Marantz High Fidelity Sound Engineering 

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Index:

HDAM | Top
The HDAM (Hyper Dynamic amplifier module), introduced in 1992, is a key component of Marantz' high fidelity technology and cannot be left out of any discussion of Marantz Super Audio CD/CD players or amplifiers. Research and development of the HDAM has progressed since it was first used in the Marantz CD-15 (1992), which was also fitted with Philips Bitstream DAC "DAC 7" (TDA1547) blue star.
Around that same time, the same group of engineers also used HDAM in the high-grade integrated amplifier Marantz PM-99SE they developed.
The formal name for the HDAM is "hyper dynamic amplifier module". Newer analog circuits primarily use all-purpose op-amps with specifications that look fabulous. However, after careful repeated testing, the Marantz engineers, with their thorough knowledge of live sound and the timbre of live musical instruments, felt that there was a limit to the fidelity of audio circuits manufactured using conventional op-amps.
They confrontend their dissatisfaction in sound quality by developing a prototype modular analog circuit with highly efficient (not to mention great sounding) discrete elements. This module, incorporates FETs, superior chip parts, and has a quadruple layer substrate construction. Elaborate metal shielding prevents noise from entering the module.
The effect HDAMs have on sound quality is quite remarkable. They make the music sound fresh and alive, without the large amount of local feedback commonly found in all-purpose operational amplifiers, and provide an open, uninhibited, original sound. The first HDAM was manufactured at the Kumamoto factory, where the communications department is based.

The main features of the HDAM are that it is an extremely low noise single step amplifier with a folded cascade construction capable of 60 to 75dB of gain (amplification factor). In addition, its through rate is high at 70 to 80V/µ s, enabling high-speed response across all bands. Furthermore, the intermediate gain of the HDAM, which is difficult to achieve with standard op-amps, is optimized at the output stage of the CD player. The roomy construction of the HDAM makes it highly adaptable and permits modification of the internal elements and performance characteristics to suit a variety of applications. Further, since it has a high S/N ratio, it can also be applied to the main circuitry of phono equalizer amplifiers. The HDAM has also been used in filter amplifiers since the release of the Marantz CD-7 in 1998.

Although HDAM is the common name for all technology of this kind, the interior and circuit structure of each unit differs with each product. Recently, we have seen examples of HDAMs being directly incorporated into main audio circuit substrates without metal shielding (such as with the Marantz SA-14 ver.2 Super Audio CD/CD player) to improve sound quality as a result of listening tests. The method used in the Marantz SA-14 ver. 2, which also reduces the number of contact points and increases production efficiency, will probably be emplyed for a variety of purpose in the future.


Current Feedback Circuits | Top
The introduction of current feedback circuits is a new feature common to the latest Marantz products. Previously, feedback circuits used in audio circuitry were mainly voltage feedback type circuits.
In contrast, current feedback is used in high-frequency range amplifiers circuits for image circuitry, wireless technology, etc. and has the advantage of a wide frequency characteristic and low phase variation. Marantz first introduced current feedback in its Super Audio CD/CD players with the Marantz SA-14 in 2000.

Of particular interest is that instead of the voltage phase lagging 90 degrees, the current phase is advanced by 90 degrees. Thus, as far as the time line is concerned, feeding back the current is extremely natural. The superiority of current feedback is evident from its suppressed to a low 100 ohms. The beautiful sound of the Marantz SA-14, which skilfully represents the detailed and complex timbre of acoustic instruments, is surely a result of the benefits of current feedback.


Internal Chassis Construction | Top
The internal layout of a player is reflective of the design philosophy of its audio manufacturer. Although many manufacturers prefer a symmetrical arrangement with the drive mechanism in the center of the chassis, Marantz has devoted itself to developing a layout where the drive mechanism is located on the left side of the chassis.
From the perspective of industrial design, a symmetrical arrangement is often preferable, but Marantz' decision was based on their philosophy of giving sound quality the highest priority.

The most important point is to suppress the effect of noise generated inside the chassis to an absolute minimum. The power supply transformer, the principle source of leakage flux, is located as far as possible from the digital filter elements that handle high frequency signals. This layout also effectively isolates noise from the drive mechanism. As a result, plenty of board space is made available for analog output circuits. This is also useful for realizing effective power transfer from the power supplu section to each of the circuit boards and drive mechanism.
When the drive mechanism is located at the center of the chassis, digital circuits and analog circuits are often arranged separately. Such cases often result in longer transmission lines, which are more vulnerable to noise. On the other hand, if both the digital and analog circuits are arranged on the same side of the drive mechanism, the crowded circuitry can ghave an adverse effect on the sound quality of the component.
Although some manufacturers install separate dedicated transformers for each analog and digital circuit, Marantz has chosen a method that uses a single large transformer with the secondary winding supplying the analog and digital circuits separately. When 2 independent transformers are used, the size of the transformers must be reduced due to space restrictions. Reduced core volume in the transformer however, is a serious disadvantage. Marantz has used high-efficiency super toroidal transformers in its components since the release of the Marantz CD-16 (1993).

Analog circuit design has a great deal of impact on the sound quality of a product. At Marantz, although high sound quality is achieved by installing the above mentioned HDAM and other carefully selected components, the engineers also placed added importance on the design of the analog filter circuits, which affect the clarity of the individual sounds within the sound stage. Not only the isolation characteristics of the filter itself, but also the accompanying sound quality are of paramount importance.
For example, the Marantz SA-1 and Marantz SA-12S1 Super Audio CD/CD players both employ a 5th order Butterworth filter. This filter has a structure similar to that of a 2nd order filter that has been added to a 3rd order filter. The Marantz SA-14 ver. 2, Marantz SA-14, Marantz SA-17S1, Marantz SA-8260 and Marantz SA-8400 all use 5th order Bessel filter circuits, that can be switched between standard and custom (with a switch on the rear panel). Although the default is standard setting, sound clarity is slightly improved when the custom setting is selected. Depending on the type of amplifier used, operational stability may be better when with the standard setting, thus this setting must be decided on a case-by-case basis.


Absolute SA Technology | Top
Since the release of the Marantz SA-1, Marantz technicians have been aggresively developing Super Audio CD players. In order to utilize the ful potential of Super Audio CD technology with its 100-kHz ultra-wide range and 120-dB or more audible dynamic range, Marantz proposes guidelines for expanding "absolute SA technology" to fully develop Super Audio CD/CD players and amplifiers.
Although the ultimate aim of this is to improve various characteristics of Super Audio CD technology, the main goal is to improve actual sound quality. Through advances in development and repeated testing Marantz is gradually increasing the quality of its sound.
By using DACs in a differectial structure, common mode noise can be canceled and secondary high frequencies reduced. This means using two DAC circuits for a single channel. Naturally, this method is directly linked to increased cost, so DACs in a differential structure are only currently used for the Marantz SA-14 ver.2 and Marantz SA-1 (using four circuits per channel).
The Marantz SA-14 ver.2 uses a Cirrus Logic CS4397 DAC with built-in digital filter. Each CS4397 has a dual channel structure, and if you look at the circuit board, you can see hat one CS4397 is mounted on the board for each channel (dual DAC).

It is important that the analog signal is specified (as a single-end signal) using the following formula: the differential generated by a differential drive < balanced = hot (+) / cold (-) ground > analog signal.
With players manufactured by other companies (especially companies outside of Japan), the differential output is not synthesized, and although the output may naturally be balanced, Marantz has eliminated common mode noise within the player and reduced secondary higher harmonics using the above formula. In other words, sound quality is totally dependent on the player. Therefore, the balanced output of the Marantz SA-14 ver.2 creates a new output source from one single-end signal.

It is worth noting that a sophisticated strategy for improving sound quality by decreasing the impedance of the chassis was realized through the addition of copper plating to the inside of the unit, effectively reducing high frequency noise. In the past as well, Marantz has concentrated on making the unit structure as rigid as possible bu using aliminum die-casting and low-noise measures in their CD players.
By copper plating the inside of the chassis, Marantz discovered that it could soften the faint background noise level. This is also advantageous with respect to external high-frequency noise, and although it increases production costs, this measure of copper plating the chassis (which cannot be determined simply by looking at the exterior of the unit) is used to improve sound quality for high-end machines. Thus, this method is used for all players except the Marantz SA-8260 and Marantz SA-8400 Super Audio CD/CD players which are relatively lower prices machines.

Circuit paterns design has also experienced advances in development and manufacturers have started designing circuit board patterns with greater attention to further reduction of noise levels due to the emergence of the Super Audio CD audio format and its overwhelming potential.
Although Super Audio CD/CD-compatible drive mechanisms feature independent high-frequency demodulation circuits for CD and Super Audio CD, the drive mechanism circuit boards developed by Marantz feature a signal flow optimized so that the signals do not cross haphazardly.
Similarly, DAC and analog output circuits are carefully constructed to prevent signal crossover. For example, the rear terminals (analog output terminals) on multi-channel Super Audio CD-compatible machines such as the Marantz SA-17S1, Marantz SA-8260 and Marantz SA-8400 are arranged opposite the industry standard. This is so the analog output circuit can have a straight signal path from the DAC (digital filter input) to the DAC output to the actual output terminals on the rear panel. Although some care is needed when making connections, this definitely results in better sound quality, and is well worth the trouble. With multi-channel playback in particular, reproduction of the sound stage created between the speakers (which produce 5 fields) is of utmost importance. This is where the design and refinement of the circuit pattern come into full play.

The CD format has a frequency characteristisc of 20 kHz and a dynamic range of approximately 98dB (16 bit). In comparison, Super Audio CDs have such a wide dynamic range that in most cases it is limited only by the capabilities of the respective audio components. Up until now, circuit designs only needed to be concerned with noise within the limits of CD format.
The Super Audio CD audio format however, presents a new and difficult hurdles to manufacturers had to overcome. Marantz "absolute SA technology" confronts this head on. The result is not just higher fidelity Super Audio CD playback, but a definite and noticeable improvement in the sound quality of CD playback.

(Source: All about Marantz - Stereosound)

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