Una de las marcas que mas desarrolaron esto es Marantz con sus modulos Hdam ( o Modulos de Amplificacion Hiper-Dinamica )...
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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.