Theta History
The Early Beginnings

Theta was a research project long before it became a manufacturing company.

When it began to become clear that compact discs were going to become the dominant music recording format, a small group of music lovers started to seek out ways to deal with the harsh, lifeless, irritating sound they were getting from what had been introduced as a "perfect" medium. The very best of the CD players on the market was horribly below the standards of these audiophiles. They examined flaws in design and execution, and just plain shoddy standards—everything from misunderstandings about what human hearing perceives to how cheap a part can be used and still make sound. Over a two year period of working on weekends and spare evenings, this little group experimented, listening to the results every step of the way, to see where improvements could be made, and what kind of changes had beneficial effects on the sound.

The very first units from this design team, in early 1986, were modifications to early Philips CD players. Modifications included new analog "brick wall" filters utilizing Mills resistors, Teflon and polystyrene capacitors and digital signal re-clocking. These improvements led to a whole new analog section with new DACs, op-amps and power supplies on a Teflon circuit board. The improvements that these modifications made clearly showed that digital had potential.

Next came "Frankenstein". This was a three-box set connecting a CD player used as a transport, a power supply, and a digital/analog unit. All of the analog section from the CD player was removed and only the necessary circuitry needed to play a CD and get a digital signal from it were left intact. The digital signal from the transport was then fed to the processing section, which re-clocked the signal, oversampled the data by 8x, and calculated accurate interpolated data points.

This was the first step in the implementation of DSP (digital signal processing) in a consumer digital to analog converter. It used Texas Instruments 16 bit microprocessors running at 10 MIPS (10 millions of instructions per second). The signal was then routed to the analog section. A Teflon circuit board contained circuitry similar to those early modified Phillips CD players, with additional improvements like more advanced 16 bit DACs (Burr-Brown PCM 56) and optical isolators which kept digital high frequency signals from corrupting the analog section.

This was also the first implementation of the Buf 03 output buffer. The digital to analog converters themselves were hand trimmed on a $10,000 Hewlett-Packard dynamic signal analyzer. This was not being done by any other manufacturers, despite the clear necessity of doing so to assure acceptable low level linearity, and a reliably standardized level of performance. The early Frankensteins were not pretty to look at (OK, they were ugly) and were cumbersome (three units connected together) but were a huge leap in digital sound.

The Frankensteins were not intended to be in production and were never sold to the general public. They were only sold to friends and their friends who wanted better sound from digital. The demand became so great for these units that a more affordable, better-looking, less cumbersome "Theta" unit became the thrust of the design team’s efforts.

The result of those efforts was the original Theta Digital DS Pre, released in 1988. This was the first DSP-based outboard digital to analog converter. This unit was an instant success due to its dramatic superiority over the then state-of-the-art solid state and vacuum tube CD players. The wealth of reveled musical information previously unknown to digital sound reproduction was the most obvious and remarkable aspect to the Theta.

The unit had several unique design aspects worth noting. It contained totally isolated power supplies, digital board and analog board within a single chassis using Faraday cages. This was a direct result of research and development invested in the Frankenstein, which confirmed that this isolation was critical for a truly breathtaking listening experience. The power supply featured four totally isolated transformers, which separately powered the digital, DAC and analog sections. An advanced phase locked loop was implemented to cope with the large amount of jitter being generated by early CD players.

The digital section was designed to accept plug-in ROM (read only memory) chips so that as research into better sounding algorithms progressed, Theta owners could keep their units current.

The DS Pre was radical in many ways, most of them technical, but perhaps the least appreciated advantage was its function as a preamplifier. By including some basic switching and a superb analogue volume control – using discrete resistor networks to turn the high-voltage output signal down – the DS Pre offered to eliminate an entire component; a series of gain stages and all the signal degradation that went with them. It had an analog input, balance control and a muting circuit so that the unit could be used in a system sans customary preamplifier. However, we did not supply a phono stage for playback of vinyl records. Many audiophiles, still devoted to LPs, were happy with the phono stages in existing high-end preamplifiers and had no desire to go to an outboard phono stage.

We recognized the need for what became known as the DS Pro: essentially the same as the DS Pre, minus all preamplifier functions. The DS Pro was embraced by audiophiles who already had high quality preamplifiers. The disadvantage of the DS Pro/preamplifier configuration was the routing of CD music signals through an extra set of wires and gain stages. A great secret of the late 1980’s was that most all-digital systems could have been dramatically improved by omitting a component most people thought of as indispensable.
Research into all aspects of the Theta continued. Specifically, more processing power was needed to run a newly developed algorithm that could more accurately interpolate oversampling points. New DACs with higher resolution were becoming available from Analog Devices. Microprocessors from Motorola were released which had higher accuracy and speed. The use of tantalum electrolytic capacitors was found to decrease noise in the digital section, due to the higher frequency capability of these components.

The result of that research was the DS Pre Generation II and DS Pro Generation II, released in 1990. These products incorporated all-new digital and analog boards. The digital board utilized two 24 bit Motorola 56001 microprocessors running at 24 MHz which was a two-fold increase in computing power over the DS Pre. The analog board was upgraded to 18 bit Analog Devices AD 1860 DACs.

Shortly thereafter, a new product line was released. The DS Pro basic and DS Pre basic, lower priced versions of the Generation II predecessors, allowed many more music lovers to obtain satisfying digital sound. A Basic unit had a thin-line chassis containing a single circuit board, which had all three of the required sections (power supply, digital, and analog), on it. The digital and analog sections were similar to the DS Pro Generation II, so the Basic had a very similar sound, but didn’t have as much resolution as its larger sibling.

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