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SMSL SA100 Audio Amplifier Review

amirm

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#1
This is a review and detailed measurements of the SMSL SA100 Stereo Audio Amplifier with analog and Bluetooth inputs. It was kindly sent to me by the member @lunagreenjp who is a distributor for SMSL. The M100 costs just US $73.99 on Amazon including shipping.

Form the outside the SA100 matches its sibling, the M100 DAC:

SMSL SA100 Bluetooth Amplifier Audio Review.jpg
Pushing the power button multiple times lets you select between Aux RCA in and Bluetooth. Pushing and holding the volume control lets you select Bass and Treble amounts. I was surprised that the unit had shipped with both set to max instead of zero.

The volume control works well and overall, you feel like you are getting more than the $74 price indicates.

Here is the back panel:


SMSL SA100 Bluetooth Amplifier Back Panel Connectors Audio Review.jpg
An external "laptop style" switching supply powers the unit. It is almost as large as the SA100 itself although not as thick.

I was pleased that my rather large and unwieldy banana speakers securely mated with the jacks on the SA100.

Overall, my impression is positive about the look and feel of this little, and I mean little, integrated amplifier.

The heart of the unit is TPA3116D2 class-D amplifier IC from Texas Instruments. I suspect it is made for Bluetooth speakers and such. In use the SA100 ran cool no matter how hard I pushed it.

Amplifier Audio Measurements
As usual, we start with our dashboard of a 1 kHz tone at 5 watts into 4 ohm load:
SMSL SA100 Bluetooth Amplifier Audio Measurements.png


As is typical of amplifiers with volume control, one can get slightly different results depending on how you set the input level relative to volume control on the unit itself. The above is with volume control set to -1 I think.

High distortion dominates the output resulting in one of the worst numbers we have measured with respect to SINAD (noise+distortion relative to main signal):

Best Bluetooth Stereo Amplifier.png


Frequency response droops at both end some:

SMSL SA100 Bluetooth Amplifier Frequency Response Audio Measurements.png


The sharp drop after 20 kHz tells me that input is perhaps digitized to provide tone control?

Signal to noise ratio "OK" for the class:

SMSL SA100 Bluetooth Amplifier SNR Audio Measurements.png


Measuring distortion and noise relative to output power with 8 and 4 ohm gets us:
SMSL SA100 Bluetooth Amplifier Power into 8 ohm Audio Measurements.png

SMSL SA100 Bluetooth Amplifier Power into 4 ohm Audio Measurements.png


Distortion sets it very early and climbs after that. Specified power ratings are quite inflated as is typical of these chip amps.

The sharp filter limit the measurement of harmonic distortion when we sweep frequency and power level:
SMSL SA100 Bluetooth Amplifier THD vs Frequency vs Level Audio Measurements.png


The red curve for example is for 20 kHz but since we can't see any of its harmonics, it looks artificially low.

Here is the spectrum of a 1 kHz tone without any kind of filter (the above had filters):
SMSL SA100 Bluetooth Amplifier FFT spectrum Audio Measurements.png


Speaking of filter, even though I used an AES-17 filter to get rid of ultrasonic noise, the level was still so high as to confuse my Audio Precision analyzer. It would often not be able to capture the input signal properly.

Conclusions
If we measured the SMSL SA100 on an absolute level, it would rank horribly of course. But I don't think that is proper here. The SA100 costs so little and probably gets use in tertiary applications such as a workshop amp to drive cheap speakers you don't mind getting stolen or destroyed. And maybe for casual desktop use.

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

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RayDunzl

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#2

Tks

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The volume control works well and overall, you feel like you are getting more than the $74 price indicates.
Ehhh

Maybe save some cost on the volume control and trade for some better performance next time?
 

confucius_zero

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#5
I look at this frequency response... seems to be that old old saying "No highs, no Lows, must be Bose"
 

SEKLEM

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#6
I look at this frequency response... seems to be that old old saying "No highs, no Lows, must be Bose"
In practice you’d be hard pressed to hear much difference between this and a much better performing amplifier on a relatively inexpensive set of speakers in terms of frequency response. The graph looks dramatic however we are only down 1.7 dB @ 20kHz. However... Bose...
 

amirm

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#8
So the measured THD+N is 4 times the quoted value?
I measure at 5 watt. THD+N is slower below that which is likely what they/TI used.
 
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#10
If input is digitised, can you try a 5 watt output from a bluetooth input? use tidal 1khz 16/44 test tone ?
 

scooter

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#11
Amir why do you measure SINAD without nominal input level of 2 volts? I see it is set as 0.18V.
 

RayDunzl

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#12
Amir why do you measure SINAD without nominal input level of 2 volts? I see it is set as 0.18V.

It's an amplifier.

Small voltage in --- 0.18V yields 5V output in this case, the standard for the output level for his SINAD test.

That calculates to 28.87dB voltage gain.

Measured voltage gain was 27.9dB in this amp.

---

If 2V were applied to the input, with 27.9dB gain, the output would try to be 49.6V, yielding 615W into the 4 ohms load.

That won't happen with this unit.

---

PS: I read through the test twice, can't see where you see 0.18V Now I finally see it. Doh.
 
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scooter

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#13
Small voltage in --- 0.18V yields 5V output in this case, the standard for the output level for his SINAD test.

That calculates to 28.87dB voltage gain.
Maybe it's good to see what SINAD we'll get when applying nominal input and adjusting amp gain somewhere before the clipping level. Won't this show more real world application?
Or is this a usual standard when testing the amps which I'm not aware of ?
 

RayDunzl

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#14
It's Amirm's standard power amp (for speakers) test level. To level the field among amplifiers of different maximum power, I'd say.

Amplifier Audio Measurements
As usual, we start with our dashboard of a 1 kHz tone at 5 watts into 4 ohm load:

5W continuous would be pretty loud into a typical speaker.

Casual listening levels might average a tenth or a quarter of a watt or so.

Listening to music, rather loudly, here at my place, a 5W average would create roughly 500W peaks... with easily observed 20dB peak above average SPL.

And my not green amps would warm up to 130~140F on the heat sinks after a little while.
 
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scooter

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#15
IMHO the most important factor in correct gain staging is to ensure we get the cleanest signal amplification from an amplifier, if we choose "small" input level then we amplify more noise than signal.
 

scooter

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#16
Listening to music, rather loudly, here at my place, a 5W average would create roughly 500W peaks... with easily observed 20dB peak above average SPL.
Correct, but what I'm trying to address here is a usual and proper way one could wish to set an input level according to the sensitivity ratings of there amplifier model.
You say when you are listening at around 5W at home but not stating what an input level is fed to amplifier, I'm sure it's nominal and later attenuated by amp' volume control. If it was set to lower than sensitivity rating then you'd need to crank the volume up to reach the same spl, which would be full of distortion and noise.
 

RayDunzl

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#17
IMHO the most important factor in correct gain staging is to ensure we get the cleanest signal amplification from an amplifier, if we choose "small" input level then we amplify more noise than signal.
If you choose large input level the result is too loud to listen to without hearing protection.

My big amps give 700W into 4Ohm at a 2.45v input. They claim 26.4dB gain.

Obviously, I don't feed them their "nominal input" as you call it.
 

RayDunzl

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#19
Correct, but what I'm trying to address here is a usual and proper way one could wish to set an input level according to the sensitivity ratings of there amplifier model.

All amp input sensitivities may be different.

The ouput levels should be matched - by the measuring theory espoused here.


You say when you are listening at around 5W at home but not stating what an input level is fed to amplifier,

No need to know, really.

Typical:
DAC -> 2Vpk -> analog volume control (reduces voltage and noise if there is some) -> an appropriate voltage -> power amp -> speakers -> desired listening level.

So:
DAC -> 2vpk -> volume control -> 0.18V -> amplifier -> 5 watts into 4 ohms and it is likely very loud of speakers are attached.

Test:
AP -> 0.18V -> volume control almost not attenuating I think, at -1 setting -> 0.18V -> amplifier -> 5W @ 4 Ohms


I'm sure it's nominal and later attenuated by amp' volume control. If it was set to lower than sensitivity rating then you'd need to crank the volume up to reach the same spl, which would be full of distortion and noise.

The sensitivity rating at the amplifer is for maximum output, not necessarily the same as sane listening level.

Maybe we're talking about different things.

It's really not something I find a need to worry about.
 
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