(Also see this ADCOM GCD-575 CD PLAYER page.)
ADCOM GCD-575 CD PLAYER
Reviewed by Hampton Childress
Frequency Response: 5Hz-20kHz +0.1/-0.5dB S/N Ratio: 105dB (A Weighted) Dynamic Range: 98dB THD: 0.0025% Channel Separation: 95dB @ 1kHz Fixed Output Level: 2.5V RMS Var. Output Level: Greater than 4.5V RMS Sampling Rate: 176.4kHz Resolution: 16-bit linear Dimensions: 17 by 11.25 x 37”. Weight: 12 lbs. Suggested Retail: $600
AUDIO AMATEUR'S TECHNICAL REVIEWS of kits and home-brew projects do not normally consider commercial products sold as complete units. With the ADCOM GCD-575, we step outside this realm to examine a product which reflects a design philosophy I consider to be outside the norm in today's CD audio industry.
This is not the all-too-common OEM CD player package with a customized front plate, but rather a conglomeration of what ADCOM considers the best components available for specific applications inside the player, while keeping the unit 'competitively' priced.
Clean and Quick
This machine sports a host of controls, features, and cosmetics. Upon first power-up and playback, I was impressed with the smooth and extremely quiet disc drawer operation. The drawer and laser assembly mechanisms are by Sony. Operation is clean and quick, so you're not left waiting for it to open or close. The disc tray is designed to accommodate 3 inch CDs without requiring any kind of adapter, as well as the standard 5-inch type.
This mechanism slides the disc tray in and then raises the CD above it via an elevating spindle. It removes the danger of discs being damaged by spinning be fore they are completely free of the tray.
This has been a past rub (pun intended) against some manufacturers, whose trays contain spring-loaded rubber pads upon which the disc sits. The disc can begin rotation without being entirely free of the support pads, which may chafe the read side (bottom) of the CD.
The PLAY button is illuminated by a green LED when it is pressed. It will work with the drawer open or closed, so loading a disc and playing it can be a single step. The disc tray can be closed without beginning play via the OPEN/ CLOSE front panel button. It can also be closed with a gentle push on the front of the tray.
Operation
Just press PLAY to hear the whole disc. The INTRO button will allow you to hear just the first 10 seconds of each track in succession or, you can set the INTRO length from one second to one minute.
Unfortunately, altering the duration is only possible via the remote control's numeric keypad; the CD player itself has no keypad. All the front panel control buttons provide a light click when press ed, like the feel of a gentle switch action.
The remote control functions work in the same fashion, but with a slightly softer click.
Should you decide not to listen to an entire CD at once or to change the play back order of the tracks, up to 24 tracks may be programmed into memory in any order. As you program each track, the TIME display is updated to show the total time. When you've set up programmed play and wish to possibly add another track, the player calculates the new total time without actually programming the track. That makes it easier for those wishing to make cassette tapes for car or other use.
It can be time-consuming if you make a mistake in entering programming sequences. There is no provision for either canceling the last programmed track or removing a programmed track from any where else on the stack. You must cancel the entire program and start over, via the MEMORY CLEAR button or opening and reclosing the disc drawer.
The AUTO SPACE button will allow you to add a four second pause between tracks. This is not calculated into the playing time display, however.
The PAUSE button will do just that until the PLAY button is pressed to continue. You can use the REPEAT feature to replay an entire disc, or in conjunction with the A-B button, to repeat a specified segment of a disc. This feature is particularly handy for studying a performance with score in hand.
Fast forward and fast reverse provide two-speed search functions with the out put level audibly lowered. Using this feature is somewhat inconvenient. I was already 15 minutes into the Reiner/ Chicago Symphony classic recording of Ein Heldenleben, when I stopped the disc to test the INTRO function, thinking I could easily return to the same point in this 43%-minute track. As it turns out, even with the numeric keypad, you can not access the CD by time. Using the fast forward/fast reverse functions, it took a full minute to spool up to the 15 minute point in the track. I can assure you I was careful not to repeat this episode during Karajan's Alpine Symphony recording, which is a single 50:47 track! If you own a CD with an index, you must call up the desired track and then fast forward to the point of interest.
Access to various tracks is provided via the TRACK buttons-one each for forward and reverse. Also, the 10-digit numeric keypad on the remote control al lows you to begin play at any track on the disc or to program tracks for group play as discussed earlier.
Features First, a POLARITY button, by default, is set so that the player's output is in correct absolute polarity. Depressing POLARITY causes its center red LED to extinguish, and the output reverses polarity 180°. I'm not certain this a very useful feature, or even whether any CDs among the several hundred in my library are recorded with incorrect polarity. I have been using the CD almost since its first commercial availability and have never needed this capability.
Some will find the Analog Frequency/Phase Contour (AFPC) control useful.
It is an on/off toggle with the front panel button illuminated in the center to let you know whether it's on or not. ADCOM claims the AFPC will make your CDs sound like analog disks played via a phono cartridge. This circuit basically warms the sound a tad by increasing the lowest bass frequency by approximately 0.5dB and smoothly rolling off signal amplitude as frequency increases, to approximately -5dB at 20kHz.
I am somewhat concerned, if this is what ADCOM thinks good analog phono reproductions (ought to) sound like. I'll take mine with a dead flat frequency response and carefully engineered to grab all the detail on a record whether it's good or bad. Frankly, I believe the warmth many associate with naturally recorded phono is available from CD when recovered accurately. It simply takes a different circuit approach to realize it. At any rate, probably many will appreciate the warm coloration this circuit can give to cover roughness on some recordings.
The back panel includes the standard fixed output, a standard digital output for outboard D/A conversion type preamps, and a variable output. The variable out put is controlled by the volume control on the front panel, which also controls the front panel headphone output. Actually, the variable output and the head phone output are the same, derived from the fixed output, amplified by a 4556 dual IC op amp, and coupled to both the headphone and variable outputs. For this reason, ADCOM recommends you do not use both outputs at the same time.
A set of low impedance headphones will load the 4556 sufficiently to affect the variable output considerably.
Construction
Let's continue with the circuit design, starting from the input (laser) and following through to the output. As I mention ed, the disc read mechanism is a Sony design and is supported by a complement of Sony ICs, surface-mounted on the foil side of the large, main circuit board containing most of the audio circuitry. The drive mechanism is solid and may be shipped without any type of transport Screws.
Through normal usage I experienced no mechanical problems with the GCD 575. However, when I tapped on the front panel to test resistance to vibration, discs could be made to mistrack with a good rap from the knuckles. This was not the case tapping on the top or sides; only the front and back--and near the drive itself. The drive mechanism is mounted directly to the metal chassis, but em ploys internal spring damping. While the disc mechanism's vibration damping could always be better, this is as good as any other unit I have seen in the same price range.
The player's logic for input control execution and display is provided mainly by a 64-pin, dual in-line package (DIP) NEC chip. The actual CD operations such as servo control, digital filtering, er ror correction, and so on, are handled by surface-mount Sony ICs on the main board.
Following that, 16-bit digital-to-analog conversion is performed by the venerable Philips TDA1541 dual D/A converter.
The unit is supplied with the mid-grade TDA1541, which guarantees better low level linearity and resolution than the less expensive TDA1541s found in cheaper players. ADCOM uses film dielectric 0.1uF bit filter capacitors instead of the more common and less expensive surface-mount, high-k chip ceramic types.
This has a decidedly beneficial sonic effect.
After D/A conversion, the TDA1541s' current mode left and right outputs are directed to a 21-pin, single in-line pack age. This Soshin circuit converts current to voltage and provides low-pass analog filtering of frequencies outside the audio spectrum, as well as de-emphasis shaping. Unfortunately, ADCOM personnel were unable to supply any specific information regarding this device. The manual simply refers to ‘innovative analog filters.’ Output from the Soshin module is capacitively coupled to the left and right channel output amplifiers. These carry the in-house label 6A. They are high speed, precision JFET input devices from the same high quality manufacturer as the 5E op amp used in ADCOM's GFP 555 preamplifier. In this application they sonically out-perform the 5E, since they have the capability of handling much greater dynamic range without slewing induced distortions (SID).
These op amps appear to provide further low-pass analog filtering, as well as output drive, through to the rear panel RCA jacks. Inexplicably, the - 3dB point of this final filter pole is designed for approximately 442kHz, far outside the frequency spectrum we are normally concerned with in four-times oversampling topologies (176.4kHz). The mute function provided at this point is realized with relay switches. Within this filter block, some film capacitors appear to be polystyrene dielectric types.
In the tradition of pursuing Class A circuitry, the 6A outputs are biased in this manner via external pull-down resistors to the -15V supply, thus eliminating the possibility of output stage crossover distortion at low levels, where it is most noticeable.
ADCOM advertises direct-coupled audio amplifiers. Output from the 6A amplifiers is direct coupled to the rear jacks, but the audio signal is coupled by an electrolytic capacitor from the output of the Soshin chip to the input of the left and right 6A. However, it would require a significant amount of circuitry to effectively and safely replace this capacitor because the TDA1541 D/A converter forces a constant DC offset. This would add considerably to the cost and design complexity of the unit.
The electrolytic coupling capacitor used here to block DC offset is very high quality in terms of its frequency response, and flat equivalent series resistance (ESR) versus frequency. Also each (one each per channel) is shunted with a 0.22 uF film capacitor, so quality at this critical point is fairly high. You could replace the electrolytic with a smaller film cap and increase the resistive element of the time constant, but this would likely alter circuit gain, which would require compensation elsewhere.
This trade-off is one every manufacturer must wrestle with when designing with the Philips TDA1541 D/A converter. I believe the GCD-575 contains the best possible solution at this price.
I mentioned the fixed output is routed to a 4556 dual op amp for additional gain and drive to the headphone and variable outputs. Output level is set via the front panel VOLUME control. The component quality within this circuitry is cause for concern. I looked into it, prompted by listening to it. I found ceramic capacitors; 100ohm carbon film, power supply decoupling resistors; and undersized (only 33uF) supply bypass electrolytics.
The power supplies which drive all the internal circuitry includes the mains power transformer, a multi-winding type which appears capable of being rewired for foreign line voltages. I'm concerned that it becomes fairly warm to the touch after being energized for some time, even when the player is idling. This could indicate fairly high resistance in some or all of the windings.
AC currents are bridge rectified and IC regulated. Regulators, 7815 and 7915 types, provide +15V and -15V. Regulated outputs are each bypassed with a 470uF electrolytic capacitor. These regulators have the capability of being used with reasonably good sonic results, but could be improved considerably with larger, low ESR output bypass caps.
Quite a lot of current is demanded from them. In fact, they require heatsinks.
The small, clip-on heatsinks attached to them may not be enough. These TO-220 style + 15V regulators are so hot that you cannot touch them. They are thermally protected internally, but I wonder whether this thermal overload protection is constantly active. How will all this heat affect the life span of these devices? If one or both should fail, how will it affect the direct coupled output amplifiers, and your system attached to them? These questions require attention.
Additional 78xx regulators, without heatsinks, supply current to logic circuits, DAC, and front panel displays.
These devices do not require heatsinking.
The GCD-575 is rugged. The chassis and top cover are steel; the front panel is anodized aluminum. The cover over the top and sides is treated inside with absorptive material, lending a quality feel and weight to this CD player. Tapping it on the top produces a thump rather than a ringing twang. Proponents of vibration damping in CD players will appreciate this attention to detail.
Internally, the layout is neat and un cluttered, except the necessary wiring harnesses. With the 8 by 8-inch (approx.) main circuit board, a vertically-mounted front panel board contains circuitry for the fluorescent display. remote control sense, and front panel programming.
Sonics
While I have been studying the ADCOM GCD-575 for review I have enjoyed it. The sound is clear and lacks much of the midrange and high frequency grit I've noticed on several other players-enough so that I must criticize the AFPC feature, at least a tiny bit.
In my collection, some CDs are overly bright; not necessarily grungy sounding, just bright. The AFPC circuitry does not produce a winning compromise for these, but tends to make the bass a bit boomy and less tight, as well as adversely affecting image focus and stability. Upper frequencies are rolled off, so the recording sounds dull. Perhaps in worst case CDs it would be useful, since it does give the impression of warmth, but this unit has a pleasing enough top end that I do not choose to use the AFPC very often.
I suppose that's a backhanded compliment regarding the unit's treble reproduction. I have heard CDs reproduced with cleaner top octaves, however. Com pared to the very best, this one has a slightly de-focused quality and a slight softening and spreading of the sound, without the last ounce of power the very high quality players reproduce. I prefer the ADCOM to other players which screech their treble at you, and it is quite listenable for extended periods.
The mid frequencies are clear enough, but impact is slightly softened. Low frequencies are a different story. I prefer my all direct-coupled player which reaches right down into the bottom octave with power and lack of effort. The GCD-575's bottom appears at times to be rather ex tended, however it lacks the bloom to give it the sustained, liquid quality with out effort. If you listen exclusively to pop recordings this probably won't bother you much, but with orchestral music I find the bass a little stuffy.
Left-to-right imaging and focus are pretty solid. Front-to-back depth is moderate-that is, for a CD recorded with very good depth perspective, the sound stage is not rectangular at the back, but rather it is rounded; the farthest corners seem no farther away than the dead center back of the orchestra.
My high quality electrostatic head phones must be driven by a power amplifier, but with a moderately priced pair of 'phones the headphone output seemed rolled off in the high frequency, com pared to my preamplifier headphone out put. Also, it seemed to lack weight and became rough when driven very hard. In general, I do not believe ADCOM’s description: ‘Very high-quality variable headphone output.' Unfortunately, for those considering using the rear panel variable output to directly drive a power amplifier, the same comments generally apply; the sound stage becomes flat and images become less focused, reducing the sense of space or openness. While I did not experience increasing roughness with increasing output amplitude, the sound was not at all comparable to the fixed output’s, in terms of clarity and cleanness at any output level.
Digits and Dampers
The remote control, an infrared transmitter, is easy to use, and duplicates all the front panel functions except VOLUME, AFPC, POWER, TIME, INTRO, and AUTO SPACE. It does include the OPEN/CLOSE feature for some reason.
In my room it operates consistently, 25 feet away from the player even when pointed quite a bit off-axis from the player's sensor in any direction.
The light blue, fluorescent display, with the track/time readout in 1/4-inch digits, is bright enough to be read across the room, but not at all glaring. The left side of the display is ADCOM’s 'Music Calendar, ’ which displays up to 20 of a disc's tracks, plus an over-20 indicator Smaller indicators are included for REPEAT, A-B, INTRO, SPACE, and those associated with the TIME button.
The TIME button allows you to toggle the time display between track elapsed time, total disc elapsed time, track remaining time, and total disc remaining time. Again, this information is handy when making cassette copies.
The unit's four wide feet are reversible and mountable in different positions on the chassis bottom. When reversed they become isolation points which can be used in the often discussed three-point configuration.
The unit is shipped with a stereo interconnect cable with gold plated RCA plugs and shielded with a surrounding copper ground braid. While sonically not as transparent as some of the more exotic high priced interconnects, it is a far cry from the poor quality cables shipped with many more and less expensive CD players. The end user who isn't interested in spending lots of money on inter connects will be pleased with this higher quality.
I tried a commercial metal disc damper, and I found this very beneficial to the sound. My comments under ‘Sonics ’ can be taken as applicable with or without the disc-damper, as they apply proportionately. The damping unit I own will barely slide into the GCD-575 without rasping, but I suspect a thicker one might pose problems during disc loading.
Conclusions I enjoyed auditioning the ADCOM GCD-575, both for its sonics and immediate ease of operation. My most common mode was whole disc play, using the fixed output jacks. Users of this player will find the variable output to be a good idea in concept, but one poorly executed for sound quality. A good preamp will likely cause much less sonic coloration and provide a more spacious and open reproduction quality.
The unit's functions are clearly documented in the user manual and are easy to operate. The remote control's one advantage is the numeric keypad not found on the front panel of the player.
Tests of this unit's frequency response and de-emphasis error measured within specifications. ADCOM tested this sample before shipping to ensure it is a fair representative of normal stock. The test data they were kind enough to supply seems very much in line with what one expects from a high quality, four-times oversampling, 16-bit CD player in this price range.
The suggested retail price is $600. For this many shekels you get a quality drive mechanism which will probably last many years, solid metal cabinet construction, a nice selection of features, remote control, and generally good sound from the fixed outputs. My only notable objection to this player's physical operation is the inability to access the disc directly by minutes and seconds. Do audition the ADCOM GCD-575 for yourself.
ADCOM's C. Victor Campos comments:
Thank you for the unusual, thought-provoking and in-depth review of the AD COM CD player model GCD-575. There are, however, a couple observations we would like to make.
The first of these concerns the comment on the TO-220-style regulator and the totally speculative comment that the regulators' heat could affect the life span of these devices. This comment, it should be pointed out, is not only pertinent to the GCD-575, but also to any direct coupled device that uses plus and minus power supplies.
We subjected the GCD-575 to a life test for a period of seven months, 24 hours a day, seven days a week, in which the regulators in question were continually temperature monitored, without heatsinks. All indications were that the regulators remained well within the temperature specifications for the devices and the five units being life tested show ed no signs of failure from heat or any other condition. The addition of the heat sinks to the regulators, in the design stage, was a further assurance.
Certainly, the variable outputs are not as sonically ‘'pure ’ as the fixed outputs, since they must be fed through a second, and additional, stage to achieve the high voltage output required to drive power amplifiers to full output (in those cases where the variable outputs are used to feed the power amplifier directly). Nevertheless, we believe that the variable out puts will provide superior performance, used directly into an amplifier, compared to the fixed outputs when fed into the typical, multiple active circuits used in run-of-the-mill preamplifiers. In any case, the purchaser of aGCD-575 has the choice of the superior direct outputs or the sometimes more utilitarian variable outputs. To the best of our knowledge, the GCD-575 is the only CD player whose (variable) outputs can drive to full output any amplifier presently available in the marketplace.
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ABOUT THE AUTHOR: Mr. Childress is assistant principal contrabassist with the Baltimore Symphony Orchestra and a partner in Jung-Childress Electronics, who market CD player modifications and kits. Copyright 1989 by Hampton Childress, all rights reserved.
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