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 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.

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

georgehifi's picture

Wow!!! stunning set of measurements JA, must have a listen to this one.
Direct in to the poweramp/s with this baby, (hope you got to do this with the Halo's JA??), nothing says to me more that active preamps are obsolete and a backward sonic step when used with this dac, like these two sentences of your measurements.
JA: "
"Helios's maximum output level at 1kHz feeding 100k ohms was 16.4V with the level set to "0dB"
"The balanced output impedance was 93.5 ohms at all audio frequencies in both Loudspeaker and Headphone modes; the unbalanced output impedance was 47 ohms in both modes."

Cheers George

cognoscente's picture

But then again, that price? How does that compare to everything else? Are such prices still in proportion to everything else in life? Someone who buys this, how much does he pay for a bottle of good wine? For a good coat? For an armchair? For a car? 800? 4K? 20K? 400K? Then it would be proportionate. Of course everyone has their own thing, choice (freedom), hobby and pleasure. Naturally! I just wonder.

georgehifi's picture

At least with this, you'd save thousands by not having to have a preamp and be better off sonically for it.

Cheers George

Scintilla's picture

I ran direct for many years from an NAD M51 using its volume control, then a D90 for another year and finally a Holo May for about 6 months before adding back a Holo Serene preamp to provide better gain-matching for my system. Not only did that addition drastically improve the sound quality it also allowed me to have proper gain matching. There are plenty of utterly transparent preamps on the market and they serve a useful purpose beyond source switching. I believed the dogma for too long that no preamp was the best preamp and I have seen the light. So have a lot of us that went all digital a long time ago and have ben using digital gain structures. The May and the Serene are designed for each other and work and sound magnificent, and much better than the May direct using a digital volume control in HQPlayer. This hobby isn't about "saving thousands" it is about getting the best sound quality -for the dollars- and that doesn't mean eliminating a useful component because it costs money. Listening isn't about theories, its about listening, with your ears, not your ideas.

georgehifi's picture

If you go direct and have enough volume level for listening up to your loudest level with the quietest recording you have, then you have enough gain. (and are "gain matched")
Any more gain by adding an active preamp is not going help it sound any better "what so ever" if anything it's adding more noise and distortion.

And as far as impedance matching, the Weiss Helios D/A processors output stage is perfectly impedance matched for any poweramps input impedance.

And I repeat: "At least with this, you'd save thousands by not having to have a preamp and be better off sonically for it."

Cheers George

JRT's picture

I want to preface my comment with sincere thanks for another well considered and well written review in combination with extensive measurements and associated commentary (a lot of work, and very well done), before continuing with some negative criticism of the component that was the subject of the review.

"...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." — J.Atkinson

That would seem to imply that changing output from loudspeakers to headphones requires some cable swapping, detaching the cables interconnecting the rear ports to the loudspeaker power amplifiers, and connecting an adapter cable to those rear ports to power the headphones. To me that seems like a truly shameful asnine engineering solution on a product marketed at a $22k pricepoint, a workaround that might be acceptably accomodated on some kid's entry level cheap-fi system. This should have proper headphone ports on the front panel, classic conventional 1/4 inch (6.35mm) TRS for single ended stereo headphone connection, and the newer 4.4mm Pentaconn for "balanced" (differential) stereo headphone connection, while using internal relays for the switching, and a proper control system.

Scintilla's picture

I know what gain matching is. I also know how to use a network analyzer. In my system, I apply room correction filter in a convolution engine and I have insertion loss so having 6db of clean, class-A gain available without resort to digital is very helpful so I can keep well under the threshold for digital overs/clipping. You do it your way and Ill do it mine. But in my system, I know which way sounds better because I have listened.

georgehifi's picture

Scintilla: "I can keep well under the threshold for digital overs/clipping" "George, I'm an EE"

JA: Even set to its highest output level, the Helios produced very low levels of harmonic distortion with full-scale data even into the punishing 600 ohm load"

Cheers George

Glotz's picture

the Swiss Army knife of digital.

After reading this review I thought that this product is a landmark in the field of modern DACs.

I can see a lot of owners feeling like pros when it comes to tailoring their sound like no other. 20 grand is a steal for what it does after considering how expensive DACs can get.

georgehifi's picture

"20 grand is a steal for what it does after considering how expensive DACs can get."

Yeah, I've seen the preamp "aficionados" spend that much and more on active preamps they don't need, that are just adding more noise, colorations and distortions to the sound, that wouldn't happen if they just went direct instead.

Cheers George

Charles E Flynn's picture

It appears that a URL was not finished at this point in the text:

"After the Q Acoustics speakers had been returned, I used my content/kef-ls50-anniversary-model-loudspeaker">KEF LS50 minimonitors,"

John Atkinson's picture
Charles E Flynn wrote:
It appears that a URL was not finished at this point in the text: "After the Q Acoustics speakers had been returned, I used my content/kef-ls50-anniversary-model-loudspeaker">KEF LS50 minimonitors,"

Fixed. Thanks for the catch.

John Atkinson
Technical Editor/Part-time Web Monkey, Stereophile

Charles E Flynn's picture

You are welcome, and it is interesting to see that you are still using those KEFs.

georgehifi's picture

Hi JA: Interested to know what preamp you used with the JC1 Halo's, as you didn't state if you did or went direct.?

Cheers George

John Atkinson's picture
georgehifi wrote:
Interested to know what preamp you used with the JC1 Halo's, as you didn't state if you did or went direct.

I don't use a preamp, instead going direct and using the processor's digital-domain volume control. I have the Parasounds set to low sensitivity so the volume control is operating near the top of its range.

John Atkinson
Technical Editor, Stereophile

georgehifi's picture
ok's picture

but digital attenuators subtract information.

Glotz's picture

Many of them now.

ok's picture

..are less lossy according to their creators - but lossy nevertheless especially at lower volumes. I have extensively experimented with direct-to-poweramp modern dacs and I first thought they sounded clearer.. but they just sound simpler; your mileage may vary.

Glotz's picture

They sell a preamp module purposely for that need. To assume that modern active preamp all have undesirable levels if noise, etc. is naive. Technology has come a looong way.

Benchmark is a great example. They too, like most DAC makers, feel that their digital volume control sounds worse and measures worse than their stand alone active preamps. My experience and reviews find that totally true. DCS and others would be the exception. They clearly have spent enough and designed well enough to ignore a pre.

ok's picture

..but I generally agree that most dacs tend to sound better when connected to a decent active preamp. Added distortion is negligible, noise less so, but dynamics and nuance compensate for both.

georgehifi's picture

Going through an active preamp adds less detail, more noise, more distortions and more colorations.

Cheers George

ok's picture

instant swapping between direct mode and preamplification, so nothing to worry about in case of change of heart. Anyway there are also practical reasons for going preamp. First of all I use multiple sources and outputs (cd player, turntable, dac, tape, headphone amp) which render a control center sine qua non. Moreover with no preamp buffering an accidental push of a little button in the remote can turn on the dac's full output mode and blow the whole system apart.

georgehifi's picture

Even at the lowest level, the amplitude error is <1.1dB, which implies very high resolution. An increase in bit depth from 16 to 24, with dithered data representing a 1kHz tone at –90dBFS, dropped the Helios's noisefloor by 33dB (fig.6). This implies a resolution between 21 and 22 bits, which is the highest I have encountered

ok's picture

..I read and hear much better than you do. Now get off my back. I have no time for talking to a tape loop.

georgehifi's picture

Yeah right!! you hear real good.

Glotz's picture

I have read that the latest ESS ES9039MSPRO chip specifically addresses the 'IMD hump' in the past chip iteration.

What magic has Weiss wrought from a the '38 and would they see lower IMD from the new chip? Would it matter? Kudos to Weiss for creating a very special DAC.

Glotz's picture

Hilarious name even beyond 'Schiit' and released in December of 2023. Their new flagship. It even includes MQA-CD from coax and boasts a striking new design with tempered-glass fascia. The price point $1000 and measurements I've seen could be worth a listen and test. There does seem to be one note issue with DOA power after a week or two.

That being said, I would even rather the reviewers to test and listen to the new Holoaudio Cyan 2 at $1199 (or $1350 with shipping). "Equipped with R2R network and vector step resistor network at the same time. The R2R network is used for primary digital-to-analog conversion of the PCM stream, and the vector step resistor network is used for primary digital-to-analog conversion of the DSD stream."

There is support for DSD 1024x and up to PCM 1.536M (32bit). Being more at my price point for digital, I am impressed with either DAC's details.

RustyGates's picture

Hi JA, what was the RMS voltage level at the output when the impulse response was captured? I would like to know if the unit was able to rise to full 0dBFS when given an impulse sample, like the Mola Mola Tambaqui.

John Atkinson's picture
RustyGates wrote:
Hi JA, what was the RMS voltage level at the output when the impulse response was captured?

The Weiss's maximum output voltage was set to "-12dB" (4.1V RMS) for the impulse response measurement.

RustyGates wrote:
I would like to know if the unit was able to rise to full 0dBFS when given an impulse sample, like the Mola Mola Tambaqui.

It didn't have a problem in this regard.

John Atkinson
Technical Editor, Stereophile

bracondale's picture

at about $20k I would want to hear the forthcoming Grimm.

weiss2496's picture

Just a short comment on how good a digital level control can be these days. The quality depends on the quality of the D/A Converter. It should be as linear as possible and as low noise as possible. With today's high quality DACs the digital level control can yield extremely good results.
Of course dithering noise has to be applied. Dithering means adding a low level noise signal to the audio signal and then do the quantisation. Quantisation is required because the input word-length of a DAC is not high enough to accommodate for the output after the digital multiplication (i.e. the level control). As an example - if we have a 16 Bit audio signal and multiply that with a 16 Bit gain factor the result is 32 Bit long. For a 16 Bit D/A converter those 32 Bits have to be reduced to 16 Bits. This can be done by cutting them off (i.e. truncation which is bad) or by adding that dithering noise before cutting the Bits off. Dithering causes the quantisation error to become de-correlated from the audio signal and becoming pure noise.
Here are three listening examples with an 8 Bit (!) quantisation.

This example cuts off the bits after the level control to a mere 8 bits without adding dither noise:
The quantisation distortion can be easily heard.

This example adds dither noise before the 8 bit quantisation:
Already much better. The music is undistorted, just noisy because of the 8 bit resolution. The noise is not modulated by the music.

This example adds dither using a shaped noise, i.e. a noise which has a lower level at frequencies which can be heard and higher levels and very high frequencies:
An astonishing quality considering that the resolution is 8 bits (256 level steps).

Daniel Weiss

Glotz's picture

SQ depends on the quality of the D/A converter. Price of the product factors in heavily, I would assume.

georgehifi's picture

And it doesn't depend on cost, I've seen the same ESS ES9038PRO d/a converter used in the $899usd Topping D90SE dac with stunning objective measurements.
And then also used in the $40,000usd Gryphon Ethos D/A processor, 44 x the price, would be interesting to do a subjective listening A/B between the two.

Cheers George