Robert Harley

American audiophiles have long had a love-hate relationship with British integrated amplifiers. On one hand, they often provide superb musicality, sell for a moderate price, and don't take up much room. On the other, these British alternatives to Adcom or B&K separates often have low power output, nonstandard connectors, idiosyncratic appearance (footnote 1), and dictate the kind of speaker cable and interconnects you can use.

His background may have been in tubed audio product design, but Theta Digital's Mike Moffat is now at the forefront of computer-based digital processor development. His Theta D/A processors are among a handful of products that use Digital Signal Processing (DSP) chips and custom filtering software instead of off-the-shelf filter chips (footnote 1). I recently visited Mike at the Theta factory to get his current ideas on digital audio reproduction and what goes into designing a good-sounding processor. I began by asking Mike if he had always been an audiophile.

If there's one buzzword in high-end audio for the 1990s, it's undoubtedly jitter. "Jitter" describes timing variations in the clock controlling the ones and zeros that represent the analog audio signal. If that clock isn't stable to an extraordinarily precise degree, the sound quality of the digital processor will be degraded.

A CD transport/digital processor combination introduces jitter in three ways: 1) the transport puts out a jittered signal; 2) the S/PDIF or AES/EBU interface between the transport and processor creates jitter; and 3) the digital processor adds its own jitter to the clock. These additive factors are largely responsible for the great range in sound quality we hear from different transports and interfaces.

In 1988, Bob Carver set out to design the best amplifier he possibly could, without regard for cost. It was more of an ego exercise than an attempt to build a product with wide commercial appeal. The result was the four-chassis, $17,500 Silver Seven.

Interestingly, Bob Carver chose vacuum tubes to realize his dream of building the ultimate power amplifier. The Silver Seven uses fourteen KT88 output tubes per channel, and puts out 375W into 8 ohms. Bob built three pairs of Silver Sevens, not expecting to sell many at the $17,500 asking price. When those sold quickly, another 10 pairs were manufactured. Now, demand is so great that Silver Sevens are built in groups of 30 pairs.