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New Op-Amps Promise High-End Sound

New Op-Amps Promise High-End Sound

August 16 – A new generation of operational amplifiers (op-amps) and power-amplifier drivers from National Semiconductor might result in a wholesale improvement in sound quality across a wide range of audio products.

Op-amps are everywhere: preamplifier linestages, CD players, digital-to-analog converters, and the front ends of power amplifiers, to name just a few product categories. Any component with analog input or output jacks probably employs several op-amps.

Many high-end product designers face the decision of whether to use op-amps in their products or to realize the circuit with discrete transistors and associated parts (resistors and capacitors). Op-amps are much smaller, cheaper, and easier to implement than discrete circuits.

An op-amp a fraction the size of a postage stamp can replace a dozen or more discrete components that would consume several square inches of circuit-board real estate. Historically, op-amps have not matched the sound quality of a well-designed discrete circuit (tube or transistor).

The highest-end products use discrete circuits exclusively; a few designers would never even consider using an op-amp. That’s largely because the op-amps available today are designed for mass-market applications where low cost is the primary consideration.

But National Semiconductor, a giant in the integrated-circuit industry (revenues of nearly $2 billion), has begun shipping a new family of premium op-amps that were designed from the ground up for optimum sonic performance.

National’s goal from the outset was to develop an entirely new breed of op-amp whose technical and sonic performance met or exceeded that of a discrete circuit. The result is the LME49xxx series of devices, which sports noise, distortion, and bandwidth specifications that are unprecedented in a monolithic (integrated circuit) audio amplifier.

For example, THD+N (total harmonic distortion plus noise) is specified at just 0.00003%, and the gain bandwidth is 55MHz.

As we all know, great specs don’t guarantee great sound quality. Surprisingly, National Semiconductor also realized this and built a dedicated listening room to evaluate the sound quality of its new performance-audio products. The listening room features a fully floating floor and complete treatment with diffusers and bass absorbers.

The electronics are custom designed, and the monoblock power amplifiers drive Wilson WATT/Puppy 7 loudspeakers. It’s unusual, to say the least, for an integrated-circuit manufacturer to perform listening evaluations on its products.

The company simultaneously announced the LME49810, a 200V IC that replaces the discrete driver stage in a power amplifier. A power amplifier’s driver stage takes in a line-level signal and amplifies it to drive the amplifier’s output transistors. The LME49810 replaces the approximately 25 components of a discrete driver stage.

The LME49xxx series of op-amps is aimed at higher-end audio-video receivers (those starting at about $3k at retail), high-end preamps, CD players, digital-to-analog converters, and power amplifiers. The devices are also starting to be used in professional products (a recording console uses hundreds of op-amps).

National Semiconductor wouldn’t specify which high-end manufacturers will be using these new op-amps, but suggested that the list reads like a Who’s Who in high-end audio. (An illustration in National Semiconductor’s literature shows a Mark Levinson product.)

The company reports that high-end designers who have tried the new op-amps are extremely enthusiastic about the new devices’ sound quality. If these new op-amps are indeed a breakthrough, listeners might enjoy a significant step up in sound quality in a variety of products.

By Robert Harley

My older brother Stephen introduced me to music when I was about 12 years old. Stephen was a prodigious musical talent (he went on to get a degree in Composition) who generously shared his records and passion for music with his little brother.

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