Review: Niimbus Audio – US4+

Niimbus US4+

Audeze MX4


Audeze’s studio headphone sounds great when combined to the right amp but it can be a hit or miss. With the Niimbus US4+ it’s a hit and that’s no surprise really as the Violectric amplifier series are famous for their excellent synergy with the Audeze planar magnetic headphones.

In balanced mode the MX4 sounds powerful and very clear, yet it still has a slight smooth delivery. Bass has good/neutral body as you’d expect from a studio monitor, yet it isn’t the tightest, especially when compared to the HE-6SE. The mids are perfectly in line with the bass but the mids aren’t the most spacious though the separation is excellent. As we reported before the sound stage with of the MX4 isn’t the very best compared to other headphones, but for an Audeze it’s quite good.

The treble section is energetic and dynamic but soft. The extension and texturing in the treble region could be a little better but that’s not really the US4+’s fault.

In Single Ended mode you get a rather thin and light sounding MX4. Studio people will probably prefer listening to it this way, while the balanced output will please the listeners looking for a higher musicality with more impact and bass.

Kennerton Thror

Some people prefer Odin and other prefer Thror. At High End in Munich, the majority of people actually admitted liking the Odin most, but they’re actually both great.

My favorite way to listen to the Thror and US4+ combo is in balanced mode, as it makes Thror impactful, texturized, extended and clean. Thror with the right amp – like this one – is both precise and musical and it’s an absolute joy to listen to.

You get great bass body and impact, smooth yet detailed and clear mids with excellent depth and layering and soft, natural voices which are a little more upfront.  Extension and detail simply are excellent. The treble region is not the most exciting but you get a softer, clean and musical approach to treble. The extension probably could be a bit better on top, but again, that’s a Thror characteristic and it has nothing to do with the amp.

In single ended mode you – to no surprise by now – get a lighter and thinner sounding Thror with a flatter and very linear presentation. It’s neutrality what counts here but you still get good bass body and the presentation, though less energetic, is still musical. In DE mode, Thror is precise, detailed and fast, just lighter.

Thror sounds good with both outputs, but I personally prefer it from the balanced output.

Vs the Violectric V281

The biggest difference with the V281 isn’t power related but it’s all about the lower noise level. From what we understand he noise figure is over 10 dB better compared to the Violectric series. With the V281 or the other Violectric amps the relay attenuator is an option but on the US4+ it’s stock. You get a motorized, remote controlled volume section via a 256-step reed-relay attenuator.

Sound-wise what really stands out compared to the V281 is the increased clarity and cleanness.  To me the US4+ sounds more energetic and further extended, especially on the higher end. The US4+ doesn’t sound as warm as the V281 and the V81 has a smoother delivery with softer vocals.

Bass isn’t as tight as on the US4+, it’s more musical in the V281 than it’s precise and fast as it is in its big brother. The sound stage is more extended in the US4+ and you get a better separation and spaciousness, where the V281 is more intimate and thicker sounding.

The treble section in the US4+ is cleaner and wider, but the V281’s decay and note extension/decay is something special.

The US4+ is the better technical and higher end sounding amp but the V281 still is one hell of an amplifier as well and those who prefer musicality, impact, smoothness, fun and warmth will probably still prefer the V281. The US4+ is a high end sounding amplifier with a reference level sound. It sounds and does exactly what it’s supposed to do at this price level, but it’s always up to you in the end to decide if the price difference between both amps is worth it. The sound signature is different as well, so it might not be the logical upgrade you’re after if you already have the V281 and crave for more of the same.


Lake People set out to build a reference level amplifier and with Niimbus Audio and the US4+ unit they have done exactly that.

When you think US4+ you have to think: Cleanness, silence, power, extension, tightness, speed, balance/linearity (SE) and musicality.

To me the balanced output, just like with the V281 is the one to go for. It delivers the most musical, extended, spacious sound, with the best bass impact and body overall.

The Niimbus Audio US4+ is a great amp, with a reference/high end sound and price. If you’re looking for a well built and excellent sounding high end amplifier with both single ended as well as balanced in and outputs, then the US4+ will probably check all your boxes if you have the budget for it.

Will I be keeping the Niimbus Audio US4+? I haven’t made up my mind yet. Not because I don’t want to, as I love it, but in the past I have always sold the “actual” model to help fund the new one. But in this case it’s more difficult. I don’t really want to let go of the V281 and I don’t have the budget to fund the US4+. I’ll have to sleep on it many more days, until Niimbus asks me to send it back, that is.

A recommended buy for sure.

4.6/5 - (60 votes)

Lieven is living in Europe and he's the leader of the gang. He's running Headfonia as a side project next to his full time day job in Digital Marketing & Consultancy. He's a big fan of tube amps and custom inear monitors and has published hundreds of product reviews over the years.


  • Reply June 1, 2019


    i dont think v850 would make jusctice for amp like this. This dac i below average. We get it youre fanboy of violectric but atleast try other dacs maybe? im sure Chord qutest would do much better let alone costlier dacs. Good read though

  • Reply June 7, 2019


    v850 is not a bad DAC. It does about everything right except the detail retrieval compared to others in the price range. For a detail freak like myself, it’s not an ideal DAC. But, it can be a great DAC for music lovers who focus more on the timbre, naturalness, etc. But I do agree Chord qutest is better, and I suppose that’s about the minium DAC people, who spend 5k on a headphone amp, will use together.

  • Reply October 7, 2020


    Read the owners manual, thank you L.
    It is so Fried, LoL.
    I’ve never read manuals the way they do them. Not only do you
    understand how to operate it, you learn why it operates the
    way it does.
    It was just what I needed.

    Always in the background
    Always reading around

    • Reply October 7, 2020


      Thanks for commenting 🙂

  • Reply June 7, 2022


    “In single ended mode the Utopia sounds lighter and more linear with less bass impact and overall better linearity and balance. The sound signature again is more neutral in single ended mode and the impact and body are more civilized. For some the balanced signature/synergy might be a bit much body wise, and those listeners for sure will prefer the single ended mode. I can appreciate both the balanced as well as the single ended output, and the Utopia does sound better in SE mode than the HE-1000SE does.”

    You nailed this. Absolutely nailed this. I purchased the Niimbus 5 Pro to pair with the Utopia and the body was overwhelming (compared to my Taurus MKII). I like bass but it was just too much. I was very disappointed then found your review and switched from my XLR Gravedigger cable to a SE Gravedigger Cable. So much better. You clearly take the time to listen and try different uses and to do that with multiple headphones – impressive!

    • Reply June 7, 2022


      Thank you Greg for the nice words. I have sold my Utopia in the meantime though 🙂

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