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.
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:
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:
Notice the great channel match in addition to very good SINAD which represents noise and distortion. Same is true with 32 volt supply:
This nicely lands the BT20A Pro in the "very good" category of all amplifiers tested regardless of price:
Zooming in to see the competition:
SNR is good for the class:
I expect load/impedance dependency in this class of switching amplifiers but here, the peaking is almost entirely out of band which is good:
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:
Crosstalk is very good:
Let's start our 4 ohm power measurements with 48 volt supply:
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:
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]
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:
Finally there is not much of a pop on but there is for off:
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/
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:
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:
Notice the great channel match in addition to very good SINAD which represents noise and distortion. Same is true with 32 volt supply:
This nicely lands the BT20A Pro in the "very good" category of all amplifiers tested regardless of price:
Zooming in to see the competition:
SNR is good for the class:
I expect load/impedance dependency in this class of switching amplifiers but here, the peaking is almost entirely out of band which is good:
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:
Crosstalk is very good:
Let's start our 4 ohm power measurements with 48 volt supply:
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:
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]
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:
Finally there is not much of a pop on but there is for off:
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/
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