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Theta Generation VIII DAC/Preamplifier

Part I

March, 2003

Jason Victor Serinus

Specifications:

Digital inputs: 2 RCA, 1 BNC, 1 AES/EBU, 2 optical (1 Toslink, 1 optional AT&T)
Analog Inputs: 1 stereo pair on single-ended RCA jacks, 1 stereo pair on balanced XLR jacks
Input Impedance: 10 K ohms
Frequency response: DC - 20 KHZ ±.2dB
THD+Noise: <0.0005% @3VRMS in and out, balanced
Dynamic Range: 125dB ref 18VRMS Bal
Signal to Noise Ratio: 125dB ref 18VRMS Bal
All DSP processing is 24-bit with 56-bit accumulator
D/A Conversion: 24-bit Ladder (8x oversampling); 2 DACs per channel for differential operation
Volume Control: Proprietary switched resistor network in the analog domain
Digital Filter: 8x oversampling proprietary FIR filter running on Motorola 56362 DSP
Size: 17 5/8” W x 5” H x 17 3/4” D
Weight: 29 lbs
MSRP: $10,000 USA

Theta Digital

www.thetadigital.com
 

 

Introduction

Equipment reviews ordinarily begin with an introduction, proceed with discussions of design, functions and technical specs, and then move onto time-honored listening assessments. At one extreme, those assessments read like:

“When I played my favorite recording of Mahler’s Eighth Symphony, otherwise known as the Symphony of a Thousand, I heard orchestral details I had never heard before. Due to the infamous squeaky chair under the extremely animated eighth violinist in the orchestra’s second row - a squeak that has made this recording a cult favorite among audiophiles inhabiting the outer islands of Japan - I was never able to locate the sound of the third row of violinists within the recording’s massive soundstage. But with this new preamp, I could not only hear the resin on the bow of the sixteenth violinist in the third row, but could also identify the exact moment when she, in a fit of rage, momentarily lifted her bow from her instrument and jabbed it into the back of the eighth violinist. The thrill of actually feeling this outburst of anger in the middle of Mahler’s greatest expression of spiritual exaltation makes the asking price of $49,798 seem most reasonable.”

This, however, is no ordinary equipment review. While it will undoubtedly include some listening assessments, I prefer to proceed in less formulaic fashion. My rationale? To paraphrase an oft-quoted axiom, extraordinary equipment calls for extraordinary measures.

Gen. X - The Experience

Have you ever spent years fantasizing your ideal relationship, even passing the person on the street from time to time, yet finding yourself unable to make an actual connection? Have you ever carried on an internet relationship with someone living a great distance from yourself, but had to wait years before meeting face-to-face? Are you someone who, assuming marriage was a legal option from day one, was forced to wait many years before popping the question? Are you a person who had to search many years before finding the house of your dreams?

If you have ever had an experience that even remotely parallels any of the above, you can begin to understand what it was like for me to wait well over four years before receiving the Theta Gen. VIII.

Theta was the first audiophile company to produce separate outboard DACs. They continue to honor their long-standing policy of producing fully upgradable units.

Theta's ambitious plans for the Gen. VIII ultimately required designing an entirely new unit, a combined DAC preamp that features both single-ended and fully balanced inputs and outputs. Theta claims that this new design brings the performance specs of its single-ended outputs close to the same level of excellence as its balanced outputs. This is important factor for those like myself whose amps only feature single-ended inputs.

When the Theta Gen. V first came on the market in 1994, a number of reviewers who had previously pledged total allegiance to analogue hailed it as the first two-channel DAC to render digital recordings not only listenable but also distinctly musical. The unit came in two configurations: for a hair less than $4000, you got a single-ended DAC equipped with coaxial outputs; several thousand dollars more got you a purportedly quieter and superior fully balanced unit with XLR outputs.

I first obtained my Theta Gen. V single-ended DAC in January 1996. While I did not have a decent analogue set-up with which to compare it, I certainly found the Gen. V rewardingly musical when compared to live acoustic music presentations. It didn’t sound remotely the same, of course, but it was musically satisfying. The unit in fact proved so satisfying that, besides upgrading it to V status within the year, it remained a constant in my system until two months ago.

As we all know, digital technology has made great strides since 1994. First came 24-bit chips. Then arrived separate bit interpolating and upsampling devices, external DACs that performed the same functions, and 24/96 one-piece CD players. All claimed to make 16-bit/44.1 khz sampling rate redbook CDs seem as though they had been recorded and issued in 24-bit/96 khz or higher sampling rate.

I probably first began contacting Theta about such upgrades to the V sometime in 1999. I was immediately assured that the next generation product was in the planning stages.

Every three or six months I would check in. Sometimes I was told that the Gen. VI was only six months away. At one point the Gen. VI was listed on Theta’s website; then it disappeared. Six months became a year, a year became two. By whose calendar did Theta operate, I began to wonder.

At first the reason I was given for Theta’s seeming intransigence was that the company was unable to find a 24-bit chip that sounded as good as what they had accomplished with the V’s outdated 20-bit chip. When that story could no longer hold water, it became clear that, in the face of changing listening preferences and economic downturns, Theta Digital had chosen to insure its survival by building a strong presence in the multi-channel home theater market. The Casablanca, mega amps, and various other audio and home theater products debuted to great acclaim while the company’s two-channel DAC technology languished.

Over two years ago, a Bay Area Audiophile Society member who had spoken with Theta President Neil Sinclair reported that the Gen. VI was no more than six months away. Hardly. I even saw the empty shell of the “expected shortly” Gen. VIII at CEDIA 2002. But the wait continued.

After 9/11, the economic downturn reduced Theta’s ability to put their main focus on a product that, given the state of the audiophile market, they now considered (to quote Theta’s Mary Cardas) “a bit of a ‘vanity product.’” Happily, the designer of the original V remained with the company. Yet, each time he proceeded to design an upgrade, another state-of-the-art chip came on the market that tempted him to experiment anew. The combination of continued experimentation and development and low priority added a good year and a half to the final release date.

Finally, the decision was made to proceed no matter what new developments might occur. (To paraphrase a Buddhist phrase, there’s always another chip). Given the arrival of new DVD-A and SACD formats, Theta also chose to rethink its design in order to provide a DAC that could also decode those formats’ higher-resolution signals.

In the end, it all boiled to the company’s long-standing motto, “Digital Done Right.” Theta took as long as it felt necessary to get it right.

Theta’s ambitious plans for the Gen. VIII ultimately required designing an entirely new unit, one that offers both single-ended and fully balanced outputs as well as an internal preamp. (Theta claims that its new design closes the gap between the unit’s single-ended and balanced outputs for those like myself whose amps only accommodate single-ended inputs). Though such fundamental design changes mean that the Gen. VIII shares only a small number of parts with the Gen. V, and is housed in an entirely different chassis, Theta continues to honor its long-standing “fully upgradeable” policy for original owners of all versions of the Generation DAC. In this instance, however, the “upgrade” means that you receive an entirely new unit.

After the Gen. VIII’s design was completed and beta tested, the first units were released in late spring of 2003. A few went to print reviewers, a few more to dealers, and a few to buyers. But while the first units seemed to function smoothly, the need to integrate a two-channel DAC with all of today’s electronics (including satellite and various limited-use digital devices) took Theta many, many additional months.

I had originally hoped to obtain a demo Gen. VIII after CEDIA 2003. Alas, all the CEDIA demo units returned to the company arrived too beatup to refurbish. Then more problems arose with the next round of units. The wait became longer and longer.

I must confess that, in the face of yet more delays, I was sorely tempted to throw in the towel and obtain another company’s DAC. Not only was I frustrated on a personal level, but I also felt a responsibility to Secrets readers to review with state-of-the-art equipment. Yet even in my most exasperated moments, a strong belief that the company was doing all it could to honor their promise to me, combined with my faith that the Gen. VIII would turn out to be something else entirely, kept me hanging in there by a thread.

By CES 2004, a few exhibitors, notably Genesis and Thiel, had rooms equipped with correctly functioning Gen. VIIIs. (Theta’s own exhibit in the Las Vegas Convention Center only offered a static display). It is one of those CES demo units that, after a round of tests and retests, made it to Oakland on Friday, February 13, 2004. Given that was the same day I became Jason Victor Bellecci-Serinus, I am happy to report that my feelings about Friday the 13th have forever changed.

What is the Gen. VIII?

The Generation VIII is a full differential balanced two-channel DAC featuring custom-designed software-programmable digital filters feeding into two digital-to-analog converters per channel, one for each phase angle. Several Gen. VIIs can be strung together and connected to the Theta Casablanca or Casa Nova for multi-channel operation. While this represents a considerable investment, Theta assures me that as good as its current multi-channel processors are, the Gen. VIII takes digital-audio conversion to another level. Since my set-up is strictly two-channel, I am not in a position to evaluate this claim.

Theta has posted a host of technical information about the Gen. VIII on their site. I refer you to same. The site includes a white paper that discusses the truths and myths of upsampling vs. oversampling. The Reader’s Digest version is that the Gen. VIII’s multi-stage digital filter brings the signal up to a sampling rate of 384 kHz.

The unit also offers the option of Theta’s proprietary “Jitter Jail” which the company claims reduces jitter (time alignment distortions which are a major factor in the degradation of digital signals and cloudy sound) to almost zero.

Notes by Colin Miller: The rest of the industry calls this a Phase Lock Loop (assuming it is similar), operating with a healthy FIFO buffer to reclock the data, or simply reclock it completely without the PLL (a la Meridian) and attenuate if not eliminate jitter, but 'Jitter Jail' is a snazzier name. It may be that the Theta can alternate between these two methods, but it all boils down to a FIFO buffer on the input, and a new clock feeding information to the DAC process.

Jitter is a timing error, an error in data rate, either over a very short time, or a very long time. Short periods of data rate error (too close together for a few samples, too far for a few more, etc.) are high-frequency jitter. Long periods of data rate error (too close for very many samples, gradually shifting to too far for many more, and so
forth) are low frequency jitter. The only way to correct the error is to correct the timing. The only way to correct the timing is to space the data evenly at either a derived rate, or a known rate. The only way to do this is with some working room, which requires an input buffer, and then you can do what needs to be done, reclock it to the most uniform (evenly spaced) and preferably correct data rate.

In a perfect world, jitter would be no issue at all. In a next to perfect world, the DAC device would control the transport device's servo-controller that determines the data rate, and the only clock would be the master clock that times the DAC process, and so jitter would be very easily avoided with a small FIFO. That has yet to happen, to my knowledge.

In a world almost as perfect as that, you have a FIFO buffer at the input, the DAC device figures out the rate by looking at the data, and reclocks the data completely independently of the incoming rate that would be carrying the jitter. In this scenario, the only jitter possible is that of the DAC's own clock itself, and any jitter prior to that is completely and utterly irrelevant, with one exception. If the error is of low frequency, i.e., goes too fast for awhile, then slows down for awhile, or as a most extreme example of the lowest frequency jitter, spits CD information out at 44,003 samples/second instead of 44,100 samples per second, you'll have buffer over- or underrun, in which case you either get dropouts, no sound, or a really nasty mess of a sound when the DAC tries to resynchronize with the rate. From the comment that your DVD player doesn't work with the "Jitter Jail," I'd guess that they're going this route for higher quality digital sources and that your DVD player is a particularly poor one.  Stacey had this problem with his Meridian anti-jitter reclocking circuitry when he used a particular DVD player with the AC power, but it worked fine with the onboard battery power supply or when he used his Power Plant. He had to set his unit to operate in the more standard PLL with that source.

The above illustrates why most of the industry resorts to a PLL, or Phase Lock Loop. This uses the same FIFO buffer, and attempts to smooth the data rate. It'd be like having a bunch of unruly school kids come in clumps through the gates at Disney Land, and the teacher assistant tries to get everyone evenly spaced before the turnstile and going through at a constant rate. He can't hold people up so that they're standing in the parking lot, nor can he get people to run to the parking lot, but if the average flow is steady, he can provide an even stream of screaming children. Every off-the-shelf DAC has a PLL, though some are better than others, and it's quite possible that Theta's is better than most.  A better PLL requires a larger FIFO buffer, so to accommodate larger swings in the tide, so to speak, without having to compromise the new clock. For instance, if a CD was fed at 44,003 samples per second, a PLL would simply shift the master clock to 44,003 samples per second, not underrun the buffer, and still be able to attenuate the higher frequency jitter. This extreme example would result in a slight pitch shift, but where it gets really difficult is when it's shifting fast enough to cause modulation problems in the DAC, but slow enough to cause the FIFO buffer problems, an area where better jitter reduction schemes really shine.

This extreme example would result in a slight pitch shift, but where it gets really difficult is when it's shifting fast enough to cause modulation problems in the DAC, but slow enough to cause the FIFO buffer problems. Although the PLL circuit is the best way to attenuate jitter while managing the FIFO buffer with poor sources, the strength of the PLL's continuity is also its weakness in jitter reduction. In order to avoid buffer overflows or underflow with low frequency variations, the PLL will adjust the clock to match the data rate over a particular period, and if that jitter period is large enough (low in frequency) to make the PLL circuit adopt the change in data rate, the clock essentially tracks the jitter, passing the same timing errors on, even if slightly attenuated.

It is here that we see that all PLL circuits are not created equal. A larger FIFO buffer, and possibly better buffer management in terms of how the clock adjusts to the amount of data in the buffer, mean that different PLL circuits have differing amounts of jitter attenuation, particularly in terms of low frequency jitter.

With better jitter reduction methods, the input buffer and the PLL can manage more low-frequency jitter while still attenuating the lower frequency jitter, whereas a poorer PLL circuit will simply begin to let the clock follow the lower frequency jitter, essentially passing it right onto the DAC. Since it is the lower frequency jitter that's the most audible, this is where the better jitter reduction schemes really shine. They still follow the rate of the incoming data, but their clocks remain more stable and jitter free in the presence of a less desirable source.
- CM -

As noted above, the Gen. VIII’s rear panel features:

● Six digital inputs (two RCA, one BNC, one AES/EBU, one toslink, and one optical)
● One set single-ended (RCA) analog inputs
● One set balanced analog inputs
● One set single-ended (RCA) analog outputs
● One set balanced analog outputs
● Options for remote extensions and external volume data inputs for owners of the Theta Casablanca or Casa Nova
● A main on/off switch

The front panel offers:

● 24 character by 2 row vacuum florescent display
● Standby/on button LED
● Five programmable input select buttons
● A setup button used to access setup menus that choose all user parameters
● A lock light
● A mute button that mutes all audio outputs. The mute button is not active when optional fixed volume cards are installed.
● Level left and right buttons as well as level up and down buttons, designed to appear and work like four pieces of a pie. These buttons perform such functions as balance, editing, master volume and setup menu adjustment

All of the above features are controlled by an easy-to-use remote control powered by three AAA batteries. The remote control, which operates up to 20 feet from the unit, includes:

● Standby button that puts the unit in Standby mode or initializes it for playing or programming
● Input Select buttons (1-5)
● Display button to control brightness
● Mute button (not active with fixed volume card installed - see below)
● Setup button to enter/exit setup menus and set all user parameters
● Level up/level down buttons for master volume and setup menu values
● Level left/Level right buttons that shift the balance and adjust master volume within submenus
● Phase button to shift between 0 and 180 degrees at speaker outputs

Purchasers can order the Theta set to either adjustable volume (ideal when using it as both a DAC and preamp) or fixed volume (which those who use an external preamp may prefer). Since this adjustment must be made at the factory, those considering purchasing a Gen. VIII would be wise to read this entire review before making the decision.

The heart of the Theta is a sophisticated internal computer that can be reprogrammed by linking it to an external PC and downloading data from either an upgrade CR-ROM supplied by the company or from the Theta website. The unit’s computer-based circuitry requires that it be grounded via a three-prong AC Power cord. If your outlet is not grounded, before you connect the unit, ground your outlet via a grounding wire to your cold water pipe or a grounding pipe driven into the earth before you connect the unit. Be sure not plug the unit into a line conditioner that defeats the ground. (Some units, such as PS Audio Power Plants, do not read as grounded when tested with a Radio Shack polarity tester. Rest assured that the Power Plant is a fully grounded unit).

When I first received my Gen. VIII and discovered a 29-page binder filled with instructions on how to use and program the unit, I held my breath. No need. Programming the Gen. VIII is pretty simple. Within a short amount of time, I had labeled the four inputs I am using as phono, tuner, CD, and DVD; chosen the form of jitter reduction I wished to use for CD and DVD; and made sure all other features (such as balance and startup volume) were set as I wished. Features such as the built-in burn-in signal option that provides white noise to burn in the Theta as well as cables and other electronic devices, remote trigger, RS232 protocol interaction, baud rate, IR remote jack, and screensaver time did not require adjustment on my part. If they do in the future, adjustment is easily accomplished. The only thing that confused me was exactly which buttons to push to choose the form of jitter reduction. But since I could do no harm by pushing the wrong button, I just pushed away until I figured it out.

The Theta requires a good week of constant signal playing through it to break in. Either music or the built-in break-in signal may be used. Since your amp need not be on, you don’t have to listen 24 hours a day.

Any already broken-in Gen. VIII started up cold needs 72 hours warm-up to sound its best. The first 24 hours are most significant, with increasing levels of refinement obtained in the next 48. Those needing to turn the unit off completely via the power switch at the back would be wise to do so for not more than 1 or 2 minutes to avoid having to go through this extended warm-up period.

I have experienced only one problem with the Gen. VIII. Within a week of its arrival, the unit began to freeze up. I would initialize it and start to play, only to discover that I couldn’t adjust the volume or switch inputs. Sometimes the problem would self-rectify, but most of the time I would need to put the unit in standby mode, turn it off in back for two minutes, turn it back on, reinitialize and play.

When the freezing became more common, I contact Theta’s technical expert, John Baloff. He suggested that the software had become corrupted, and I needed to hook the Gen. VIII to a PC and reinstall. When I couldn’t find the Theta Digital Downloader CD that had been sent with the unit - I am a music reviewer as well, and there are piles of CDs and boxes of review equipment scattered around chez Serinus - John was good enough to send me another. (I now know exactly where I’ve put it). This Mac user then called upon John and Mary Cardas to help walk me through the inner recesses of David’s PC laptop. Once we were able to locate where the appropriate upgrade file had been stored, reinstalling the software was accomplished in no more than 30 seconds. Since then, the Gen. VIII has sounded significantly different and far more impressive than what I heard after the initial 72-hour settling in period.

What Mary, John and I have surmised as the cause of the problem lay in the way I changed frequencies on my Power Plant. We think that changing my P600’s frequency back and forth between SIN, TubeWave, and P-1 while the Gen. VIII was on had corrupted its software; hence the need to reinstall.

I now keep my PS Audio Power Plant set to P-1 (the setting I like best with my reference system) unless I am playing LPs. (The motors in most turntables do not function properly if fed other than a standard Sin wave.) When switching frequencies, I first put the Gen. VIII in standby mode, then scurry around one of my speakers and two racks, turn the Gen. VIII off completely via the rear on-off switch, scurry back in front and reset the P600’s frequency, zip to the back and turn the Gen. VIII back on, and finally come back to the front of the Theta and reinitialize. I may not enjoy doing this at age 80, but at 58 3/4, it’s fine. Following this procedure will hopefully insure that I won’t need to re-download the software anytime soon. But I do expect, given that I need to reinstall programs in my Mac from time to time, that I will eventually have to reconnect the PC and perform the procedure again.

The good thing about this experience is that I not only have learned the best protocol for Power Plant users to follow, but have also discovered how easy it will be for Gen. VIII users to upgrade the unit’s software when and if new software and/or codes become available.

Click Here to Go to Part II

© Copyright 2004 Secrets of Home Theater & High Fidelity

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