Review: IOTAVX AVXP 2-840 -Stereo Power Amplifier

Review: IOTAVX AVXP 2-840 -Stereo power amplifier - is definitely exactly the officially heavyweight, bursting with power amplifier power plant that you always wanted to get in the rack

I’m sure it’s been in earlier reports: I like power amplifiers and I really like testing them. Simply because of their classic audiophile, puristic task, which can be summed up so wonderfully simply: “Amplify – and nothing else”. And isn’t the physical separation of preamp and power amplifier, which is overly ambitious by normal standards, simply the metallic expression of passion for (better) sound? As if that wasn’t enough, especially with power amps, aspects that inspire respect, such as mass and performance, come into play: With the new IOTAVX AVXP 2-840 (2,199 euros) we’re talking about a fighting weight of 30 kilograms and – yes – twice 580 watts (!) of output power at an eight ohm load. The eponymous “840” refers to the power at four ohms.

If so much power can be pressed into the loudspeaker terminals, a correspondingly potent substation is of course required. Or better yet, two: The IOTAVX AVXP 2-840 comes in real double mono, the stereo channels are designed separately from each other and are each kept live by a dedicated 1320 VA toroidal transformer. This is anything but a matter of course for the price range, especially since many manufacturers of significantly more expensive amps claim a “double mono” for themselves, even if only one integrated transformer supplies both channels.

Since this often gets mixed up: The channel-separated layout of double mono circuits may look nicely symmetrical – with a “fully symmetrical” circuit concept, in which each channel is routed twice (inverted and non-inverted), something else is of course meant. The IOTAVX AVXP 2-840 does not offer such symmetry, the sense and nonsense of which developers often disagree about, and the input signals behind its XLR interfaces are debalanced accordingly. A cinch double is of course also available.

At the other end of the circuit, eight bipolar transistors per channel are involved in a push-pull configuration (see amplifier classificationsin ), which suggests a typical Class AB design, but the IOTAVX AVXP 2-840 is designed as a – related – Class H. Unlike in the PA area, where extremely high demands are placed on the output power of amps, Class H is rarely encountered in the hi-fi area. The high potential output power of the IOTAVX requires a corresponding supply power, which would cause an unnecessarily high power loss in the final transistors at low input signal levels – not least typical for dynamic music signals. In a Class H circuit, the input signal modulates the supply voltage, low input signals lead to a lower supply voltage and thereby reduce the losses in the output stage.

When I asked whether special or even proprietary solutions (such as the Enleum AMP-23R-2022 ) were used in the IOTAVX AVXP 2-840, the developers replied that this was not the case, but that they were trying to use proven technical solutions Implementing concepts as high-quality as possible and at the same time as cost-efficiently as possible: with the exception of the power supply unit, the classic, discrete circuit design is evidence of this. By the way, here one works deliberately with high negative feedback , which contributes to a low output resistance and therefore high damping factor or increased control of the loudspeakers .

The exterior of the English power pack is also free of frills: instead of a thumb-thick front panel or sandblasted aluminum lid, there is eight or two millimeter thick sheet steel. Nevertheless, the case appears to be cleanly constructed without any problems. This expressly includes the mechanically integrated sockets and switches that inspire confidence. The backlighting of the front button, which is easy to use and changes from red to blue when it is switched on, is the only optical gimmick on the IOTAVX AVXP 2-840, which is otherwise designed and processed as well as tools.

Speaking of tools: The power amplifier comes with protective circuits to protect it against direct current components or excessive operating temperatures. A perfectly working inrush current limiter ensures that no flickering can be observed in the living room lamp when the IOTAVX AVXP 2-840 is started up, and certainly no flickering fuses are to be feared.

Sometimes I want to check amplifiers for the short circuit resistance promised by the manufacturer. So: clamp cable bridges to the loudspeaker terminals of the 2-840, switch on the amplifier and slowly increase the volume on the Funk MTX. Finally, you can hear quiet switching noises inside the IOTAVX, the illumination of the power button changes to a paler blue and finally begins to flash red-blue as a warning. The IOTAVX AVXP 2-840 has deactivated itself as planned for self-protection. And after pressing the rear power switch and now correctly connecting the speaker cables, it plays as if nothing had happened… great, that’s the way it should be.

IOTAVX AVXP 2-840: Sound Test & Comparisons

I’ve just sent the 2 x 25 watt “strong” Enleum AMP-23R-2022 on its way home – and now a 2 x 580 watt power plant is preparing to sound the alarm in my listening room. A truly impressive power upgrade. Can you hear that?

Sheer amplifier power and the right nose for goal

Sure, of course. However, I don’t find it that easy to put the effects of the “upgrade” into words, apart from the profane volume potential: Because the formidable Enleum also plays controlled, dry in the entire transmission range and officially digs deep on the bass side. In addition, the IOTAVX AVXP 2-840, which was fed by the ore-neutral radio MTX in my tests, does not add tonally at all – so that’s not the reason either. And yet the Brit conveys more sovereignty, more pressure, more headroom in terms of listening psychology and shovels standing bass areas as well as eruptive impulses noticeably more impressively into the listening room – this drives my Wilson SabrinaX to energetic peak performance.

Okay, the fact that sheer performance does score goals may seem trivial to many readers. But even my significantly more expensive (6,200 euros), at least up to 2 x 150 watts (all values ​​mentioned refer to 8 ohms, by the way), pushing cleanly into the speaker terminals Norma REVO PA 150 maintains a surprisingly large respectful distance in terms of coarse dynamic power and bass sovereignty. Only when I send my Monos Bryston 7B3 (currently just under 18,000 euros) into the ring is there a tie in terms of “sovereignty”: Numerically – the Bryston each have an output of 600 watts – and, for me, what is really decisive, acoustically. Truly not a bad debut for a 2-kilo amp.

Bass, rough dynamics and clichés…

A tie … so everything equal in terms of bass and coarse dynamics? Well, funnily enough, the IOTAVX AVXP 2-840 sounds even more like “classic Bryston” to my ears than the 7B3, which “rather jagged-fluid slide down the bottom than they push massively and deep black”, as I wrote in the test at the time. In fact, this ran counter to the clichés I cultivated about Bryston amplifiers.

The rhythm figure of snare and bass drum heard on Steven Wilson’s “Only Child” (Album: Insurgentes ) then sounds a bit more serious, stoic, roughly dynamically brazen via the IOTAVX power amplifier than via my Bryston monos and also Norma , which seem more rhythmically dance-like, throw a little more light-footedness, more swing into the balance. The differences aren’t huge, but at least you can feel them well over high-quality speakers, especially when you sink deeper into the music. From memory, I actually see similarities between the IOTAVX AVXP 2-840 and the famous Bryston 4-series power amps.

The calm itself

The pleasant subliminal calm that the IOTAVX AVXP 2-840 radiates due to its sound purity and freedom from gritty sounds goes well with the bass-side and coarse-dynamic imperturbability. Especially considering the price range of the 2-840, I find this to be a surprisingly high-end property. Last but not least, it is interesting to take a look at the well-hung Myryad MXA 2150 , also a stereo power amplifier for just over 2,000 euros at the time, which by chance survived in my extended fleet of devices – and against which IOTAVX does not stand a chance: the treble of the MXA 2150 sounds more porous and he also doesn’t keep the famous “black background” as black or clean as possible.

A fine touch for the mids

The IOTAVX AVXP 2-840 transports the special charisma of Matt Berninger’s voice in the almost anthemic “Mistaken for Strangers” (The National – Boxer) just as clearly and transparently as my Norma amp or my Bryston monos. The slightly mumbling Berninger is not a gifted singer – paradoxically, his singing is still captivating. Or maybe that’s exactly why, I think there’s something particularly credible, empathetic about his voice. Despite its fat 580-watt biceps, the IOTAVX demonstrates a fine, delicate knack for subtle textures in the mids and for not just pure, but also tonally uncolored tones . The “contradictory” effect of Berninger’s art of singing is then as emotionally appealing as I know it from my reference amplifiers.

Straight clean: the treble

Speaking of “tonal”: It shimmers through from the previous lines, but I’ll write it explicitly: The IOTAVX AVXP 2-840 is one of the power amplifiers that is tuned neutrally from head to toe. This also includes the straight and not classic English “softened” treble. To be honest, I would have feared one or the other discrepancy here due to the high performance, negative feedback and the bipolar output transistors in the context of the price range in which the British bolide is moving. Well, I wouldn’t describe the upper registers of the IOTAVX as aesthetic or trimmed to be “palatable”, but unnatural sharpness or hissing shine through the absence, the 2-840 sounds at the top as you would expect from a quality studio power amplifier.

And so bad, “hard” recording qualities are revealed as such – Peter Gabriel’s “Sledgehammer” tastes a bit like plastic, and the great album New River Head by Bevis Frond likes low fidelity at its best –, nevertheless served edible. If you like it even milder, which objectively does not necessarily mean “better”, you will probably prefer power amplifiers à la Rotel Michi S5 (also great mid-range reproduction/sound colors) or Meridian 857 Reference (very supple) that come with a warmer and more subtle high-pitched than strictly neutral sound. By the way: The fact that I fell for the idea of ​​filing comparisons of the IOTAVX AVXP 2-840 with significantly more expensive amps more or less under questions of taste shows how far this still affordable heavyweight can get in terms of sound.

Pragmatic vs. celebratory

An objective limitation that affects the treble as well as the resolution and fine dynamics stems – so I guess – from the overtone spectrum. Individual sounds seem a bit more naked, surrounded by less air or aura. In English-language sound descriptions (such as Robert Harley in his “The Complete Guide to High-End Audio”), the term “Bloom” is sometimes used in this context. And so the IOTAVX AVXP 2-840 is balanced in terms of treble tonality and as smooth and sharp in terms of resolution and fine dynamics as it should be for neutral, high-end amplifiers, but it doesn’t get down to the last bit of subtlety:

The individual stops of Daniel Fritzen’s interpretation (Klavierwerke 2 – Naturmystik) of Alexander Scriabin’s piano music, the IOTAVX works out at least as clearly and impulsively as my Norma REVO PA 150. In a quick “heady” AB comparison, no class differences can be identified with certainty. If you listen more intensely to what you are hearing, the tones of the Italian, surrounded by finer overtone webs, feel a little richer, as if adorned with a very last touch, and not least as a result more supplely linked. However, all of this is one of the particular strengths of the REVO PA 150, which costs almost three times as much as the IOTAVX AVXP 2-840. You could put it in a nutshell: the pragmatic IOTAVX shows with sound engineering precision, quickly and unmistakably on individual notes and the soulful Norma is able to celebrate them more often. And my Bryston 7B3 are basically equally good at both.

In good spirits: the stage depiction

“In good spirits” is a nice keyword for the stage skills of the IOTAVX AVXP 2-840: In terms of localization and clean structuring, it can easily keep up with more expensive amps like my Norma REVO PA 150. The reduced overtone spectrum actually gives it an advantage over the Norma at this point, as it spatially contrasts instruments with a bit more clear outlines against the background. Only the Enleum AMP-23R-2022 mentioned above shows that there is more to it than that, but the miniamp is conceptually and tonally (impulse reproduction and black background are at their best!) quite a special case. The fact that the spatial imaging of the IOTAVX also emanates something powerful, striving forward towards the listener, fits with its overall characteristics, the width of the stage seems reduced a notch (really no more) if you listen very closely; in the vertical, the sound pattern opens up in an exemplary manner.


For many listeners, the IOTAVX AVXP 2-840 is definitely exactly the officially heavyweight, bursting with power amplifier power plant that you always wanted to get in the rack – and that is now finally affordable. If the spoiled audiophile could wish for something else from the 2-840, it would at best be an even more dancing, light-footed representation of the otherwise unhesitatingly dry bass and an even more ethereal feel for overtones. These are by no means obvious weaknesses, especially since there are always more or less pronounced tendencies in this price range with other amps and I would rather speak of a “less” with a view to the IOTAVX AVXP 2-840. From a clear “more” may then in terms of control, sovereignty, Bass depth/pressure and coarse dynamic imperturbability – the IOTAVX block really sounds like a great power amp! And – that should also be mentioned – a bit like a clarified studio tool:

If you want to bring more flair or romance into the music, you should experiment with appropriate preamps – tubes are certainly a good idea here. Either way, the IOTAVX AVXP 2-840 lives and solves the demanding ménage-à-trois of “fine audiophile properties”, “unbridled power” and “down-to-earth price” more skilfully than any other power amplifier I know of on the market. My explicit test hearing recommendation.

The IOTAVX AVXP 2-840 is characterized by:

  • Whether powerful impulses or fat standing deep bass areas – the English amp from China stands up like a German oak even at high levels! In terms of control and sovereignty, clearly located in the Premier League.
  • A deep, powerful, powerfully shoveling, yet neutral and dry bass, to which the word “rather” fits better than “dance-like”.
  • Tonally neutral, beautifully clear and well-resolved mids and highs with very good tone color contrast, also thanks to the “black background” and therefore the very commendable purity that the sound radiates for the price range. However, it doesn’t seem overly ethereal, the overtone aura of individual sounds seems slightly reduced. Fast but not electrifying fine dynamics.
  • A horizontally not excessively expansive, vertically perfectly large format and overall involving spatial image, as one would expect from high-end amplifiers. The locatability and outlines of instruments appear to be well defined, the reduced overtone fog seems to promote a clearer view of instruments and vocals.
  • unfussy and luxury-free, but clean, confidence-inspiring “tooly” processing.


  • Model: IOTAVX AVXP 2-840
  • Concept: transistor stereo power amplifier
  • Price: 2,199 euros
  • Dimensions and weight: 435 x 183 x 423 (453) mm (including connections), 30.4 kg
  • Inputs: 1 x high level unbalanced (Cinch), 1 x high level symmetrical (XLR)
  • Outputs: Stereo speaker terminal
  • Power: Speakers: 2 x 580 watts into 8 ohms, 2 x 840 watts into 4 ohms
  • Guarantee: 2 years