Musical Fidelity Digilog D/A processor
These ideas are particularly relevant to digital audio. The proliferation of digital audio technology in the early 1980s left many people unprepared, especially audio professionals. Analog audio thinking permeated the digital world. Suddenly, people who had worked in analog for decades had to accept a whole new set of precepts antithetically opposed to a lifetime of learning: digital tape copies are sonically identical to the original, cables carrying digital audio make no audible difference, any differences in sound quality between digital media are attributable to analog phenomena (A/Ds, D/As, line sections, etc.).
Recently, however, these principles of digital audio that were accepted without question have come under closer scrutiny. Many people's real-world experiences are in conflict with established science. As a result, a whole set of tenets relearned for the digital age has been called into question. Do optical cables sound different from coaxial cables? Do different optical cables have their own sonic signatures? Do CD transports have audible differences even if it can be proved that their bit streams produce identical data? Until just recently, I would have answered an unhesitating "no" to these questions. Now I'm not so sure. My confidence in established digital audio theory was shaken by the demonstration of JVC's K-2 Interface, described in last month's "Industry Update" column.
This review gives me an opportunity to explore these questions (footnote 2). The Musical Fidelity Digilog and the Arcam Black Box represent the first wave of a flood of outboard D/A converters. Physically separating the analog electronics from player servos and digital noise has advantages. The analog section does not "bathe" in the radiated digital noise of the player. Digital noise can still get into the analog electronics if a coaxial cable connects the transport and digital processor: both units share the same ground through the coaxial shield. When the optical cable is used, however, the analog section is also electrically isolated from transport electronics.
Musical Fidelity Digilog
After unpacking the Digilog and examining its cabinet, I was surprised to learn that it cost under $1000. The heavy metal chassis and thick (¼"), machined faceplate seemed to belong to a much more expensive unit. The Digilog's front panel contains a row of four pushbutton switches and corresponding status-indicating LEDs. The user must select the input, whether DAT, CD, or optical. The fourth pushbutton/LED combination reverses absolute signal polarity. Two other LEDs appear on the front panel: a deemphasis indicator and an LED marked "LCK" that illuminates to show that the Digilog has locked-up to the incoming data stream. When lock is achieved, a relay click can be heard inside the unit.
Inside, the Digilog's component quality appeared equally high, with a large ILP toroidal transformer, metal-film resistors, and capacitors marked "Specially made for Musical Fidelity" (footnote 3). The Digilog's circuit topology is nearly identical to Musical Fidelity's preamplifiers, each stage having its own regulated power supply.
Like the Arcam Black Box 2 (and countless other players and decoders), the Digilog uses the Philips TDA1541A dual D/A converter and SAA7220P/B digital filter chip. The TDA1541 dual-DAC is available in three grades, listed in ascending order of quality: R, A, and S1 Crown. This designation, appended to the TDA1541 model number, identifies how well the DAC performs regarding overall linearity. Although they all start out as generic TDA1541s, manufacturing tolerances create performance differences. The DACs are measured and grouped into performance (and price) categories (footnote 4). Antony Michaelson of Musical Fidelity explained that they chose not to use the more expensive version of the chip because their listening test revealed no sonic differences between them. However, they did select the premium grade SAA7220P/B filter chip. Confusingly, the "B" designated filter chip is superior to the "A" designation, unlike the DAC.
My only complaint about the Digilog's construction is the flimsiness of the RCA jack mountings. To reduce point-to-point wiring (and cost), all jacks are mounted on the PCB. When plugging in RCA cables, the jacks moved, flexing the circuit board. It's a shame that such an otherwise well-constructed unit didn't get good, panel-mounted RCA jacks.
Before listening to the Musical Fidelity converter, I left it turned on for several days. Digital/analog converters are very temperature sensitive, working their best only when warm.
The Digilog was compared with the Arcam Black Box 2, Theta DS Pre, and the just-refined Precision Audio DIVC-880, a modified Philips 880 player I reviewed in Vol.12 No.8. The same playback system and source material was used in evaluating each decoder. Starting with the guitar and bass recording, I heard a more natural tonal balance on the guitar. Through the Digilog, it sounded more like the live mic feeds to which I had grown accustomed. The midrange had a warm, yet uncolored quality that more accurately represented the sound of the real guitar. This neutrality extended to other aspects of the frequency spectrum. Treble was smoother and more laid-back than the Black Box 2, but still had a slightly strident edge when compared with the Theta DS Pre. In contrast with the Black Box 2, bass was taut and controlled, with excellent definition, though not matching the DIVC-880, an area where the Precision Audio player excels. Low-frequency impact was particularly impressive, contributing to the Digilog's sense of dynamics. Musical climaxes were presented with a sense of power and ease not heard through the Black Box 2 or the DIVC-880.
That brings me to the Digilog's best characteristic: the ability to reveal subtle detail lost in other CD players and decoders. Playing a CD I engineered of a five-piece, straight-ahead jazz group (recorded live to DAT with tube microphones) was particularly revealing. During the ensemble playing, the saxophone was clearly delineated from the flugelhorn. The breathy quality of the sax, previously obscured by the flugelhorn, suddenly became apparent. I had not been made aware of this before, despite having heard the recording countless times. I had the same experience with another recording I am very familiar with Light as a Feather. Subtle percussion effects in the back of the soundstage came to life. However, this increase in clarity was not the result of a shallow soundstage in which all instruments sound close. On the contrary, the soundstage had remarkable depth, though it still fell short of the transparent, see-through quality of the Theta. However, the Digilog's ability to resolve detail and present that detail in its correct spatial perspective, plus its reasonably neutral tonal balance, added up to a very enjoyable musical experience.
Incidentally, when I connected a 48kHz S/PDIF signal from a DAT machine to the Digilog's DAT input, I heard a periodic burst of clicks, reminiscent of the sound a decoder makes when it won't lock to the incoming data. It turns out that there is a trim pot (RV1) that adjusts the detection threshold of the incoming pulses. Somehow, the review sample was misaligned, necessitating my adjusting the pot until the clicking stopped. I hope my sample is not representative of the production run: end users should not have to open the case and adjust trim pots.
The Digilog is certainly a notch above other CD players and decoders in its price range. The fact that I brought out the much more expensive Theta to discover its liabilities speaks highly of it. The Digilog had excellent dynamics, detailed bass articulation, uncolored midrange, spacious soundstage, and ability to resolve detail, but fell short in all these areas when put next to the Theta. My only complaints are the flimsy RCA jack mountings and slightly edgy treble presentation. However, considering the Digilog's $995 price, these caveats are minor. In short, the Digilog does everything very well, without any serious deficiencies. I highly recommend the Digilog as an inexpensive way to greatly improve the sound of your CD player.
Footnote 1: Alvin Toffler, in his book Future Shock, writes "Future Shock [is] the shattering stress and disorientation that we induce in individuals by subjecting them to too much change in too short a time." Or, as a card pinned to JA's office door notes: "There has been an alarming increase in the number of things I know nothing about."
Footnote 2: Perhaps it would be wiser to heed Plato's advice in Dialogs, Parmenides: "You are young, my son, and, as the years go by, time will change and even reverse many of your present opinions. Refrain therefore awhile from setting yourself up as a judge of the highest matters."
Footnote 3: Musical Fidelity's products were known as British Fidelity in the USA at the time of this review, due to the appropriation of the Musical Fidelity brandname by a US retailer.
Footnote 4: See JA's excellent discussion of the TDA1541 in Vol.12 No.6, as part of his review of the Philips LHH1000 CD player.