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SMSL VMV A2 Review (Stereo Amplifier & DAC)

amirm

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This is a review and detailed measurements of the SMSL VMV A2 stereo "desktop" DAC and amplifier. It was sent to me by the company and costs US $999. VMV is the higher-end brand in SMSL lineup.

The look and feel of the A2 is similar to the latest line from SMSL:

SMSL VMV A2 Review DAC Stereo Amplifier.jpg


It looks nicer though in this "widescreen" presentation. The rotary encoder feels a bit looks physically but is very responsive.

As noted, there is an integrated DAC in the A2:

SMSL VMV A2 Review DAC Stereo Amplifier back panel DAC USB.jpg


I like the diagonal binding posts which gave me more room than I typically find in these smaller desktop amplifiers.

As set of stick on feet were provided that I did not like that much but they also supplied tall spikes which you may have to use to provide ample room for the little fan underneath to suck air into the unit:
SMSL VMV A2 Review DAC Stereo fan Amplifier.jpg


I could not feel much air moving though as the only exhaust are the two slots in the back. I rather have something moving air than nothing though. Then again, at close distance you can hear the fan running. Music though overwhelms it so probably not a big issue in practice. In use, the A2 got warm to touch but nothing that concerned me especially given the very solid chassis.

A remote control is provided which I did not use. Instead, I used the intuitive user interface to select inputs and such. A number of EQ profiles are provided which I did not try to understand or use. There is no documentation on what they do in the manual. Best to look up the same from ST Micro datasheet on which this amplifier is based on.

Edit: this amplifier topology uses a good baseline class D amplifier from ST Micro but then augments it with the AX5689 digital feedback control system from Axign. This serves to highly linearize the response of the amplifier as you see later.

SMSL VMV A2 Measurements
I started with analog input but ran into an issue I have seen with some ST Micro implementations that pull in the loop filter:


VMV A2 Analog Input Measurements Amplifier.png


There seems to be low frequency energy or DC pumping into my analyzer causing SINAD to jump from 65 to 83 dB. No amount of messing with grounding and such helped in any way. What completely eliminated it was using Coax or USB Input:

VMV A2 Digital Coax Input Measurements Amplifier.png


Now we are talking! This is excellent performance for a desktop amp, putting the A2 in the likes of Hypex class D amplifiers:

Best desktop stereo st amplifier review.png


Signal to noise ration is very good:

VMV A2 SNR Digital Coax Input Measurements Amplifier.png


We are clearing the 16 bit audio hurdle at just 5 watts which is my target which sadly many amps fail to achieve.

The second puzzle was the frequency response. Here I am driving the amplifier using Coax at 192 kHz sampling so we should have flat response to half of that but we don't:

VMV A2 Frequency Response Digital Coax Input Measurements Amplifier.png


Indeed, you can set the sample rate to anything you want, change to USB, etc. and you always get what seems to be 44.1 kHz sampling! SMSL advertises the "high-res" capability heavily in this amp but while the DAC is likely capable of delivering that, the amplifier happily shuts any extra spectrum above audible band.

The subwoofer output has gain control but not any other parameters:
VMV A2 Subwoofer Frequency Response Digital Coax Input Measurements Amplifier.png


Note also that the main speakers will always run full-range.

Crosstalk is insanely good:
VMV A2 SNRCrosstalk Digital Coax Input Measurements Amplifier.png


Maybe the DAC is muting one channel and hence the excellent results. I did not try to investigate.

We have plenty of power into 4 ohm:

VMV A2 Power into 4 ohm Digital Coax Input Measurements Amplifier.png


Not much headroom though as is typical of class D designs:

VMV A2 Peak Power into 4 ohm Digital Coax Input Measurements Amplifier.png


An aggressive protection circuit would shut the unit down when I tried to get max power at 1%. Fortunately the box automatically reboots and is back to business without any user intervention.

8 ohm load cuts the power in half:
VMV A2 Power into 8 ohm Digital Coax Input Measurements Amplifier.png


As we have seen from other STM measurements, this is one linear amplifier with no care about the frequency or level:

VMV A2 Frequency vs Power into 4 ohm Digital Coax Input Measurements Amplifier.png


SMSL VMV A2 Listening Tests
I test the A2 with my lab infinity Reference R253. The A2 had no problem pushing these speakers to insanely loud levels while volume level remained between 45 and 50 dB (all testing was using USB). The sound was absolutely clean, authoritative with zero issues to complain about. If the amp has a limit, it doesn't show up in this type of testing.

Conclusions
SMSL pushes the boundaries of desktop amplifiers producing a powerful and very clean design if you use digital input. Analog input has some low frequency problem which has a tiny chance of being instrumentation issue. Hopefully they can comment. BTW, if you use a-weighting, the problem disappears since it filters that spectrum. And this is not an audible problem due to very low frequencies involved.

Use of a fan is a bit of bummer but I don't think it is a practical concern.

Subjectively the A2 delivers with plenty of power to drive any small to medium system with plenty of headroom left. And oh, those of you who hate high-res, now have the perfect amplifier as it won't try to reproduce ultrasonics anyway! :) Fortunately feeding 24-bit data does work so don't through out high-res content that quickly.

Overall, I am going to recommend the SMSL VMV A2 amplifier. The combination of the Axign controller and good baseline Class D amplification seems to be a winner.

NOTE: this is a review of a new product. My recommendation is strictly based on its performance in the limited time I had with the unit. You are responsible to research issues of reliability, functionality, support, long term stability, etc. on your own. Please don't be an early adopter if are risk averse in these regards.

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As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
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Despite generally good perfornace, there are some issues here, and I have, quite frankly, lost a lot of faith in SMSL fixing anything unless excessively pressured to do so.
 
400w out of that lil box!?! With those measurements?!? The future's bright even if it doesn't play over 20khz - no one will notice.

I have to wonder about long term reliability though.

Edit: Thank You Amir! How rude to forget.
 
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Thanks for the review amirm! Looks like a good product with an accompanying price tag.

In the past you have shown frequency response measurements at 4 and 8 Ohms. At what load was the response for this review measured at and can you also provide the other one? In the same vein, I wish you brought back frequency response measurements with either simulated or real speaker loads.

Thanks again!
 
In the past you have shown frequency response measurements at 4 and 8 Ohms. At what load was the response for this review measured at and can you also provide the other one? In the same vein, I wish you brought back frequency response measurements with either simulated or real speaker loads.
I forgot to run that but I suspect zero difference as this amp has a feedback loop after the filter. As you see, the response is already dead flat. If it had load dependency, it would show up.

On my simulated load, it didn't show much of substance so I stopped using it. And I think I stole some parts from it so it is not working anymore. :)
 
I forgot to run that but I suspect zero difference as this amp has a feedback loop after the filter. As you see, the response is already dead flat. If it had load dependency, it would show up.
OK thanks Amir.
On my simulated load, it didn't show much of substance so I stopped using it. And I think I stole some parts from it so it is not working anymore. :)
Its not like you don't have any real speakers laying around =)
 
Its not like you don't have any real speakers laying around =)
The problem is that they are loud to use indoors. If you look at the date stamps on the above measurements, they were made after midnight. If I have to make noisy measurements, it would severely limit what I can test.

That said, occasionally I can test with a real speaker if there is interest for some reason.
 
The problem is that they are loud to use indoors. If you look at the date stamps on the above measurements, they were made after midnight. If I have to make noisy measurements, it would severely limit what I can test.

That said, occasionally I can test with a real speaker if there is interest for some reason.
Mainly tubes.
 
The amp technology has good potential but the cons of using a fan, frequency response limitation and bad analog input are very disappointing.
 
I don't understand the issue with the analog inputs. Is there DC offset when switched to the analog inputs with no signal? If so how much? Is it safe for the speakers to use analog inputs?
 
Sub-out is unfortunately too low a frequency for my liking... I can imagine people going back to multichannel methods to make sure they have more control over the 50-100Hz region, instead of simply using the sub-out plus the subwoofer's own crossover.
 
Thanks for the review!

I find it interesting from cost perspective to compare this unit to Deonon AVR3600H since the price is similar. It's DAC and Amp measures slightly better and It puts out extra ~40w per channel into 4 ohms compared to the Denon. Similar figures into 8 ohms. I doubt the difference is really audible.

However the Denon has ..8 amplifiers, it doesn't have DC problem messing up the RCA inputs. It has greater selection of inputs and extra 7 HDMI inputs should you need them. It has HEOS streaming capabilities for your favourite music streaming service and internet radio you can control via app - wired or wireless. Multi room setups. Audyssey ext32 DSP dohiggery for room correction and decent eq, bluetooth for your headphones or streaming from phone. Two subwooofer outputs you can configure at your heart desire. Headphone output, power savings mode and bunch of other features few of us will ever use and I don't recall while writing this.

Sure, the Denon is bigger if you are short on space.
 
You missed a big minus on the Denon. You can't buy it anymore.
True, I used it as example because I own one. I bought it and was surprised by it's sound quality until I stumbled on this website and discovered amirs review. Then it made sense. Without searching I suspect one can buy something similar for similar price from Denon today - the AVR 3700?
 
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