Subjective impressions of Fosi Audio BT20A Max

[LeRoi]

Opened the Case again to connect a short cable to the 5V jack of the old tiny Fan with an adapter for my 120mm Fan. The new fan running at 5V actually uses less current than the stock Fan, according to the specifications printed on the sticker (not measured the old one). I also applied new thermal compound between the heat sink and the Case for better heat transfer. Now I just have to press one button on the Topping DXII which triggers the Fosi Audio Max which turns on the new big Fan. Works great, absolutely quiet and really cold.

 

[motleypixel]

Opened the Case again to connect a short cable to the 5V jack of the old tiny Fan with an adapter for my 120mm Fan. The new fan running at 5V actually uses less current than the stock Fan, according to the specifications printed on the sticker (not measured the old one). I also applied new thermal compound between the heat sink and the Case for better heat transfer. Now I just have to press one button on the Topping DXII which triggers the Fosi Audio Max which turns on the new big Fan. Works great, absolutely quiet and really cold.

FANTASTIC mod!

 

[Dr Schweinsgruber]

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.

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

​

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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)

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.

​

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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.

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

​

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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

Thanks for your detailed account. Very useful! I just received mine...plus a video how to open the box up and tighten the fan screws. Question: what size wrench do I need to remove the front nuts.

Thanks.

 

[LeRoi]

Thanks for your detailed account. Very useful! I just received mine...plus a video how to open the box up and tighten the fan screws. Question: what size wrench do I need to remove the front nuts.

Thanks.

Just take a small long-nose pliers for the front nuts. The main reason for the noisy fan is the grille on top of it.

 

[putridspecies]

Following the “subjective” theme, I agree that out of the box (tone controls bypassed) the bass is deeper on this than my topping, or the ampapa d1 that I tested for a couple weeks. I have not tried to level match yet but it is something that was audible right off the bat. Switched to a 36v 5a power supply and the unit runs noticeably cooler than with the 48v, especially since I have the fan unplugged, and is plenty power for my use case (medium sized living room). Would love to see some real measurements for this amp

 

[dtaylo1066]

On ASR, subjective review =:

On the opposite end of the spectrum, Amir has measured a lot of low cost amps of late, and many measure quite respectably, and some post quite good measurements, and get high ratings. So good power is cheaper and more available than ever before in audio.

Fosi Audio BT20A Pro Amplifier Review

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...

www.audiosciencereview.com

 

[Dr Schweinsgruber]

Just take a small long-nose pliers for the front nuts. The main reason for the noisy fan is the grille on top of it.

Thanks. Fosi measured the nut for me...6.22 mm, which is neither metric nor 1/4 inch (6.35 mm). Therefore, I wonder whether they use metric or imperial nuts and screws.

I ordered a nut driver, however am worried that the socket is too thick for the hole around the nut and it therefore won't fit.

Yep, I have all sorts of pliers...if I can generate enough torque with them is another question.

 

[Dr Schweinsgruber]

On ASR, subjective review =:

View attachment 513609

On the opposite end of the spectrum, Amir has measured a lot of low cost amps of late, and many measure quite respectably, and some post quite good measurements, and get high ratings. So good power is cheaper and more available than ever before in audio.

Fosi Audio BT20A Pro Amplifier Review

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...

www.audiosciencereview.com

Every evaluation of a product is to some degree subjective as long as humans are involved, including measurements (as the chosen parameters are subjective and their informativeness is limited). Yes, it is useful to have an internally consistent series (what hardcore ASR disciples wrongly and obsessively refer to as "objective"), but this also does not tell us the whole story. And after all these observations ("measurements") follow the interpretations, which are entirely subjective.

I stick subjectively to my Questyle CMA 12 Master and subjectively tell you that you get what you pay for. Yep, it cost $2000 USD new ($1100 CAD 2nd hand for me) and I will be able to enjoy my bias and other inferred deficiencies without forced double blind testing but also without ASR compulsion for the next 20 years. I also have the FiiO K17, but it is not good enough to take full advantage of my Sennheiser HD 800S's capabilities.

I also have great gear that measures miserably according to ASR (not according to Stereophile, but obviously Stereophile's measurements are not "objective"), such as the AudioQuest DragonFly Cobalt dongle DAC, and it sounds better to my ears, that is more natural, than any of the many dongles I have tested for audioreviews.org. I must have had this delightful bias for 5 years now - and probably cannot be helped. My problem is my classical music education aberration: I subjectively know what a cello sounds like and I don't care too much about static sine waves...and only static sine waves can objectively and absurdly represent sound and sound quality.

But what do I know...at least I do not impose myself on others...

As to the forced title of this thread which is the result of bullying its creator: EVERY impression is subjective.

 

[RandomEar]

Thanks. Fosi measured the nut for me...6.22 mm, which is neither metric nor 1/4 inch (6.35 mm). Therefore, I wonder whether they use metric or imperial nuts and screws.

They will use ISO standard metric nuts and bolts. Imperial stuff is rare outside the US, with the exception of products made specifically for the US market. The inner diameter they measured is compatible with an M7x0.75 thread, which is a bit uncommon but is specified by the standard.

 

[dtaylo1066]

Every evaluation of a product is to some degree subjective as long as humans are involved, including measurements (as the chosen parameters are subjective and their informativeness is limited). Yes, it is useful to have an internally consistent series (what hardcore ASR disciples wrongly and obsessively refer to as "objective"), but this also does not tell us the whole story. And after all these observations ("measurements") follow the interpretations, which are entirely subjective.

I stick subjectively to my Questyle CMA 12 Master and subjectively tell you that you get what you pay for. Yep, it cost $2000 USD new ($1100 CAD 2nd hand for me) and I will be able to enjoy my bias and other inferred deficiencies without forced double blind testing but also without ASR compulsion for the next 20 years. I also have the FiiO K17, but it is not good enough to take full advantage of my Sennheiser HD 800S's capabilities.

I also have great gear that measures miserably according to ASR (not according to Stereophile, but obviously Stereophile's measurements are not "objective"), such as the AudioQuest DragonFly Cobalt dongle DAC, and it sounds better to my ears, that is more natural, than any of the many dongles I have tested for audioreviews.org. I must have had this delightful bias for 5 years now - and probably cannot be helped. My problem is my classical music education aberration: I subjectively know what a cello sounds like and I don't care too much about static sine waves...and only static sine waves can objectively and absurdly represent sound and sound quality.

But what do I know...at least I do not impose myself on others...

As to the forced title of this thread which is the result of bullying its creator: EVERY impression is subjective.

I in no way intended to bully, just stated the rather unequivocal POV of ASR, and the reason it was created. We live in a greatly subjective world, and we also all hear differently, and many prefer certain aspects of audio reproduction -- bass, imaging, depth of field, etc. -- which in my opinion a measurement may not always address. I have admitted on this Forum in the past I greatly enjoy certain tube amps, and thus that I must like 2nd or 3rd order harmonic distortion, which Nelson Pass claims is the case for many, based on his tests.

I am not a staunch objectiveist as most on ASR indeed are. I blend my take on audio between the objective and subjective, but after reading a lot on ASR I lean more to the former. But, also, when I play in the ASR sandbox, I know and respect the philosophy and raison d'être and, if I buck that, I will get some blowback. My can of worms ws meant more as a joke.

I do know what my ears and brain like to hear in audio. I have listened to 60K systems that I thought were shrill or bright, to the point they did nothing for me. Measurements were impeccable.

My comments were simply to point out that a fully subjective review on ASR will get blowback, right or wrong, and that his favorable impressions on the amp match the fact that the earlier version of the amp measured quite well and was recommended by Amir. Not a coincidence. On the contrary, people love many components that measure like poop.

I would apologize to the OP if he took my comments as bullying. In the end, buy what you like and listen to what makes you happy. The music and how you hear it, and like it, is the end product, not the component.

At my computer desktop, my little Edifer M60s sound just dandy. For their price and design, they measure decently in spinorama by Erin. They are all I need in desktop nearfield listneing. When I tried them next to my TV they sucked.

Different story with my KEF LSX II LT. Different design, different cost segment, larger driver, capable of a small room high-quality listening experience or desktop NF. Also measure pretty decently on Erin's spinorama. Subjectively, like the M60, they also sound good to my ears.

In my man cave I enjoy a WiiM Ultra feeding a Hypex UCD DIY amp with robust linear power supply, and the speakers are 6.5" DIY monitors based on SEAS drivers. I very much like the sound, which is made better by DSP EQ. Mostly stream via Tidal. Also have a TT, but have to admit that I do not find my once beloved vinyl matching up to digital, though some would strenuously argue to the contrary.

 

[Dr Schweinsgruber]

I in no way intended to bully, just stated the rather unequivocal POV of ASR, and the reason it was created. We live in a greatly subjective world, and we also all hear differently, and many prefer certain aspects of audio reproduction -- bass, imaging, depth of field, etc. -- which in my opinion a measurement may not always address. I have admitted on this Forum in the past I greatly enjoy certain tube amps, and thus that I must like 2nd or 3rd order harmonic distortion, which Nelson Pass claims is the case for many, based on his tests.

I am not a staunch objectiveist as most on ASR indeed are. I blend my take on audio between the objective and subjective, but after reading a lot on ASR I lean more to the former. But, also, when I play in the ASR sandbox, I know and respect the philosophy and raison d'être and, if I buck that, I will get some blowback. My can of worms ws meant more as a joke.

I do know what my ears and brain like to hear in audio. I have listened to 60K systems that I thought were shrill or bright, to the point they did nothing for me. Measurements were impeccable.

My comments were simply to point out that a fully subjective review on ASR will get blowback, right or wrong, and that his favorable impressions on the amp match the fact that the earlier version of the amp measured quite well and was recommended by Amir. Not a coincidence. On the contrary, people love many components that measure like poop.

I would apologize to the OP if he took my comments as bullying. In the end, buy what you like and listen to what makes you happy. The music and how you hear it, and like it, is the end product, not the component.

At my computer desktop, my little Edifer M60s sound just dandy. For their price and design, they measure decently in spinorama by Erin. They are all I need in desktop nearfield listneing. When I tried them next to my TV they sucked.

Different story with my KEF LSX II LT. Different design, different cost segment, larger driver, capable of a small room high-quality listening experience or desktop NF. Also measure pretty decently on Erin's spinorama. Subjectively, like the M60, they also sound good to my ears.

In my man cave I enjoy a WiiM Ultra feeding a Hypex UCD DIY amp with robust linear power supply, and the speakers are 6.5" DIY monitors based on SEAS drivers. I very much like the sound, which is made better by DSP EQ. Mostly stream via Tidal. Also have a TT, but have to admit that I do not find my once beloved vinyl matching up to digital, though some would strenuously argue to the contrary.

Haha, I did not refer to you at all. Don't you worry. And thanks for your explanation.

I went to a Hifi show and listened to a $20,000 setup that sounded shrill and fatiguing to me. The one I liked cost $80,000, but I did not know that at the time. Topping devices typically measure well and sound harsh...strangely enough their sister company SMSL produces more "agreeable" sounding gear.

And yes, technicalities like depth of field, timbre, stage etc. cannot be measured. And they may be perceived differently by different people based on their ear canal geometries, even mood. That's why I always recommend reading many different qualified opinions.

I own a few TWS earphones and like clip-ons in certain situations when you still have to be somewhat connected to the outside world. One of the best sounding ones for me are the TOZO Open Earring, which cost a measly $27 USD on Black Friday. Everybody who tested the TOZOs confirmed this. Do many overlapping subjective opinions result in a somewhat objective overall result?

 

[Dr Schweinsgruber]

Currently testing the BT20A Max with different speakers...and, at the current state, it is impossible to make definitive statements. The fact is that the bass is a bit elevated, which adds a tad of warmth. The lowermost speakers are Heybrook HB1s, which I have had since 1985, so I know them well. With those, the Fosi sounds a bit lean and close to neutral/analytical. With the two pairs of small speakers (PSB Alpha P3 with some old JVCs on top), it sounds richer and more organic with good rhythm/PRAT...to my ears. Pleasant, agreeable...for me. Yes, this is totally subjective as it should be.

The Fosi is surely far from the audiophile endgame, but I am mildly impressed by how well this little rascal performs. Earlier today, I ran the Bluesound Powernode Edge streamer on these speakers...which I did not like as much. The name is program with that one as it is edgy.

And although the fan is (still) whisper quiet, I grossly dislike the idea of having to deal with fan noise and ball bearings wearing out. What Fosi need to do is creating a corrugated metal case with largely increased surface area for heat dissipation, like Burson does. But that would mean more metal and therefore a higher price.

I also tested the $90 SMSL A100, which sounds tinny. The Fosi runs circles around the A100.

 

[dtaylo1066]

Haha, I did not refer to you at all. Don't you worry. And thanks for your explanation.

I went to a Hifi show and listened to a $20,000 setup that sounded shrill and fatiguing to me. The one I liked cost $80,000, but I did not know that at the time. Topping devices typically measure well and sound harsh...strangely enough their sister company SMSL produces more "agreeable" sounding gear.

And yes, technicalities like depth of field, timbre, stage etc. cannot be measured. And they may be perceived differently by different people based on their ear canal geometries, even mood. That's why I always recommend reading many different qualified opinions.

I own a few TWS earphones and like clip-ons in certain situations when you still have to be somewhat connected to the outside world. One of the best sounding ones for me are the TOZO Open Earring, which cost a measly $27 USD on Black Friday. Everybody who tested the TOZOs confirmed this. Do many overlapping subjective opinions result in a somewhat objective overall result?

Not worrying and my presumption is you were not pointing out me.

 

[Dr Schweinsgruber]

After two hours of use, the fan screams like crazy and causes high-pitched vibrations (a "whistle") under the hood - which disappear temporarily as long as I push down on the chassis.

I also did a crude measurement of the frontal nut (underneath the knobs)...not 6 mm but rather 8 mm as it seems. Ordered the wrong sized nut driver after getting the wrong number from Fosi.

Nuisance all around.

 

[Dr Schweinsgruber]

Just take a small long-nose pliers for the front nuts. The main reason for the noisy fan is the grille on top of it.

All long nosed pliers are too thick to fit in that hole...bummer!

 

[Balinus]

Thanks for your detailed account. Very useful! I just received mine...plus a video how to open the box up and tighten the fan screws. Question: what size wrench do I need to remove the front nuts.

Thanks.

Hello, I used a 10mm wrench I had to remove the nuts behind the tone buttons.

 

[Balinus]

After two hours of use, the fan screams like crazy and causes high-pitched vibrations (a "whistle") under the hood - which disappear temporarily as long as I push down on the chassis.

I also did a crude measurement of the frontal nut (underneath the knobs)...not 6 mm but rather 8 mm as it seems. Ordered the wrong sized nut driver after getting the wrong number from Fosi.

Nuisance all around.

I also had the rattling noise from the fan while testing. After tightening the fan screws it is now under control... But, until when? Bad design choice to a lovely, simple amp.

 

[Balinus]

Regarding the title change. The tone was rude, but I recognized that this forum is steering on one side of the spectrum analysis. That is why I complied without complaints from me, I prefer a living thread where people exchange ideas compared to a thread where people are angry!

Thanks for the support @Dr Schweinsgruber

 

[LeRoi]

I also had the rattling noise from the fan while testing. After tightening the fan screws it is now under control... But, until when? Bad design choice to a lovely, simple amp.

Just simply remove the grille. The fan alone free spinning is nearly silent.

 

[dtaylo1066]

Be gentle with those forward nuts! It is a pretty cheap component, so no biggie. But when I have to mod a piece of audio gear to make it sound or perform better, I tend to lose interest, even though I am a devout DIYer.