the best reproductions of the midrange I've ever heard through any speakers. My mind was being blown.

I searched through my records, pulling out LPs that I thought might sound good through the Diana Forte amp, and found quite a few. I decided to play a "Super Analogue Disc" pressed by King Records of Japan of Shostakovich's String Quartet No. 8 (paired with Borodin's Quartet No. 2) performed by the Borodin Quartet that was originally released on Decca/London in 1962. So, I put the LP on my turntable. I listened. I took notes, dredging through the most unexplored parts of my brain for the most appropriate descriptive terms I could find to chronicle what I heard when playing the Shostakovich side of this album, and all I could come up with was, "Wow!". I regained my composure, and thought back to other times I played this string quartet through the Sound Labs. Nine times out of ten, it's a pleasure, because this is an excellent sounding record, and when listening to it through a good system the instruments are spaced far enough apart that I can enjoy each instrument's contribution to the score. The Aries Cerat Diana Forte could certainly do this, and more.

The instruments on the record became part of a huge soundstage that occupied the front portion of my listening room. I was able to listen to not only the sonic qualities of each of the four string instruments, but was also able to bask in this extremely emotional piece of music. Shostakovich wrote this quartet in the summer of 1960, shortly after he was diagnosed with ALS, Amyotrophic Lateral Sclerosis, as he was beginning to feel the effects of this disease. He also had recently joined the Communist Party, which some say did against his will. Shostakovich dedicated the composition to "the victims of fascism and the war", also against his will, supposedly imposed by the Soviet authorities that were closely following his career. There were reports by those close to him that he actually dedicated this piece to himself, as an epitaph, because he was going to commit suicide after the piece was finished. Of course, he didn't commit suicide, and ended up publishing a total of 15 string quartets before he finally died of lung cancer in 1975.

While this string quartet was unfolding before me, the source of the music disappeared, leaving me only the sonic hologram of the string quartet projected by my speakers. As it played, my thoughts switched between amazement at the effortless detail of the sound of each instrument, and Shostakovich's "orchestration" written into the quartet enabled each instrument to support the others. At the same time, it was easy to hear that each player took a lead role in the many themes. During the fourth movement (out of 5), marked Largo, there are three short bowings, or perhaps gunshots, or outbursts, which have been interpreted as many different things by many different people. As they occurred I could imagine rosin flying off the bows as each musician hunkered down on their instrument. During these enigmatic, energetic moments, I could hear that the Diana Forte had more than enough in the area of transient response combined with delicacy as was called for to make each instrument's down-stroke not a simple action, but a complex series of finely controlled muscular movements by four very talented individuals. Obviously, the musicians of the Borodin Quartet have taken this piece of music to heart, and sound as if they are totally immersed in its performance.


Dynamic Distance
Many tube amps have a trait I like to call "dynamic distance", that is audible when two or more instruments are playing simultaneously, at the same volume, and occupying the same space of the soundstage. Even though these instruments or vocals occupy the same space, there is patent definition between them -- so these instruments and voices remain separated in space. This distance that separates them can be front to back, or they might occupy the same plain yet there is still air between them, each instrument or voice reproduced with its three-dimensional outline intact. With all this sonic information before me I still was able to hang on every note, and since I'm very familiar with the score even though I could anticipate each note, it was as if I was listening to the score for the first time. After the side of the record ended, I exhaled, exhausted (in a good way!) from the experience.

I apologize if the above musical example uses some obtuse language. But there is much more to this amplifier than simply reproducing the signal it was sent, as its idiosyncratic approach to reproduction is unlike an amp I've ever auditioned before, yet at the same time it is also the most "musical" amplifier I've ever had in my system, as it somehow is able to know that this is music it is reproducing, not simply electrical signals. I also hope that using a string quartet as an example doesn't lead anyone to think that the Aries Cerat Diana Forte amplifier can only handle simple fare. No way. Although, I wouldn't go as far as to say that this amp would be perfect for reproducing a Mahler symphony, I did enjoy quite a few different genres. I didn't feel as I was giving up too much. I even played a good deal of rock through the Aries Cerat. If I didn't expect the volume to be too loud, I was awfully impressed at what I heard.

Got a little carried away and played the DSD file of Black Sabbath's first album, ripped from a Japanese single layer SACD. Black Sabbath, you say? Yes, Black Sabbath. They were recently in the news because after being together in one form or another for nearly 50 years, they embarked on their final tour. Their groundbreaking premier from 1970 has some powerful stuff on it, alright. But, it isn't that complex, really, as it is basically a power-trio (guitar-bass-drums) with a vocalist with some overdubs. Many might be surprised that there are also some more dynamic moments on the album, including many passages played with other acoustic instruments besides the drum kit. Nevertheless, the best of it is hard hitting, and although I didn't play it too loudly, the big surprise (other than that the Diana Forte not exploding due to satanic possession), is that I could enjoy this album from beginning to end. And the Diana Forte reproduced every snare drum whack, every vocal shriek, every cymbal crash, and every guitar wail with its SET-magic intact.


Aries Cerat Diana Forte Stereo Power Amplifier Review


As I said earlier, the treble of the Diana Forte is slightly attenuated, giving the album a bit of a dark tonal characteristic, but as compensation I was completely engulfed by the humongous soundstage coming through the speakers. This made the band members sound as if they were playing together in a very large studio space. Yes, the bass was also more than a bit, but the Diana Forte was a champ at letting me hear bassist Geezer Butler's fingers slapping the strings, sometimes rattling off the fretboard when he struck them hard, melding perfectly with Tony Iommi's uber-fuzz guitar. I'm saving the best for last young Ozzy Osbourne's vocals. His crystal-clear voice didn't sound as if it was in the room with me, but sounded as if I was eavesdropping on the recording session, his voice reproduced as a three-dimensional person singing these vocals. It was scary-real. And the dynamic-distance I mentioned aided in the separation of the instruments and sounds, making this album as far from a cacophonous mess as one could imagine.


I agreed to this review because I was told that the Diana Forte would have no problem driving my large electrostatic speakers. That is how I used this amplifier for most of the review period. But I couldn't resist hearing what I would hear if I connected smaller dynamic speakers. The only speakers that I had in-house other than the Sound Labs were my EgglestonWorks Isabel Signature two-way floor-standers. With a nominal impedance of 8 Ohms and a woofer that measures only 6-inches, I thought that the Diana Forte might be a pretty good match for this amp. I was correct. Even though these speakers aren't super-sensitive (rated at 87dB/W/m), they let me hear what the "sound" of the Diana Forte amp was all about. To my surprise (or maybe not) using the smaller speakers revealed that the Diana Forte is an amazing amplifier capable of delivering plenty of "single-ended-triode magic", along with some other traits that were lacking when the amp powered electrostats.

The Aries Cerat Diana Forte showed itself to be the most "organic" sounding amplifier I have ever heard. I will admit to using the term "organic" because I was floored by what I heard, and at the time I couldn't come up with any other term to best describe this amp's sound. There was a sound that can be described as "tube" sounding, yes. But at the same time there was quite a bit of transparency, and a human, reach-out-and-touch reality from just about any recording I played that I haven't heard from these speakers in all the years I've owned them. The treble wasn't nearly as attenuated as compared to when using the electrostats, but instead had a sparkling and authentic sound.

It is obvious I was being treated to upper-frequency extension that I might have heard through my Sound Lab electrostats if I had a Diana Forte with the optional impedance selector. The sound I was getting from the EgglestonWorks speakers made me forget about this, though, as I was hearing this amp performing at its full potential. The mids were the star of the show, of course, and as this is where the music lives, it was almost too much for me to take, especially when this amp was reproducing vocals.

When I played the Analogue Productions SACD of Ella and Louis, it was as if I entered a sonic time machine that brought me back 60 years into the past. It was a bit strange that a monophonic recording could actually have a soundstage that enable me to see in my mind's ear Ella Fitzgerald and Louis Armstrong singing centered between my two speakers with startling reality. The Diana Forte's type of sonic wizardry is something that I've never experienced before. This is why I think most audiophile terminology might be useless in this situation. My listening notes were all about the music I was hearing, not any characteristics of the amplifier.

I also played some rock through the Aries Cerat/EgglestonWorks combo, and was taken aback by the amount of dynamics that this amp could reproduce, both of the micro- and macro- varieties. When I played Patti Smith's first album Horses, I was not only able to luxuriate in Smith's distinctive voice, but this amp had enough slam to faithfully reproduce her rhythm section built around Jay Dee Daugherty's drums and Ivan Kral's bass with enough authority and pitch stability that it finally made sense that the Aries Cerat amplifier weighed as much as it did. The beefy power supplies and capacitors hidden within this amp's chassis were obviously doing their job, made evident by my speakers taking on a personality that belied their size. I was not hearing "room filling sound" from these speakers, I was hearing "a room filled with music". Once again, the source of the music disappeared, and what remained was the sung poetry of Patti Smith and her band, with Lenny Kaye's guitar solos piercing the air with his sinuous licks.


I was excited to have the opportunity to review the Aries Cerat Diana Forte power amplifier. Yet, at the same time, I wasn't very excited about it. My main speakers are certainly not the type that welcome relatively low-powered tube amps, even if this amp might the highest-powered stereo SET amp on the market. I'll remind readers that I said I would nominate both Aries Cerat owner/engineer Stravos Danos and Aries Cerat's US distributor Believe High Fidelity's Joshua Masongsong for a Nobel Prize if the Diana Forte amp sounded as good as Joshua said it would though my large electrostatic speakers. As the Norwegian Nobel Committee is responsible for the selection of eligible candidates for their prizes, I'm not sure if an e-mail to them stating that yes, the Diana Forte amp did indeed sound good, would be of any use.

If one can undertake the responsibilities associated with setting up and owning an amplifier that weighs 250 pounds, uses huge tubes that puts out enough heat to warm a large room or make a small one quite uncomfortably, takes up as much floor-space as a small refrigerator, and can afford it, I say -- go for it. I think that one would be wise to match the Aries Cerat with more appropriate speakers than electrostatic panels, because the resulting sound will be magical. This is fact, not opinion. And for that reason, I think those responsible for designing, manufacturing, and selling this power amplifier should receive a reward. And many customers.



Sub-bass (10Hz - 60Hz)

Mid-bass (80Hz - 200Hz)

Midrange (200Hz - 3,000Hz)

High Frequencies (3,000Hz On Up)



Inner Resolution

Soundscape Width Front

Soundscape Width Rear
Soundscape Depth Behind Speakers

Soundscape Extension Into Room


Fit And Finish

Self Noise

Value For The Money


Type: Stereo vacuum tube amplifier
Tubes: Two 814 and four 813
Maximum Power: 60 Watts per channel, single-ended Class A
Frequency Response: 15Hz to 110kHz
Noise Floor: 100dB
Combined Gain: 26dB
Dimensions: 22.5" x 23.25" x 13.75" (WxDxH)
Weight 242 lbs.
Price: $27,500


Company Information
Aries Cerat
52 Vasileos Pavlou A
Limassol 3052

Voice: +357 25565916
Fax: +357 99307099
Website: www.Aries-Cerat.eu


United States Distributor
Believe High Fidelity
11307 Samson Dr.
Hutto, TX 78634 

Voice: (512) 470-2709
E-mail: j@ibelieveinhifi.com 
Website: www.iBelieveInHiFi.com














































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