Analog Domain Isis interview with Angel Despotov

Matej Isak of Mono & Stereo exclusive interview with Angel Despotov of Analog Domain on the topics of company latest Isis integrated amplifier and the Excalibur circuit. 

It's been quite some time since our last interview. What happened in between? 

I got married! ☺ And managed to complete the Isis project… 

Analog Domain Isis has finally being revealed. Your first comment? 

I’m happy! The project has reached its objective – to produce a relatively compact amplifier that approaches the performance of the big Analog Domain monoblocks.

Isis is the first Analog Domain product that implements the Excalibur. Please tell us more why Excalibur is so special? 

The Excalibur circuit differs from conventional topology. The significant difference is in the output stage, which has both voltage and current gain. This helps to reduce distortion.

Will you offer Excalibur as an option for of your amplifiers?

The monoblocks in the DX9 range have shown exceptional performance that is difficult to beat. The real issue is – is an upgrade necessary? If and when I am fully convinced that there would be a significant advantage, we may roll forward the Excalibur to the mono blocks.

How about the already existing power amplifiers? Can Excalibur be installed in them?

It is my philosophy that once you are a customer, I will do whatever it takes to deliver the latest technology while preserving the original investment as much as possible. If an upgrade is made available, it would be compatible with existing models, allowing a cost-effective replacement of the electronics only. As I said above – the monoblocks are not easy to beat.

I can sense the unlimited power on the first note strikes with Isis. For a such compact size this quite an achievement!?

The Isis achieves impressive performance for its size. My goal was to pack as much power as practical in a relatively compact chassis, and also I applied a little “trick” that maximizes the dynamic power output.

What is your perception of real amplifier power?

Dynamic headroom is very important for a realistic experience. A good amp should be able to deliver high power transients cleanly. Music is a complex mix of frequencies at vastly differing amplitudes. Subtle changes in timing or relative amplitudes can completely alter the perception, rendering an “artificial” sound.

Why no other high-end audio manufacturers talk about the current slew?

I really don’t know the answer. The typical loudspeaker is a demanding complex load. Its parameters can vary while it is operating. Anyone familiar with an oscilloscope can connect it in X-Y mode and observe the relationship of voltage and current in a loudspeaker. The picture may be very surprising to some.

Excalibur brings the endless energy, yet its not squashed. Where is the secret? 

Dynamic headroom and current delivery ability, i.e. current slew rate. The DX Drive is responsible for its exceptional resolution.

What is the relation between Class A, Class AB and actual implementation of gain stages in Isis? 

The main voltage gain stage in the Isis operates in Class A. The stages after it operate in Class AB, but this is not uncommon. The key is in the overall circuit topology.

Is it a true balanced operation?

The inputs of the power stages are differential (or “balanced”), yet the output of each channel is single-ended. When the Isis is used in bridge mode, then it may be considered as “fully balanced” monoblock.

Isis can also operate as both preamplifier and power amplifier. Please elaborate...

The preamplifier stage is completely separate. Its output is available on a socket at the rear panel, as is the input to the power stage. They can be internally connected to each other or can be decoupled. This is useful if you would like to use an external processor - e.g. a room correction system, or two or more amps in parallel, with or without an external crossover to split the signal into two or more bands and drive your speakers separately. By adding an Isis power amplifier, one has the option of using 2x2 channels for bi-amplification, or to switch both units to bridge mode and use each one as a ‘monoblock’, controlled by the preamplifier in the main unit.

How to properly understand the inherited deficient most amplifiers have regardless of so called technical specifications? 

Technical specifications are important, yet the “standard” specifications do not reveal the full picture. To fully evaluate the performance of an amplifier, one needs to see a much broader set of specifications and measurements. The final verdict comes from our ears, of course.

How much importance have you dedicated to Isis preamplifier stage? Can you elaborate what is special about your take on preamp stage? Will this consequently lead to Analog Domain official preamplifier?

The preamplifier in the Isis is a minimalist design, based on extensive experience. A lot of attention was given to the volume control methods in the two versions to preserve the sound quality as much as possible.

How do you see the relation between preamplifier and amplifier and it's importance? 

It’s very important to properly distribute the voltage gain of the various stages in a system to achieve the maximum possible signal-to-noise ratio and headroom.

I’ve spotted the unique limiter function. Why implemented and how it works? 

The limiter in the Isis engages only when you attempt to overdrive the amplifier. It prevents distortion, and more importantly – it protects the speakers from clipping.

Subsonic filter at 7hz? How much DNA of your flagship Analog Domain [monoblocks] is Isis carrying? 

The Isis is essentially a high power dc design. Subsonic frequencies can be very harmful to speakers. The subsonic filter in the Isis protects the speakers from subsonic frequencies, thereby increasing their usable power output, especially with turntables - they can produce significant amounts of infrasound. The cutoff frequency was selected so as to minimize the audible effect on sound.

The Isis, like the monoblocks, is based on our proprietary DXDrive circuit. This gives it its transparency and extreme resolution.

How and where you would position your new Isis?

I would say that the Isis is positioned in the top end of the integrated amplifier domain. It has substantial power output, yet its sound quality is refined and dynamic at any output level.

Still made in Germany importance? 

All our products are manufactured in Germany, and our customers seem to like this.

What kind of speakers would you recommend for Analog Domain Isis? 

Any speaker that is properly designed will be a good match with the Isis. Resolution, low distortion and high power handling are very important for achieving a realistic experience.

Isis "mojo" for sure feels like few times larger then it's box. Why and how? 

The power output of the Isis with music material is higher than typical designs due to the configuration of the two channels – they work in inverse phase. When there is a simultaneous peak in both channels, in a conventional design they would draw current from the same pole of the power supply, causing significant voltage sag. So here is the “secret”: if one channel is inverted, the effect is like doubling the capacitance of the power supply. I learned this neat trick from the pro audio world where the objective is to squeeze out the juice to the last drop.

Tell us more about the differences in the Isis line?

The various models are based on the same circuit. The differences are in the input stage – the power amplifier does not have volume control. Otherwise they are identical.

Design wise, Isis feels really like a refined and ergonomic product. How much [time] did it exactly take to develop it?

The design of the Isis went through many, many revisions. Its complexity is hidden from the user, making it simple to operate. It has been designed to be very reliable in operation. Overall, it took around three years of intensive work.

Transparency or musicality? 

Both! Who likes limits?

Any final thoughts for our readers?

Plug, play and enjoy. I believe the Isis will set the standard in compact integrated amplifiers for years to come.

Questions and photos by Matej Isak of Mono & Stereo. All rights reserved. 

The Isis 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 Isis 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 Isis 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:

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

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

Isis M75P – Stereo power amplifier



Condition Isis M75D Isis M75A Isis M75P

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
1kHz, 4ohm, bridged mode >500

20kHz BW, 8ohm, nom. power <0 p=""><0 class="Apple-tab-span" span="" style="white-space: pre;">
<0 p="">THD+N

20kHz BW, 4ohm, 1W output <-93dbr p=""><-93dbr class="Apple-tab-span" span="" style="white-space: pre;"> <-95dbr p="">
Power bandwidth

2 ohm, THD<0 .1="" class="Apple-tab-span" span="" style="white-space: pre;"> 5Hz-50kHzPeak current
Noise output

20kHz BW, rms <35uv p=""><35uv class="Apple-tab-span" span="" style="white-space: pre;">
<25uv p="">
mm Including feet and rear handles 440W x 454D x 123H

With packaging 560W x 560D x 200H

Net weight