Fosi Audio BT20A Pro Bluetooth stereo amplifier with antenna, treble, bass and volume knobs
Fosi Audio BT20A Pro Bluetooth amplifier rear panel: RCA input, pre-out, speaker terminals and power input - view 2
Fosi Audio BT20A Pro size, weight and what is in the box: amplifier, antenna, manual and 32 V 5 A power adapter - view 3
Fosi Audio BT20A Pro Bluetooth amplifier on a shelf between two bookshelf speakers - view 4
Fosi Audio BT20A Pro Bluetooth stereo amplifier with antenna, treble, bass and volume knobs
Fosi Audio BT20A Pro Bluetooth amplifier rear panel: RCA input, pre-out, speaker terminals and power input - view 2
Fosi Audio BT20A Pro size, weight and what is in the box: amplifier, antenna, manual and 32 V 5 A power adapter - view 3
Fosi Audio BT20A Pro Bluetooth amplifier on a shelf between two bookshelf speakers - view 4

Fosi Audio BT20A Pro Bluetooth Amplifier: TPA3255, 300W x 2, Tone Knobs and Pre-Out

Fosi Audio BT20A Pro: the 2023 Bluetooth 5.0 stereo amp on the TPA3255 chip, with bass and treble knobs, RCA in and a 3.5 mm pre-out. Fosi rates it 300 W x 2 at 4 ohms.

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Video Review

Fosi Audio BT20A Pro: TPA3255 Bluetooth stereo amp with bass and treble knobs and a pre-out

The BT20A Pro is Fosi Audio’s 2023 Bluetooth stereo amplifier built on the Texas Instruments TPA3255 chip. Fosi rates it at 300 W x 2 into 4 ohms and lists two inputs, Bluetooth 5.0 and RCA, terminals for passive speakers and a pre-out for an active subwoofer or a second amplifier. In Fosi’s own line-up it sits between the original BT20A (2020, TPA3116, 100 W x 2) and the newer Fosi BT20A MAX (2025).

Key features

  • TPA3255 power stage, 300 W x 2 at 4 ohm (Fosi rating). Fosi lists speaker impedance of 2 to 8 ohms and a supply range of DC 24 to 48 V. Treat the 300 W figure as a maximum rather than a continuous rating, because it depends on the power supply (see below).
  • Bluetooth 5.0 with SBC and AAC. The amp remembers paired devices, and holding the volume knob for five seconds clears the pairing list. There is no aptX or LDAC, which the MAX adds.
  • Bass and treble knobs. Fosi says to set both to the middle to hear the sound without tone effects, and Audio Science Review found that the controls reach a flat setting.
  • Two socketed NE5532 op-amps. Fosi names SS3602, MUSES02 and OPA2134PA as possible replacements for people who like to experiment.
  • Pre-out. Fosi lists a 3.5 mm pre-out for an active subwoofer or another amplifier. FutureAudiophile points out that it is a mini-stereo jack, not RCA, so you need a suitable cable.
  • Distortion and noise (manufacturer figures). Fosi quotes THD of 0.005% or lower and a signal-to-noise ratio of 108 dB or higher.
  • Compact case. 4.1 x 1.4 x 6.5 in (105 x 35 x 166 mm) and 1.2 lb (547 g), according to Fosi’s product images. Blue and gray finishes are sold.

Which power supply to choose

Fosi sells the BT20A Pro with a 32 V 5 A supply, a 48 V 5 A supply, a 48 V 5 A GaN supply or without a supply. Reviewers agree that the supply changes the result. Audio Science Review found that the 32 V supply lowers the 4 ohm output compared with 48 V. FutureAudiophile reported about 70 W per side into 4 ohms on the 32 V supply and “just shy of 150 W RMS” on 48 V, and he recommends 48 V (his figures, not a bench test). If your speakers are rated 4 ohms or are not very sensitive, the 48 V options are the safer choice. Prices change often, so check the variant and price on the store page.

Who it is for

Desk and small-room listeners who want a low-cost Bluetooth amp for passive bookshelf speakers rated 4 to 8 ohms, with bass and treble knobs and a feed for a subwoofer. It also works as the wired amp for a streamer or DAC through the RCA input. For speaker ideas, see our best budget bookshelf speakers guide.

Who should skip it

Skip it if you need a remote control. Fosi’s box list has none, and FutureAudiophile notes it as well. It has no USB, optical or coaxial input and no balanced input. Audio Science Review heard a pop when the amp is switched off, and FutureAudiophile found the speaker posts tight. If you want a remote, a built-in fan, post-filter feedback and a wider choice of Bluetooth codecs, look at the Fosi BT20A MAX. If you want balanced inputs and a stereo or mono switch, look at the Fosi Audio ZA3. The Bluetooth AIYIMA rival with tone knobs is the AIYIMA A07 Pro, and our three-way comparison sets the three side by side.

What independent reviewers found

Audio Science Review (April 2023, unit supplied by Fosi, 32 V supply) recommended the amp, found the tone controls correct and noted the lower 4 ohm power on 32 V. FutureAudiophile reached the same conclusion about the supply. HiFiVision (September 2023) compared the BT20A Pro with the original AIYIMA A07 on Elac Debut B2.6 speakers, level matched and blind, and could not tell them apart apart from a subtle bass difference. We have not tested this unit ourselves; these are the reviewers’ findings.

Where to buy

The Fosi Audio store sells every power supply option, including the GaN supply. The Amazon listing is the alternative if you prefer Prime delivery and returns. We show no price here because the price depends on the supply you pick and changes often.

Common questions

How much power does the BT20A Pro have? Fosi rates it at 300 W x 2 into 4 ohms. Reviewers got less on the 32 V supply, so choose a 48 V supply for demanding speakers.

Does the BT20A Pro have a remote? No. Neither Fosi’s box list nor the reviews mention one.

Can it drive a subwoofer? Yes, through the pre-out, which Fosi lists as a 3.5 mm jack. It is meant for an active subwoofer or a second amplifier.

What does the BT20A MAX add? The newer MAX adds a remote, a built-in fan, more Bluetooth codecs and a second RCA input; the Pro keeps things simple. Our comparison guide explains the differences.

SKU: fosi-audio-bt20a-pro Category: Brand:
Summary of independent reviews and public listener reports, read on 2026-10-31. It is not our own testing and it is not a collection of owner testimonials. Sources are named in the text.

What reviewers consistently praise

  • Value for a TPA3255 amp with Bluetooth and tone knobs. Audio Science Review (April 2023) added the BT20A Pro to its recommended list.
  • Tone controls that work. Audio Science Review found that bass and treble reach a flat setting, which is the opposite of the complaint it made about the AIYIMA A07 Pro.
  • Sound next to a rival. In a level-matched blind comparison on Elac Debut B2.6 speakers, HiFiVision could not tell the BT20A Pro from the original AIYIMA A07 apart from a subtle bass difference. Prime Audio, comparing it with the A07 Pro, described the Fosi as fuller and the AIYIMA as airier and more precise.
  • Replaceable op-amps. Two socketed NE5532 chips let you experiment, as Fosi suggests.

Common critical notes

  • The 32 V supply limits 4 ohm power. Audio Science Review and FutureAudiophile both saw lower output on 32 V; FutureAudiophile estimates about 70 W per side into 4 ohms and recommends 48 V.
  • No remote. Neither Fosi's box list nor FutureAudiophile mentions one.
  • A pop at power-off. Audio Science Review heard little at power-on and a pop at power-off.
  • Tight speaker posts and a 3.5 mm pre-out. FutureAudiophile found the binding posts tight and notes that the pre-out is a mini-stereo jack rather than RCA.
  • Bluetooth is basic. Version 5.0 with SBC and AAC only, so there is no aptX or LDAC.

Related amplifiers

  • Fosi BT20A MAX: the newer model with a remote, a fan, more Bluetooth codecs and two RCA inputs.
  • AIYIMA A07 Pro: the Bluetooth rival with tone knobs and a line out.
  • Fosi Audio ZA3: balanced inputs and a stereo or mono switch, without Bluetooth.

Verdict from the reviews: a simple, inexpensive Bluetooth amp that does what it promises when it gets a 48 V supply. Skip it if you want a remote or a wide codec choice; the three-way comparison shows the alternatives.

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Specification

BrandFosi Audio
ModelBT20A Pro
TypeBluetooth stereo Class-D integrated amplifier
Amplifier ChipsetTexas Instruments TPA3255
Op-ampsTwo socketed NE5532 (replaceable; Fosi names SS3602, MUSES02, OPA2134PA)
Max Output Power300 W x 2 at 4 ohm (Fosi rating; depends on the power supply)
Speaker Impedance2 - 8 ohm
InputsBluetooth, RCA
OutputsPassive speaker terminals, 3.5 mm pre-out
Bluetooth5.0, SBC / AAC
Tone ControlsBass and treble knobs (middle position = no tone effect)
THD0.005% or lower (Fosi)
Signal-to-Noise Ratio108 dB or higher (Fosi)
Supply VoltageDC 24 - 48 V
Power Supplies Sold32 V 5 A, 48 V 5 A, 48 V 5 A GaN, or none
RemoteNone
Dimensions4.1 x 1.4 x 6.5 in (105 x 35 x 166 mm), W x H x D
Weight1.2 lb (547 g)
FinishBlue or gray
Warranty24 months (Fosi)
Released2023

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