Simaudio Moon Evolution 880M monoblock power amplifier Measurements

Sidebar 3: Measurements

Before performing any measurements, I ran one of the Simaudio Moon Evolution 880M amplifiers (serial no. L6311636) for an hour at one-third its specified maximum power of 800W into 8 ohms, thermally the worst case for an amplifier with a class-B output stage. By the end of the hour, the side-mounted heatsinks were way too hot to touch, at 148.5°F (64.8°C). The chassis was cooler, with the top plate measuring 126.4°F (52.4°C), though the aluminum vertical corner pieces were 164.3°F (73.5°C). Though the distortion with the amplifier completely cold was a low 0.00825%, this was predominantly crossover distortion, which will be subjectively disturbing because of its high proportion of high-order harmonics. At the end of the preconditioning period, the distortion had almost halved, to 0.0045%, and the crossover spuriae had disappeared. This suggests that potential purchasers of this amplifier should not audition it until it has warmed up.

I performed a full set of measurements on the amplifier, using Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system (see and the January 2008 "As We See It"), using the 880M's balanced input. I repeated some of the tests using the unbalanced input with a shorting plug connecting pins 1 and 3 of the 880M's XLR jack.

The voltage gain into 8 ohms was the same for the balanced and unbalanced inputs, at 31.5dB, which is about 4dB higher than the norm. Both inputs preserved absolute polarity (ie, were non-inverting), the XLR jack being wired with pin 2 hot. The input impedance at low and middle frequencies was 23k ohms for both sets of jacks, dropping inconsequentially to 18k ohms at 20kHz. The output impedance (including 6' of speaker cable) was slightly higher than usual for a solid-state design, at 0.125 ohm at 20Hz and 1kHz, rising to 0.132 ohm at 20kHz. Nevertheless, the modulation of the amplifier's frequency response by the Ohm's Law interaction between this output impedance and the impedance of our standard simulated loudspeaker was just ±0.1dB (fig.1, gray trace).


Fig.1 Simaudio Moon Evolution 880M, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (blue), 4 ohms (magenta), 2 ohms (red) (0.5dB/vertical div.).

The frequency response was flat in the audioband, but with a slight rolloff evident starting just below 20kHz and reaching –3dB at 90kHz. A 10kHz squarewave was reproduced with short risetimes (fig.2), and a 1kHz squarewave had superbly sharp corners (fig.3).


Fig.2 Simaudio Moon Evolution 880M, small-signal 10kHz squarewave into 8 ohms.


Fig.3 Simaudio Moon Evolution 880M, small-signal 1kHz squarewave into 8 ohms.

The unweighted, wideband signal/noise ratio, ref. 1W into 8 ohms with the input shorted, was 81.8dB, due mainly to some low-level, odd-order harmonics of the AC supply frequency (fig.4). Switching in an A-weighting filter improved the ratio to a good 91.4dB.


Fig.4 Simaudio Moon Evolution 880M, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (linear frequency scale).

The Moon Evolution 880M comfortably exceeded its specified maximum power of 800W/29dBW into 8 ohms, clipping (defined as 1% THD+noise) at 1050W (30.2dBW, fig.5). The AC wall voltage had dropped from 123V with the amplifier idling to 120V with it clipping. However, the 10A fuse on the rear panel blew at the same 1050W into 4 ohms (27.2dBW, fig.6). Clearly, the 880M is not comfortable driving sustained high powers into low impedances with sinewaves—with its much higher crest factor, music will be less demanding than sinewaves, of course—so I didn't test its maximum output into 2 ohms.


Fig.5 Simaudio Moon Evolution 880M, distortion (%) vs 1kHz continuous output power into 8 ohms.


Fig.6 Simaudio Moon Evolution 880M, distortion (%) vs 1kHz continuous output power into 4 ohms.

The rising shape of the traces below a few tens of watts in figs. 5 and 6 suggests that the measured THD+N percentage is dominated by noise at low powers. I therefore measured how the THD+N varied with frequency at a level, 12.65V, equivalent to 20W into 8 ohms and 40W into 4 ohms; that way, I could be sure I was looking at actual distortion. The result is shown in fig.7. The THD rises above 1kHz into both 8 ohms (blue trace) and 4 ohms (magenta), presumably due to the circuit's open-loop bandwidth being insufficient to apply the same amount of corrective negative feedback at high frequencies as at low frequencies. Unusually, the midband distortion is actually lower into 4 ohms than into 8 ohms. When I tried plotting the THD against frequency into 2 ohms at 12.65V, the rear-panel fuse again blew. As that was the last of my spare 10A fuses, I replaced it with an 8A fuse and continued testing. Fortunately, no more fuses were blown!


Fig.7 Simaudio Moon Evolution 880M, THD+N (%) vs frequency at 12.65V into: 8 ohms (blue), 4 ohms (magenta).

Once the 880M is fully warmed up, its distortion is predominantly the subjectively innocuous third harmonic (fig.8), followed by the second (fig.9). However, some higher-order harmonics are visible in fig.9, albeit at or below –110dB (0.0003%). Intermodulation distortion was also low, even at high powers (fig.10).


Fig.8 Simaudio Moon Evolution 880M, 1kHz waveform at 35W into 4 ohms, 0.0031% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).


Fig.9 Simaudio Moon Evolution 880M, spectrum of 50Hz sinewave, DC–1kHz, at 300W into 8 ohms (linear frequency scale).


Fig.10 Simaudio Moon Evolution 880M, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 300W peak into 8 ohms (linear frequency scale).

Simaudio's Moon Evolution 880M is a powerhouse of an amplifier, though its ability to drive low impedances does rely on the fact that music has considerably wider dynamic range than do test tones. And it should never be listened to cold.—John Atkinson

Newton Road
Boucherville, Quebec, J4B 5H2
(450) 449-2212

xsipower's picture

Well after years of being on the sidelines I decided to voice my concerns for the high end industry. Since my teenaged years I have loved the listening to good music through good equipment. I became an Electrical and Mechanical engineer, which was due in part to my love for building my own DIY equipment at home.

After reading Stereophile’s review of the Simaudio’s Moon Evolution 800M, I just couldn’t stand on the sidelines and not voice a concern about specmanship in the highend audio industry. I thought the large differences in published specifications vs. actual measurements was relegated to consumer electronics and not to five and even six figure (hopefully) state of the art audio equipment. The Evolution 880 clearly does not achieve some of the most important specifications that amplifiers are measured to.

Here below I distilled my concerns and finding:

Spec’d Output Power 8 ohms: 800W in 8ohms   

Measured Output Power 8 ohms: 800W in 8 ohms

Meet Spec.: Yes


Spec’d Output Power 4 ohms: 1600W in 4 ohms

Measured Output Power 8 ohms: 1050W in 4 ohms (fuse blown)*

Meets Spec.: No (<1.5x discrepancy)


Spec’d Output Current: 42A continuous

Calculated Output Current: Fuse blew into 4 ohms @ 1050W which is 16Arms

Meets Spec.: No (<2.6 discrepancy)


Spec’d Output Impedance: 0.004 Ohms

Measured Output Impedance: 0.125 – 0.132

Meets Spec.: No (<30X discrepancy)


Spec’d Frequency Response: 10 – 200Khz (0, -3db)

Measured Frequency Response:  90khz -3db

Meets Spec.: No (<2X discrepancy)


Spec’d Slew Rate: 70V/us

Actual Calculated Slew Rate: 20.5V/s

Meets Spec.: No (<3.4X discrepancy)


*With a 10A “long fast blow” fuse maximum input power is 1200W max.



The output power specification for this amplifier is continuous for only an 8 ohm load. The 4 ohm specification of 1600W is clearly momentary, or “peak” as the 10A fuse limits the output power to 1050W.

The argument that using a continuous sine wave to test amplifiers is not fair to the amplifier is incorrect. Wattage is Wattage, whether it’s from a music source or a function generator. A music source is said to have dynamics and therefore not tax the amplifier as a continuous sine wave does. This is true, but to do away with the ambiguity of testing amplifiers, the Industry uses the term as “rated continuous output power”.  If an amplifier is rated to output 800W most manufactures that follow IEC specification would specify it for continuous output power. This should be done with a sine wave a 1khz, but even if it’s done with a music source, the average power must equal a continuous 800W. Of course to output 800W of continuous RMS music power would require clipping the signal or having the music highly compressed. Power is Power. Can the Evolution output 1600W of continuous music power into 4 ohms? No.


The other very alarming measurement of the Evolution 800M is that a 1/3 power into 8 ohms the heat sinks reach dangerous temperatures. Other that than the high end amplifier industry, most manufactures limited exposed surface temperatures to 50C or less.  The high end industry seems to be fine with much higher temperatures. The Evolution 800M has surface temperatures of 73.5C. The SAFETY standard UL/ IEC 60950-1 for electronics allows for metal surfaces to reach 70C.

As with all of Simaudio's amplifier, the heat sinks are mounted with the fins in a horizontal plane rather than the traditional vertical plane. I assume they chose this for looks rather than cooling efficiency, since this arrangement is a very poor utilization of natural convection cooling. The purpose of using a heat sink with vertically mounted fins is to take advantage of the rising natural convection air moving over as large of a surface area as possible, with little or no obstruction in its motion.


I wish Stereophile would include in their review language that clearly states that the product does not meet its specification in the final summary of the measurements section of the articles. Instead in this article a poor excuse is given for it not being able to drive low impedance loads, but the review said that’s OK because music is not a sign wave. For heaven sake, this is a $42,000 amplifier and should perform as specified as do many "afordable" Best Buy purchased equipment.

I am very happy that Sterophile does actually test the equipment they listen to. Most other reviewers do not. It is a great service to all of us. The whole purpose of the review is to provide both objective and subject information to the reader so that they may know what they will be getting when they purchase the item.

I understand that the subjective portion of the review can have no objective scales, but when objective measurements are made they are very much tied to real physical scales set forth by various international agencies. My only other concern is that I have found in the last few sentences of the measurement section, a subjective assessment made of the objective measurements that not only seems to trouble others ( as I have read in posts on but myself as well. There have been recent reviews of amplifiers that for their astronomical price have very poor measurements.  At the end of the review a subject remark is made like “This is an amplifier that is as well-engineered as it is beautiful to look at.” That may be the reviewer’s opinion, but as an Electrical Engineer of 20 years’ experience and who closely follows both DIY and professional audio design, I had a very different opinion and hold the standards for saying “This is an amplifier that is as well-engineered “for such high priced equipment to a higher level. I would never have said what the review said for that product.

I am trying to be constructive with my comments and mean no disrespect to any of the reviewers.

John Atkinson's picture

To address a couple of the points you make:

1) My measurements of output impedance include the series resistance of 6 feet of approximately 14-gauge speaker cable.

2) Yes, the fuse blew under sustained drive into 4 ohms. But it is entirely possible that with a pulsed signal with a low duty cycle, the fuse would remain intact up to the clipping point. Note, BTW, that I don't hold the wall voltage constant for these tests, feeling that this is more representative of actual use.

John Atkinson

Editor, Stereophile

Robby's picture

1) 14 AWG cable has a resistance of 2.52 mOhm/foot

6 x 2.52 = 15.12 mOhms or 0.0152 Ohms which still makes the output impedance figure look bad compared to the spec.

2) Most energy will come from low-frequency musical elements and those are everything but low duty pulses. Most of them will be closer to sine waves and they will suck a lot of power when driven into speaker loads so there is still a risk to blow the fuse on bass-heavy music played loud.

JohnnyR's picture

Please be consistant at removing posts or don't bother removing any. Thanks

Just because some people can't face facts doesn't mean they are correct.

Robby is correct about the output impedance and the wire used to measure it, he is also correct that low frequency content tends to be sine wave not impulses.

This amp FAILS at a number of tests and should have been criticsed for doing so NOT praised.

We now return you to the usual excuses thanks for your patience.

John Atkinson's picture
JohnnyR wrote:
Please be consistent at removing posts or don't bother removing any. Thanks

You have been warned multiple times, Johnny R, that posts of yours that in our opinion are nothing more than abuse or trolls will be deleted without notice. You don't want your posts deleted, please refrain from personal attacks and stick to addressing the points being made by others.

JohnnyR wrote:
This amp FAILS at a number of tests and should have been criticised for doing so NOT praised.

Please think about where you learned about this amplifier's apparent shortfalls in its measured performance.

John Atkinson
Editor, Stereophile

anjeza1987's picture

I agree with your comments xsipower.Additionaly,the high temperatures,will shorten the life of the equipment.And this one is very beautiful.

And greatly appreciated the measurments carried out from Mr Atkinson.

Regards from Greece.

GeorgeHolland's picture

just change the specs to be a bit below where actual problems arose then jack up the price even more and they would have a "winner"  wink I understand it could double as heater during the cold months. This brings about the possibility of owning another amp that doesn't get hot for the summer months. A win-win for the high end dealers that wish to double their

freddiek40's picture

Hmmmm.  800 watts, 1 year warranty = $42,000


Or you could buy 2 sets of Bryston 28B.  1000 watts, 20 year warranty, $36,000 (remember this is for 4 of the 28Bs).


I think the Sims are clear losers.

John Atkinson's picture

freddiek40 wrote:
Hmmmm.  800 watts, 1 year warranty = $42,000

From the company's website: "The Standard Warranty is 1 year parts and labour.

"Upon receipt of a validated Product Registration (via our website or by regular mail), the warranty can be extended up to an additional 9 years.

"To receive this free-of-charge extended warranty (up to 10 years), the product must have been purchased new, from a MOON Authorized Dealer. and registered with us within 30 days of your invoice date."

John Atkinson

Editor, Stereophile

MVBC's picture

And that includes the cooling fins...

xsipower's picture

Hello Freddiek40,

If you read Stereophile's review of the Bryston 28B-SSTyou will find that it was another very “hot” amplifier.

From Stereophile review:

“I preconditioned the Bryston 28B-SST by running it at 330W into 8 ohms for an hour. ….. The amplifier's heatsinks were way too hot to touch after 60 minutes, but despite the thermal abuse, the amplifier didn't turn itself off.”

What is way too hot to touch? This can be quite subjective, but is usually considered starting between 65-70C. That is when contact for more than a brief few seconds leads to a burn. The Bryston 28B-SST temperature was clearly above this threshold based on Stereophile’s test.

I would not consider the Bryston 28B-SST to be designed thermally any better than the Evolution 800M. That being said, the Bryston 28B-SST functioned through the entire tests without failure.

I agree that with higher temperature two things must be considered by a buyer. First is the placement of the equipment where it will get enough ventilation as well as not being touched when driven hard.  The second consideration is that the MTBF (Mean Time before Failure) increases with higher operating temperature. Temperatures of 70C are not destructive to most electronic components since most are rated much higher. The component that is most affected by high temperatures are electrolytic capacitors the bulk of which are the main power supply filter/storage capacitors. The life time of these are impacted quite drastically as temperatures go up.

 You would defiantly want a robust warranty on a “hot” running amplifier.

I appreciate the difficulty that designers of amplifiers face. There are many unknowns to the designer. The most unknown is the load. Some speakers are easy to drive, some are very difficult. Speakers are complex loads and can drop their impedance to half or less of their rated impedance at certain frequencies. Not only that, but during these low excursions the current and voltage can be way out of phase and that puts the highest stress on the amplifier’s output transistors.

 I believe that over the many decades that this industry has been around; the adoption of standardized testing methods and specifications has helped to alleviate the ambiguity of how a particular amplifier can perform.  Tests like the 1/3 power test into load, the specification of continuous RMS power into 8,4 or 2 ohms loads, etc., give the buyer the tools with which to marry a speaker with an amplifier. Of course the tests do not reflect “real life” music listening, but they are not meant to. They are meant to give assurance that they can at least play music continuously at a rated power in to a rated load.

Do we listen to music at continuous RMS value of let say 800W. Most likely not. But then, what music are you listening to. Is it highly compressed? Does it have a lot of low frequency component which where most of energy goes in recreating music. What speaker are you driving?

ON…and On….

John Atkinson's picture

xsipower wrote:
What is way too hot to touch? This can be quite subjective, but is usually considered starting between 65-70C. That is when contact for more than a brief few seconds leads to a burn. The Bryston 28B-SST temperature was clearly above this threshold based on Stereophile’s test.

The Bryston was reviewed before I bought an infra-red thermometer. But I was taught at university that "too hot to touch" or more accurately, to keep your hand on" was equivalent to >60C.

And the one hour at 1/3 power test is very much a worst case for amplifiers with a class-B or -AB output stage like the Bryston and Simaudio.

John Atkinson

Editor, Stereophile

xsipower's picture

Thank you Mr. Atkinson for the elaboration on "too hot to touch". Yes I agree that 1/3 power is very rigorous on the amplfier with a class-B or AB output.

xsipower's picture

Sorry. I need to make a correction in my above post. I wrote "MTBF increase with temperature". That I wanted to write was MTBF decrease with increase in temperature.

tmsorosk's picture

Yeah the Brystons are clear winners until you hear both offerings , then there is one clear winner ( Simaudio ). Warranty and watts are one thing but for the true audiophile your ears must decide .

JohnnyR's picture

Sorry but , "I think this amp sounds better" with no objective testing is guess work and just opinion. Amps need to meet their specs otherwise the manufacturer is making a faulty product. If they can't meet their own specs then how can you trust it to last or perform at it's best?

GeorgeHolland's picture

My oh my with such an under engineered amp, they are going to see plenty of repairs that is if anyone buys it to begin with.