Analog Domain integrated amplifier review and test

All NEW Analog Domain integrated amplifier was personally delivered by Angel Despotov of Germany’s Analog Domain. For connoisseurs of high-end and ultra high-end audio, he needs no introduction. For those of you who wish to learn more, refer to my exclusive interview with Angel here. Together with his lovely wife, Ani and fellow engineer Svetilio, they brought the first production model (A001) of the Analog Domain Isis integrated amplifier. The elegant appearance of this integrated belies it’s tank like build quality. It weighs in at a surprising 25 kgs.

“The M75 range of dual channel amplifiers from Analog Domain represents the current state of the art in linear amplification technology. It is the result of 15+ years experience in high-performance amplifier circuit design, created to deliver exceptional performance at an attractive price point. 
The M75 features our recently disclosed proprietary Excalibur circuit. Near-zero distortion, a noise floor well below the human perceptual threshold and the generous power output capability of the Excalibur give the Isis its ability to amplify signals with extreme resolution and control, raising the enjoyment of music to an unprecedented level. “

The M75D is available in three configurations: two integrated amplifiers and a matching 2-channel power amplifier, for installations requiring more power in stereo, or for building multi-way systems with frequency splitting, or multi-channel systems:

M75D – Stereo integrated amplifier, stepped analogue volume attenuator, remote control 

M75A – Stereo integrated amplifier, linear analogue volume attenuator, manual control 

M75P – Stereo power amplifier 

What sets this integrated apart from a bevy of others? According to the white paper, this is Analog Domain’s first product to incorporate a groundbreaking circuit concept. The Excalibur circuit brings something new and different, that one can hear from the first strike of a note. You can find more elaborate insights here in my special Isis Q & A with Angel here, but in simplest terms, it stresses the importance of current rather than voltage. The Isis possesses thunderous energy, that fully grasps speakers at their entrails and doesn’t let go for a micro second. When on test I was already quite impressed with the Magico S1 speakers and as such for the first time I’ve heard Magico speakers actually sang. Once paired with the Isis, performance shifted to a different plane. The change was drastic and immediate. The level to which reproduction was enhanced left me dumb-founded.

An iron grip (kept by my excellent preceding equipment), morphed into a titanium one. I’ve never, repeat never heard music so alive, lifelike and direct in my room through any integrated amplifier. Being a gain junkie, my demands are not easily met. People who know me can confirm that satisfying my need for dynamics is one of my obvious listening biases. Not because I wish to go deaf or unnecessarily disturb the neighbours ;), rather, getting the music replayed in the closest measure of reality requires real control.

One compromise most audio designers make, (willingly or not) is the handling of power and the structure of their gain stages. With most power or integrated amplifiers, I get the feeling that someone is trying to suck 1000 litres of water through a straw. This effect can not only be heard, but felt subliminally. This effect results in an artificially muted reproduction that has little resemblance to real music.

The Analog Domain Isis Integrated is the first integrated amplifier in my experience completely absent of this effect. I’m intrigued by its ability to portray music in this way. This is a direct, purely interactive experience, that has raised the bar of performance so high, that my head is still spinning.

This new level of performance warrants a more precise look at what’s going on beneath the bonnet. There is much to be learned.

One of the most coveted secrets of Analog Domain Isis is The Excalibur Circuit:

“The figure above shows a highly simplified schematic of the Isis power amp stage. We have named this topology “The Excalibur”, knowing you understand the humour 😉 The main difference from popular topologies is in the final stage topology – the output devices are connected in a “common emitter” (CE) rather than the popular “common collector” (CC), also known as emitter follower, Darlington configuration. The drive currents in a CE configuration flow between the supply rails and ground and not into the load as in CC, leading to improved linearity, among other benefits. Despite its advantages, the CE topology is not popular as it is prone to thermal runaway and self-destruction if conventional bias control methods are attempted. Our proprietary DXDriveTM technology resolves this “minor inconvenience”, allowing us to take full advantage of the superior common emitter topology.”

One notable advantage of the Excalibur topology is its unrestricted current delivery capability. The internal resistance of the circuit is essentially zero as there is no local current feedback loop in the signal path. There are no “difficult loads” for the Excalibur. The near-zero internal resistance reduces back-EMV-induced distortion when driving loudspeakers. Back-EMV1 created by loudspeakers and its interaction with the output resistance of a power amplifier is a significant contributor to overall distortion and is one of the reasons why most NFB designs fail to perform adequately with real world loudspeakers. The Excalibur uses multi-point negative feedback to vastly improve performance over conventional NFB or non-NFB designs. 

Only protection circuits limit the current output current of the Isis. The protection circuits would disable the output stage if the load attempts to draw current in excess of the safe maximum. Normal operation resumes automatically when the overload condition is remedied, e.g. when a short circuit is removed.”

So how all these translates into the performance and actually sound?

It was evident from the start. Nothing came as a chance with Analog Domain Isis. From the excellent high-tech build of the chassis, that is in absence of any visible screw to multiplexing of the device operational skills. This Made In Germany machine instantly shows its mojo and swing away with the grandest pace. There is something ultra substantial about the Isis, that simply works within music realms. You’ve might be tricked by its moderate size, but on the closer inspection and any interaction of moving reveals the “mean” part of the machine. This is heavy metal! It spots 25+ kgs in weight and sturdiness one would relate with the amplifiers twice the size and appearance of the Isis. Analog Domain team took the extra time and refined everything around the Isis in profound and elaborated way. It spots refined industrial look, that radiate the confidence and authority. 

• Extremely stable M7 modular, thick plate aluminum chassis for vibration immunity 
 • Stereo mode or bridged mono mode 
 • 2x 250W @ 8ohm, 2x 400W @ 4ohm in stereo mode 
 • 1x 500W @ 8ohm, 1x 800W @ 4ohm in bridged mono mode 
 • XLR balanced line inputs, RCA line inputs with individual gain adjustment 
 • 120+ dB dynamic range, THD+N < -93dB ref. 1W/4Ohm 
 • Built in slow-acting clipping limiter to protect loudspeakers 
 • Fully protected against overdrive, overload and short circuits 
 • 5 year unconditional warranty against defects in materials or workmanship 

Secondary voltage management for optimal loading 

Most amplifiers operate off a fixed voltage internally. When a typical stereo amplifier is switched from single-ended mode to bridged mode, the voltage output doubles relative to single-ended mode as the load is connected across the two outputs. Power output quadruples for the same load relative to single- ended (stereo) mode. If the power supply were sized for bridged mode, it would limit the power output of the amp in stereo mode, as the supply voltage would be lower than is required for nominal power output. If it were sized for nominal output in stereo mode, it would be overloaded in bridged mode. 

The Isis is automatically reconfigured upon mode change to provide a higher voltage in stereo mode, thereby achieving the same combined power output as in bridged mode. The full output capacity of the power supply is available to the power stages in either mode without risk of overloading. While such a voltage changeover is desired, it is practically unachievable with conventional circuits – any change to the supply voltage typically causes DC offset, bias drift and degradation of performance, and catastrophic failure in some cases. 

The Excalibur circuit features our proprietary DXDriveTM bias control technology that maintains optimum bias and zero DC offset regardless of supply voltage, allowing the Isis to deliver nominal performance in single-ended and in bridged mode. 

In the high-end world where we mostly deal with dynamic speakers  Analog Domain Isis came as an panache for the hungry crowd of technical advanced machine with the real state of the art musical DNA. Angel is as wit as it gets and bit Isis and Excalibur names refer it. Yet, his profound understanding of electronics offers a unique projection of an ultimate musical scope. As few of the top ultra-high end audio designers he constantly pushes himself and his team to their limits and beyond. This is the only way of pursuing something unique and special in upper echelon of high-end audio league. 

I’m a gain junkie and immortal defender of the so called power attitude simplicity. When we’re talking about the real ultimate control of the speakers there must be an unlimited reserve of power and gain capability in creating a viable and palpable illusion. Without the real control everything collapses. When it comes down to the basic and primal role of any amplifier they simply need to control the speakers. Analog Domain Isis literary grabbed Magico S1 guts and didn’t let it go for even a millisecond. It showed an impressive iron grip locking, that produced effortless foray into the musical drama. Never for an instance I’ve felt the lack of control and this with such a small embodiment. This is something unexpected from amplifier of this size and power. Analog Domain Isis transformed Magico S1 into something different and soulful. That is an attribute I would never easily relate typically with Magico. Angel witnessed the same in my listening room and it was interesting to see his reaction. We were both surprised of what came out of the Magico S1. Along my review same thing happened with other speakers being at my reach. The authority was evident and sealed for good. 

Coming from the pro-audio side of things Angel see things through the different perspective. Everything mush be aligned to the core of the matter. Functionality, high performance and unaltered sound. Technical solutions must embrace the ergonomic/practical way of dealings. Isis is no brainer to use and feature packed like very few. 

From -20dB button, mute button, phase inverse switch, dedicated headphone amp, switchable +6dB RCA inputs, preamplifier output, direct power amplifier input, dedicated ground connector and even an LED indicator for the mode of speaker terminals. 

Lets get our facts straight. We live in the 21st century and as such its a logical conclusion, that we should enjoy the benefits and results of industrial breakthroughs and true achievements of technology advancement. There should be no excuses for high-end audio industry in this regards. We’ve seen emperor new clothes being sold and revived each new year with vast array of different so called high-end and ultra high-end audio products. From audio cables to speakers. Sadly and worrying, there are not really, that much true breakthroughs at the end of the day. Even if we want them so badly. 

Therefore I’m enthralled with the products like Analog Domain Isis and with people like Angel Despotov. His urge and even more importantly technical knowledge is of vast and alway impresses me. Before taking things into realms of so called esoteric ultra high-end audio, there must be a common ground. These means a solid, resolved and applicable knowhow, that will set the corner stones for anything special. To put it into the earthlings language. It has to fill the basic rule of electronics. Many companies or individuals are trying to avoid this and exploit the high-end audio society for easy and quick money. We have many daydreamers in this industry, but very few that actually live the dream and morph it into real physical object of art. From all the people I’v met in my 20+ years in high-end audio I’ve concluded, how there is no cut back when it comes to the pure engineering. When combined with profound knowledge and vast mileage, the esoteric/mystical concepts can take a place. I’m not talking about voodoo approaches, but the electronic solutions, that goers beyond everyday solutions. Angel showed his white paper of Excalibur to few of electronic engineers outside of high-end audio domain. And they all replied with the same answer. “This cannot be stable in implemented in real life!” Well, it can…

Strong determinations and special things needs complete persons behind the any special product and project. Only with such a grand pace they can project their ideas into the finalised ideas, that stand on their own. Only with all that paraphernalia one can combine the pure passion and love for music into the product, that interacts with musical reproduction in most profound way. Here is where the real magic happens and new breeds are being born. 

If the highly sophisticated productive language and direction of electronic design is not impregnated with the pure passion for music, then results are anaemic, mediocre and lifeless. Electronic designer choices create the uniqueness of the sound outcome. As much as we’re witnessing the emerging and ongoing “calling” of certain people, that represent the doubtful and “everything sounds the same” movement and school of thought, every little nuance actually DO matters in the sound outcome. This signature “transfer”  can be of subtle nature, sub consciousness or lucid one, but the results are avidly evident. As with everything else in life and with different fields of industry. In the world of high-end audio we’re dealing with the world of music and its utmost believable reproduction. Along the energy transfer we are also talking about an emotional impact. Without this there is not even a slightest reference to the high-end way. What to talk about ultra high-end. When rendered in right way listening to music will simply feel right and relaxed. It will be a natural experience with the lasting effect. 

This is something, that happens rare in high-end audio and something that Analog Domain Isis is capable of. Ultra high-end audio reproduction is a complex technical foray, that builds the bridge between the technology and music in the most lucid way. As much as this is often promoted actually presence is of rare kind. 

Isis can act and integrated amplifier, preamplifier and power amplifier. This opens up the flexible nature and elaborated connectivity. I’ve highly enjoyed the combination with Robert Koda Takumi K-10 preamplifier. When these two connected something profoundly different emerged, then I’m used to. Rarely two machines benefits each other, but in this case it felt like match made in heaven. 

Finding the synergy between two components can be an endless task, but in the joint efforts of Robet Koda K-10 and Analog Domain Isis the musical result is of special kind. It only further shown of what material Isis is made off and how the upper plane of high-end audio project the balancing act of refined system approach. 

Among all the positive sides of Isis the effortlessness is one of the most stand out. Music is such a complex universe and its viable reproduction is never ending an on going challenge. Analog Domain Isis emerges the pursue of music in the vivid and eclectic way. 

The listening brings the harmonious effect of joint nature from musical fractal like complexity into something harmonious and involving, that can be enjoyed in its ultimate simplicity. It works. It clicks. It connects. Period! 

This is highly sophisticated MACHINE made in Germany with the heart of lion. Analog Domain Isis comes as something fresh, special and of potency, that leaves a big thunderous lingering effect. This is a modern, exotic high-end audio integrated amplifier, that packs profound technology in the simplest and straightforward way of daily operation. Its created by the music lover with the ability to shift electronics to his heart desire.  

It took Analog Domain team lot of time to conquer all the challenges. From Angel’s wizard like Excalibur circuit to refined chassis, everything is finalised in impressive and complete way. 

In these day and age not many product truly impresses me, but Analog Domain Isis for sure took my understanding and experience of solid state amplifiers to the completely new plane. For an integrated amplifier Isis represent a pinnacle in its class and far above. Considering the pricing, this product sets a new milestone and take no prisoners. This is musical machine, that transcend all the genres and ages. It acts like a time machine with the ever lasting ticked into the musical universe. 

Angel told me long time ago about his wish for brining the Analog Domain performance to the more affordable grounds. Here is the best way to finally explore his vision. For a normal sized room with applicable matched speakers, there is nothing to left to be desired for. Isis takes the speakers at its guts and never let it go. This is a true F1 of integrated amplifiers with the musical heart.

Based on my initial experiences, it became evident, that I’m in trouble. How can one go back to a lesser level of performance after having seen the promised land? This is a pure reference level solid state integrated amplifier (and for that sakes also a power amplifier), that has up-ended everything I thought I knew about listening at home. There is no rational way of letting something as musically empowered as The Analog Domain Isis get away from my home. This ones stays permanently. 

I’m wholeheartedly giving out the Upper Echelon Class award to Analog Domain Isis. It would be duplicitous not to act upon everything I’ve discover on my prolonged journey with The Isis. At this level of performance for me Isis can act as an reference tool and a musical box for the musical enjoyment. I can simply forget about the technology and immerse into the music regardless of being a great sounding or bad mastered song. This is the real magic. When technology is implanted in the translucent way, we can forget about it. And in absence of defining things music happens. What else to grasp for!?

Text: Matej Isak

Isis M75A – Stereo integrated amplifier, linear analogue volume attenuator, manual control

Power output

8 ohm, sine wave, rms 250W

4 ohm, sine wave, rms 400W

8 ohm, bridged, music material 500W

4 ohm, bridged, music material 1000W

Damping factor

1kHz, 4ohm load, single-ended >1000

1kHz, 4ohm, bridged mode >500

THD+N

20kHz BW, 8ohm, nom. power