The Isis
MONO AND STEREO HIGH-END AUDIO MAGAZINE
Mono & Stereo exclusive review unit will be heading toward me soon. So as it shows, this will be a grand start into 2014 and a clear winner for the Über amps sections. Angel and Plamen really took the time to do the things right and I'm crazy eager to finally hear the finished product.
You can enjoy the exclusive preliminary info and pictures below and after the jump...
"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 at any output level, raising the enjoyment of music to an unprecedented level."
"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 at any output level, 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
Highlights:
- 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
Configurations and finishing options 
Features:
- Volume control via switched, low-noise discrete resistor matrix
- 96 dB attenuation range in 128 precise steps of 0.75dB
- Stereo mode and bridged mono mode
- 2x 250W @ 8ohm, 2x 400W @ 4ohm in stereo mode, 2ohm capable
- 1x 500W @ 8ohm, 1x 800W @ 4ohm in bridged mono mode
- 2x XLR balanced line inputs + 2x RCA line inputs with individual gain adjustment
- 6Vrms input level compatible, 10Vrms max input level
- Pre-out and Main-in connectors for connecting an auxiliary processor or power amp
- High-performance dedicated headphone amplifier
- Full function remote control
Possible configurations with two units, as pictured above:
4x250W/8 (4x400/4) – 4-way system or 2x 2-way split system
2x500W/8 (2x 800W/4) in bridged mono mode – 2-channel high power system 2x250W/8 (2x400W/4)+ 1x500W/8 (1x800/4) – 3-way split system
Source selection, volume and power on/off are managed by the M75D unit
Features:
- Volume control via precision, long-life potentiometer
- 100’000+ cycles typical potentiometer life expectancy
- Stereo mode and bridged mono mode
- 2x 250W @ 8ohm, 2x 400W @ 4ohm in stereo mode, 2ohm capable
- 1x 500W @ 8ohm, 1x 800W @ 4ohm in bridged mono mode
- 2x XLR balanced line inputs + 2x RCA line inputs with individual gain adjustment
- 6Vrms input level compatible, 10Vrms max input level
- Pre-out and Main-in connectors for connecting an auxiliary processor or power amp
- High-performance dedicated headphone amplifier
The Excalibur
The figure below shows a highly simplified schematic of the Isis power amp stage. We have named this topology “The Excalibur”, knowing you understand the humor ;) 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.
1 Motion-induced voltage produced by the movement of the voice coil of a loudspeaker in its magnetic field.
The Isis in bridged mode
The Isis in bridged mode is a differential (balanced) amplifier. The popular method of bridging is to feed the input of the inverting side of the bridge from the output of the non-inverting side. This leads to increased distortion, among other issues.
When the Isis is switched to bridged mode, the balanced inputs of two sides of the bridge are simply connected in inverse parallel, producing two identical, inverted signals at the outputs. This is possible since channel gain is matched to within 0.1%. There is no loss of performance in bridged mode; in fact performance improves over single-ended mode as the even harmonic distortion components appear in phase at the load and tend to cancel out.
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.
CPU control and EMI
Internal logic and remote control functionality in the Isis M75D is performed by a high-reliability automotive grade microcontroller. Digital signals produce electromagnetic interference (EMI) due to the fast switching between logic states. To keep EMI to an absolute minimum, all drive circuits in the Isis feature slew rate limiting. Furthermore, when the microcontroller is idle it is completely shut down, including its system clock. Operation resumes upon an internal event, if a front panel button is pressed, or if a command is received from the remote control. The front panel display will illuminate briefly to show the operating status and will shut down in a few seconds, reducing EMI to zero.
Pricing and availability
The official launch of the Isis will take pace at the upcoming High End Show in Munich, 15-18 May 2014. Units will be available for review in late February 2014. Commercial deliveries will start from March 2014.
List prices, EUR, EXW, Incoterms 2010*
Isis M75D, remote control ......................................................................................................14’990.-
Isis M75A, manual control ......................................................................................................13’990.-
Isis M75P dual channel power stage........................................................................................13’490.-
Dual color anodized finish........................................................................................................... f.o.c.
Mirror Chrome finish .........................................................................................................add 2’500.- *
MSRP. Subject to local duties and VAT/sales tax. ADA reserves the right to adjust prices without prior notice. 
Packaging: reinforced 5-ply carton, 560x560x200mm. Gross weight: approx 27kg. Specifications*
* Preliminary data based on measurements of pre-production prototypes, subject to improvement. ADA reserves the right to change specifications without prior notice.
Packaging: reinforced 5-ply carton, 560x560x200mm. Gross weight: approx 27kg. Specifications*
* Preliminary data based on measurements of pre-production prototypes, subject to improvement. ADA reserves the right to change specifications without prior notice.
Analog Domain Audio GmbH • Johann-Sebastian-Bach-Str. 38 • D-85591 Vaterstetten, Germany Tel.: + 49 (0) 1520 / 202 5404 • mail: info@analogdomain.eu • www.analogdomain.eu
Matej Isak. Mono and Stereo ultra high end audio magazine. All rights reserved. 2006-2013. www.monoandstereo.com. ..:: None of the original text, pictures, that were taken by me, links or my original files can be re-printed or used in any way without prior permission! ::..