Aesthetix Audio Mimas integrated amplifier Measurements

Sidebar 3: Measurements

Before measuring the Aesthetix Mimas with my Audio Precision SYS2722 system (see the January 2008 "As We See It"), I installed its two Electro-Harmonix 6922 tubes and left the amplifier's internal jumpers as set by the factory. Before I test an amplifier, I precondition it with both channels driving a 1kHz tone at one-third power into 8 ohms for an hour. The Mimas turned itself off after 30 minutes, however, its front panel displaying the message "Temp HIGH RITE." The amplifier's top panel was hot, at 126.6°F (52.6°C), the temperature of the side panels was 110.4°F (43.6°C), and that of the internal heatsinks was 163.5°F (73.1°C). The Mimas doesn't have quite enough heatsink capacity for sustained high-power use.

After letting the Mimas cool down, I continued the testing. Looking at the line inputs—our review sample didn't include the optional phono and digital input modules—the maximum voltage gain at 1kHz from the speaker terminals into 8 ohms, with the volume control set to the maximum, measured 48.2dB for both balanced and unbalanced signals. The maximum gains at the preamplifier and headphone jacks were 29.3 and 27.1dB, respectively, both higher than the norm. Both inputs preserved absolute polarity from the speaker and preamplifier outputs (ie, were noninverting), meaning that the XLR input jacks are wired with pin 2 hot. The headphone output inverted polarity, however. The unbalanced input impedance was close to specification at a relatively high 19k ohms from 20Hz to 20kHz; the balanced input impedance was twice that value, as specified and expected.

The headphone output impedance was an appropriately low 6 ohms at all audio frequencies, while the preamplifier output impedance was 100 ohms from the unbalanced jacks, 200 ohms from the balanced XLRs. The output impedance at the speaker terminals was 0.25 ohm at low and middle frequencies, rising to 0.26 ohm at the top of the audioband. As a result, the modulation of the Mimas's frequency response with our standard simulated loudspeaker was ±0.3dB (fig.1, gray trace). This graph was taken with the volume control set to its maximum; commendably, there was no change in response or channel balance at lower volume-control settings. The Aesthetix's frequency response at the speaker terminals is down by 3dB at 120kHz; as a result, a 10kHz squarewave was reproduced with very short risetimes (fig.2), and there was no overshoot or ringing with a resistive load. A 1kHz squarewave was perfectly square (fig.3). The response from the headphone outputs was down by just 0.4dB at 200kHz.


Fig.1 Aesthetix Mimas, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (1dB/vertical div.).


Fig.2 Aesthetix Mimas, small-signal 10kHz squarewave into 8 ohms.


Fig.3 Aesthetix Mimas, small-signal 10kHz squarewave into 8 ohms.

Channel separation was superb below 2kHz, at >95dB R–L and >100dB L–R, though at 20kHz these ratios respectively decreased to 72 and 78dB. The unweighted, wideband signal/ noise ratio, taken with the unbalanced inputs shorted to ground and the volume control set to its maximum, was a disappointing 46dB (average of both channels), this improving to 57.5dB when the measurement bandwidth was restricted to 22Hz–22kHz, and to 61.2dB with an A-weighting filter in circuit. These ratios improved at lower settings of the volume control and are related, I believe, to the Mimas's higher-than-usual preamplifier gain.

Spectral analysis of the low-frequency noise floor (fig.4) indicated that the AC-supply spuriae were at 60Hz and its odd-order harmonics, which suggests that they were due to magnetic interference from the power transformer perhaps being picked up by the tubes' steel pins. The spectra in fig.4 were taken with the volume control set to "88" (blue and red traces) and to "68" (green, gray). Though the levels of the random noise components remain the same, lowering the volume reduced the levels of the AC spuriae, particularly the 60Hz component in the right channel (red and gray traces).


Fig.4 Aesthetix Mimas, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms with volume control at "88" (left channel blue, right red) and "68" (left green, right gray) (linear frequency scale).

Aesthetix specifies the Mimas as offering 150Wpc into 8 ohms (21.76dBW) and says it will typically deliver 185W (22.67dBW). With both channels driven and with clipping defined as when the THD+noise in the output reaches 1%, I measured the clipping power into 8 ohms as 180Wpc (22.55dBW, fig.5). Aesthetix specifies the maximum power into 4 ohms as "nearly double" that into 8 ohms; I measured 275Wpc into 4 ohms (21.4dBW, fig.6).


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


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

I also examined how the THD+N percentage varied with frequency at a fairly high level, 20V, which is equivalent to 50W into 8 ohms and 100W into 4 ohms. The THD+N was low into 8 ohms (fig.7, blue and red traces), but higher into 4 ohms (cyan, magenta). The usual rise in the treble due to the reduction in the circuit's open-loop gain at high frequencies was absent.


Fig.7 Aesthetix Mimas, THD+N (%) vs frequency at 20V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta).

The right channel's THD+N waveform at this level (fig.8) indicates that the distortion is predominantly third-harmonic in nature, though spectral analysis (fig.9) reveals that there are also higher harmonics present, and there was a much higher level of second harmonic in the left channel (blue trace) than the right (red). Tested with an equal mix of 19 and 20kHz tones a few dB below clipping into 4 ohms, the Aesthetix produced fairly low levels of high-order intermodulation distortion (fig.10). However, while the difference product at 1kHz lay at a very low –106dB (0.0006%) in the right channel, it was much higher in the left channel (blue trace), at –84dB (0.006%). This is still low in absolute terms, however.


Fig.8 Aesthetix Mimas, right channel, 1kHz waveform at 50W into 8 ohms, 0.069% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).


Fig.9 Aesthetix Mimas, spectrum of 50Hz sinewave, DC–1kHz, at 50W into 8 ohms (left channel blue, right red; linear frequency scale).


Fig.10 Aesthetix Mimas, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100W peak into 4 ohms (left channel blue, right red; linear frequency scale).

Its measured performance indicates that Aesthetix Audio's Mimas integrated amplifier is generally well engineered, though its noise floor at high settings of the volume control is higher than it need be. However, as the high gain will mean keeping the volume control low, this will not be a factor in the amplifier's sound quality.—John Atkinson

Aesthetix Audio Corporation
5220 Gabbert Road, Suite A
Moorpark, CA 93021
(805) 529-9901

MZKM's picture

Yet another integrated amp that has measurements on-par with the Outlaw RR2160 (well, no DAC or phono measured for the Mimas), yet has far less features (subwoofer output with selectable crossovers, main in for DSP, A/B speaker outputs, tone controls, etc. and yet costs magnitudes more.

Jason Victor Serinus's picture

I don't know how they compare sonically. From my perspective, assuming you can afford both products, sound quality rather than the number of features is the prime consideration. Otherwise, it could be a case of paying for 537 cable channels, only to discover that there's nothing worth viewing.

MZKM's picture

I just don’t see any high end engineering or purposeful colorations that warrant the price. It even has more odd order harmonics than even, which I don’t understand with hybrid design like this. Even if dead accurate isn’t your thing, but at least one can appreciate the feat of engineering that Benchmark’s products have. And it Outlaw can sell an integrated for <$1000 with all the features mentioned and have similar distortion, wattage, channel separation, etc. as this integrated which is around $10,000 fully loaded, I personally don’t see how the price is justified. May sound cynical, but I believe this is the best the company can make, and they simply can’t compete with the saturated lower end market, so they priced it high enough to where a few units sold keeps them solvent.

johnnythunder's picture

Aesthetix amplifier. I have and they sound beautiful - on the warm, tube-ish side of beautiful for sure. They also look beautiful, bespoke and massive. Impeccable build quality. Sorry that yhey don't make "home theatre" products. Not sure why you read a subjectivist audio magazine like Stereophile if you think measurements are the most important barometer of sound quality. You must have loved the late Julian Hirsch's audio criticism. And probably Consumer Reports. Instead of instant skepticism - probably based on monetary sour grapes - why don't you refrain from commenting until YOU have made a meaningful comparison of the two products.

MZKM's picture

I haven’t listened to this amplifier, but I have listened to many high end ones. You claim it has a warm sound (no doubt due to the hybrid design), but the measurements clearly show that to be false, it is dead neutral like most any other solid state amp, and I doubt you are hearing the high levels of odd-harmonics as warmth.

I visit Stereophile to find well engineered products, from speakers like the Vivid Audio Giya models to amps like the Benchmark AHB2.

If you can find an instance where during a DBS that measurements did not accurately predict listener preference, then I’ll stop instant skepticism.

What does home theater have to do with this? Wanting a 2-way crossover with dual subs as well as DSP, or at least tone controls, for the speakers is very beneficial for music.

johnnythunder's picture

Home theatre amplifiers are rarely audiophile products. That doesn't mean they may not sound decent but this magazine is 99% dedicated to 2 channel (or even one channel) systems DECICATED TO PLAYING MUSIC. And tone controls have not been part of audiophile equipment for eons. That doesn't mean that some audiophile integrated don't have them. Certain Japanese high end manufactures such as Luxman, Leben, Accuphase have tone controls that don't harm the integrity of the signal. " Well engineered" is a very slippery slope. You seem to be equating well engineered with a plethora of features. I prefer bespoke and hand made with attention to detail and with sound quality in mind rather than something with large heatsinks and 900 inputs. Less is more with audiophile equipment. An Apple Watch has more features than a Swiss Watch. They both tell time but one is a modern feature laden appliance and one is an heirloom product.

MZKM's picture

Well, not in this case, you get similar measured performance compared to an amp that’s 1/10 the price. Unless you believe there is a large factor in sound quality that isn’t captured in Atkinson’s measurements (remember that this isn’t magic, if there is a difference in the electricity it’s outputting, it has to be measurable).

Doesn’t matter if not traditional, there is hardly a case for being against DSP (unless the case is if done poorly). Most high-end HiFi manufacturers are behind the times, some may offer a Loudness control but many AVRs use the ELC to perfectly preserve tonal balance regardless of listening volume, because as a fact, no passive speaker on Earth sounds the same at low volumes and at reference volumes, our hearing doesn’t work like that.

johnnythunder's picture

You may want them to tell you the whole story but that's not possible. It's not that easy. Audio is part science and part magic and part subjective tastes. Give 2 audio designers the same components to work from and the component they assemble from those parts will sound different. It's like the cooking show CHOPPED - use the same ingredients and some people will produce amazing stuff and others not so much. Ask Nelson Pass if all things sound the same. It's a very very subtle art. Price will dictate many things besides sound quality so it's not just $$$$ that is the deciding factor.

Glotz's picture

Comparing products is only accomplished while listening.. not theoretical garbage. Measurements never tell one how a unit sounds... Never.

Bogolu Haranath's picture

"Music exists in the space between the notes" .......... Is it the 3rd harmonic space? :-) .........

Ortofan's picture

... Luxman L-509X, the Marantz PM-KI Ruby and the Parasound Halo HINT 6.

In the meantime, Aesthetix Audio can redesign their product to incorporate adequately sized heatsinks.

Jason Victor Serinus's picture

kindly arrange to have Jason sent a new car, a 48-hour day, and a new storage facility for all the products on Ortofan's list.

Bogolu Haranath's picture

Has JVS seen the pictures/video of the new, first ever, mid-engine Corvette Stingray? ......... May be JVS could take it for a spin and write a review about the car and the 10 speaker Bose audio system, which comes with the car :-) ........

Ortofan's picture

... trade in your pair of D'Agostino power amps on a new car - problems solved.

Bogolu Haranath's picture

As far as storage space is concerned ........ JVS could get some PODS ........ not the iPods ........ They are also, kinda portable :-) ..........

Anton's picture

48 hour days are not all they're cracked up to be, Jason!


johnnythunder's picture

it was perhaps the loveliest sounding amplifier I ever heard. How can you criticize a product without actually listening to it?
PS - I know tube amps theoretically do not need heatsinks. Was just making a point.

Allen Fant's picture

Great review- JVS
The Integrated Amp has certainly come a long way over the decades, so much so, I am seriously considering my next purchase. This newest offering from Jim White peaks my curiosity.

briandx11's picture

Great review; thoughtful and complete. What I am not 100% clear about is, at its base price point of $7000 can you recommend this item, and is it Class A material?

I am especially interested as I have a Mimas on order from Aesthetix that will arrive hopefully by the end of next month. What is clear to me from the review is that the Mimas should have no worries adequately driving my Wilson Yvette's.

P.S. As my piano teacher points out routinely to me, the space between the notes is the performance, not the composition.

Jason Victor Serinus's picture

Thank you for the strokes. Hopefully they are deserved, because the recommendation I state in the conclusion may not seem conclusive enough for you. It is, however, my honest opinion, complete with the stated caveat.

Heard in the context of my considerably more expensive system, I consider the Mimas, in its initial base iteration (without phono preamp, DAC, headphone upgrade...), deserving of a solid Class B rating . It is possible that, with all its options, the rating could conceivably rise to B+.

A question to your piano teacher. Is the space between the notes solely in the performance, or is it perhaps inherent to / lying dormant in the composition, waiting for the right artist to bring it to life?


briandx11's picture

Thanks Jason for your additional comments. Your review is one of the reasons I subscribe to Stereophile.

As far as my piano teacher is concerned, her assertion is that the notes on the page is simply structure, a kind of baseline. It is true that many composers add suggestions and other marking to further clarify their original intent, however until the performer(s) actually plays the piece, no music exists.

Bogolu Haranath's picture

Both the Wilson Alexia2 and the Wilson Yvette present difficult low impedance loads and phase angles ....... See Stereophile measurements ........ Mimas may not be supplying enough current to handle those difficult loads :-) .........

briandx11's picture

Before making the decision to purchase the Mimas I read a review from Great Britain where the reviewer actually owns Wilson Yvettes. It is clear from this review that the Mimas should have no problems properly driving my speakers.

Bogolu Haranath's picture

Yes ..... I have also read that Hi-Fi News review ....... Wilson Yvettes are relatively easier to drive than Alexia2 ...... Hope you enjoy listening to the Mimas driving the Yvettes :-)

Bogolu Haranath's picture

You may want to consider Mark Levinson No.5805 integrated amp, which is approx. in the same price range as Mimas ...... See Stereophile review of ML-5805 :-) ..........

Robin Landseadel's picture

"Is the space between the notes solely in the performance, or is it perhaps inherent to / lying dormant in the composition, waiting for the right artist to bring it to life?"

Good question. Sviatoslav Richter's performance of the opening movement of Schubert's B flat sonata is more space than notes. Probably the most dramatic performance of the work we will hear.

mmole's picture

...Cage's "4'33" so compelling: All space with no notes at all.

Bogolu Haranath's picture

I'm waiting for JVS' reviews of D'Agostino Progression integrated and darTZeel LHC-208 integrated amps :-) ........

Bogolu Haranath's picture

Space .... The final frontier? :-) ..........

mcrushing's picture

So glad I kept reading this discussion. Perhaps for the first time ever, the tired old argument about how amps should sound the same if they measure the same actually gave way to an interesting discussion about music.

briandx11, I LOVE your piano teacher's idea that "the space between the notes is the performance." But JVS's insight about notes and spaces lying dormant in a composition until an artist brings it to life reminded me of a video I saw recently which compared Dusty Springfield's version of "Son of a Preacher Man" to Aretha Franklin's. A great example of two artists bringing totally different experiences and points of view to the exact same piece of music. (It's worth noting also that both recordings were produced by Jerry Wexler.) Here's a link for anyone interested:

It's part of the Vox "Earworm" series, which tackles some pretty advanced musical theory in an accessible way that I'd think many Stereophile readers would enjoy.

JohnPM's picture

The dBW power figures seem to be reduced depending on the load relative to 8 ohms, for example:


Aesthetix specifies the maximum power into 4 ohms as "nearly double" that into 8 ohms; I measured 275Wpc into 4 ohms (21.4dBW, fig.6)

275 W is 24.4 dBW, why the 3 dB reduction? Watts are watts, surely.

John Atkinson's picture
JohnPM wrote:
275 W is 24.4 dBW, why the 3 dB reduction? Watts are watts, surely.

Stereophile's convention follows that established by Martin Colloms and others in the 1980s, in that all our dBW figures are referenced to 2.83V into 8 ohms, ie 1 8 ohm W. That way, an amplifier's departure from being a perfect voltage source is evident.

If the Mimas were a perfect voltage source, it would deliver 22.55dBW into 8 and 4 ohms. As it actually clips at 180W and 275W, the latter a shortfall of 1.15dB, it is clear that this amplifier is not a voltage source.

John Atkinson
Technical Editor, Stereophile

JohnPM's picture

Thanks for the clarification. Perhaps the unit should be dBW8R or similar. Or perhaps the rms voltage delivered into the different loads should be stated, as V or dBV.

Bogolu Haranath's picture

For some of the integrated amps such as the Mark Levinson No.5805, the 2 Ohm power output is measured ..... However, for some of the integrated amps such as this Aesthetix Mimas the 2 Ohm power output is not measured :-) .........

John Atkinson's picture
Bogolu Haranath wrote:
For some of the integrated amps such as the Mark Levinson No.5805, the 2 ohm power output is measured ..... However, for some of the integrated amps such as this Aesthetix Mimas the 2 ohm power output is not measured :-)

When a manufacturer specifies maximum power into 2 ohms, I do measure the clipping power into that load. However, if they don't I tend not to. This is because the manufacturer is basically saying that the amplifier does not have the necessary power supply capability to deliver continuous clipping power into 2 ohms - something that would add considerably to the price.

In the past when I have still tested the power into 2 ohms, the amplifiers have tended to break on this test. Even with 2 ohm-specified amplifiers, I leave this test to the very end.

John Atkinson
Technical Editor, Stereophile's picture

I own an Atlas, a Janus and a Calypso. I greatly admire the design and engineering in all of these products but my experience has been that the Atlas amps lack dimensionality and simply don't convey the complex timbre of symphony orchestra and other acoustic instruments. Having said that, my particular sample of the Atlas might be the culprit. A couple of years into its life it was sent back to Aesthetix I think twice, and the last time it required over a thousand dollars in repairs and no really adequate explanation of why except that a fuse blew on a single board but the fuse failed to protect the board. A smaller power supply (not the main giant Mercury supply) had to be replaced also. I finally gave up and purchased an ARC Reference tube amp for the Magnepan 20.7s and was astonished at what I'd been missing. In short, Aesthetix designs really beautiful products, but I think their preamp products outperform their power amp products. You can alter their preamp products to your liking through tube rolling and customize the sounds of their preamps accordingly, making them very flexible units.