Audionet Max monoblock power amplifier Measurements

Sidebar 3: Measurements

I measured one of the Audionet Max monoblocks (serial no. 9.16.20) with my Audio Precision SYS2722 system (see the January 2008 "As We See It"). Before doing any testing of a power amplifier, I precondition it by running it at one-third its specified power into 8 ohms for 60 minutes with a 1kHz tone: This power level results in the highest thermal stress on the output devices of an amplifier having a class-B or -AB output stage. The Max turned itself off after 42 minutes, its front panel displaying the message "SEVERE ERROR OVERHEATING." The Audionet's top panel at that point was fairly hot, at 117.3°F (47.4°C).

What I found interesting about the amplifier's behavior was that its THD+noise, which was extraordinarily low with the amplifier cold, at 0.0008%, stayed close to that level for almost the entire 42 minutes, but then rose to around 0.03% (fig.1). If I then reduced the level of the input signal so that the output power was lower than one-third power, the THD+N remained around 0.03%. If I didn't reduce the input level, the amplifier turned itself off several seconds after the increase in THD. I let the amplifier cool down for a couple of hours, then resumed testing. The Max's protection circuits kicked in several times during the measuring when I was operating it at high powers, particularly at high frequencies, giving me the message "SEVERE ERROR HIGH FREQUENCY." Each time, I let the amplifier cool down before continuing the testing.


Fig.1 Audionet Max, THD+N (%0 vs time (seconds).

The voltage gain into 8 ohms for the balanced input was a low 23.4dB. Unusually, the gain via the unbalanced inputs was 6dB higher. Both inputs preserved absolute polarity, the XLR jack being wired with pin 2 hot. The input impedances were close to the specified values, at 35k ohms unbalanced and 3k ohms balanced. The latter is very low; if this amplifier is used with tubed preamps, which typically have a high output impedance at low frequencies, the bass will sound rolled off.

The output impedance was very low, at 0.045 ohm (including the speaker cable) at 20Hz and 1kHz, rising slightly to 0.07 ohm at 20kHz. The response with our standard simulated loudspeaker varied by just ±0.05dB (fig.2, gray trace). The Max offered a wide small-signal bandwidth, with the response into 8 ohms (blue trace) down by just over 1dB at 200kHz. The Audionet's reproduction of a 10kHz squarewave into 8 ohms (fig.3) thus featured very short risetimes, and no overshoot or ringing was visible.


Fig.2 Audionet Max, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (blue), 4 ohms (magenta), 2 ohms (red) (0.5dB/vertical div.).


Fig.3 Audionet Max, small-signal, 10kHz squarewave into 8 ohms.

Not only does the Audionet Max have very low distortion—it is also very quiet. Its unweighted, wideband signal/noise ratio, ref. 1W into 8 ohms and taken with the input shorted to ground, was a superb 85.4dB, which increased to 98.5dB when the measurement was A-weighted. Fig.4 reveals that the only spuriae present in the output were at the 60Hz supply frequency and its odd-order harmonics, but these are all at very low levels.


Fig.4 Audionet Max, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (linear frequency scale).

The Audionet Max exceeded its specified output power of 400W into 8 ohms (26dBW), clipping at 450W into that load (26.5dBW, fig.5). Note that in this graph, the actual distortion lies beneath the noise at powers below 30W, indicated by the upward slope of the trace as the power decreases. Fig.6 reveals that the amplifier also exceeded its specified power of 700W into 4 ohms (25.4dBW), clipping at 750W (25.75dBW). The Max clipped at the specified 1100W into 2 ohms (24.4dBW), though the AC wall voltage had dropped from 123V to 118.5V at the clip point.


Fig.5 Audionet Max, distortion (%) vs 1kHz continuous output power into 8 ohms.


Fig.6 Audionet Max, distortion (%) vs 1kHz continuous output power into 4 ohms.

Fig.7 plots the THD+noise percentage against frequency at a level, 20V, that is equivalent to 50W into 8 ohms and 100W into 4 ohms, and where I could be sure I was looking at actual distortion rather than noise. Even so, the THD+N percentage remains very low, with only slight rises in the top octave and into the lower impedance. I haven't shown the THD+N plotted against frequency into 2 ohms at this level (equivalent to 200W), as despite repeated attempts, the amplifier's protection circuit cut in and displayed the "SEVERE ERROR HIGH FREQUENCY" message. At low frequencies and high powers into low impedances, the highest-level distortion harmonic was the third (fig.8), though with a 1kHz tone at the same output voltage into 8 ohms, the second harmonic was the highest in level (fig.9). Intermodulation distortion was also extremely low (fig.10), even at a level close to visual waveform clipping on an oscilloscope, where the 1kHz difference product rose from –120dB (0.0001%) to –96dB (0.0015%, fig.11).


Fig.7 Audionet Max, THD+N (%) vs frequency at 20V into: 8 ohms (blue), 4 ohms (magenta).


Fig.8 Audionet Max, spectrum of 50Hz sinewave, DC–1kHz, at 200W into 4 ohms (linear frequency scale).


Fig.9 Audionet Max, spectrum of 1kHz sinewave, DC–10kHz, at 100W into 8 ohms (linear frequency scale).


Fig.10 Audionet Max, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100W peak into 8 ohms (linear frequency scale).


Fig.11 Audionet Max, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 300W peak into 8 ohms (linear frequency scale).

As I am coming to expect from expensive German amplifiers, Audionet's Max performed very well on the test bench, offering high powers with very low levels of distortion and noise. It doesn't quite have enough heatsink capacity for its power-output capability, but I suspect that that shortcoming will not be a problem in normal use, especially given its very effective protection circuitry. (Despite the abuse I gave it during testing, the Max didn't break.) My only reservation concerned its very low balanced input impedance, but this won't be an issue with modern solid-state preamps and digital source components.—John Atkinson

Idektron GmbH
US distributor: GTT Audio & Video
(908) 850-3092

Owen1's picture

I thought I was going to read a review of the Audionet MAXes but ended up feeling like I just read a rave review on the the Pass XA200.8 monoblocks and the Nordost Odin 2s at the expense of The MAXes and Kubala Sosna Elation!s. Perhaps the funniest or saddest comment depending on how you look at this was the admission that the MAXes may have been at a distinct disadvantage due to them NOT being on the Grand Prix Audio amp stands like the Passes WERE when evaluating. YOU THINK? That's like saying "we didn't feel the Ferrari handled as well as the Lamborghini but perhaps it was because the tires on the Ferrari were worn out retreads and the Lamborghini was test driven with Perelli P ZERO CORSAs". Wow!

Jason Victor Serinus's picture

I spent months with the Max monos in my system, properly positioned on the Grand Prix Audio amp stands. All my conclusions were based on that proper set-up, using the volume control of the dCS Rossini (which, I might add, needs no apologies).

The PNWAS visit took place after I had reached my own conclusions about the sound of Max monos. It was only during that brief visit, which extended over several hours, that the Max was at a disadvantage due to the lack of four amp stands and sufficient space to put them.

In retrospect, it was a mistake to have devoted so much space to comments made by others, at a demo where one set of amps was at a disadvantage. If you skip those comments, and read the rest of the review, I believe that it will make sense.

icorem's picture

I'm a proud owner of the Audionet Max.
I didn't find in the "associated equipment" section the pre that was used in that review.
I, as Owen1, found the review a little bit confusing...

John Atkinson's picture
icorem wrote:
I didn't find in the "associated equipment" section the pre that was used in that review.

No preamplifier - the dCS DAC, with its own volume control, was connected directly to the Max amplifiers.

John Atkinson
Editor, Stereophile

chhue's picture

Some years ago, I wanted to upgrade from my Bryston 4B SST. Because I already owned a Audionet Preamp, I aimed for the Audionet Amp. But I got an Audionet Max to audition at home. Because I was in search for a little more warmth and colour I finally got the Pass XA 60.5. But I always missed the last bit of rhythm and tight bass and also being more "effectful", traits the Max provided in my system.

I can relate to this review, though it was never a real A/B comparisson, because I've got the Pass some weeks later than I had the Audionet Max at home. Reading the review here, was greatly in line with my own memories.

The Pass XA 200.8 is surely an improvement over the XA 60.5.

The Pass and Audionet are very good amps, but for me they aim at opposing tastes. So I would not recommend choosing between them in a short period of time or even try to call one better or worse. At least this is how I understood this review, even if there is a slight bias in favour for the pass.

In fact, I think there are many amplifiers in between these sonic signatures. Because I build my own speakers with an cross over running in my computer, I've switched to two NAD M27. Though I might miss some of the XA 60.5's strengths, I do not miss their tradeoffs.

tonykaz's picture

I feel your concern.

It could've gone the other way and this comment section would have the Pass owners griping.

As an Salon Owner using Electrocompaniet Gear, I was never able to find any Amplification that could out-perform it but nearly all Reviewed Amps were "said" to be superior, I sampled nearly all to find them lacking.

Customers listen with their Eyes and when it comes to Amps.

Customers eagerly "listen" to all pricy Wire Products, they will always hear differences.

Customers can (and easily do) hear differences in PreAmps, nooooooooo problem.

Audiophile Amplification is the most Psychotic component, it's 2+2= something different for each person.

All this makes me wonder : What is the most popular Audiophile Amplifiers ever? I'd guess it's the NAD 3020.

Tony in Michigan

Ukcolin99's picture

Wondering what version of Toy you have my copy has neither track you referenced. Thank you

Jason Victor Serinus's picture

The 24/48 download from HDTracks. I have not heard other versions. Whenever possible, I work with hi-rez files or SACD (or perhaps, in the future, MQA CD), because the sound is so much better.

Double Fun's picture

Found this on Facebook, maybe it'll help:

"The Audionet review in this issue is perplexing. We have had 16 reviews of Audionet systems in the US since becoming the distributor and all of those reviewers come up with a different conclusion.
We strongly recommend using amplifiers with a companion preamp or at least a preamp. We don’t believe a DAC going direct with a digital volume control that trims bits is ever superior to a proper preamplifier. Further if a system is filled with tweaks and you are going to evaluate a component we strongly encourage detweaking the system and then reoptimizing the system. Only then can you really tell what a particular component really sounds like.
Also note that when using a digital volume control and playing DSD files the DSD is converted to PCM for the volume adjustment.
Any system’s sound is a sum of its parts. The system in which the MAX amps were placed might have been the Audionet showing off other parts of the system rather than the actual sound of the MAX.
At the most recent Axpona 2017 where the MAX amplification was used Jason reported,
“proved once again that this was a perfect, synchronistic match of components.
Perfect match? How about "highs that were brilliant without being piercing, impressive bass (albeit nowhere near as overwhelmingly powerful as from the far more expensive Sonja XV system), and excellent timbres? The bottom end may not have been as focused and clear as it could have been—this was a hotel room set-up, after all—but the excellence of timbres made for a winning presentation. Reservations aside, I loved it."
It is these types of experiences of our setups that peaked Jason’s interest enough to give the Max a try in his system. We just wish the recommendation of a preamp was used and a bit more care in the setup addressed. A true apple to apple comparison would have been appreciated.
We are not quite sure why Audionet was chosen for this beta-test-experiment of amplifier comparisons for an Audio Society when according to Jason, “the Maxes were at a distinct disadvantage” and the system clearly optimized for his reference amplifiers. Not only did the end results end in differing conclusions but amounted to a severely flawed experiment. True A/B test should be on an apple to apples basis which this clearly was not.
We appreciate John Atkinson’s measurements and his conclusion that “Max performed very well on the bench, offering high powers with very low levels of distortion and noise”.
We would like to highlight and clarify a couple of things in the measurement section. The measurement spikes which are shown in Figure 3 have nothing to do with the 1 kHz Signal. These are 60 Hz components from the mains. The procedure which Max turned off after 42 minutes has no practical attempt for a speaker but this was stated later on. All shut downs from the safety circuit are correct.

supamark's picture

makes you think it's a digital volume control? That makes zero sense from a design standpoint. Also, from the Audiostream review:

"...The summed latch outputs drive the second portion of the Analog Board: a balanced, Class A mix amplifier and filter stage. The mix amplifier and filter stage removes any unwanted noise and switching artifacts created by the high-speed latch mapping, and provides a variable-voltage, very-low output impedance, balanced analogue output signal."

That variable voltage output signal sounds a lot like an analog volume control, eh? dCS doesn't seem to say where the volume control is in the signal chain in their lit, but analog (after DAC) is the only one that makes engineering sense for a component like this.

supamark's picture

seemed as much about cables as amps. I don't personally buy into the cable thing, though I'd like to see all copper connectors/wire from imput to output. sending the signal through multiple metals, each with different electrical properties, is going to cause far more harm than some teflon dilectric layer can possibly fix. was funny that the the "B" option was overwhelmingly preferred (even when the amps were switched)... makes you think about the validity of those "lemmie swap in our high priced cables after listening to yours" demos, hmmm?

Would have much preferred the space spent going on about cables be spent comparing the sound of the two (or more) amps (even better if you could use multiple speakers since that's the interaction that determines if the amp will work for someone).

Joonas Viinanen's picture

In a triode, the signal has to travel through many connections and pieces of wire, many of different materials and very different connection methods, mechanical contacts, welded, crimped and soldered. The signal comes to the socket where it is soldered to a lug. If you are lucky, the solder lug and connection element to the tube pin are made of a single piece of metal. Sometimes, especially in sockets for larger tubes there are two. From the socket there is a mechanical contact to the tube pin. In Octal tubes, the pin is actually a shell which contains the wire which goes through the glass, it is soldered to the pin inside. Also the pins of directly heated triodes like 2A3 and 300B which have UX4 bases are made like this. The wire which traverses through the glass is not selected based on good sound, not even by good electrical properties. Here the thermal and mechanical behaviour is important so that no cracks in the glass appear when the tube heats up and cools down. Sound wise this type of wire is probably at the same level as barbed wire used in fences. Let's move on with the signal path. Inside the glass, there is another piece of interconnecting metal between this wire and the vertical rods which hold the electrodes like plate, grid and cathode. The actual electrodes then are clamped or welded to these rods.

So on average there are about 5 pieces of different metal and 5 connection points through which the signal has to travel. And that for each electrode of the tube. Assuming triodes only this sums up to 15.

How much difference do you think cables make if this is the reality?

Anon's picture

What did you think about the Xpander?

Also, which PowerCell are using?

Thank you for any answers you can provide! :)