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Fosi Audio BT20A Pro Amplifier Review

Rate this stereo amplifier

  • 1. Poor (headless panther)

    Votes: 3 1.0%
  • 2. Not terrible (postman panther)

    Votes: 33 10.8%
  • 3. Fine (happy panther)

    Votes: 180 59.0%
  • 4. Great (golfing panther)

    Votes: 89 29.2%

  • Total voters
    305

amirm

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This is a review and detailed measurements of the Fosi Audio BT20A stereo class D amplifier based on TI TPA3255 IC. It was sent to me by the company and costs US $99.99 with 32 volt power supply.
Fosi Audio BT20A amplifier stereo class D amplifier TPA3255 Review.jpg

Despite its low cost, the case gives a feeling of quality. I am not usually fan of tone controls in low cost amps because you can never set them to flat response (the detents are there but don't work). As you will in the measurements, Fosi has made sure that they work correctly in this instance. A stout power switch controls power. In addition to 32 volt supply, company also shipped the optional ($40) 48 volt supply which is quite a giant:
Fosi Audio BT20A amplifier stereo class D amplifier TPA3255 back panel power supply Bluetooth ...jpg


As you see, Bluetooth input is also supported.

FYI there is an included orange volume control knob to give the unit some color.

Fosi Audio BT20A Pro Measurements
The tests are in 48 volt unless I say otherwise (I had mistakenly assumed it was the standard, not the 32 volt). Here is our dashboard:

Fosi Audio BT20A amplifier stereo Measurements.png


Notice the great channel match in addition to very good SINAD which represents noise and distortion. Same is true with 32 volt supply:
Fosi Audio BT20A amplifier stereo 32 volt supply Measurements.png


This nicely lands the BT20A Pro in the "very good" category of all amplifiers tested regardless of price:
Best desktop audio amplifier review 2023.png


Zooming in to see the competition:

Best desktop audio amplifier cheap review 2023.png


SNR is good for the class:
Fosi Audio BT20A amplifier stereo SNR Measurements.png


I expect load/impedance dependency in this class of switching amplifiers but here, the peaking is almost entirely out of band which is good:
Fosi Audio BT20A Frequency Response Measurements.png


Seeing how you have tone controls anyway, you could tailor any peaking with adjustment of the treble control. Won't be exact but should be good enough.

That aside, note how the response is more or less is flat in audible band with the treble and bass controls set to their detent, center position.

Multitone is good enough for the class:
Fosi Audio BT20A amplifier stereo Multitone Measurements.png


Crosstalk is very good:
Fosi Audio BT20A amplifier stereo Crosstalk Measurements.png


Let's start our 4 ohm power measurements with 48 volt supply:

Fosi Audio BT20A amplifier stereo Power into 4 ohm Measurements.png

Fosi Audio BT20A amplifier stereo max and peak Power into 4 ohm Measurements.png


Wow, this little box can pump out some serious watts, albeit in the short term testing! Switching to 32 volts cuts this down even though 4 ohm is mostly current limited:
Fosi Audio BT20A amplifier stereo Power into 4 ohm 32 volt Measurements.png

Fosi Audio BT20A amplifier stereo max and peak Power into 4 ohm 32 volt Measurements.png


The larger power supply must have more capacitor reservoirs than the 32 volt.

Switching to 8 ohm we naturally see the biggest hit to power: [Edit early version had the wattage wrong]
Fosi Audio BT20A amplifier stereo Power into 8 ohm Measurements.png


Although to be fair, I put the cursor at an earlier point than for 48 volt supply (not enough measurement points there).

I was pleasantly surprised by the transfer function being so smooth:
Fosi Audio BT20A amplifier stereo Power vs Frequency Measurements.png


Finally there is not much of a pop on but there is for off:
Fosi Audio BT20A amplifier stereo pop on and off Measurements.png


Conclusions
The TI TPA3255 seems to be a capable platform when paired with a good implementation which is what we have in BT20A Pro. You get a sense of that in company marketing material which includes Audio Precision measurements. Usability is excellent with high quality case and controls especially with respect to ability to set the tone controls to flat.

It is also nice to see so much power coming out of this little box with the beefy 48 volt power supply, showcasing the advancements in amplification density we have today.

As an aside, the company has been a joy to work with. They were exceptionally polite, cordial and patient as I went through my testing and evaluation. They tell me they have internal R&D team and it shows.

I am happy to add the Fosi Audio BT20A Pro to my recommended list.

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

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
Last edited:

Billy Budapest

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It’s very decent for a tiny little thing that costs a hair under $100 USD, but I’m not going coo coo for Cocoa Puffs over it. Hence, the “Fine” rating.
 

Fosi Audio

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Many thanks to Amir’s honest review and measurements. Happy Easter to Amir and all ASR fans!

We really appreciate ASR which allows us to listen to and gather users’ feedback on our old models. We absorbed a lot from the voices and develop this BT20A Pro. It’s not a perfect amp but we will keep making effort to improve it.

Here we want to give an exclusive 20%-off discount promo code for the BT20A Pro to all ASR fans. (Valid from today to April 30.)
20APROASR20

Hope you will be interested in this new amp!
 

Hipster Doofus

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DONT GET ME STARTED ON TONE CONTROLS ;)

OK...i am an audiophile by osmosis only, with no real knowledge of electronics. But I have met a few who do.
My good friend was in business with Dick Olsher from Stereophile and another Stereophile reviewer lives up the street. I have been in on testing Ongaku amplifier clones. and on and on.

I have seen people, including myself spend hours and hours and thousands of dollars all trying to discern minute differences, in test that took way too long to even remember what the first tone sounded like.

Things like... (all quite fun by the way)

upgrade capacitors in amps and speakers
roll tubes!
change cables.
change cartridges.
mix and match so much equipment it would make your head spin.

And every once in a while, I would say in my wise-ass way, if you want a different sound why don't you use the tone controls.

oh yeah ... audiophile equipment does not have tone controls, I would hear.

SO, 3 CHEERS FOR TONE CONTROLS
 

AdamG

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Holy moly. We are practically in the pocket change category <$100 bucks. Incredible time to be a Consumer of Audio Products. Great review Amir. The budget crowd should be ecstatic over the last two Products reviewed. :cool:
 

Ra1zel

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I mean for 100$... it's a miracle you can buy anything for that money in the current times.
 

Erici

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Many thanks to Amir’s honest review and measurements. Happy Easter to Amir and all ASR fans!

We really appreciate ASR which allows us to listen to and gather users’ feedback on our old models. We absorbed a lot from the voices and develop this BT20A Pro. It’s not a perfect amp but we will keep making effort to improve it.

Here we want to give an exclusive 20%-off discount promo code for the BT20A Pro to all ASR fans. (Valid from today to April 30.)
20APROASR20

Hope you will be interested in this new amp!
Thanks Fosi Audio! Looks like a great product that's well executed.
It may be just my computer, but FYI I clicked on the Fosi Audio link above and my MalwareBytes antivirus app gave me a compromised site message.
 

dweeeeb2

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I would love to see spinorama/fr data from a good set of speakers comparing this with a “top” amp
 

Beershaun

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For $140, wow.
 

AaronJ

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4 ohm is mostly current limited
Maybe this is something you plan to cover in your dummy’s guide to amplifier measurements, but how can we tell when something is current limited by the measurements?
 

JDS

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This is a review and detailed measurements of the Fosi Audio BT20A stereo class D amplifier based on TI TPA3255 IC. It was sent to me by the company and costs US $99.99 with 32 volt power supply.
View attachment 278411
Despite its low cost, the case gives a feeling of quality. I am not usually fan of tone controls in low cost amps because you can never set them to flat response (the detents are there but don't work). As you will in the measurements, Fosi has made sure that they work correctly in this instance. A stout power switch controls power. In addition to 32 volt supply, company also shipped the optional ($40) 48 volt supply which is quite a giant:
View attachment 278412

As you see, Bluetooth input is also supported.

FYI there is an included orange volume control knob to give the unit some color.

Fosi Audio BT20A Pro Measurements
The tests are in 48 volt unless I say otherwise (I had mistakenly assumed it was the standard, not the 32 volt). Here is our dashboard:

View attachment 278413

Notice the great channel match in addition to very good SINAD which represents noise and distortion. Same is true with 32 volt supply:
View attachment 278414

This nicely lands the BT20A Pro in the "very good" category of all amplifiers tested regardless of price:
View attachment 278415

Zooming in to see the competition:

View attachment 278416

SNR is good for the class:
View attachment 278417

I expect load/impedance dependency in this class of switching amplifiers but here, the peaking is almost entirely out of band which is good:
View attachment 278418

Seeing how you have tone controls anyway, you could tailor any peaking with adjustment of the treble control. Won't be exact but should be good enough.

That aside, note how the response is more or less is flat in audible band with the treble and bass controls set to their detent, center position.

Multitone is good enough for the class:
View attachment 278419

Crosstalk is very good:
View attachment 278424

Let's start our 4 ohm power measurements with 48 volt supply:

View attachment 278420
View attachment 278421

Wow, this little box can pump out some serious watts, albeit in the short term testing! Switching to 32 volts cuts this down even though 4 ohm is mostly current limited:
View attachment 278422
View attachment 278423

The larger power supply must have more capacitor reservoirs than the 32 volt.

Switching to 8 ohm we naturally see the biggest hit to power:

View attachment 278425

Although to be fair, I put the cursor at an earlier point than for 48 volt supply (not enough measurement points there).

I was pleasantly surprised by the transfer function being so smooth:
View attachment 278426

Finally there is not much of a pop on but there is for off:
View attachment 278427

Conclusions
The TI TPA3255 seems to be a capable platform when paired with a good implementation which is what we have in BT20A Pro. You get a sense of that in company marketing material which includes Audio Precision measurements. Usability is excellent with high quality case and controls especially with respect to ability to set the tone controls to flat.

It is also nice to see so much power coming out of this little box with the beefy 48 volt power supply, showcasing the advancements in amplification density we have today.

As an aside, the company has been a joy to work with. They were exceptionally polite, cordial and patient as I went through my testing and evaluation. They tell me they have internal R&D team and it shows.

I am happy to add the Fosi Audio BT20A Pro to my recommended list.

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

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
How extraordinary is it that we can buy a competent, cool-running stereo amplifier for $99.99?

The Dyna Stereo 70 power amp launched in 1959 at a price point of $99.95. For a kit.

In 2023 dollars, that's more than $1000.

This may not be a great time to be a boutique high-end hifi maker, but it is a pretty amazing time to be an audiophile.
 
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