Weiss Engineering DAC502 D/A PROCESSOR
Stereophile|August 2020
Weiss Engineering DAC502 D/A PROCESSOR
Hi-fi system resolution has long been the cause of heated arguments. But when it comes to converting digital data to an analog signal, there can be no argument.
JOHN ATKINSON

Data go in at one end of a DAC and an analog signal comes out of the other end, with a noise floor directly rated to the combination of the converter’s digital and analog resolution. Ever since I started measuring digital products for Stereophile, I have been expressing a D/A processor’s effective resolution in terms of the equivalent number of bits. With a typical FFT-derived analysis of 16-bit data, the levels of the individual FFT bins lie around 130dB below full scale. When the noise floor drops by 6dB, that’s equivalent to another bit of resolution.

Two of the highest-resolution D/A processors I have measured have been from Swiss pro-audio company Weiss Engineering: the Medea, which Kalman Rubinson reviewed in February 2003,1 and the Weiss DAC202, which Erick Lichte reviewed in January 2012.2 Both offered superb resolution— almost 20-bit performance with the Medea and 21-bit with the DAC202—and both paired that resolution with sound quality to die for. “The Medea . . . remains in my mind as one of the only digital systems I’ve heard that could compete with the very best that vinyl has to offer while still doing what digital does best. In other words, there were warmth and musicality, staggering dynamics, and real silent backgrounds,” wrote Kal. Erick concluded that the DAC202 was “easy to recommend for those who want a digital system that doesn’t sound ‘digital.’ The Weiss . . . offers a sound that will be very pleasing to many audiophiles tired of fatiguing hi-fi sound.”

Now comes the subject of this review, the DAC502, which costs $9850, and while it doesn’t have the DAC202’s FireWire input, it offers USB and Ethernet connectivity and adds a balanced headphone output.3

Design outside

The DAC502 is a utilitarian-looking component, with a black-finished steel chassis with a damped top panel—this connected to the main system ground with a wire—and a chamfered aluminum front panel that’s 10mm thick. On the left of the front panel is a 1/4 headphone jack. On the right is a rotary control, and next to it a fairly small four-color touchscreen. In use, this panel displays the source, whether the line or headphone outputs are selected or muted, the sample rate, the metadata text when the DAC is receiving network data, and DSP and Setup information. A short push on the rotary control activates the Menu function; the control then acts as a scroll wheel, allowing various options to be selected and adjusted with the touchscreen; more on this later.

On the back panel are the IEC AC power inlet; an array of digital inputs—AES/EBU, coaxial and optical S/PDIF, USB Type-A for connecting external storage, USB Type B, and Ethernet (Roon Ready or UPnP)—balanced and single-ended output jacks; and a 4-pin XLR jack for driving headphones in balanced mode.

Pressing the power switch on the front-panel rotary control—short push for on, long push for off—or on the remote control operates a semiconductor relay that only switches at zero crossings of the mains voltage to ensure glitch-free switching. Mains-voltage selection is done automatically by measuring the mains voltage before power is applied to the rest of the electronics.

The DAC502’s complexity resides within.

Design inside

Looking inside the DAC502 left an impression of a component constructed to a high standard. The DAC502’s circuitry is split into two. A large printed circuit board running front to back behind the display carries the power supply with its two toroidal transformers. Separate voltage regulators provide power to the left and right channels. The input-receiver circuitry and the signal-processing module are also mounted on this board, and a small daughterboard carries a Texas Instruments Arm Cortex-A8 microprocessor chip.

A ribbon cable connects this board to a completely shielded module that houses the D/A conversion and output stages. Digital-to-analog conversion for each channel is handled by a pair of ESS Sabre 32-bit DAC chips, these clocked, Weiss says, with a high-precision/low-jitter generator. The clock and DACs operate at a fixed sample rate of “about 195kHz,” which is the frequency that results in optimal performance from the DAC chips. While the DAC502 will accept all the standard PCM sampling frequencies up to 384kHz, as well as DSD64 and DSD128, the data are sample-rate–converted to PCM at 195kHz before being presented to the DACs.

Digital signal processing

The DAC502’s core functionality is controlled with a fourth-generation Analog Devices SHARC DSP (digital signal processing) chip. The following DSP algorithms are implemented:

  • Room Equalizer can apply high-shelf and peaking/notch filters to deal with low-frequency room modes.
  • Creative Equalizer is a tone control with low boost/cut, high boost/cut and mid boost/cut.
  • De-Essing automatically removes overly bright sibilance from human voices. Two modes are offered: “Surgical” and “Smooth.”
  • Constant Volume, aka Dynamic Adaptation, is a “party mode” that normalizes loudness for all the tracks played.
  • Vinyl Emulation allows “that special sonic character of a record player based playback chain” to be applied.
  • Crosstalk Cancellation (XTC) compensates for the fact that with loudspeakers, the left ear also hears the right channel’s output and vice versa. This mode allows dummy head, binaural recordings to be correctly played back on loudspeakers. The user has to enter their head width, the separation of the loudspeakers’ centers, and their distance from the listening position.
  • Loudness Control is promised for a future firmware upgrade. It will equalize the output to compensate for the ear-brain’s differing frequency sensitivity at different listening volumes.
  • Headphone Equalizer is another yet-to-be-implemented function; it will adjust the frequency response of the headphone output to suit the listener’s ears.

Once you have chosen the parameters for each of these functions, the settings can be saved as a snapshot and recalled at the touch of a button. I report on the effect of some of these DSP settings below.

Setup

The DAC502 can be controlled in three ways: with the touchscreen and rotary control; with the supplied metal remote; or with a web browser, by entering the address http://dac502-serial number.local. Both web and front-panel interfaces provide access to volume, balance, mute, and polarity-inversion controls. Also selectable there is a choice of four full-scale output levels: “0dB,” “–10dB,” “–20dB,” and “–30dB.” I wanted to connect the DAC502’s balanced outputs directly to power amplifiers from Lamm, Parasound, and Classé, controlling volume with the DAC502’s high precision volume control while remaining near the top of its range. The “–10dB” setting, equivalent to a maximum level of 2.2V, was the best choice for achieving those aims.

I connected the DAC502 to my network, opened the local webpage, and checked for firmware updates. (“FW is up to date,” it told me.) The processor was recognized by the Roon app as “Weiss DAC502,” and Roon allowed me to control its volume. (The Roon volume setting was immediately reflected in both the local webpage and on the front-panel display; the webpage duplicated Roon’s transport controls and displayed the artwork of any album that had been selected with Roon.) I was ready to play music.

Listening

The immediate impression was of extraordinary clarity. This wasn’t as if the edges of the objects within the soundstage had been enhanced, as can be done to images with PhotoShop, but as if the pixel count of the image had been increased. It didn’t manage this by emphasizing treble detail, but to resort to an audio reviewer cliché, the DAC502 cleaned the window into the recorded soundstage to an impressive extent.

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August 2020