Gemini Digital Engine(GDE)®
Sonically speaking, the textbook implementation of HD DACs leaves a lot to be desired. This justified the decision to continue with the same innovative and comprehensive digital approach as the CD-777 and the CD-77 before that.
AMR’s HD Gemini Digital Engine is an ingenious implementation of two separate DACs; a HD 32-Bit DAC and a Classic 16-Bit DAC with Field Programmable Gate Array (FPGA) and Digital Signal Processing (DSP) to handle all core digital duties, including the memory buffer and managing the signal processing. AMR has in reality, created custom-built DAC chipsets to its exacting specifications which is akin to programming many discrete logic IC's worth of circuit boards onto one chip. This approach is technically arduous and time-consuming, but is soon justified upon listening to just the first few notes of music from the DP-777.
Organic Digital Algorithm incorporating SMART®
At the top of AMR’s unique Digital Filter Algorithms is the “Organic Algorithm” which incorporates SMART®: (S)oft roll-off, (M)inimum-phase, (A)podising, (R)ingless, (T)echnology. This is AMR’s technical expertise at its very best where it has developed an original and comprehensive digital algorithm to address the sources of “digital ringing”; pre-ringing & post-ring in the recordings and in the playback of the DAC. Being the only manufacturer in the world with the “Organic” filter, in conjunction with the rest of the far-reaching digital and analogue implementation, the DP-777 is the first High-Definition DAC in the world that truly makes music to stir the soul.
AMR appreciates that “no one sound fits all” and that the highest quality of music reproduction is to ensure the original signal bit/sample rate is maintained all the way through. Hence, AMR developed the DP-777 with OptiSample® via both its High Definition and Classic Multibit DACs to ensure the original recording is preserved end-to-end.
The DP-777’s High Definition DAC offers: Organic, MP Listen, Apodising 808, and Traditional digital algorithm modes.
Under the DP-777’s Classic Digital DAC, the DP-777 offers: Bit-Perfect I and Bit-Perfect II filter modes.
All are all user-selectable, via the remote control and offer different perspectives on the sound but most important of all, reproduce the original recording to the highest degree.
Global Master Timing®/Intelligent Memory System®
Before the arrival of the DP-777, the issue of solving jitter introduced via SPDIF using a Phase Locked Loop (PLL) Clock recovery was seen as sufficient. However, this analogue “solution” to a digital problem is woefully inadequate yet is not even commonplace.
AMR’s Global Master Timing (GMT)/Intelligent Memory System (IMS) represent a total “out of the box” systematic digital solution that solves the digital SPDIF jitter issue once and for all. The Intelligent Memory System holds a large number of complete audio samples, so it may completely absorb a large amount of variation (jitter and drift) in the incoming signal, while still sending out data at a fixed and precise clock rate, regardless of variations in the incoming clock.
Central to the GMT clock system is an ultra-low jitter, quartz-driven clock system capable of producing over 28 million different frequencies. When engaged, the GMT system intelligently and dynamically controls the clock that drives the DAC chips and takes the data out of the memory buffer. The GMT Clock is set to precisely match the principal frequency of the incoming clock with a precision of better than 0.001Hz. Hence, if the frequency shifts from 192,000.002Hz to 192,000.003Hz over a period of minutes (drift) which is the minimum to be meaningful, the GMT clock will intelligently and precisely track the change.
Once the GMT clock has correctly calculated the incoming clock, the rate of updating the DAC's clock with the minimal 0.001Hz step (~0.004ppm accuracy) step is at most, once every few minutes or less. As a result, the DAC clock is completely decoupled from the source and completely stable.
With the GMT clock that drives the DAC Chips and to clock the data out of the memory buffer at the same exact frequency as the incoming clock, there is nil jitter in the source clock, as there is no physical PLL link between the source clock and the clock driving the DAC Chips.
The GMT System is not a secondary PLL as used in some cases and some DACs since the late 1990's, but an entirely new concept. Instead, GMT is a system that will completely block jitter and only react to compensate any slow drift in the clock source or to adapt to a change in sample rate.
The GMT Zero Jitter mode is available for all digital inputs including the USB input and is the new clock standard reference for the digital audio world.
Asynchronous 24/192 USB Input
The DP-777’s Asynchronous USB 24/192 means native and future-proofed playback on OSX and Windows.
Asynchronous USB 24/192 uses USB Audio Class 2.0 in Asynchronous Mode and is fully compatible with USB 2.0 and USB 3.0. It should be keenly stressed that USB Audio Class 2.0 should not be confused with USB 2.0. USB Audio Class 2.0 is required to support sample rates above 96kHz (that is, high-definition music). AMR is one of a handful of companies to have brought such a standard to market following the industry definition of the USB Audio standard.
Most USB DACs do not follow the global USB Audio standard and hence will require drivers for all PCs (including Macs, Linux) which may be unavailable and must be supplied by the manufacturer into perpetuity, for each new operating system.
By comparison, USB Audio Class 2.0 is built into Mac OSX and many versions of Linux and supported by Microsoft on Windows and is set to be recognised as an industry-wide standard to achieve native "plug & play" support in all future operating systems.
Asynchronous mode means the clocks are on the DAC side and the PC is synchronised to that stable clock. Compare this to the common way of USB audio workings where the DAC attempts to synchronise to the PC using a jitter inducing PLL to follow all the PC's clock changes, be they caused by software directly modulating the clock or indirect clock modulation due to the varying processor loads (this is called software-induced jitter).
By combining our Asynchronous USB Audio Class 2.0 connection with the Global Master Timing/Intelligent Memory System we are not only delivering future-proof, cutting-edge computer connectivity with virtually nil jitter, but we also completely remove the jitter of the clocks.
Crucially, the USB signal is completely decoupled (i.e. isolated) from the DP-777. So any power supply noise, RFI and ground noise from the PC is not able to enter and contaminate neither the DP-777 nor its signal.
Presently, virtually all CD players and DACs are NOT “Bit-Perfect”. Such machines are only “Bit-Perfect” at the input interface section. None are truly “Bit-Perfect” end-to-end because the use of traditional digital filters will artificially manipulate the signal and the sonically damaging artefacts that result is readily detected by the human hear. Any DAC using oversampling (to any frequency) or asynchronous upsampling is NOT Bit-Perfect.
The DP-777 is one of a select few able to deliver a true, “Bit-Perfect” signal all the way through to the output as it preserves the signal integrity from the input (SPDIF/USB) right through to the pure valve analogue output stage.
HD SPDIF Inputs with Valve Digital input technology
The Compact Disk standard was never conceived with the notion of distinctly separate transport and DAC sections but once this became so, SPDIF was adopted as the method to link the two together. However, SPDIF is an analogue transmission system that uses what was originally a video signal format to transmit a digital system. Clearly, this is not an elegant solution as the SPDIF clock and signal are transmitted together as if the red, blue and green signals for a television were cobbled into a single run.
At AMR, to overcome this set of essentially analogue problems we devised a completely analogue solution. AMR’s proprietary Valve Digital input technology (VDi) is a world’s first: it is the use of the NOS 6N11 (high-speed valve operating into the 100MHz region) in a zero feedback circuit derived from military radar technology to re-establish the clean waveform of the original incoming signal from the two HD SPDIF Inputs.
Firstly, this ensures that even if the input SPDIF signal has an incorrect output level or poor waveform, the SPDIF input receiver will have a clean and perfect SPDIF signal to lock onto.
Secondly, as all SPDIF receivers use Schmitt Trigger input circuitry, the receiver will create a glitch noise at the trigger point, this noise travels back into the SPDIF cable, returning to the source component. It is this errant noise that is at least in part responsible for the major differences between SPDIF cables and sources in the input system of common DACs. As the HD-VDi isolates the SPDIF receiver from the outside world, HD-VDi eliminates the detrimental effect caused by this noise once and for all.
The DP-777’s HD SPDIF inputs employ a NOS valve input circuit for everything all the way up to the 24/192 high-definition standard. The result is clearly visible on an oscilloscope as the SPDIF signal is restored back to its perfect wave form. This input ensures the “right note at the right time” to give the music the “life” that is missing from all other DACs.
AMR believes that having the ultimate in digital execution would count for little if the analogue section was not just as committed. Hence, the analogue section of the DP-777 utilises AMR’s OptiValve® analogue stage with zero negative feedback and NOS 6H1n-EV valves. The “EV” designation represents the premium version of this valve. Being a double triode per channel design; in the DP-777, one half amplifies and the other buffers. Rectification and filtering in the DP-777 uses zero-noise Schottky diodes with additional noise filtering, an electronic inductor and a virtual battery design. The analogue stage of the DP-777 is identical in concept and function to that of the CD-77. With no operational amplifiers or solid-state devices, this is a major factor behind the DP-777’s organic and “vinyl-like" sonic performance that will embarrass many a high-end DAC.
Direct-Coupled/Buffered Analogue Volume Control®
The DP-777’s Direct-Coupled, Buffered Analogue Volume Control (AVC) system is AMR’s ground-up analogue volume control system that is both transparent yet dynamic across the whole 71-step range. The AVC gives a completely noiseless change of volume and virtually nil distortion but with more steps and finer resolution that betters even the best stepped attenuators. The AVC functions as a series of near perfect switches, with no ageing, no degradation and no wear. It is finely adjustable in 1dB steps but the beauty is the extreme transparency that is second only to the famous transformer volume control (TVC) approach first developed by Western Electric at the turn of the century. Partnered with a fitting power amplifier such as the AM-77 or AM-777 (in Power Amplifier mode), the signal path does not get any shorter, rendering the music virtually palpable.
AMR’s expertise in specialised transformer design for audio use has led to the development of transformers with individual windings that offer the sonic benefit of individual transformers without the space demands. Again, AMR has shunned the mainstream (and more cost-effective) approach to the use “off the shelf” transformers, preferring to have its own dedicated transformers, with multiple layers of shielding built-in, hand-wound and hand-made. Power supply is an integral part of circuit design and AMR’s steadfast approach has ensured the highest possible quality of music performance.
The Finest, Cherry-Picked Components
Underpinning the design of each and every AMR component is the use of premium components which were selected after careful evaluation and exhaustive listening. These include AMR silver leaf capacitors, Sanyo Oscon capacitors, precision wire wound resistors, 70um gold plated military-grade printed circuit boards, AMR's own German-made premium film and foil capacitors, power supply polypropylene film Music Capacitors and zero-noise Schottky rectifiers. We positively encourage a closer inspection of the DP-777’s internal componentry.