Fosi Audio BT20A Bluetooth Amplifier with TPA3116 Chips

UPDATED REVIEW SEPT 2026 Amazing. Since purchasing in Feb 2025, this Fosi Audio BT20A amp has suffered extreme temperatures from 4 deg C to 37C (it played in this heat which is a form of abuse). Its hasn't been moved from where it was installed on a back garden patio. And its been subject to extreme humidity. And high volumes. It's been flogged. Its casing has got very hot. Yet its still pumping out great music. We were predicting it would have failed by now or severely deteriorated. But its as good as the day we first installed it.

I'm so impressed I'm upgrading to another Fosi. Got my eyes on the Fosi ZD3 Desktop DAC with Qualcomm aptX HD codec. It misses out on the higher tier LDAC wireless codec option in the similarly priced xDuoo MU-605.

But Fosi Audio has proven its durability with the BT20A. And that kind of personal experience is worth more than a thousand 5-star reviews on another product

UPDATED REVIEW MAY2025: Since first impressions I update the original review (below) as follows:

DISTORTION Evident at 75% Bass (bass tone knob set to 3/4) or higher at 80% volume or higher - its audible at this setting (rock music) but not VERY noticeable.

Is distortion caused by Amp or Speakers? The Fosi BT20A is rated (by Fosi) as follows: "100W X 2(4 ohms), 20 Hz - 20 kHz, 0.04% THD)". Not sure this can be trusted. Elsewhere the manufacturer claims THD ≤ 0.5% (big difference between 0.04% and 0.5% !!). Refer: https://fosiaudio.com/products/

The JBL "Balboa10" 8 ohm bookshelf speakers (2 way 5"driver+tweeter) are rated as follows: Frequency Response (–3dB) = 68Hz – 20kHz, Recommended max power = 125W, Recommended Continuous power = 60Watts, Peak power handling (spikes) =250watts. At 8 ohms I doubt the Fosi is outputting more than 60W per channel. I do not think these speakers are over-driven at 80%+ volumes. I have doubts about the Fosi's 100W rating into 4 ohms!!

So it appears from specs the bookshelf speakers are not responsible for the distortion. No, we didn't focus on distortion when we had the larger 8 ohm Energy towers (with better power handling) hooked up. But the JBL Bookshelf's have a sensitivity of only 86db which means they need more volume from the Fosi to drive them loud, which makes distortion more evident if its coming from the Amp.

CORRECTION: these surround speakers have an 86db sensitivity NOT the 90-91db specified in the original review below (the Balboa towers we hooked up were 91db, not the JBL surrounds we settled on). This means the surrounds require more volume to drive them.

DROPOUTS At 80-100% volume and Bass set to 75% or more we noticed a very slight dropout (less than .5 of a second) every now and then - when the Amp was fairly warm, during long, loud bass heavy music sessions. I wonder if this would be more noticeable with 4 ohm speakers drawing lots of current (as they do) at the same volumes? Very likely.

REVISED IMPRESSION? Definitely not Audiophile quality after finer evaluation. The barely noticeable, not too frequent dropouts under high volume/high current demands (including THD) rule out any notion of audiophile quality. But it still sounds amazing. The Fosi is more than acceptable and I think it sounds brilliant unless pushed really hard. Especially given its Price/Performance ratio and its intended usage as an outdoor patio amp.

======================================================================= original review (Feb25): Fosi Audio BT20A Bluetooth Amplifier for Speakers, Mini Stereo 2 Channel Amp Class D, with TPA3116 Chips 100W x 2 and Bass Treble Controls. Purchased 17-Feb-2025 New from Amazon.com.au. (Price paid: $80 AUD after a 40% discount plus free postage on Amazon.com.au)

GOOD SOUND from a small budget mini-amplifier. Value for money is WOW! RATING = EXCELLENT

1. Sound Quality Fosi Audio BT20A Bluetooth Amplifier is a class D amplifier with an AC adapter/power supply (step-down transformer). This means it is driven by low current and all I can say is this makes it amazing how it can produce such good Bass and overall volume into 8 ohm passive speakers. It performed admirably and flawlessly (so far). It digs deep with surprisingly little distortion, no dropouts or crackling at high volume, playing a variety of genres including heavy rock. It is NOT an audiophile quality device but it comes just as close as many mid-priced (now vintage) Class-A Amplifiers.. Its Bass is full-rounded and deep...which is surprising since the capacitors must be small for such a unit. Sure the Bass is a little muddy (with the bass turned up to 75%) but not much for a unit with no bass-damping specification. It was really good.

DISCLAIMER: There is no telling if this amp could burn out in a few months to a year of regular usage without abuse - so this review is not about longevity.

2. Temperature The Fosi BT20A ran cool when connected to 8 ohm speakers and it got warm (not hot) after hours of cranked-up volume in hot weather (ambient temperature 32 deg C !). It didn't seem to run much hotter using 6 ohm speakers. With Class D circuitry this makes sense as it utilizes very little reserve current between peak music demands (peaks in Bass and volume). This is totally unlike inefficient Class A amplifiers that draw higher current and dissipate more energy as heat, even when not playing demanding music. Class A amps require larger power supply components, larger capacitors, large ventilated casings with heat sinks/fans and are some of the best sounding amplifiers in the world. Now I understand why cheap efficient mini Class D devices like this Fosi have made classic amplifiers redundant for the mass-market.

3. Connections and test equipment used It pumped good clear sound into 2 Energy tower speakers rated to 200w (twin 5.5" woofers+tweeter per speaker). These Energy speakers are not very efficient (rated at 89db sensitivity) which makes them harder to drive than modern 4-6 ohm speakers with high sensitivity (91db+). We got the same result with a range of other speakers - including JBL Balboa floorstanders which were WAY louder due to their 91db sensitivity rating. We settled for a pair of ordinary JBL bookshelf speakers (8 ohm/91db sensitivity) that were the rears from a 5.1 home theatre set and the sound is phenomenal. VIP: none of the speakers tested had a driver (woofer) larger than 6 inches

We got the best sound by connecting the Fosi to our outdoor TV headphone-out jack (cable had one 3.5mm jack at the TV end and two RCA plugs at the Fosi end). Then we streamed music videos (you-tube) and Spotify from our tablets to the TV using WiFi. This was much better sound than: 1. streaming to the TV via bluetooth with the Fosi connected by RCA, or 2. streaming directly to the Fosi via bluetooth (using Spotify). But the Bluetooth still worked well, connected seamlessly, and sounded good.

4. Power Output No way can it produce 100 watts RMS per channel with 8 ohm speakers (i'd say about 50 watts RMS max into 8 ohms) but still very loud. The claimed 100 watts x 2 is listed for 4 ohm speakers sounds hugely exaggerated.

At the price its a bargain! GET ONE. ----end----