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Fosi Audio BT10A Bluetooth Stereo Amp Review

amirm

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This is a review and detailed measurements of the Fosi Audio BT10A Bluetooth Class D stereo amplifier. It is on kind loan from a member. The B10A seems to have just been updated with tone controls and sells for US $50 from Amazon with free prime shipping.

This is a very small amplifier:

Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Audio Review.jpg

You can't see the depth but it is quite shallow. Other amps like this I have tested have complicated interface to change built-in digital tone controls. There are none here so it was easy to use.

The back connectors is identical to what you see on myriad of such amps:
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Bluetooth Connectors Power Sup...jpg
While the external laptop replacement power supply is large compared to the size of the unit, it is not as huge as some others. Note that it comes with a three-prong, figure-8 AC socket so you have less options to replace the cord.

I did not bother testing the Bluetooth. I am assuming it autoselects it if in range as the priority input as there is no switch to select it.

Speaker terminals are tiny of course but I managed to plug in my heavy and large banana jacks into it.

Amplifier Audio Measurements
As usual, we start with our dashboard view of 1 kHz tone into 4 ohm load with volume adjusted for 29 dB gain (THX recommendation):
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Audio Measurement.png


Second harmonic dominates to the tune of -65 dB which sets the SINAD to the same value. This says that noise is not a contributor to SINAD and as such, any gain setting would have produced similar SINAD. The 65 dB SINAD value doesn't put a smile on anyone's face but it is a couple of steps above $30 units (e.g. Lepy LP-2020A):

Best mini amplifier review.png


Noise figures are barely adequate:
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D SNR Audio Measurement.png


32-tone test signal shows more or less uniform distortion at all frequencies:

Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Multitone Audio Measurement.png


19+20 kHz tones shows 55 dB of distortion-free range:
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D 19+20 kHz Measurement.png


Their full (and unrealistic) amplitude shows higher distortions than multitone test does.

Frequency response shows truncated low and high frequencies:
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Frequency Response Audio Measu...png


Above with a resistor load. Subjective the amp to my new complex speaker model of a 2-way speaker generates:
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Frequency Response with Simula...png


The speaker model has a its impedance shooting up in high frequencies causing similar issue here. There is a question of whether the model is similar to mass of 2-way speakers so don't run with this yet. What you can conclude is that the speaker choice does impact the speaker response. In audible band though, the impact is minimal and in some way is correcting the dip toward 20 kHz. A good amp would have no speaker load dependency.

Let's see how much power the BT10A can produce into 4 ohm load:
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Power into 4 Ohm Audio Measure...png


At 33 watts with both channels driven this is good bit of power. Similar story with 8 ohm load:
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Power into 8 Ohm Audio Measure...png


Lack of power is by far the #1 issue in these amplifiers. You may not be able to hear their noise and distortions but you absolutely will hear them complain when they clip. At these power levels you should have a reasonable experience unlike some other budget amps that stop at 10 watts or so.

Allowing for more distortion (1% THD+N) and testing with a short-term sinewave and long term produces identical numbers:
Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Peak and Max Power into 4 Ohm ...png


The input power supply is regulated so there is no reservoir to provide short-term juice.

Thermal Stability
Performance gradually improved by a 2 dB or so after 30 minutes of playing at 5 watts:

Bluetooth 5.0 Stereo Audio Amplifier Receiver 2 Channel Class D Warm Up Audio Measurement.png


Above tests were performed after this warm-up period.

Conclusions
The Fosi Audio BT10A doesn't seem half bad. I am not going to provide a verdict one way or the other. You can decide for yourself if the performance is good enough for your application.

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

You know the money situation is bad when I have to get a $50 amp on load to test! So please, help improve my bank account balance by donating as much as you can using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

bigx5murf

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This looks suspiciously similar to the "breeze audio" ones on aliexpress. Can you confirm it's running a tpa3116/3118 chipset? If so, there are single and dual chip versions, the latter being more powerful.
 

bigx5murf

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It says TPA3116 on the front of the unit.

Sorry I missed that, I have two "breeze audio" amps that look exactly like this, but don't have BT.

Do you know if this is a single or dual chip?
 

Toku

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The characteristics are similar to SMSL SA100 which uses the same TPA3116D2.
Is this the performance limit of the TPA3116D2 chip?
 

NTomokawa

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I've seen many similar devices being sold under a variety of names. I wonder which sweatshop is cranking them out.

Some of the tubes in the "tube amps" being sold under the name "Nobsound" are purely decorative. Maybe they ought to rename themselves "Noobsound" instead... Makes me wonder whether that "6J4x2 tube amp" up there is the same...
 

phoenixdogfan

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The FR initially looked like the most worrying thing, but the 48k resonance takes care of it at the high end with moost loads, and, let's face it, no one will use this amp with speakers that go much under 50 hz at the low end. So it could be good 'nuff for a lot of lower fi use cases.
 

IowAudio

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I sent this in to be tested just cause there is so many little amps similar to this one. I got this one used for $25 and the new version is $40 so the performance isn't a surprise but pretty fair at this price. In my opinion performance by ear this beats my other little Kinter K2020A+ Limited Edition Original Tripath that also sells for $40 and doesn't have bluetooth or binding posts.
 

Tangband

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The characteristics are similar to SMSL SA100 which uses the same TPA3116D2.
Is this the performance limit of the TPA3116D2 chip?
No, the sound can probably be even better with a better switched mode supply at 24 volt and 6 A. I have done a lot of testing with Tpa3116D2 and with different PSU:s. I can recommend psu:s from Meanwell.
The sound gets better if there is more than the usual 1000 uF at the input terminal.

With those conditions , 24 volt, 6 A and maybe 5000-6000 uF , the chip sound very clean up to the point if clipping.
Personally I rate the sound from a good implementation of the tpa3116D2 as sounding better than a LM3886 amp chip. ( I have a pair of those to ).
If you read the Texas instruments application notes of the tpa3116D2, you can se they have a bit better test result than this review. For example, you really need a psu with less than 200 mV ripple.
The psu:s following those cheap amplifiers are often crap.
The pictures below shows my own version of tpa3116D2 with a bigger external psu from Meanwell and capacitors ( 6*1000 uF ) from panasonic.
 

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Jeephead

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I am using this amp and am surprised how well is sounds. I actually connected my Schiit Headphone set up to it. I am currently running a Magni, Modi Dac, Loki EQ, and a Mani phone pre-amp through a SYS. I use a Raspberry Pi running Moode audio going to DAC. I do not use the BT for streaming music. The bass and treble controls are helpful on the Fosi but the additional Loki EQ really helps the lo/hi end roll off of the Fosi. I send this all to a pair of Bose AM5 dual cubes and sub. It is in a small room for near field listening of vinyl and digital. It really makes the Bose finally sound good. Not my ideal setup but good for what I had on hand. Wanted a Schiit Vidar $699 or an Emotiva Basx A-100 $239. Schiit is not in the budget. Emotiva is doable but it seemed to not get a favorable test result here and I am not sure how much better it will make speakers sound with my setup. Class A/B vs D is sure to sound better but do I really need to improve? Thoughts?
 
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