Ultimate in digital audio

Today's digital circuitry is capable of truly remarkable rednitions of the clarity and emotional content of music. And nowhere is this more clearly seen than in the latest Reference CD players from Marantz.

At the very top of the Reference range stands the Marantz CD-7, a multi-bit design with unsurpassed rhythmic intensity an a quality of dynamics and pace more usually associated with the recording studio. At its heart is the legendary 'Double Crown' digital-to-analogue converter (DAC) and a new and specially tailored Digital Signal Processing (DSP) chip, the MZ777f. Together they form an unbeatable combination, setting a new level in CD performance.

What's more, a digital input makes the high end DAC and DSP accessible to other digital sources. The top-flight reproduction of the Marantz CD-7 can be extended to DAT, say, for an instant and spectacular upgrade in performance.

Digital breakthrough

In the past, lack of finesse in filtering the singal's spurious images and unwanted noise compromised even technologically advanced multi-bit DACs by introducing 'ringing' distortion, without sophisticated filtering even the Double Crown would be humbled. But for the Marantz CD-7 Marantz has stepped right into the digital domain and by usiing Digital Signal Processing, developed a brand new filter which acts with extreme subtlely and precision before the datastream is converted to analogue.

Dubbed the Linear Music Filter (LMF), the new digital design makes possible extraordinary accuracy of reproduction by responding to instructions encoded within the MZ777f DSP chipset. It can compensate for the characteristics of analogue filters to ensure a flat frequency response and zero phase distortion in the audio band, while its four times oversampling shifts spurious images and noise far outside our range of hearing.

FIR's audio characteristics

It's a much advanced manifestation of the standard 'FIR' digital filter used in many of today's less exalted applications. It remains true that the original FIR's audio characteristics are preferred by music lovers, on the downside, it introduces 'pre-' and 'after ringing' distortion when it fails to respond with sufficient precision to amplitude impulses. Its variant, the more precise-acting 'Short FIR', shows less attenuation above 20kHz whilst retaining the same sonic character. For the LMF, however, Marantz created a filter preserving that sonic character, but whose impulse response (behaviour in time) is so precise as to significantly cut down after and especially pre-ringing distortion, so that reproduced music retains all the attack and dynamsim of a live performance.

In tandem with this, a gentle-acting 3rd order bessel analogue filter in the Marantz CD-7 offers optimum impulse response and lowest phase distortion after D/A conversion.

The DSP chip incorporates other advantages too. Among them is Soft-Mute, to eliminate signal noise 'click' when activating stop and pause controls. Another is automatic selection of the appropriate de-emphasis filter for CD and DAT applications when detecting 44.1Khz or 48kHz sampling frequencues. Plus, digitally attenuating the signal by -12dB makes it possible to clearly identify track content during high speed reverse or forward search.

Multi-bit at its best

In lesser multi-bit players, with l ower grade digital-to-analogue conversion systems, 'bit weighting errors' accumulate and ultimately destroy linearity and musical accuracy. When designing the Marantz CD-7, however, Marantz insisted on near-zero tolerances during the DACs manufacture: so, linearity is preserved and the analogue output level tracks the digital input code exactly. Even low level signals are delivered with pin-sharp clarity, and listening ambience is acutely heightened.

No compromise construction

Beyond D/A conversion, the Marantz CD-7 is built to rigorous standards, including solid metal casing and rigid copper chassis. Internally, non-magnetic copper shielding protects the most vulnerable parts of the siganl path from stray electro-magnetic radiation, while op amps are eschewed in favour of discrete circuit components. Analogue, ditigal, control and power supply blocks are independent, each fed by a stabilised power suuply.

An ultra-low-noise ring core toroidal transformer maintains tonal and image accuracy, and the player's Philips CDM12 'Industrial' laser assembly is fully floating, with rigid, anti-vibration meal chassis, to protect CD tracking from vibration.

Finally, at both balanced and unbalanced output stages, copper screened Hyper Dynamic Amplifier Modules (HDAM) retain waveforms transient character to ensure that reproduced music has all the speed and impact of studio sound.

Features Marantz CD-7

  • Multi-bit Double Gold Crown D/A converters (one per channel) and Marantz-developed DSP digital filtering guarantee wide dynamics and superb linearity between input and output signals
  • Solid metal casing, copper-plated die-cast chassis, and shielded analogue, digital, power supply and control blocks prevent signal interference from vibration and electro-magnetic radiation
  • Dual HDAM at output stage preserves signal's transient character, while rectifier noise is eliminated by the use of Current Conversion Noise Eliminators (CCNE) at the power feed
  • Balanced output for superior sound quality with balanced-input amplifier
  • Digital input makes top quality DAC accessible to other players/recorders
  • DSP provides auto-selection of appropriate sampling rate and silent switches
  • Choice of coaxial and optical digital outputs for best cable connections
  • On/off display and non-tarnishing gold-plated terminals
  • Remote controlled Auto Music Scan (AMS) of CD contents
  • Several random and repeat play modes for non-stop music


Specifications Marantz CD-7

Audio Characteristics
Channels: 2 channels
Sampling frequency (CD mode): 44.1kHz
Sampling frequency (D/A mode) 32/44.1/48kHz
Quantization: 16-bit linear/channel
Error correction: CIRC
D/A conversion: 1-bit linear/channel
Wow & flutter: precision of quartz

Optical readout system
Laser: AlGaAs semiconductor
Wavelength: 780nm

Frequency characteristics:
Frequency range: 2Hz-20kHz
Dynamic range: >98dB
S/N ratio: >102dB
Channel separation (1kHz): >100dB
THD(1kHz): 0.002%

Analog output
Output level (cinch Jacks): 2.2V RMS
Output impedance: 250 Ohms

Digital output
Output level (cinch Jack): 0.5 Vp-p/75 Ohms
Output level (optical Jack): -19 dNm

Power supply
Power requirement:
K version: 110 / 220V AC 50/60Hz
/02 version: 230V AC 50Hz
Power consumption: 19W

Cabinet, ect.
Dimension (wxhxd): 454x139x344mm
Weight: 16,6kg

Accessoires
Remote control unit (RC-7CD): 1
AAA (R03) Batteries: 2
Stereo audio cable with cinch pins: 1
AC power cord: 1


The Consumer Electronics Hall of Fame: Marantz CD-7

A project to build the ultimate CD player hinged on the design of a low-pass filter

Best Disc-Spinner Ever? The Marantz CD-7, the result of one man’s quest for disc-playing perfection, dazzled audiophiles when it was introduced in 1998.

There are a handful of perfumers who can identify each of the several dozen scents blended into a high-end perfume. The video industry, meanwhile, hires people who can look at whatever is being depicted on an 8K display and detect if image fidelity is marred by just a few thousand errant pixels out of the approximately 33 million in each frame. Their perceptions can be objectively verified.

And then there are audiophiles. Some of them say they can hear the difference between silver and copper hookup wire in an audio amplifier. They posit traits such as “warmth,” “dryness,” and “darkness,” which are difficult to explain, let alone quantify, and they can argue about these parameters as if they were divvying up Alsace and Lorraine. So when audiophiles agree unreservedly on the quality of some specific piece of sound-reproduction equipment, odds are that that machine is a stellar example of whatever it is. Such is the Marantz CD-7 compact disk player, a nearly complete redo of the CD-15, the Marantz system that preceded it to market.

A bedrock principle of the digital era is that things get better with technological progress, and so it was with Marantz CD players through the CD-15. Indeed, the CD-15 was initially hailed. But before long, the dissent began. Some audiophiles found it “too high fidelity.” Whatever that means. Marantz engineer Ken Ishiwata, who had worked on the CD-15, was among those dissatisfied with it. Ishiwata went to work on a new model that rejected the nominally more advanced digital-to-analog converter (DAC) chip used in the CD-15, the one-bit (bit-stream) TDA1547, in favor of an older model, the 16-bit TDA1541, which had been used in several Marantz models well before the CD-15. Ishiwata knew that if the older chip, the TDA1541, was used with care it could deliver remarkable sound.

Ishiwata told IEEE Spectrum his idea was to pair the older DAC with a superior filter. Unconvinced of the quality of the long FIR (finite impulse response) filter used in the CD-15, Ishiwata decided to “maximize the wonderful power and timing of music” by creating his own filter. To understand what he did, and why, requires a bit of tutorial.

A CD player does not merely take the digital samples from a compact disc and send them to the DAC for conversion to an analog waveform. It uses a process called interpolation, in which additional samples are created and inserted in between the “real” samples to produce a higher sampling rate. This process increases the sampling rate by, typically, a factor of 4 or 8. Interpolation, also called oversampling or upsampling, has the benefit of greatly easing the demands on the low-pass filter that follows the DAC, and which is needed to remove some high-frequency artifacts created by the DAC that would otherwise reduce the sound quality.

In the CD-15 the TDA1547 DAC was paired with a filter (SM5803APT, from Nippon Precision Circuits) that provided 8 times upsampling. To create the superior filter Ishiwata wanted for his new disc player, he began by extracting the source code of Philips’s SAA7220 digital filter chips. He then added some custom code, and ran it all on a pair of Motorola 56000 digital signal processors that he’d yoked together (and dubbed the Double Crown). That configuration allowed him to revert to 4X upsampling, which some audiophiles insist provides better audio quality than 8X upsampling (at least when comparing those two specific Marantz models).

Ishiwata’s tinkering on the CD-7 didn’t end at the circuitry. The mechanism in CD players that incorporates the lasers and lenses used to read a disc is called a transport. A CD player’s accuracy reading discs is dependent on the quality of the transport. Marantz’s preceding model, the CD-15, was also lauded by audiophiles for its use of Philips’s CDM4 Pro, one of the highest-quality CD-player transports ever created. Philips had stopped making it by the time Ishiwata was designing the CD-7, however. Ishiwata was dissatisfied with the widely available replacement (designated the CD12.3), though, so he and Marantz essentially rebuilt the CD12.3, including, by one account, diamond-milled stainless-steel slide bars for luscious disc loading.

The resulting CD-7, introduced in 1998, looked like other Marantz players in that it had the stylish and balanced faceplate design and the characteristic champagne-gold finish. But it was hailed immediately for providing sound quality as good as anything found in recording studios, including what one reviewer called “unsurpassed rhythmic intensity.” Whatever that means.

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