AMR
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CD-777
Frequently Asked questions about the CD-777
The USB input on the CD-777 is of the "USB Peripheral" type, meaning the CD-777 will function as a professional USB soundcard for a suitably-equipped host computer.

The CD-777 will not recognise a data CD with music files or detect or access an external hard-drive or USB memory stick with music files attached directly to the Player.

The CD-777 will work without requiring additional drivers with all recent PC/Windows systems. At this stage AMR does not support the use of the CD-777 under Unix/Linux-type operating systems.

The minimum computer system requirements are: Pentium III, Windows 2000/XP/Vista or Mac G3 or G4 with native USB support, 256 MB RAM, Mac OS 9.1 or greater or OS X.

The playback ability for file types is limited only by the playback software employed, for example iTunes on a Mac or Windows Media Player cannot handle certain popular file types. However third party player software capable of handling all known audio file types either natively or via plug-ins exist for both Windows and Mac computers. In our experience, the playback software is just as critical to the optimum musical performance as the format itself.

Please consult the AMR CD-777 manual for connection details.

The Philips UDA1305AT Multibit DAC at the heart of the CD-777 was designed strictly for CD/DAT use and is a 16-Bit Converter that is limited to 48 KHz as maximum sample rate. As a result, the S-P/DIF and USB inputs to the CD-777 are also limited to a maximum sample rate 48 KHz and to 16-Bit.

Music files with a higher sampling rate and/or longer word-length may still be replayed through the CD-777. Even 24/196kHz files. This is because most playback software will automatically handle transparently the conversion (using a high quality resampling engine such as SRC or SOX) to 16Bit - 44.1/48 Khz during playback (may require setting changes other than standard). Thus such files may still be left in the original resolution/sample-rate format and still be played through the CD-77.

Notwithstanding, when audio is played back via this medium, regardless of the resolution, because it still fully utilises the Philips UDA1305AT Multibit chipset to convert the signal from digital to analogue which is then subsequently sent through the NOS valves for and all the ancilliary power supply sections, the CD-777 is still able to provide superior muscial enjoyment to most expensive HD capable DACs.

For Mac users, having verified with Apple, AMR has deemed that the sample rate conversion in OSX is of a high enough quality for both the CD-77 and CD-777. The output sample rate on the Mac platform should be set to 44.1KHz as the source files are mainly CD-sourced and to 48KHz if they are 96/192KHz files.

In recent years, technologies such as "Upsampling" as well as one called "Zero-Oversampling®" or "Non-Oversampling" have gained in popularity with CD player and DAC manufacturers. Having compared these approaches to traditional "Oversampling" we at AMR feel that in most cases, the omission of Oversampling or Upsampling and the use of a straightforward analogue circuit is the most musically accurate and satisfying.

However, with only a minority of recordings, we found that either traditional Oversampling or Upsampling was preferable. Therefore, we have implemented all of them and made them user-selectable.


Philips Electronics ceased production of its own 'industrial standard' compact disc transports in 2001. Presently, new so-called Philips CD transports are far-eastern clones constructed to much lesser standards, of questionable reliability and are the only remaining off the self dedicated CD transports.

Furthermore, the exceptional Victor (JVC) transport the XL-Z900 was based upon has been discontinued and several other suppliers of high-quality transport solutions have cancelled their CD lines in favour of Multiformat DVD designs.

At AMR we found that if CD replay is the desired application neither computer CD Drives nor the current "universal" DVD based solutions perform equal to the highest quality dedicated transport mechanisms. AMR therefore set out to create a proprietary CD transport system that would provide the same or better performance than the legendary transport solutions of yesteryear, be they the original Philips swing arm type transport or Victor's XL-Z900.

AMR combined genuine parts from a number of major manufacturers and mounted these to our machined platform. This platform is then suspended on dampeners to isolate the Transport further from any vibrations. The resultant OptiDrive® Transport maximises the accuracy of the data retrieval. (Please refer to OptiDrive® in the Advanced Design Features section for more details).

Yes, the CD-777 has a 16-frame buffer (or 512K Bit of Memory). That said, nearly all CD players have a memory buffer of one form or other. This buffer is used among other things to allow for error correction if the data is read incorrectly.

The error correction, IF implemented correctly, recovers the original data through the use of redundant data written to the CD in almost all cases. This process does NOT "interpolate" but actually recovers the exact data originally written on the CD.

The necessary calculation may however take a short time. Without a large enough buffer, the timing of the data would be effected negatively. Only in case of gross problems does the error correction fail and then ALL CD-Players, even computer-based ones or software such as Exact Audio Copy, will first attempt to interpolate samples that cannot be read correctly (in many cases the software will first attempt to re-read the samples several times) from samples before and after the affected area.

The data transmission from the drive to the DAC is timed by the clock supplied to the CD-Transport or generated in the transport itself. The spindle motor servo keeps the buffer normally 1/2 full and therefore is linked to that master clock indirectly.

If the master clock driving the transport is accurate and the buffer large enough (8 frames or more) the output from the memory buffer is "jitter free". Some chipsets designed for portable CD players have a larger amount of memory, to provide "jog proofing". This means that even if the player is violently shaken and hence mistracks, several seconds of music are in the buffer and the player normally can re-acquire tracking before the buffer runs out.

Other than this (which is of no relevance to a CD player used at home on a solid surface) there is no further advantage from excessively large memory buffers and such buffers usually slow down operation, by delaying the time from pressing play to hearing music by the time needed to fill the buffer, track skipping etc is equally delayed.

The situation changes dramatically if we use a separate CD-Transport and DAC linked via S/P-DIF or AES/EBU cables. The problem when using a DAC with an S/P-DIF or AES/EBU input, which combine the data and clock is that the DAC itself must recover the clock from the datastream, which is not a very accurate process and made more problematic by the specific way the clock is modulated to carry the data.

To address this significant problem, additional memory buffers have been occasionally used in the highest "high-end" DACs, both pro-audio and consumer audio in order to allow a local clock which is NOT PLL synchronised (PLL = Phase Locked Loop - a process analogous to Negative Feedback, except in the time domain).

The clocks between CD-Transport and DAC may now differ to a small but significant degree. The CD Specification allows +/- 1000ppm or 0.1% deviation, meaning that up to 1 in thousand samples would be "too much" or "missing" per second, so the memory buffer must hold many more frames than the one in the CD player.

In fact, it needs to be able hold around 44 frames per second playtime of CD. Thus the minimum memory buffer needs to handle around 210,000 32-Bit frames of under or overrun and needs at least 2MB in size to accommodate this.

Further, the buffer would need filling with 210,000 frames and would introduce around 5 second delays between data being read and received on the audio output. As no "off the shelf" solution exists to provide such a memory buffer, it would need to be designed from ground-up.

We hope this brief explanation has shed some light as to why DACs very rarely have memory buffers (no simple and readily available solutions) and CD players always have them (< 1KB required to work properly and built into most commonly available chipsets).

The key to high sound quality is not in the size of the memory buffer, but first in the implementation of the mechanical system to maximise the correct reading of data followed by the error-correction routines, which requires extended routines beyond the original "red book" specification to correctly recover the original data.

This correct and original data then needs to clock into the DAC with a precise, jitter-free clock, so following the mechanical implementation of the drive, equally important is the master clock for the CD player.

In summary, yes the CD-777 as a one-box processor, has a more than ample 16-frame memory buffer but so does almost every other compact disc player. However, DACs need much larger memory buffers but due to the lack of a readily available solution, very few actually have a buffer.


AMR recommends critical listening after 24-hours of use.
Compact Disk is an optical format. The presence of varying external light conditions such as that admitted by a transparent lid was found to be detrimental to the sonic performance.

No. The CD-777 uses a completely single-ended signal path as we have found this to give a more realistic reproduction of music. However, in terms of sound quality, we found the XLR connector preferable to the RCA connector, even when used with non-balanced signals.

Consequently, we have offered the XLR output in a manner that is fully compatible with balanced equipment: taking full advantage of balanced connections yet retains the desirable single-ended signal circuitry.

The analogue section of the CD-777 utilises AMR’s OptiValve® analogue stage with zero negative feedback and 6H1n-EV valves. The “EV” version is the premium type which offers longer life and improved mechanical construction.

The CD-777 may be fitted with ECC88, E88CC, 7308, Cca, 6DJ8, 6922, 6N23P-EV valves.

Please consult you AMR distributor/dealer for installation advice/service as accessing the inside of your CD-777 will void the warranty.

In a word, uncompromising. With 1 virtual battery power supply section; 10 Series Regulators and 3 Constant Current Sources, this approach of 14 stages of passive filtering is far more costly but ultimately, the most uncompromising. Along with hand-wound, bespoke transformers, the power supply section of the CD-777 will embarrass even the best five-figure CD players.

Many CD sources may have an output voltage of 3V with some even as high as 6V! While this may impress on first blush, in a real-world listening environment, this level of output is far too high, characterised by a coarse, sound quality.

Listeners are able to differentiate between excessive and normal levels of output. The CD-777 is firmly in the latter camp, being a thoroughly well-designed product that does not seek to artificially enhance its output so it is louder during comparative situations to the detriment of long-term enjoyment.

At the heart of the CD-777 is the Philips UDA1305ATdigital-to-analogue converter. In AMR's opinion, the Multibit era of chipsets are second-to-none even when compared to the "latest and greatest" modern day chipsets (where the actual sonic performance varies somewhat). We consider the TDA1541A to be the pinnacle of Multibit chipset design. Having studied and auditioned just about every other chipset, we came to the conclusion that the Philips UDA1305AT in design and performance comes a close second to the TDA1541A; significantly more so than even the much lauded TDA1543 and TDA1545 both of which have been extensively used in high-end digital playback as "successors" to the TDA1541A.
Between different recordings usually, the techniques used to record as well as those used to master the recordings differ: as do the skills and aims of recording engineers and producers.

Therefore, it is very unlikely that two CDs recorded and produced by different engineers and producers will sound identical. Some engineers and producers are better able to achieve high sound quality recordings than others.

As with Moore’s Law, over the last few years, the pace of technological advancement has continued unabated. AMR in its imitable way has left no stone unturned in its pursuit of performance and flexibility to meet the needs of the music enthusiast. We have therefore arrived at solutions to receive and output the music signal without increased jitter which was not the case only several years ago. This has allowed the development of the CD-777 to incorporate maximum flexibility, which with its unrivalled sonic performance, means it is able to play music to the very best of its ability but also work alongside a separate CD-Transport or computer for alternative audio configurations without compromise.
The S-P/DIF on the CD-777 allows the CD-777 to be used as a professional, dedicated DAC.

If the Transport is not a CD-Transport but a computer-based drive, the playback ability for file types is limited only by the playback software employed, for example iTunes on a Mac or Windows Media Player cannot handle certain popular file types. However, third party player software capable of handling all known audio file types either natively or via plug-ins exist for both Windows and Mac computers. In our experience, the playback software is no less important to the optimum musical performance as the format itself.

Please consult the AMR CD-777 manual for connection details.

 
   
   


     
 
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