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Review Fosi Audio BT20A Pro + speaker Yamaha NS-BP401


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The Fosi Audio BT20A Pro is a very compact Class-D amplifier based on the TPA3255 amplifier chip (Texas Instruments).
Its controls include a toggle switch for on/off, 2 controls for treble and bass (both with locking in the centre position)
and a volume control (with slight play, probably due to the pressure function). The housing is made of metal and makes a
high-quality impression. A LineIn (RCA) and Bluetooth (with small rod antenna) are available as inputs. As outputs it has
a PreOut (3.5 mm jack, regulated!) and speaker connections. Banana plugs should be used here, as the connection space is
is a little tight. The included power supply has 32V/5A and thus provides the small amplifier with an output power of 2 x 100W (into 4 ohms).
You also have the option of replacing the standard op-amps (NE5532) with others (possibly of higher quality). I have the device with the standard op-amps.

My first test configuration consisted of the BT20A Pro connected to Yamaha NS-BP401 compact speakers and Cabasse Santurin 21 subwoofer.
I first tested the Bluetooth connection and then the LineIn (RCA). The music was streamed from the streamer WiiM Pro Plus (MP3 files
from the NAS (250-320 kBit/s). I have refrained from using the sound controls, as this always depends on the room and is a matter of taste.

First of all, flowery sound descriptions like those used in many reviews are not my thing. I tend to be more pragmatic, I like the sound yes/not bad/no.

The connection via Bluetooth is quick and stable, but still has room for improvement as codecs such as aptX are not supported.
The BT20A Pro selects the Bluetooth connection as the primary connection. Once the smartphone is paired, for example, the LineIn (RCA) is inactive.
To make the LineIn usable, the smartphone must first be disconnected or decoupled. This is also done by pressing (approx. 5s) the volume control.
Although this works reliably, it is not very practical in terms of handling as the smartphone has to be paired again.
A small selector switch would be more practical here.

The sound via the Bluetooth connection is not bad (Yamaha NS-BP401, solo mode). With clear basses and well accentuated mids and highs as well as
a flawless stereo image (approx. 2m apart). Here, the BT20A Pro does a good job together with the Yamaha speakers, even at a high volume.
That's enough to fill a 15 square metre room with good sound. Of course, this also depends a lot on the type of music
(Allan Taylor "Colour to the moon" has more bass/volume than an old Genesis recording "Mad Man Moon"). The tone controls for treble and bass work affectively.
Everyone can choose the right setting to suit their taste.

However, the BT20A Pro is at its best when signals are fed in via the LineIn, such as with the WiiM Pro Plus streamer. Here the sound got even
significantly more volume and was really fun. I have to say that the Yamaha speakers harmonised well with the BT20A Pro, even at low volumes.
To test the PreOut, I connected a subwoofer here. In conjunction with the subwoofer, everything was much fuller in the bass range. The BT20A Pro did a very good
job here. For me, the BT20A Pro is an ideal small amplifier that can be used for a 2.1 configuration without any problems. A subwoofer of course fulfils the special
requirements, but is not absolutely necessary (depending on the speakers), e.g. the Yamaha speakers were completely sufficient for solo operation.

The subwoofer connection via the PreOut was very simple and the control was carried out without any problems. This was simply done via a 3.5 jack/RCA adapter
to which the mono cinch cable for the subwoofer was then connected. The heat development of the amplifier housing was just warm to the touch, even after
several hours of operation at a high room volume.

If you don't want to connect your mobile phone or PC via Bluetooth, you can also connect it by cable via the LineIn RCA with, for example, a small USB DAC
(in my case a HIRESFI USB DAC5122A with OTG adapter for the Android smartphone, the PC is connected directly without an OTG adapter). The sound quality compared to Bluetooth is subjectively much better (I would prefer it in any case).

Finally, I combined the BT20A Pro with my main speakers Dali Opticon 2 MK2 (1200€/pair) (which probably nobody will do :).
The WiiM Pro Plus and music from the NAS were again used as players. The BT20A Pro had no problems with these speakers and enough power to drive them even at higher
volume levels. The result in terms of sound and volume was absolutely top for its price range. For a low cost and manageable follow-up costs
(for speakers, streamer or DAC), the Fosi Audio BT20A Pro is an amplifier solution that is worth every euro and is also extremely compact.

As speakers for the Fosi Audio BT20A Pro, I can also recommend the following speakers from my subjective opinion (the pair between 100-350€,
matching the price of the BT20A Pro). With these additional speakers you could also (depending on your taste) do without a subwoofer.
Q Acoustics 3020i, Fyne Audio F300 or F301, Audio Acoustic AE100 MK2

- Good neutral sound
- Good power reserves
- Tone control with centre position
- PreOut controlled
- Subwoofer connection
- Very compact
- High-quality housing
- Low heat generation
- Price

- Bluetooth without aptX
- No Bluetooth/LineIn selector switch
- PreOut not as cinch
- Somewhat narrow at the speaker connections


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