Digital Processor Reviews

As an equipment reviewer, I find it helpful to talk to audiophiles and music lovers about their systems and upgrade plans. Fortunately, Stereophile's computer supplier and troubleshooter, Michael Mandel, also happens to be an avid audiophile. I say "fortunately" because I rarely get a chance to talk to people who put down their hard-earned money for hi-fi components. Instead, I usually converse with equipment designers, technicians, and marketing types, hardly people who reflect the buying public. It is thus a valuable education to get feedback from real-world consumers to find out what kind of products they want, their priorities, and how much they're willing to spend for certain levels of performance. They have a view distinctly different from that of the often jaded reviewer who is used to enjoying the best (albeit temporarily) without agonizing over its cost.

It is significant, therefore, that whenever Michael sees me, the first words out of his mouth, even before "Hi Bob," are "What's good in reasonably priced digital processors?" Although he would like to own a Stax, Krell, Wadia, or the Theta DSPre, he cannot afford such an expenditure, especially with the knowledge that remarkable price/performance breakthroughs are occurring very rapidly. He is, however, willing to fork over a couple of kilobucks, provided the processor provides truly musical performance and isn't likely to be significantly surpassed at the price point anytime soon. I see his quest for affordable digital as representative of many audiophiles who own CD players, even good ones, who are ready to take the next step to an outboard processor. Like Michael's attitude, there has been a "wait and see" approach to investing in good digital playback. Inherent in his question is a growing impatience, with the implied secondary question of "How much longer do I have to wait?"

Since Michael comes from the computer industry, he is well aware of the huge technological leaps, coupled with equally large and often simultaneous price reductions, in any competitive electronic field. Buy too early in the cycle and risk paying too much for soon-to-be-obsolete performance. Buy too late and miss owning the product during the wait for better performance and lower prices that are not immediately forthcoming.

What does all this have to do with the new $2000 Theta DSPro Basic?

Everything.

Technical description
As its name implies, the DSPro Basic is a simpler, more cost-effective version of the highly regarded DSPre digital processor/preamplifier from Theta Digital. When it was introduced, the DSPro set the standard for digital playback, making it into Class A of Stereophile's recommended components. The DSPro was, to my knowledge, the first software-based digital processor, employing Motorola 56001 DSP (Digital Signal Processing) chips.

The DSPro Basic is rather simple, with the front panel home to just two toggle switches and two LEDs. One switch selects between CD (44.1kHz) and DAT (48kHz) inputs, while the other inverts absolute polarity. The left LED indicates the unit is locked onto the incoming data, while the right indicates power is applied. The rear panel contains the analog outputs, two digital inputs (CD and DAT), and a digital tape-out loop for driving a DAT machine input, all on gold-plated RCA jacks. An IEC AC power-cord jack finishes off the rear panel. No power on/off switch is provided, suggesting that the DSPro Basic should be left on continuously. Construction is a bent-steel chassis with a ¼"-thick front panel. The top panel is screwed into pem-nuts in the chassis with hex-head bolts, an improvement over sheet-metal screws into chassis holes. Overall, I found the DSPro Basic's appearance attractive and its fit and finish quite good.

All the DSPro Basic's electronics are carried on a single printed circuit board, separated into digital and analog sections. The unit has two separate power supplies, one for the digital section and one for analog circuitry. The digital supply consists of a transformer, rectifier, two 4700µF filter caps, and a large heat-sunk regulator in a TO-3 package. The analog supply is more elaborate, with a similar transformer, two rectifiers, and four 2200µF filter caps. Additional analog power-supply components are located at the other end of the PCB, next to the DACs and analog output stage. Six voltage regulators are used in the analog supply, but not the typical TO-220 type (footnote 1) found in most digital processors. Instead, they are small round metal cans which, according to DSPro Basic designer Mike Moffat, offer superior sound over the less expensive and easier-to-implement TO-220s.

The digital section features the ubiquitous Yamaha YM3623B 16-bit S/PDIF decoder, along with a few chips whose markings were painted over. The Yamaha decoder extracts the clock information from the signal with an internal phase-locked loop (PLL), strips out the subcode, demultiplexes left and right audio, and sends the data to the next processing stage.

The wire carrying the digital data stream from the RCA input jack to the digital board was carefully chosen for its sonic virtues. This low-propagation delay wire was suggested by Dave Magnan, maker of the highly regarded Magnan Type V interconnects. According to Mike Moffat's listening tests, even this short (3") piece of wire carrying ones and zeros affects the processor's sound. Other design aspects of the DSPro Basic include careful attention to timing relationships and clock signals to avoid jitter, an input circuit to keep RF out, and minimizing ground-plane noise.

---

Footnote 1: A TO-220 package can be identified by its metal plate to which a plastic square has been attached, hole at the top for a heatsink, and three pins protruding from the bottom. A TO-3 package is a round metal container a little bigger than a quarter, most often used for output transistors.