Subjective impressions of Fosi Audio BT20A Max

[Balinus]

Fosi Audio BT20A MAX – User Impressions / Review

Product: Fosi Audio BT20A MAX
Type: Class D stereo / 2.1 integrated amp
Chipset: TI TPA3255 + NE5532
Disclaimer: Pre-production unit provided by Fosi Audio. Opinions are my own.

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TL;DR

Feature-rich Class D amp with PFFB, strong Bluetooth implementation, and a slightly warm tuning. Sounds good for the price, but the always-on fan and idle heat are worth mentioning. Not perfect, but very solid value.

Features (relevant ones)

• TI TPA3255 output stage
• Post Filter Feedback (PFFB) → reduced load dependency
• Qualcomm QCC3095 Bluetooth 6.0
  • LDAC, aptX Lossless, aptX HD, aptX Adaptive, etc.
• Dual RCA inputs
• Subwoofer output (2.1 capable), with HPF switch at 80Hz
• Motorized analog volume pot + remote
• Bass / treble tone controls + bypass (useful if you have a preamp)
• 12V trigger input

Specs (manufacturer):

• 300 W × 2 @ 4 Ω (peak), 180 W × 2 RMS with the 48V/10A PSU (I got the 48V/5A, giving approximately 100Wx2 into 8 Ω).
• THD+N ≤ 0.003%
• SNR ≥ 112 dB
• 2–8 Ω load support

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​

Setup / Test Conditions

• Power supply: 48V / 5A (not the optional 10A)
• Speakers tested:
  • Paradigm Monitor 7 v2
  • Kanto YU4 passive
• Use case: nearfield (desktop use, Kanto YU4) + medium-room listening (Paradigm Monitor 7 v2)

Sound Impressions

Overall tonal balance is neutral-to-slightly-warm, which is not always the case with budget Class D amps.

• Bass: Deeper and more authoritative than my Aiyima A80, but still controlled.
• Midrange: Clean, smooth, slightly warm. Easy to listen to for long sessions.
• Treble: Clean and non-fatiguing, but some loss of micro-detail at very high volume.

Compared to:

• Aiyima A80: Fosi sounds fuller and warmer; Aiyima is more analytical.
• Sansui 9090 (vintage): Obviously not the same league, but the tonal balance is closer to that relaxed presentation than to a sterile Class D sound. Instrument separation is of course better on the Sansui, with a better instrument separation. Nonetheless, the BT20A Max is on the warmer side of neutral.

Speaker matching matters. With already warm speakers, this amp could sound slightly muffled. With my speakers, it stayed balanced.

At very loud volumes, clarity drops a bit—nothing unexpected for a compact Class D amp nearing its limits.

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​

Bluetooth Performance

Very good, does what is expected from it! Used an iPhone 14 for testing, so I haven’t tested every possible codec/protocol.

• Stable connection
• Low latency (tested using a YT video)
• Codec support is better than most Bluetooth implementations in this price range

Auto-reconnection is very fast when the unit if powered on.

Fan / Thermal Behavior

There is a fan:

• Always on
• No standby mode
• Quiet, but audible within ~1 m in a silent room

The amp also stays warm at idle, with little difference between idle and moderate playback temps. Under heavy load, thermal control is actually better than my Aiyima A80.

Personally, I’d rather see:

• A slightly larger chassis
• More passive heatsinking
• No fan or a way to disable the fan or a temperature gauge starting the fan only at loud volume (which should be warmer, hence starting the fan in conditions where you can’t hear the fan).

Long-term fan reliability of the fan is an unknown (dust, bearing wear, etc.). While testing the unit, the fan developed a more “pronounced” sound that can be heard between songs or low volume part. This is only heard if the amp is close to the ears (<1 meter) though, so it might be or not a concern depending on personal setup. Fosi support has sent me instructions on how to open the unit and tighten the screws. After re-tightening, the noise is gone. Also note that is is pre-production unit.

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​

Power

Even with the 48V/5A PSU, power is more than sufficient for most use cases. Unless you’re driving inefficient speakers at high SPL, I don’t see the 10A supply as mandatory.

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​

Use Case / Final Thoughts

Despite being overpowered for them, this amp has ended up as my cottage amp, driving B&W speakers. My ideal use-case would have been for listening music while working, but the noise coming from the fan prevents me from doing that (I can’t position the amp farther away than 1 meter).

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​

Pros

• PFFB implementation at this price
• Clean, slightly warm sound
• Strong Bluetooth codec support
• Dual RCA + sub out
• Very good value for features

Cons

• Fan runs continuously, can be heard if the amp is positioned close. The fan developed a more “bassy” noise during my 2-week testing, which was settled by re-tighting the screws of the fan (needed to open up the case though). I will see if Fosi support can replace/repair the unit or not.
• No standby mode
• Slightly warm at idle (but moderately warm while listening, thanks to the fan)
• Loss of definition at high volume

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​

Rating

Good value, good sound, but not flawless. If you’re okay with a fan and want lots of features in a compact Class D amp, this one is worth considering.

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​

Music Used

• Harmonium – L’Heptade
• Miles Davis – Bitches Brew
• Michael Kiwanuka – Small Changes
• Pat Metheny – Secret Story
• Pink Floyd – Dark Side of the Moon
• Amy Winehouse – Back to Black
• Lou-Adrianne Cassidy – Journal d’un Loup-Garou

Steven Wilson – The Overview

 

[RandomEar]

Sound Impressions

Overall tonal balance is neutral-to-slightly-warm, which is not always the case with budget Class D amps.

• Bass: Deeper and more authoritative than my Aiyima A80, but still controlled.
• Midrange: Clean, smooth, slightly warm. Easy to listen to for long sessions.
• Treble: Clean and non-fatiguing, but some loss of micro-detail at very high volume.

Compared to:

• Aiyima A80: Fosi sounds fuller and warmer; Aiyima is more analytical.
• Sansui 9090 (vintage): Obviously not the same league, but the tonal balance is closer to that relaxed presentation than to a sterile Class D sound. Instrument separation is of course better on the Sansui, with a better instrument separation. Nonetheless, the BT20A Max is on the warmer side of neutral.

Speaker matching matters. With already warm speakers, this amp could sound slightly muffled. With my speakers, it stayed balanced.

At very loud volumes, clarity drops a bit—nothing unexpected for a compact Class D amp nearing its limits.

On ASR we appreciate objective results and hard, measured facts. The differences you claim do not sound plausible for amps which measure in the same ballpark (maybe excluding the vintage Sansui). Stating audiophile fairy tales like "sterile Class D sound" for which no one ever provided any objective evidence does not support your claims - on the contrary.

Unless you did double blind testing or provide measurements clearly showing differences in frequency response, distortion or SNR, your subjective impressions are likely flawed and simply another example of bias in humans. I appreciate you sharing your experience with Bluetooth stabilty, thermal properties and the remarks concerning fan noise but would consider any comments on the sound of a device which shouldn't have any sound whatsoever very questionable.

 

[Balinus]

On ASR we appreciate objective results and hard, measured facts. The differences you claim do not sound plausible for amps which measure in the same ballpark (maybe excluding the vintage Sansui). Stating audiophile fairy tales like "sterile Class D sound" for which no one ever provided any objective evidence does not support your claims - on the contrary.

Unless you did double blind testing or provide measurements clearly showing differences in frequency response, distortion or SNR, your subjective impressions are likely flawed and simply another example of bias in humans. I appreciate you sharing your experience with Bluetooth stabilty, thermal properties and the remarks concerning fan noise but would consider any comments on the sound of a device which shouldn't have any sound whatsoever very questionable.

Thanks, I agree that this is a subjective review. Is it based on measurements? No, sadly I do not have tools to measure it. Nonetheless, I find the sonic signature between the Aiyima A80 and BT20A Max to present the differences I wrote, be it human bias or not. Can they be put closer one to another by playing with the tone control? Perhaps, but I prefer to keep the tone controls on "default" most of the time. There is just more bass present in the tracks I listened to, with less present treble on those defaults settings.

Cheers!

 

[Joe Smith]

Your impressions of the amp/use case are similar to mine. (I usually don't mention any thoughts re "tonality" with amps as I think that is mostly due to speakers than amps per se.)

It's a good amp, nice feature-set. I am not bothered by the fan noise. In my workroom, where my head was about 1 meter away from it behind me, I was not aware of it at all. If I listened for it, I could hear it, when no music was playing. My workroom does have wall to wall carpet and minimal room bounce. I could see the fan being a problem in a setup where the room has wood floors and/or a lot of hard surfaces. Or where it's on a desk right in front of a workstation.

My major point of feedback I stressed to Fosi is that both this amp and the P4 preamp have kind of poor volume control at very low levels. The motorized pot is convenient, but since I often listen at quiet levels, I want/need a lot of control in the low part of the pot. The V3 pot is superior in this regard to both of these devices.

It's been interesting to see Fosi try a lot of different things over time. I think some of the feedback they got from ASR users and others was that even more cooling for device longevity would be a plus. And now we have such a unit. Did we actually want that? Well, maybe. Time will tell how this one sells. Price is a bit higher than where they've been, but they did put in a lot of nice features that hits a sweet spot for many users seeking an easy amp solution, who don't care about PEQ etc.

 

[Talisman]

A fan in a hi-fi amplifier? I'll only accept it for PA amplification.
With those, if you have overheating problems, get a bigger case instead of cramming more and more stuff into the same case.

 

[Joe Smith]

The small case approach is a bit limiting for all of the overseas manufacturers on inexpensive/non-Hypex or Purifi class D amp makers. But I imagine it's very cost efficient for them, plus market research showing that a lot of people want really small form factor units.

Emotiva is launching a new "smaller than full standard size" line, where I am interested to see how it sells. And I personally like Schiit's mid-size cases, like they are using for the Gjallarhorn amp, Saga 2 preamp, etc., about 9" wide and 8" deep. Enough width that controls in the front don't need to be crammed together, nor connections in the back.

 

[Guddu]

Fosi Audio BT20A MAX – User Impressions / Review

Product: Fosi Audio BT20A MAX
Type: Class D stereo / 2.1 integrated amp
Chipset: TI TPA3255 + NE5532
Disclaimer: Pre-production unit provided by Fosi Audio. Opinions are my own.

​

---

TL;DR

Feature-rich Class D amp with PFFB, strong Bluetooth implementation, and a slightly warm tuning. Sounds good for the price, but the always-on fan and idle heat are worth mentioning. Not perfect, but very solid value.

View attachment 507785View attachment 507786View attachment 507787

Features (relevant ones)

• TI TPA3255 output stage
• Post Filter Feedback (PFFB) → reduced load dependency
• Qualcomm QCC3095 Bluetooth 6.0
  • LDAC, aptX Lossless, aptX HD, aptX Adaptive, etc.
• Dual RCA inputs
• Subwoofer output (2.1 capable), with HPF switch at 80Hz
• Motorized analog volume pot + remote
• Bass / treble tone controls + bypass (useful if you have a preamp)
• 12V trigger input

Specs (manufacturer):

• 300 W × 2 @ 4 Ω (peak), 180 W × 2 RMS with the 48V/10A PSU (I got the 48V/5A, giving approximately 100Wx2 into 8 Ω).
• THD+N ≤ 0.003%
• SNR ≥ 112 dB
• 2–8 Ω load support

​

---

Setup / Test Conditions

• Power supply: 48V / 5A (not the optional 10A)
• Speakers tested:
  • Paradigm Monitor 7 v2
  • Kanto YU4 passive
• Use case: nearfield (desktop use, Kanto YU4) + medium-room listening (Paradigm Monitor 7 v2)

View attachment 507788

Sound Impressions

Overall tonal balance is neutral-to-slightly-warm, which is not always the case with budget Class D amps.

• Bass: Deeper and more authoritative than my Aiyima A80, but still controlled.
• Midrange: Clean, smooth, slightly warm. Easy to listen to for long sessions.
• Treble: Clean and non-fatiguing, but some loss of micro-detail at very high volume.

Compared to:

• Aiyima A80: Fosi sounds fuller and warmer; Aiyima is more analytical.
• Sansui 9090 (vintage): Obviously not the same league, but the tonal balance is closer to that relaxed presentation than to a sterile Class D sound. Instrument separation is of course better on the Sansui, with a better instrument separation. Nonetheless, the BT20A Max is on the warmer side of neutral.

Speaker matching matters. With already warm speakers, this amp could sound slightly muffled. With my speakers, it stayed balanced.

At very loud volumes, clarity drops a bit—nothing unexpected for a compact Class D amp nearing its limits.

​

---

Bluetooth Performance

Very good, does what is expected from it! Used an iPhone 14 for testing, so I haven’t tested every possible codec/protocol.

• Stable connection
• Low latency (tested using a YT video)
• Codec support is better than most Bluetooth implementations in this price range

Auto-reconnection is very fast when the unit if powered on.

View attachment 507789

Fan / Thermal Behavior

There is a fan:

• Always on
• No standby mode
• Quiet, but audible within ~1 m in a silent room

The amp also stays warm at idle, with little difference between idle and moderate playback temps. Under heavy load, thermal control is actually better than my Aiyima A80.

Personally, I’d rather see:

• A slightly larger chassis
• More passive heatsinking
• No fan or a way to disable the fan or a temperature gauge starting the fan only at loud volume (which should be warmer, hence starting the fan in conditions where you can’t hear the fan).

Long-term fan reliability of the fan is an unknown (dust, bearing wear, etc.). While testing the unit, the fan developed a more “pronounced” sound that can be heard between songs or low volume part. This is only heard if the amp is close to the ears (<1 meter) though, so it might be or not a concern depending on personal setup. Fosi support has sent me instructions on how to open the unit and tighten the screws. After re-tightening, the noise is gone. Also note that is is pre-production unit.

View attachment 507790View attachment 507791
View attachment 507792

​

---

Power

Even with the 48V/5A PSU, power is more than sufficient for most use cases. Unless you’re driving inefficient speakers at high SPL, I don’t see the 10A supply as mandatory.

​

---

Use Case / Final Thoughts

Despite being overpowered for them, this amp has ended up as my cottage amp, driving B&W speakers. My ideal use-case would have been for listening music while working, but the noise coming from the fan prevents me from doing that (I can’t position the amp farther away than 1 meter).

​

---

Pros

• PFFB implementation at this price
• Clean, slightly warm sound
• Strong Bluetooth codec support
• Dual RCA + sub out
• Very good value for features

Cons

• Fan runs continuously, can be heard if the amp is positioned close. The fan developed a more “bassy” noise during my 2-week testing, which was settled by re-tighting the screws of the fan (needed to open up the case though). I will see if Fosi support can replace/repair the unit or not.
• No standby mode
• Slightly warm at idle (but moderately warm while listening, thanks to the fan)
• Loss of definition at high volume

​

---

Rating

Good value, good sound, but not flawless. If you’re okay with a fan and want lots of features in a compact Class D amp, this one is worth considering.

​

---

Music Used

• Harmonium – L’Heptade
• Miles Davis – Bitches Brew
• Michael Kiwanuka – Small Changes
• Pat Metheny – Secret Story
• Pink Floyd – Dark Side of the Moon
• Amy Winehouse – Back to Black
• Lou-Adrianne Cassidy – Journal d’un Loup-Garou

Steven Wilson – The Overview

Just a suggestion that you update the thread subject from "Review" to "Subjective Impressions".

 

[Balinus]

Just a suggestion that you update the thread subject from "Review" to "Subjective Impressions".

good idea, done.

 

[Balinus]

A fan in a hi-fi amplifier? I'll only accept it for PA amplification.
With those, if you have overheating problems, get a bigger case instead of cramming more and more stuff into the same case.

Yeah, I would have much prefered to have a bigger case with more passive cooling. What bothers me is the fan in 8 years.

 

[Joe Smith]

I moved the Fosi BT20a MAX into my bedroom system, as it's the perfect size & power level for my available top-of-bookcase location. Shifted my Schiit Gjallarhorn and Saga 2 system back to my workrrom, for ease of use with the headphone jack and 4 inputs. I'll probably stick with these locations for a while, as they really do work well.

With use in the bedroom, due to location, the small amount of fan noise is not a factor at all.

 

[CD2]

Thank you for taking the trouble to add information to this space about a new amplifier!

 

[motleypixel]

If anyone has a Google Pixel 10 and/or Pixel 10 Pro, please turn on the BTA20 Max, RCA 1, volume to 1/2 using the remote, no signal, turn on the Pixel 10's camera, while in photo and/or video point the rear lenses at the front of the BTA20 Max and report back if anything odd happens. Thank you.

 

[LeRoi]

Hi! I really like the Fosi Max. The only thing that also bothers me is the fan noise because I use it as a desktop device. I think the solution would be a bigger case which makes it possible to deactivate the fan. Do you know any dealer (maybe on Etsy?) that can create a higher case? I don't own a 3D printer.

 

[LeRoi]

My solution for lowering the noise:
Opened the case, removed the small fan and the orange grille (the one you can see through the Max logo).
Then put the 120mm fan (from Fosi) on top of the case which pulls the air from bottom to top. Even the lowest speed works great and quietly (compared to the tiny stock fan) and the whole case stays much colder which benefits the lifespan of all components!

 

[Balinus]

Do you plug the 120mm fan in the power from the board? Picture please!

 

[LeRoi]

Do you plug the 120mm fan in the power from the board? Picture please!

No, I bought the Fosi Audio USB-Powered Cooling Fan. You can control its Voltage supply. The integrated Fan works with 5V. You could connect the fan with this port, there are 12V to 5V adapter from be quiet! for example. But you have to lay the wire through the Logo. I will try that next time. But I switch the fan and the Fosi on with one socket switch anyway.

 

[Balinus]

No, I bought the Fosi Audio USB-Powered Cooling Fan. You can control its Voltage supply. The integrated Fan works with 5V. You could connect the fan with this port, there are 12V to 5V adapter from be quiet! for example. But you have to lay the wire through the Logo. I will try that next time. But I switch the fan and the Fosi on with one socket switch anyway.

Ok, so quite a big fan underneath!

 

[LeRoi]

Ok, so quite a big fan underneath!

On top, not underneath. But it pays. Quiet and cold!

 

[Flageborg]

So far this little nice thing is running my Front/Main Speakers very well in Stereo Mode without Subs

 

[putridspecies]

I’ve had it for about a month now and I am still enjoying this amp, currently have it in my main system/living room. it’s been a few weeks now with the fan unplugged using the 48v 5a power supply and although it gets pretty warm to the touch it hasn’t gone above 40-45 C even after hours of use. It heats up somewhat quickly but also cools down quickly (I think having it slightly elevated off the shelf has helped with that). Also don’t particularly care for the trademark Fosi orange and so decided to black out the mesh grills and volume knob. Blends in much better with the rest of my system now