John Darko
In a recent video, I said that I didn’t see the utility of multi-room streaming for smaller apartments; that if I wanted to hear music while I was upstairs in my 80sqm one-bedroom duplex, I’d simply turn up the volume on whatever was playing downstairs. And yet the arrival of the WiiM AMP Ultra has made a liar out of me.
I didn’t want to tear down the high-end system I’d built in the lounge room – a pair of Vivid Kaya 45 floorstanders driven by a Marantz Model 10 and fed by a Grimm MU2 – to review the little WiiM. Besides, people might grumble that my acoustically treated room isn’t sufficiently ‘real-world’ (their words, not mine). I wondered if, with some careful storage redistribution, I could clear the shelves in my upstairs hallway to make way for a mid-century modern sideboard and a pair of standmount loudspeakers. Why the hallway? With hi-fi taking over most corners of my life, I have a rule: no hi-fi gear in the bedroom.
The result spoke for itself: a more modestly priced amplifier operating in a 3m x 4m space and – crucial to this story – untouched by physical acoustic treatments. I need only clap my hands to expose the room’s 750ms reverb time. That’s probably similar to the listening spaces used by the AMP Ultra’s target audience. Welcome back, ‘real world’.
Putting the (previously reviewed) €369 WiiM AMP and €599 AMP Ultra next to one another on the sideboard, we see that the AMP’s footprint is slightly smaller than the AMP Ultra’s – and that it isn’t as tall as the newcomer – but that they share the same rear-panel connectivity: line-level analogue, TOSLINK, HDMI ARC and USB-A for the direct connection of storage devices.
There are some cosmetic differences too: the Ultra wears a 3.5″ touchscreen on its front panel and has shed the binding posts from its rear. Don’t panic: WiiM has put banana plugs in the box; and that box still looks and feels like an Apple MacBook box; and the network onboarding process still feels as Mom-friendly as a (pre-app-debacle) Sonos product.
Build quality on the Ultra doesn’t stray from the ‘nicely done’ spirit of the AMP, the €459 AMP Pro (which I own but haven’t reviewed) and the €399 Ultra DAC (which I have reviewed). The overall fit and finish still feels about right for the money. And the top panel feels warm to the touch after an hour’s use, but it’s nothing that would harm tiny, inquisitive fingers.
The listening seat in my new space sits 2 metres from each speaker. Some might call this near-field but the Ultra AMP’s touchscreen remains out of arm’s reach. It’s a toss-up as to which is the faster way to pause music: get out of the chair to press the volume wheel or pull up a smartphone to fire up the WiiM Home (or other) app. The answer is neither — the most efficient way to play/pause, change volume, skip the Red Hot Chilli Peppers or activate presets is with the supplied Voice Remote 2.
The WiiM’s touchscreen – like that found on the Ultra DAC – shows cover art and metadata in a choice of layouts. Or we might prefer a VU meter. The screen also allows us to change inputs, outputs (loudspeakers, USB or Bluetooth) and choose EQ presets; but we cannot browse a streaming service’s library. For that, we still need a smartphone app.
Beware iPhone users! The Ultra – like the Amp Pro – does NOT support Apple AirPlay 2. Whenever I have asked WiiM about this omission, they have stood behind a wall of “no comment”. Fair enough. The whys and wherefores are their business, not ours.
The AMP Ultra’s Roon Ready certification is still in process, so I fell back to the Google Cast input, but I could have just as easily gone with Squeezelite. We get all the Connect services – Spotify, Tidal and Qobuz – with numerous other streaming services folded into the extremely comprehensive WiiM Home app.
But wait: I am getting ahead of myself.
My upstairs hallway is too far from the router downstairs to run an Ethernet cable directly to the AMP Ultra, so wi-fi it is. The WiIM pulled down a firmware update on first boot. The five minutes needed for its download and installation gave me time to place the Vivid Kaya S12 on either side of the sideboard and ready some AudioQuest speaker cable.
With two Texas Instruments TPA3255 Class D amplifier chips in play, the AMP Ultra promises 100wpc into 8 Ohms. That’s 40 wpc more than the AMP and AMP Pro’s single-chipped implementations. What about a 4 Ohm rating? Oddly, that’s not on the spec sheet. I had to ask about it at Munich High-End 2025: 200wpc.
Unlike the AMP and AMP Pro, the AMP Ultra is, according to my WiiM contact, stable down to 2 Ohms. But the AMP Ultra also inherits the AMP Pro’s “Post-Filter Feedback (PFFB) technology”. From WiiM’s German website: “Unlike conventional amplifiers, which suffer from load-dependent power fluctuations, PFFB dynamically compensates for these fluctuations, delivering a more precise, balanced, and natural soundstage.”
Say what now? My best understanding is as follows. Our chosen loudspeaker might be rated at 4, 6 or 8 Ohms, but this “nominal” value is an average of the speaker’s input impedance measured at various frequencies. Impedance variations can (but not always) mess with an amplifier’s frequency response. Lower impedances call for more current, higher impedances less. These ever-changing current demands must be met by the amplifier’s power supply and WiiM’s ‘PFFB’ tech attempts to smooth out any perturbations.
Perhaps PFFB and the increase in output power are two reasons why the AMP Ultra delivers more dynamic punch in the low end, a little more refinement in the treble and, most noticeably of all, higher midrange clarity than the AMP. That’s with the 2025 remaster of Fila Brazillia’s Maim That Tune.
The DAC inside the AMP Ultra is built around an ESS 9039Q2M chip, but that’s not a particularly helpful specification when we’re told nothing about the DAC’s power supply or its analogue output stage. They might have been improved for the AMP Ultra, or they might be the same as the AMP Pro. I’ve said it before and I’ll say it again: pre-judging a DAC on its decoder chip is like shopping for a house based on what can be seen through the front door letterbox.
The fly in the 2.0-system ointment is the Marantz Stereo 70s. Its 75wpc of Class A/B power into 8 Ohms sounds altogether beefier than the WiiM. That said, the WiiM’s more skeletal take on Thomas Fehlmann’s Gute Luft lends its dense layers of electronic stabs and percussive ticks cleaner separation. Hello, side-by-side comparison #2!
The Stereo 70s is a full-width streaming integrated that consistently sells for €650 in the EU. That puts it within spitting distance of the AMP Ultra. The more traditionally styled Marantz amplifier doesn’t support Google Cast or Squeezelite, but the HEOS-based streaming system adds Apple AirPlay 2 and Roon Ready to the three Connect services – Spotify, Tidal and Qobuz – and its in-app integrations.
Furthermore, the Marantz’s MM phono input is a nice bonus for vinyl spinners and its rear panel HDMI sockets can pipe a ‘now playing’ screen directly to a TV without the additional expense of an Apple TV and partnering app. That’s not to discount WiiM’s tvOS app, which, for me at least, remains far more visually impressive than its touchscreen.
More worryingly for WiiM, the Stereo 70s contrasts the AMP Ultra as sounding thinner and tonally greyer when playing Was (Not Was)’s “Wheel Me Out”; and the Marantz soounds less strident in the upper mids with lower-fi recordings like The Soft Boys’ Underwater Moonlight, which celebrates its 45th anniversary with a new remaster. Bottom line: the AMP Ultra does not ‘blow the competition out of the water’.
Better audible results might come from connecting a WiiM Ultra DAC to this or any other third-party integrated amplifier – I can’t say for sure – but as will soon be made clear, for my upstairs hallway setup, I need the WiiM AMP Ultra’s computational power more than I need the Marantz’s chunkier, richer sound. And I need that computational power sitting in the same box as the volume control.
The differences between the Marantz and the WiiM might also come down to a matter of perspective. I see the Stereo 70s as an integrated amplifier with an internal DAC and streaming front end, but I see the WiiM AMP Ultra as a streaming computer with an amplifier module attached. And that streaming computer allows us to push the sound of the WiiM in numerous directions via its subwoofer management, which is far more sophisticated than Marantz’s – and its RoomFit EQ room compensation that the Stereo 70s doesn’t do at all. And if you’re using both (as I am), you’ll want to integrate the subwoofer before running the room correction.
I don’t hear anything from the Kaya S12 that suggests the new WiiM box isn’t up to the task but it is emphatically lighter on low-end punch than more expensive amplifiers like the Technics SU-R1000 and Luxman L-505Z. The AMP Ultra’s bass-lite gestalt with the Vivid Kaya S12 forces me to add a subwoofer, if only to put me in more reliable contact with frequencies playing below 40Hz. However, as many know, integrating a subwoofer is a lot of work, even for experienced ears, and WiiM’s software lays the foundations for some important lessons.
I hooked a KEF KC62 into the WiiM’s single sub-out socket and set the crossover point inside the WiiM Home app. But wait! The app also asks us 1) if we want a high-pass filtered or full-range signal going to the loudspeakers and 2) if we want a low-pass filtered or full-range signal going to the subwoofer. It’s nice to have options, even if those options don’t extend to the filter slope choices offered by Lyngdorf’s software system. The most affordable Lyngdorf – the TDAI-1120 – sells for almost four times the price of the WiiM AMP Ultra.
Me? I’d rather the WiiM do the low-pass filtering than the KEF KC62. And because the Kaya S12 is a two-way standmount where the main driver handles midrange and bass, I prefer to relieve it of low bass duties with a high-pass filter, which in turn lowers the current demands put on the amplifier by the loudspeaker. Win-win.
It goes further. The on/off toggles that accompany each setting recast the WiiM Home app as a teacher. This amplifier is where newcomers and/or old timers stuck in their ways come to learn first-hand about what makes a difference to the sound of their loudspeakers and their subwoofers in their systems.
Also dispensing with the second-guessing is the Home app’s options for subwoofer delay: manual or automatic. The Wiim Home app’s wizard plays test tones that are ‘read’ by the smartphone’s microphone and returned to the app for analysis. Both iOS and Android are supported but microphone type varies more with Android, so I used an iPhone 13 Mini.
The WiiM app’s Sub-Speakers Sync Test reported that the KEF sub sitting 50cm in front of the loudspeaker plane was running 2ms behind the Vivids. The app, therefore, set the loudspeaker delay to 2ms. Did I trust that result? Not until I’d confirmed it with the manual slider. I played a few cuts from Rhythm & Sound’s eponymous 2001 album and listened for the delay setting that had speakers and sub audibly ‘thwump’ into a single source. That happened at 2ms.
WiiM’s RoomFit is similarly sophisticated but tucks some of its more advanced features behind a small settings wheel. Blink and you’d miss it. Via another wizard, RoomFit plays test tones for 1) the smartphone to ‘read’ at the listening position with which 2) the app calculates ten points of parametric EQ adjustment. We can optionally tweak those individual points once the measurement is done, but I left well alone. The frequency, gain and Q settings automatically chosen by the app opened up the soundstage enough for me to leave room correction turned on whilst savouring Thin White Rope’s The Ruby Sea in its entirety.
However, I made one important settings adjustment before running the room compensation wizard: I curtained the correction at 300Hz. Why? Because previous experience has told me time and again that room correction software does nothing for a room’s reverberant behaviour in the mids and highs. My hallway space is far more reverberant than the listening room downstairs (RT60 = 200ms) and WiiM’s RoomFit EQ – predictably – did nothing to bring that reverb down. How could it? Room compensation software’s strongest suit is tackling bass resonances below the Schröder frequency (100 – 200Hz in most rooms).
But here again, teachable moments abound. WiiM’s Home app gives us the option to exclude the subwoofer from the room correction and to choose if we want to correct the left and right loudspeakers individually or together as a unified stereo system. We get to decide what’s best for our loudspeakers and (especially) our room’s acoustics. Deeper divers can try one of three different target curves. I went with Harman for no other reason than it was the default choice. And if that’s not enough, RoomFit’s multipoint measurement system is already in beta.
With the subwoofer integrated, the 2-way standmounts high-pass filtered and the resulting 2.1 system ‘room corrected’ in the bass, I could forget all about the Marantz Stereo 70s. So too the Marantz Model M1, where a US$249 Dirac room correction software licence is added to the amplifier’s €999 asking price to push it beyond the realm of financially comparable units. From what I recall, the Model M1’s HEOS system doesn’t offer time alignment settings for subwoofers.
Lastly, I went back to the WiiM AMP and ran the subwoofer sync test and RoomFit correction again on the same Vivid loudspeakers and the same KEF subwoofer. And with the lower frequencies handled by the subwoofer’s internal amplifier (this time with a 6ms speaker delay 🤷🏻♂️) and WiiM’s RoomFit taking a broom to the room’s bass resonances (with almost identical PEQ values to the AMP Ultra’s measurement), I still noted a hit to midrange transparency and more greyness in the uppermost treble, which the Vivids keenly expose. The AMP Ultra is also the more tonally colourful of the two. Even when DSP does the heavy lifting, the costlier amplifier sounds better than the cheaper unit. Another side-by-side comparison that says we get what we pay for.
Now comes the BUT: once engaged successfully, the DSP-based subwoofer integration and room compensation common to all WiiM AMP models bring more audible uplift than the move from the AMP to the AMP Ultra whose amp chip count doubles to two and whose PFFB circuitry offers some degree of immunity to a loudspeaker’s impedance swings. WiiM’s DSP does more for the listening experience than the adjacent audio circuitry. Furthermore, WiiM’s OS does more for the end user than any other audio software system currently available, regardless of price. That all of this is taking place at hi-fi’s entry-level is an incredible achievement (and a huge irony). Take a bow, Team WiiM — I now have a multi-room streaming system sitting upstairs in my apartment.
Further information: WiiM
