Weiss Engineering Helios D/A processor

When standalone digital/analog processors made an appearance a quarter-century ago, they were limited to the CD medium’s 16 bits of resolution—at best. These days, almost every DAC can process at least 24 bits, and many models offer between 20 and 21 bits of real-world resolution. Modern models from Benchmark, dCS, , Merging, Mola Mola, Okto, and Weiss illustrate not just the skill of the circuit designer but also that of the engineer who laid out the printed circuit board.

One of the first digital processors I encountered that offered 21 bits of resolution was the Weiss DAC202, which Erick Lichte reviewed in January 2012. Subsequent processors from this Swiss company have consistently performed well, not just on the test bench but also in the listening room.

This was particularly true of the Weiss DAC502 I reviewed in the August 2020 issue (footnote 1). I concluded that review by writing, “The Weiss DAC502 retrieves more information from the digits than any other DAC I have auditioned, with the possible exceptions of the Chord DAVE and dCS Vivaldi, both of which are long gone from my system and neither of which has either a headphone output or DSP functions.” Notably, that superb transparency to the recorded data was not accompanied by glare or exaggerated treble detail. “To resort to an audio reviewer cliché,” I wrote, “the DAC502 cleaned the window into the recorded soundstage to an impressive extent.”

The DAC502 is currently priced at $10,995. The latest Weiss DAC, the Helios, which Jason Victor Serinus reported on at the 2023 High-End Munich show, is considerably more expensive, at $21,995. Intrigued to find out what the additional dollars get the owner, I asked for a review sample.

The Helios

On the face of it, the Roon Ready Helios looks identical to the DAC502: a slim, anodized aluminum chassis, though now with a stainless steel internal frame. There is still a control knob at the far right of the front panel; a four-color touchscreen next to it; AES3, optical and coaxial S/PDIF, USB Types A and B, and Ethernet digital inputs; and balanced and single-ended analog outputs. But on closer inspection, the Helios lacks the earlier processor’s headphone jack. It can still be used with headphones, however: Using optional adapter cables ($495), the Helios can drive headphones from its balanced and unbalanced outputs. This is made possible by Weiss’s new, proprietary OP2-BP discrete operational amplifiers (below), used four per channel in the analog output stage. The output mode can be switched between Loudspeaker and Headphone, and the DSP options now include settings for use with headphones.

In addition to the new op-amps, the Helios offers an upgraded digital-to-analog stage. While it uses the same eight-channel, 32-bit ESS Sabre ES9038PRO HyperStream II D/A converter chip, the Helios uses four of the DAC channels operated in parallel for each analog output. The DAC502 uses two DAC channels in parallel for the speaker feed and two for the headphone feed. The ES9038PRO will handle PCM data sampled up to 768kHz and native DSD1024 data; Weiss says that the Helios uses a “high-precision/low jitter clock generator for ultra-stable clocking of the D/A converter section.”

The Helios offers the same digital signal processing (DSP) functions as the DAC502 (although the headphone-related DSP functions had not yet been implemented when I auditioned the 502), realized with an Analog Devices SHARC chip. The following DSP algorithms are implemented: Room EQ, which can apply high-shelf and peaking/notch filters to deal with low-frequency room modes; Creative EQ, which applies low, mid, and high boost/cut; DeEsser, which removes overly bright sibilance from human voices; Dynamic Adaptation, a “party mode” that normalizes loudness; Vinyl Emulation, said to provide “that special sonic character of a record player based playback chain”; Crosstalk Cancellation (XTC), which allows binaural recordings to be correctly played back on loudspeakers; and Loudness Control, which equalizes the output to compensate for the ear-brain’s differing frequency sensitivity at different listening volumes. 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 on the control webpage or the metal remote control.


Like the DAC502, the Helios can be controlled in three ways: with the touchscreen and rotary control; the aforementioned metal IR remote control; or with a web browser by entering the address https://[helios-serial-number].local. The web and front-panel interfaces allow setting the volume, balance, mute, and polarity inversion controls, those DSP settings, and a choice of maximum output levels: “0dB,” “–4dB,” “–8dB,” “–12dB,” “–16dB,” “–20dB,” “–24dB,” and “–28dB.” I set the processor’s output level to “–12dB,” equivalent to a maximum level of 4.1V balanced and 2.05V unbalanced.

Once I had connected the Helios to my network and opened the local webpage, I was able to check for any firmware updates. (“FW is up to date,” it told me; the review sample was running v2.7.0 firmware, revision r3161, dated “2023-02-14.”) The Roon app processor recognized the processor as “Weiss Helios,” allowing Roon to control its volume. The Roon volume setting was immediately reflected on the front-panel display and mirrored in the local webpage. The webpage duplicated Roon’s transport controls and displayed the artwork of any album selected with Roon.

I noted something unusual with Roon. With PCM data sampled up to 192kHz, clicking on “Weiss processor Synchronization” in Roon’s “Signal path” window gave the following message: “The audio is being converted to a 195.312kHz sampling frequency for optimal signal quality and to help reduce any jitter related effects.” The same was true for DSD64 and DSD128 data, both of which the Helios first converted to 176.4kHz PCM before resampling.


I started my auditioning with the Q Acoustics 5040 loudspeakers I reviewed in the January 2024 issue, driven by a pair of Parasound Halo JC 1+ monoblocks. After the Q Acoustics speakers had been returned, I used my content/kef-ls50-anniversary-model-loudspeaker”>KEF LS50 minimonitors, then replaced the Parasounds with the Audio Research I/50 integrated amplifier I last wrote about in the February 2024 issue. I subsequently replaced the Audio Research with my NAD M10 integrated and the KEFs with Golden Ear BRXes. I ended the auditioning by returning to the Parasound monoblocks. I used Roon for all critical listening.

I reported on the effect of the DSP functions in my DAC502 review, so I won’t repeat my findings here. Like the earlier Weiss DAC, the Helios’s parametric EQ was useful in boosting and extending the low frequencies of the speakers I used for my auditioning. (I used a Low Shelf filter set to give a 3dB boost below 100Hz with a Q of 1.40.)

Throughout the changes of amplifier and loudspeakers, the Helios echoed the DAC502’s extraordinary clarity but with an enhanced sense of involvement with the music. I listened to the recordings I had used for my DAC502 review—both my own and those recorded by other engineers—with the Helios. It is fair to note that I hadn’t had the earlier processor in my system for more than three years, but if I had to swear on the very first issue of Stereophile, this impression was consistent throughout my auditioning of the Helios.

Footnote 1: Jason Victor Serinus also reviewed the Weiss DAC502 in October 2020.

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Weiss Engineering Ltd.
Florastrasse 42
8610 Uster
(416) 638-8207


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