Description: Digital/analog converter with 8x-oversampling digital filter and 18-bit hybrid DAC. Frequency range: 0.05Hz–20kHz (no tolerance given). Filter math resolution: 45 bits. S/N ratio: 108dB. Resolution: 18 bits. Linearity: 18 bits. THD at full output: 0.002%. Inputs: one coaxial on RCA jack, one optical on Toslink jack. Digital output: One coaxial on RCA jack. Analog output: unbalanced on RCA jacks. Output level: 2V RMS.
Dimensions: 9.5" (W) by 2" (H) by 6.625" (D). Weight: 5 lb.
Price: $599 (1993); no longer available (2019). Approximate number…
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Sidebar 3: Specifications
The $799 Theorem was originally shown at the 1992 WCES in a very small chassis that prohibited adding features or upgrades. Sumo has since become more ambitious, putting the Theorem in a full-sized chassis and offering several upgrade options that would have been impossible in the truncated version.
There's not much to say about the Theorem's features; the front panel has a power "On" LED and nothing else. Selection between the unit's single coaxial input and Toslink optical input is automatic. If a digital signal is present at both inputs, the system defaults to the optical input. The…
First, the Theorem had easily the best soundstage of the four processors. The feelings of space, depth, and air was excellent for any digital processor, never mind one costing a hair under $800. There was a distinct impression of individual instruments, each surrounded by air, hanging in three-dimensional space. The presentation was the antithesis of flat sterility, in which images fuse into a congested mess. Instead, I heard a remarkable openness, front-to-back layering of images, and a wonderful sense of bloom surrounding image outlines. I had this impression within seconds of hearing the…
Sidebar 1: Review context
I auditioned the four processors reviewed in this issue under identical conditions and at matched levels. Additionally, the reference playback system has remained nearly constant for the past year, providing a stable platform on which to audition and compare digital processors. The converters under review fed an Audio Research LS2 line-stage preamplifier, which in turn drove a Mark Levinson No.23.5 power amplifier via its unbalanced inputs. Loudspeakers were Hales System Two Signatures, occasionally augmented with a Muse Model 18 subwoofer.
A Theta Data…
Sidebar 2: Measurements
The Theorem had the lowest output voltage of the processors I review this month, measuring 1.97V when reproducing a full-scale, 1kHz sinewave. Output impedance was a fairly low 152 ohms across the band, which suggests the Theorem will have no trouble driving a passive level control.
The unit's frequency response (fig.1) showed a moderate (0.3dB) rolloff at 20kHz. De-emphasis tracking (also shown in fig.1) was virtually perfect. Interchannel crosstalk, shown in fig.2, was difficult to measure; the true crosstalk didn't emerge from the noise floor until 5kHz…
Follow-Up, from April 1993, Vol.16 No.4
Since my review of Sumo's $799 Theorem D/A converter in October 1992, the company has incorporated a jitter-reduction circuit in this popular processor. My assessment at the time was very favorable: I called the Theorem the "best-sounding converter under $1000." When I heard that Sumo had improved the Theorem's sonic performance, I was eager to audition it again. In addition to finding out how good the newer version was, it would be possible to hear the effects of lower word-clock jitter—if indeed the revision lowered jitter as claimed.
…
Sidebar 3: The Jitter Game Revisited
This "Follow-Up" provides an opportunity to clarify a perplexing issue raised in the January jitter article. From those measurements, it would appear that processors with single-bit converters have much lower jitter than the more common 8x-oversampling units that use multi-bit DACs. Indeed, 1-bit converters typically have only a few picoseconds of jitter, rather than several hundreds of picoseconds or even several nanoseconds for multi-bit converters. Is the jitter performance of 1-bit machines intrinsically lower, thus "better"?
Yes and no.…
Sidebar 4: Specifications
Description: D/A processor. Frequency response: 20Hz–20kHz, ±0.5dB. THD: ±0.004% at 2V output. IMD: ±0.01 at 2V output. S/N ratio: !w100dB. Channel separation: !w80dB. Induced jitter: ±80 picoseconds. Digital filtering: 8x-oversampling. Conversion: hybrid 1-bit/multi-bit DAC. Analog section: Fully discrete, DC-coupled. Inputs: two coaxial (RCA jacks), one optical (Toslink jack), "clock" input (see text), AT&T ST-type optical optional. Outputs: unbalanced on RCA jacks.
Dimensions: 19.5" W by 1.75" H by 9" D. Weight: 10 lb, shipping.
Price: $799 (1992…
I once told Stereophile publisher Larry Archibald it might be worth, say, a 10% loss in sound quality with CD not to have to jump up and turn over the damned record. Sometimes a CD saves you from popping up twice—Mahler's Fifth or Bruckner's Seventh on a single disc instead of three LP sides—or three times—Mozart's Magic Flute on three CDs instead of 6 LP sides. That might be worth a 15% sacrifice.
I don't know that you will need to lose even 10%. Unless, of course, you have a turntable like a Versa Dynamics 2.0 or a Goldmund Reference.
Now, if only the cost of CDs would come…
One aspect of the 582's performance was truly outstanding: its ability to track. The 582 played through track 35 of Disc 2 of the Pierre Verany test disc set—these tracks simulate dropouts. Anything beyond track 27 is beyond "standard values but inside the theoretical [sic] correction capabilities of CD players." The 582 even played track 36 without glitching too much. There are only 38 basic tracks. Moreover, the 582 played four out of five damaged discs in my collection, including two discs no other player has been able to flawlessly track.
If only the sound quality had been a bit (…