Theta History

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Fully Balanced Differential Design

At this time Theta’s engineers started investigating the benefits of balanced operation. Balancing a Generation II produced a profound decrease in digital harshness and glare, and was immediately made available as an upgrade or as an option on new units. Theta was the first digital manufacturer to "balance the hard way". This means that the whole analog section is duplicated including DACs, the only way to truly realize the improvements of balanced operation.

One-bit technology was headline news around this time. It was touted by major hi-fi manufacturers as being the next revolution in digital sound. They said multibit technology was dead. Theta’s design team tried this new technology in high-performance designs and found it smooth sounding but lacking in aliveness, dynamics and bass. They envisioned one-bit technology as a palliative for less expensive products. Most inexpensive CD players and outboard D to A converters sounded shrill and harsh. The smoothness of the one-bit D to A could be implemented to reduce "glare" and other irritating characteristics, to bring new musicality to otherwise unacceptable components. It meant Theta had something to offer in a price realm previously thought hopelessly compromised. The DS Pro Prime was introduced in May of 1991.

The Prime was similar to the Basic in construction, different in circuit design. It had a single circuit board which contained the power supply, digital and analog sections. The digital section employed a single Motorola 56001 microprocessor running at 30 MHz. It was a 4x-oversampling unit and thus didn’t have the huge amount of information presented in the Basic or the Generation III. Compared to other D to A converters in its price class, however, it was nothing short of a miraculous improvement. Where previously there was only harsh, strident sound, lacking in detail, there was now musicality and enjoyment.

Transports

Transports were the next frontier for Theta. Transports made a real, audible difference to the absolute quality level Theta’s signal processing could attain. Theta’s people searched long and hard to find a CD player that would function as a truly high-quality transport to support Theta’s digital signal processors. It seemed a bit of an absurd compromise to urge audiophiles to buy cheap CD players to extract digital signals, but that was the state of affairs for several years. People used whichever CD players had reasonably reliable transport sections and offered a way to pass a signal out of the digital stage. Experiments with numerous CD players showed them to be inadequate for the basic function of providing a clean jitter-free digital signal.

The solution to this perplexing problem was another Theta first: the Data Universal Transport, a laserdisc player used as a transport. This, of course, was not just a laserdisc player with the Theta name on it. The digital signal was extensively improved by re-clocking it with high-speed CMOS logic devices and pulse transformers. Data’s heavy-duty steel chassis and isolation spike helped suppress and neutralize vibration. The Data was a revelatory experience for audiophiles and an instant success. Other digital audio companies quickly followed with laserdisc transports of their own.

Following the original Data was the Data II. The Data II was different from the original Data mostly in its power supply. A whole new power supply circuit board was added which isolated the delicate re-clocking board from the rest of the unit. As originally conceived, the Data was only intended as a CD transport. People asked, naturally, why Theta was ignoring the opportunity to tune up the video aspects of the Data. Improvements to the video quality in Data II were much appreciated by videophiles, who quickly discovered that the Data was the best laserdisc player around for video quality.

The research that was invested into the Prime and DS Pro Generation II Balanced paid dividends in other products as well. The Basic II was released in late 1991, offering sound quality many thought comparable to the Pro II. Balancing was available as an option, which was by this time becoming a standard for many digital based systems. It was, of course, balanced "the hard way" as previously described. It also featured a new DAC from Burr-Brown, the PCM 67. This was an 18-bit combination DAC that operated as a multibit DAC for the upper portion of its range and as a one bit DAC for the lower portion. This DAC is still used today in the Prime II, Progeny and Cobalt. New op-amps, the Analog Devices AD829 and AD707 were also utilized.

The design team continued to delve into sources of dissatisfaction with digital sound. Again they found that increased processing power and digital filter accuracy was essential for further resolution enhancements. New op-amps that had faster slew rates and settling times were investigated. Improvements to the digital section’s power supply were found to decrease harshness and interference between different parts of the digital circuit.

The Generation III emerged in 1993 as the beneficiary of that research. The digital section was upgraded to include three Motorola 56001s running at 30 MHz instead of just two. This increased the computing horsepower by a factor of two again over the Generation II. Many of the high-speed logic ICs used on the Generation II board were replaced with two field-programmable-gate-arrays. The PLL (phase lock loop) circuitry was improved by separating the standard 32KHz-48KHz PLL into 3 different PLLs. On the analog side, new Burr-Brown 20 bit DACs (PCM 63) were employed in addition to new op-amps (Analog Devices AD 841) and improvements were made to the servo. More power supply capability was added.

In late 1992 Theta’s first non-DSP digital-to-analogue converter was released. The Cobalt, based on an off-the-shelf Sony digital filter chip, in comparison with alternatives in its modest price range provided a smoother, less strained, more dynamic sound. While certainly no match for any of the DSP based Thetas, it provided welcome musicality for audiophiles on a budget, and die-hard analog fans. The Cobalt uses the same construction techniques and parts quality as the most expensive Thetas, including the Burr-Brown PCM 67 DAC; Analog Devices AD 841 op-amp; and Crystal CS 8412 input receiving IC.

During all of this developmental work in digital-to-analog converters, transport development continued on its own design track. The Data basic transport, available in early 1993, quickly established itself as the standard against which all other CD-only transports would be measured. It is not a remanufactured product, as most U.S. CD transports are, but instead a wholly in-house manufactured product built to the highest standards of quality. Separately isolated power supply, mechanism and digital/re-clocking circuit boards, along with improved re-clocking circuitry, combined to produce what some reviewers refer to as its "lively, upbeat" sound quality.

Despite the promised benefits of one-bit technology, it had all but disappeared from mass-market CD players. The Prime was reevaluated using the Burr-Brown PCM 67 DAC. The smoothness in the old Prime was still present, but a new range of dynamic contrast and detail became evident. It was clear that huge leaps had been made since the original Prime was designed, both in the technology available and in our knowledge of how to produce the best digital sound. The new Prime, the Prime II, implements a similar digital section to the original Prime but includes a brand new analog section. It is now balanced using two Burr-Brown PCM 67 DACs, Analog Devices AD 841 op-amps and National Semiconductor LM6321 buffers. Special circuitry was designed to take advantage of balanced operation through the single-ended outputs. The Prime II also has extensive PLL technology to reduce the effects of jitter to a minimum.

Originally, there was only one method available to connect a CD player/transport to an outboard D to A converter, that being coaxial. The mass-market manufacturers then produced players with the inferior TosLink plastic fiber optic output. AT&T glass fiber optics also became available as a means to interconnect digital equipment. All of these termination methods posed a problem for people trying to buy components that would interface with each other. The Timebase Linque Conditioner was designed to solve these problems. It can accept TosLink and coaxial inputs and output coaxial and optionally AT&T or Theta’s Laserlinque. It also contains extensive re-clocking circuitry to combat the deleterious effects of jitter. Poor quality transports still pervaded the market, reducing the effective quality level Theta’s D to As could offer. The Timebase Linque Conditioner ameliorated some of the problems. It was even found to improve the sound of our best combination, the Data III/Generation V.

All of the digital-to-analog converters up until this time used integrated circuits (ICs) called op-amps, for the critical current-to-voltage conversion that occurs following the DAC, and for the output buffers.

At that time, integrated circuit chips generally were used as cost-efficient compromises, which lowered the quality of components that depend on them, in comparison with equivalent circuits made up of discrete elements on a circuit board. After about a year of research, a new analog section was developed for the Generation III, based entirely on discrete class-A bipolar transistor. This circuitry offered greater processing speed, which produced more detail and a smoother sound.

Previously, a balanced Generation III required two separate analog boards for balanced operation; in the new design only one board was needed for fully balanced operation. The single ended left and right analog outputs take advantage of the balanced signal, just as in the Prime II. Improvements to the power supply came with the new analog section, including regulation on the analog board itself. The vast improvements wrought by these changes deemed a new product name: the DS Pro Generation V. It was previewed at the Las Vegas CES in January of 1994. The Progeny, essentially a single ended version of the Prime II was introduced in November of 1994.

The Pro basic III was also released about the same time. The Prime II showed that the benefits of fully balanced operation and the summing circuitry utilized for the single ended outputs were worthy of introduction into the basic line. Prototyping confirmed this and soon the basic III presented itself as a true contender for the best sound attainable from a CD. New 20 bit Burr-Brown PCM 1702 DACs, which are very similar to the PCM 63 used in the Generation V, were found to bring the basic III to a new price / performance level. The digital section was also redesigned from the ground up, taking advantage of many of the techniques learned from the development of the DS Pro Generation III. Field-programmable-gate-arrays replaced huge quantities of individual CMOS ICs and the inherent difficulties of designing circuit boards with them.

The Data III Universal Transport was introduced at the 1995 Winter CES in Las Vegas. The Data III incorporated the knowledge gained from the original Data, the Data II and the Data basic. Much of the massive unit (all of one side) was reserved for power supplies. Research into voltage-controlled oscillators provided even better jitter immunity and stable signal transfer. Each unit was hand calibrated with a high-precision time-interval counter to conform to the CD standard for digital data transmission. It came with coaxial, BNC, AES/EBU and optional optics outputs for easily integration into any system. When playing a laserdisc, the Data III has the ability to play both sides without user intervention and a special CD-only drawer, which greatly reduced access time.

Theta has always maintained an upgrade policy unequaled in audio. An original DS Pre can still be converted to a current, state of the art DS Pro Generation VIII. An original Pro basic can be upgraded to a Pro basic III. Obsolescence is not in Theta's vocabulary and we shall always endeavor to hold true to this directive.

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