Sony CDP-557ESD CD-player
This, the second eight-times oversampling, 18-bit CD player to come up for detailed inspection this month, is doubly welcome because it provides a ready means of assessing one of the entirely hypothetical thoughts which have come to mind following the tests on other 18-bit machines. This is because it employs a pair of the very latest 18-bit linear digital-to-analogue converter chips recently produced by D/A specialists, The Burr-Brown Corporation. Their type PCM-64P was primarily developed for professional usage in mixing desks and the like, where multiple conversions may be needed and it is therefore desirable to have greater than 16-bit resolution available so that accumulated errors still do not rise above the 16-bit level.
The development of this remarkable device is described in the June 1988 issue of the Journal of The Audio Engineering Society where it is shown to combine two of the standard approaches to D/A design. Although each D/A converter then requires individual setting up with four variable presets, the result is an extremely linear 18-bit decoder and the first such to appear in a domestic machine. There is a possible problem with long-term drift requiring periodical re-alignment, but this is not seen as vital in the domestic application even when two are provided, one for each channel. However, what the use of this development does is to present us with an 18bit player which does not rely on the bit-shifting or ranging method of the other two models so far experienced. Neither of them, in my opinion, has quite reached the peak of performance achieved by the best of the more humble 16-bit machines as exemplified by Sony's previous CDP-555ES; and one of the possible reasons lies in the accuracy of compensation for the effects of the ranging. As this system operates to raise low-level signals to an area of the D/A chip two bits higher up the scale, when they are available, giving a corresponding improvement in gradation, then obviously they are also moved to a higher output level and this increase must be reduced by a synchronous attenuation (which incidentally reduces the noise level at the same time). Although precautions are taken to make sure that this cancellation is an accurate one, it seems possible that minute errors are occurring with complex music signals which do not show up in continuous waveforms and that tiny resulting discontinuities are responsible for audible differences. Of course there are other problem areas, such as the very high operating rates dictated by eight-times oversampling and the complex current requirements of the hundreds of individual transistor elements in each converter, but these technicalities are beyond the scope of this review so it is time to return to the other features of this latest top Sony model.
The ink was scarcely dry on my CDP-555ES report when a visit to Sony and the Tokyo Audio Exhibition showed that it was already about to be succeeded by this model 557. Prototypes and bits of mechanism were observed in various areas of their laboratories but detailed information was not forthcoming, and although the UK version was shown to us in May, it was July before I actually had one for test. Offered at the same price as its predecessor, the new model has several new and advanced user features as well as the uprated technical specification. Foremost is Custom File, Sony's overall name for an indexing scheme rather on the lines of an extension to the Philips FTS (Favourite Track Selection) first seen in their model 650. Custom File uses an 8k memory (maintained by an internal battery for about 28 days if the machine is disconnected) and a versatile ten-character display. I t can deal with 226 different discs in any of three ways; Disc Memo, Custom Index and Programme Bank. Each disc is identified by memorizing its unique TOC (Table of Contents) read from the disc on insertion into the player before any operational control is selected. Any comment you have decided to place in the Memo, such as date of purchase, name of performer, preferred volume setting, or your own library number, then appears in the display window. Custom Index enables you to go straight to any of six points on a disc, each of your own choosing. Programme Bank preserves your selection and playing order of up to 20 tracks from a multitrack disc and thereafter (unless you choose otherwise) they will be played in your decided order, omitting unwanted tracks. Entering these facilities into the memory is quite simple, although rather long-winded in the case of the Memo where you have to sequence through the alphabet and numbers repeatedly one at a time; it is desirable to have the very adequate operating instructions handy.
The fluorescent dot display will also deal with the usual Track, Time, Index and ticked-off Calender information and all the other operating facilities usual in CD players: Repeat play, A to B play, etc. are available most of them also from the hand-held remote control, including Sony's now well known physical (motorized) movement of the output control of volume option (which also decides the headphone loudness). An additional outlet at the rear now permits optical coupling of the digital output to a suitable separate decoder as well as the coaxial one and a (too easily forgotten) switch alongside selects analogue or digital feed.
It is a great pity that, for reasons of shielding, the top cover of the CDP557ESD has to be made of heavy-gauge black anodized aluminium and not glass or transparent plastics. Even a 'tyro' would find the details of internal construction a pleasure to behold and a sight of them would do more to influence the decision-making faculties of any prospective customer than any amount of sales patter. Much of the framework is of copper-plated steel, spaced double skin construction. The die-cast mechanism chassis is floated on springs in a heavy block of Sony's 'Gibraltar' loaded resin material. This and the two power transformers occupy the left half, the remainder being taken up with a number of beautifully laid out double-sided printed circuit boards (PCBs) most tidily linked with ribbon cable taped flat to the chassis members. The base is also a double heavy-gauge steel plate, the inner being copper-plated and there are four tub feet, this time labelled "fine ceramic". The underside of the pcbs hold quite a number of added resistors and capacitors, suggesting that a good few modifications had proved beneficial in production (my model's serial number was only 158) and no doubt these bits will soon find themselves a place on a new board, such is the power of modem CAD (Computer Assisted Design) facilities.
How it performed
The operation of the mechanism is fully up to the standard which Sony first established in their model 502 and which has not yet, to my knowledge, been equaled by any other maker. Fast, definite but silky describes the loading sequence and the linear motor developed for positioning the laser reading pod is close to perfection. I fed it my test CD with a deliberately enlarged centre hole, which is usually speedily rejected, and it played straight through it, seeming to have no difficulty in following the eccentricity. It can hop from track one of a disc to the last track or back again with only the smallest interruption in the music, and it has yet to give any sign of hesitation on either the standard dot and gap test or my more carelessly handled workshop 'problem' discs, although the error correction must have been at full stretch on the latter. Sony have been to great lengths to isolate the playing mechanism from any outside influence, including a soft sealing gland to mate with the front plate of the disc drawer. As a result you can (if you've a mind to) shout and bellow at it, or in desperation thump the machine quite hard, in an attempt to make it skip, and it is so quiet when playing that you have to put your ear against the top plate to hear it rotating.
The splendid performance of the mechanism was equaled if not exceeded by the electrical measurements, each of which I felt to be a personal achievement firmly based on my extreme patience, such was the low level of irregularities I was finding. Everything I checked seemed to be at the lowest level of credibility and a strain on the test gear and discs. In the end I had to put on one side my old faithful Sony YEDS2 and 7 test discs in favour of the latest Technics SH-CD001 and the Denon 38C397147 as the former pair, now much used, were providing inconsistent results. I await a new set of Sony test discs, recently announced, with interest; if they go on producing players of this standard, the test discs will have to be exceptional. As it was, figures well below 100dB kept cropping up for distortion, crosstalk and noise and it was essential to use a digital readout to gain knowledge of frequency response or channel balance because no pointer instrument will reliably indicate differences which proved to be in the region of 0.03dB. Checked against Sony's specification, the only errors were in the output voltage at 2.2V instead of the quoted 2.0V and a slight compression (3dB) at the - 90dB level. Impulse and toneburst waveforms from the Denon disc showed this to be a non-inverting machine; i.e. absolute phase is preserved. All in all the CDP-557 sets new heights of perfection in the way it measures and no possible clue was found to any lack of conviction there might be in the way it would sound.
Obviously the first thing one does when first confronted with a machine with this sort of sophistication and background is to listen to it, and it came as no surprise to find it most agreeable and musically natural with no trace of distortion, displaced consonants or evidence of shrillness, sibilance or glassy exaggerations. All parts of the frequency spectrum were given their due rendition. Strings were particularly convincing on the recent, delightful, summery record called "English Music for Strings" (RCA CD RD87761, 9/88, The Guild hall String Ensemble), and the big pipes of the Royal Albert Hall organ rumbled in a most life-like fashion under the feet of Christopher Herrick (Hyperion CDA66258, Organ Fireworks II) only surpassed by longen's Symphonie Concertante (Telarc CD CD80096) a disc I have mentioned before which has pedal notes that most loudspeakers try to ignore, as they should be felt rather than heard as harmonics only.
It was an evening much later on, after all the remarkable measurements had taken place, that I settled down to assessing possible CD contenders for our Engineering Award, already trimmed down in a previous session. Opting to use the 557 largely because of the exceptional measurements, I found myself having the first doubts about this model. As the hours went by, I began to find it increasingly difficult to become involved with the diverse material, which all seemed to have a certain sameness about it; to exaggerate, a sort of lumpy dulling and flatness, interrupted by occasional isolated and unpredictable notes from a piano or voice which seemed to stand out and bleed across the image. All this was accompanied by an inward desire to finch oneself, sit up smartly and fee reassured that nothing was really wrong, except perhaps the potency of the stilton after dinner. Around midnight however, a reluctant reversion to my Sony 555 restored condidence in the ears, and although it is all too easy to prefer something one is well used to, there was no denying the overall alertness and extreme 'validity' of the sound. I would be hard put to it to point out any single facet of performance in which the 557 is less than perfection and yet in the final summing up, and as a judgment in the long term after many more hours of listening and comparison, I stick with my opinion. The 557 is a fine machine and probably tops the bill, in both senses of the word, amongst any of the current generation; certainly it rates above, well above, the other 18-bit models, presumably because of the Burr-Brown contribution. It is beautifully made, has unique facilities and is worth every penny but, if you are out to spend this sort of money and can find a dealer who still has the 555, please make your own comparison; it will not be easy, but I for one would not willingly change from the 555 to the 557.
