Unfortunately, it may be a hearing problem if you can't hear the noise of the bt20amax fan. You can correct this with an even higher volume and hear whether it sounds right to you. However, you cannot authentically evaluate the details heard, the sound quality and the small, subtle vibrations of the music. The sound of the bt20amax fan and the flowing air can be heard well even from 2 meters between songs, or in a quiet environment, with soft music. It produces a metallic box sound. Similar to a small hair dryer. The other problem is the motorized volume control. Too fast. Of course, it also depends on what it is paired with. There are things it can be used with. However, its sound is really very good. The operational amplifiers are replaceable. But not much fits in it because of the fan. The NE5532 is in a case. The aforementioned opa828 can also be built into it. only the height is limited. more opas can be built in if someone wants.
-
Welcome to ASR. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
Fosi BT20a Max
- Thread starter F1Fan72
- Start date
Oh, I can hear it - very faintly - only when no music is playing. And thanks, I can evaluate the music just fine!
It certainly would not be a deal-breaker for me. I have some other small nitpicks, which I'll address later.
Op-amp rolling is not something that I care about anymore - dabbled, heard no difference, so no need to do more of that.
To others reading this - just know that the fan noise is going to be an individual thing that you need to consider. If the amp is to be used very close to your head (very small desktop setup) - yeah, might be an issue. I listen nearfield in my workroom, and the amp is about 3 - 4' away from my head at the moment, and "no problemo."
It certainly would not be a deal-breaker for me. I have some other small nitpicks, which I'll address later.
Op-amp rolling is not something that I care about anymore - dabbled, heard no difference, so no need to do more of that.
To others reading this - just know that the fan noise is going to be an individual thing that you need to consider. If the amp is to be used very close to your head (very small desktop setup) - yeah, might be an issue. I listen nearfield in my workroom, and the amp is about 3 - 4' away from my head at the moment, and "no problemo."
putridspecies
New Member
- Joined
- Jan 8, 2026
- Messages
- 4
- Likes
- 7
Agreed, If you are using it for nearfield/desktop and sitting right by it then yes the fan is audible and I can see it getting annoying. From a few feet away it’s barely audible to not audible at all.
Unfortunately either mine has gotten louder after a few days or all this talk has influenced to the point that I’m focusing on it too much, but I opted to unplug the fan. My listening space is fairly small so the 32v is plenty power for me, I did grab a 36v 6a power supply from Aiyima so we’ll see how that pans out in the future, heat wise.
Aside from the minor fan noise, the amp does sound good. Too early to tell if it’s a good replacement for my topping, but so far I am enjoying it.
Unfortunately either mine has gotten louder after a few days or all this talk has influenced to the point that I’m focusing on it too much, but I opted to unplug the fan. My listening space is fairly small so the 32v is plenty power for me, I did grab a 36v 6a power supply from Aiyima so we’ll see how that pans out in the future, heat wise.
Aside from the minor fan noise, the amp does sound good. Too early to tell if it’s a good replacement for my topping, but so far I am enjoying it.
yes.. that's what I'm talking about when I mention hearing. my room is 4.5 x4.35 meters. if there's no music playing, the sound is disturbing even when in time I enter in room. it's more more than 1.2 meters. but that's a personal thing. I only mentioned the op amp because there are people who want to put something else in it. I read in the previous comments. so you can do it because it's possible. I also know that not everyone is bothered by the fan sound, many people have already put it under the v3 monoblocks. so it's a fact that you can hear it. just a moment to pull the connector apart (or no). I won't bother you with any more comments. everyone can decide. but it's not true that you can't hear it. it's just that the your hearing threshold is higher than the one who hear its the loud.
It took me a few days before the constant buzzing got annoying enough to take it apart.. I haven't even seen an article that I could read. This is a really good amplifier. I took out my v3 monoblocks because this is better and takes up less space.
Last edited:
Hannez0101
Member
- Joined
- Sep 14, 2025
- Messages
- 21
- Likes
- 2
Hi
I have a Za3 my question is there any audible difference between Za3 and the new Max?
Best regards Johannes
I have a Za3 my question is there any audible difference between Za3 and the new Max?
Best regards Johannes
Here are my condensed thoughts and observations about the new Fosi BT20a MAX amplifier:
To start: It's a very good sounding amp! I compared briefly by ear to my Fosi V3, Aiyima A04 (original model) and SMSL AO 100. As expected, it sounds very good. I still like the original V3 amplifier a lot. The new BT20 amp has slightly better SNR (112dB or better versus 110 dB or better for the V3 and similar THD+N (0.003%). I was not expecting to hear a "quantum leap" in sound quality, and I didn't. But it's just as good as the other good sub-$200 TPA3255-based amps. It sounds good with a 32v 5a supply, that level of power is fine for a small to medium sized room. Lower efficiency speakers and larger rooms will enjoy the 48v 5a GaN power supply, which costs a little more.
Notable features: Nice to have PFFB incorporated to tame a rise in FR at high frequencies. Has a subwoofer output jack with an 80hz high-pass filter switch. Motorized volume pot, good remote (same as the P4 remote, and can be used for both items). Has Bluetooth 6.0, 24/96 capable, many codecs. Has a 12v trigger jack. Uses an outbound power brick, accepts 32 - 48v ones, 5a or 10a. With a 48v 5a supply, capable of about 180 wpc with a 4 ohm nominal speaker, probably about 110-120 wpc with 8 ohm speakers. Uses the TPA3255 amp chip and has 5532 op-amps* (sound perfectly fine, we seem to be moving out of the op-amp swapping push for at least some new products). 30 day money-back guarantee, 24 month warranty.
*NOTE: Correcting my review to mention what others are saying upon inspection, that the op-amps are in fact socketed and could be swapped to other IC-type op-amps. But they are proximate to the fan, so only small IC ones (same size as the 5532s) will fit. I am happy with the 5532s and will not plan on upgrading mine.
Some things I especially like:
1. Nice overall form factor -still compact, but a little wider than the V3 or the P4 preamp. Good solid aluminum case.
2. There is a faint cute "ping" sound when you change the source/mode from BT, RCA1, RCA2. Louder than the click with the P4 switch. Good aural feedback that you have switched.
3. Lots of power! But sounds very good even with a 32v 5a supply.
4. Very fast and easy BT connection to your phone, and the BT connection sounds very good. Normal range for device to antenna for a good signal.
5. Dual RCA inputs! I use a lot of sources so this makes it a more practical unit for me. (I also am using a 4-RCA split box in my actual implementation, so I have phono on RCA2 and DAC/Streaming, tape and CD via the split box into RCA1.)
6. Tone controls! If you want 'em, you got 'em. Tone control defeat switch on back. You don't have to own a P4 preamp to have physical tone controls. I like having the option to use, they are occasionally handy, especially for low level listening where one wants to bump the levels a bit.
Some room for improvement/things I don't like:
1. As with the P4 preamp, volume control at very quiet/soft levels is not great. Using the remote, coming up from 0 level, one click is still quiet, one more click is barely there and the right channel does not play, three clicks is a big jump to a quiet but "loud quiet" level. You do not have as much granular control over very quiet levels as one has with even the V3 volume pot, say. (I know this is something I am fussy about that affects few others. I sometimes like to play very quietly while I am doing other tasks, and I like to have a lot of control over that exact level. None of these smaller D amps are great in this regard; the V3 is actually still the best of the bunch, and I would say the original Aiyima A07. And, of course, the nice digital volume control chip in my SMSL AO100, now discontinued. This is very nice to use for low level listening.)
2. The small LEDs showing mode (BT, RCA1, RCA2) are small, close together, and the legends are faint. Hence, it's nearly impossible to be sure which source you've selected unless the unit is in bright light (or you use a flashlight). My listening room is on the dark side, so this is again, more of a factor for me. Wish it was easier to see.
3. The powered fan. The sound is very faint, IMO, but it's there. I do not hear it when music is playing, even softly. But my 67 year old ears are tolerant than others'. Some people with very sensitive hearing might be bothered by it, especially if using in a close desktop setting. Apparently you can open the unit and disconnect the fan, but this would probably void the warranty. I also find the top vent with the letters "MAX" a little unappealing, but not a deal-breaker. I sit about 3 - 4' away from the unit in my small room, and when music is playing, even very softly, I am not aware at all of the fan. But I read that others are very bothered by it. So I would say by note of caution, if you have very sensitive hearing or plan to have the unit within 1 - 3' feet of your head during normal playback, you may have issues.
4. RCAs 1 and 2 sets in the back are very close together. Normal jacks work, though.
5. Small aesthetic gripe - there is a slider switch for the tone bypass and a toggle switch for HPF Off/On. Would be nicer to use the same type of switches for each. But they're in the back, so...not a big deal.
6. Adjusting the volume knob by hand is a little cumbersome because of the closeness of the treble adjustment knob. Easier to use the remote to control volume.
7. The unit does get quite a bit warmer than my other 3255 amps, particularly so with the 48v5a power supply. So I am sure the fan is helpful at keeping the interior temperature more manageable, but it still feels quite warm to the touch.
NOTE: I'm hoping to borrow or buy a small subwoofer soon to test out the High-Pass filter option, I can't do that at present.
I think this new Fosi amp should be in the consideration set for many buyers/users. I think the sweet spot use case for this is:
* People with medium sized rooms/apartments who want a small amp that can handle most speakers decently
* Need two RCA inputs
* Would like to have some simple analog tone controls
* Use or occasionally want to use a high-quality BT connection for streaming
* Have a SW or might want to incorporate one in the future
* Play at medium volume levels, but sometimes want to play louder with minimal distortion
* Don't need HDMI or digital inputs in this part of their audio chain
A few photos:
To start: It's a very good sounding amp! I compared briefly by ear to my Fosi V3, Aiyima A04 (original model) and SMSL AO 100. As expected, it sounds very good. I still like the original V3 amplifier a lot. The new BT20 amp has slightly better SNR (112dB or better versus 110 dB or better for the V3 and similar THD+N (0.003%). I was not expecting to hear a "quantum leap" in sound quality, and I didn't. But it's just as good as the other good sub-$200 TPA3255-based amps. It sounds good with a 32v 5a supply, that level of power is fine for a small to medium sized room. Lower efficiency speakers and larger rooms will enjoy the 48v 5a GaN power supply, which costs a little more.
Notable features: Nice to have PFFB incorporated to tame a rise in FR at high frequencies. Has a subwoofer output jack with an 80hz high-pass filter switch. Motorized volume pot, good remote (same as the P4 remote, and can be used for both items). Has Bluetooth 6.0, 24/96 capable, many codecs. Has a 12v trigger jack. Uses an outbound power brick, accepts 32 - 48v ones, 5a or 10a. With a 48v 5a supply, capable of about 180 wpc with a 4 ohm nominal speaker, probably about 110-120 wpc with 8 ohm speakers. Uses the TPA3255 amp chip and has 5532 op-amps* (sound perfectly fine, we seem to be moving out of the op-amp swapping push for at least some new products). 30 day money-back guarantee, 24 month warranty.
*NOTE: Correcting my review to mention what others are saying upon inspection, that the op-amps are in fact socketed and could be swapped to other IC-type op-amps. But they are proximate to the fan, so only small IC ones (same size as the 5532s) will fit. I am happy with the 5532s and will not plan on upgrading mine.
Some things I especially like:
1. Nice overall form factor -still compact, but a little wider than the V3 or the P4 preamp. Good solid aluminum case.
2. There is a faint cute "ping" sound when you change the source/mode from BT, RCA1, RCA2. Louder than the click with the P4 switch. Good aural feedback that you have switched.
3. Lots of power! But sounds very good even with a 32v 5a supply.
4. Very fast and easy BT connection to your phone, and the BT connection sounds very good. Normal range for device to antenna for a good signal.
5. Dual RCA inputs! I use a lot of sources so this makes it a more practical unit for me. (I also am using a 4-RCA split box in my actual implementation, so I have phono on RCA2 and DAC/Streaming, tape and CD via the split box into RCA1.)
6. Tone controls! If you want 'em, you got 'em. Tone control defeat switch on back. You don't have to own a P4 preamp to have physical tone controls. I like having the option to use, they are occasionally handy, especially for low level listening where one wants to bump the levels a bit.
Some room for improvement/things I don't like:
1. As with the P4 preamp, volume control at very quiet/soft levels is not great. Using the remote, coming up from 0 level, one click is still quiet, one more click is barely there and the right channel does not play, three clicks is a big jump to a quiet but "loud quiet" level. You do not have as much granular control over very quiet levels as one has with even the V3 volume pot, say. (I know this is something I am fussy about that affects few others. I sometimes like to play very quietly while I am doing other tasks, and I like to have a lot of control over that exact level. None of these smaller D amps are great in this regard; the V3 is actually still the best of the bunch, and I would say the original Aiyima A07. And, of course, the nice digital volume control chip in my SMSL AO100, now discontinued. This is very nice to use for low level listening.)
2. The small LEDs showing mode (BT, RCA1, RCA2) are small, close together, and the legends are faint. Hence, it's nearly impossible to be sure which source you've selected unless the unit is in bright light (or you use a flashlight). My listening room is on the dark side, so this is again, more of a factor for me. Wish it was easier to see.
3. The powered fan. The sound is very faint, IMO, but it's there. I do not hear it when music is playing, even softly. But my 67 year old ears are tolerant than others'. Some people with very sensitive hearing might be bothered by it, especially if using in a close desktop setting. Apparently you can open the unit and disconnect the fan, but this would probably void the warranty. I also find the top vent with the letters "MAX" a little unappealing, but not a deal-breaker. I sit about 3 - 4' away from the unit in my small room, and when music is playing, even very softly, I am not aware at all of the fan. But I read that others are very bothered by it. So I would say by note of caution, if you have very sensitive hearing or plan to have the unit within 1 - 3' feet of your head during normal playback, you may have issues.
4. RCAs 1 and 2 sets in the back are very close together. Normal jacks work, though.
5. Small aesthetic gripe - there is a slider switch for the tone bypass and a toggle switch for HPF Off/On. Would be nicer to use the same type of switches for each. But they're in the back, so...not a big deal.
6. Adjusting the volume knob by hand is a little cumbersome because of the closeness of the treble adjustment knob. Easier to use the remote to control volume.
7. The unit does get quite a bit warmer than my other 3255 amps, particularly so with the 48v5a power supply. So I am sure the fan is helpful at keeping the interior temperature more manageable, but it still feels quite warm to the touch.
NOTE: I'm hoping to borrow or buy a small subwoofer soon to test out the High-Pass filter option, I can't do that at present.
I think this new Fosi amp should be in the consideration set for many buyers/users. I think the sweet spot use case for this is:
* People with medium sized rooms/apartments who want a small amp that can handle most speakers decently
* Need two RCA inputs
* Would like to have some simple analog tone controls
* Use or occasionally want to use a high-quality BT connection for streaming
* Have a SW or might want to incorporate one in the future
* Play at medium volume levels, but sometimes want to play louder with minimal distortion
* Don't need HDMI or digital inputs in this part of their audio chain
A few photos:
Last edited:
A new package has arrived from Fosi audio. Let's see what has arrived. This is their latest desktop compact amplifier, the BT20a Max, which arrived to me before the New Year. But I tested it long and hard. It was supposed to be introduced at the end of 2025, but the final date has been postponed to January 10, 2026. The price ranges from 280-320 USD ( - sale %), depending on the power supply output (32v 5a - 48v 5a and 48v 5a Gan), but as is usual with Fosi promotions, I see an introductory 20% sale on their website. This price may vary. At the time of writing this article, this is the price I saw on the official website.
Let's not wait any longer, unpack and see what's in the box:
Contents: BT20A MAX
48v 5a Gan power supply
Remote control
Bluetooth antenna
User manual.
Before we start, let's take a quick look around, front panel:
It's immediately clear that the design is new, obviously I'm mainly thinking of the front panel here. It's different from what we're used to. It has a designer, rounded front panel. With a plastic decorative strip on top. This is the first device with all four edges of the front panel rounded. We find a power button on it, which is also the channel selector. Here we can see that we have 3 input channels. We see a series of LEDs that indicate the currently used input, the remote control sensor, an equalizer and a motorized volume control. The layout is very logical, I like it too.
The device has very good parameters. I don't usually fill my reviews with specifications, I prefer real-world usage reviews. If you want more details, you can find everything on the manufacturer's website. I'll mention a few:
Hi res Bluetooth Audio, With Bluetooth 6.0, the BT20A MAX supports a wide range of high-quality codecs, such as LDAC, aptX and aptX Lossless, Qualcomm chip: QCC3095. PFFB (this is Fosi's first stereo amplifier with PFFB) 2x300 watts on 4Ohm, Hi pass filter, snr 112 pcs. distortion 0.003%. Separate power supply for digital and analog sections. Elna capacitors. Built-in cooling.
Factory data:
The housing is reminiscent of the v3 mono design. We also find the round side ventilation openings. It finally got a top opening where the heated air can escape. This is the MAX inscription itself. We know from physics that the flow of hot air rises upwards. It got a significant help for ventilation: a built-in fan, which is relatively quiet. The ventilation MAX inscription visible on the top of the housing is equipped with a perforated orange insert plate like the side vents. We can hear a discreet rustling (and airflow) from close up during operation. Since I sometimes listen to music very quietly, I hear it, and during the break between two songs can hear, which bothers me. A basicnoise during the break. After a few days of use, I couldn't get used to it, so I took it apart and pulled off the fan's contact lug because it can still ventilate through the slots and checked if it overheats. I don't encourage anyone to do this, but there was no significant heating. After a few hours of use, without active cooling, I measured 33-34 degrees Celsius. I've been using it for two days now without active cooling, with normal room volume, and there is no significant heating. So far, it has never exceeded 34 degrees Celsius. Unfortunately, I haven't measured it with the fan running before, but when I touched it with my hand, the heating was very similar. It may be that the change is only minimal. I don't want to disassemble it again for accurate measurement, I will obviously monitor the temperature in the long term and if necessary, I will restore the active cooling. If I ever notice overheating, and I need to reset the factory cooling. I will report it in the article or in a comment.
I couldn't get used to the sound of the cooling fan.
Many people are reassured by the fact that it has active cooling. It bothers me. We are not all the same...
Backside:
From left to right we find two RCA inputs. Then a bypass button to turn the equalizer on and off. Below that we find a sub output, then the speaker outputs. These are easy to use with your fingers, not too small. They are larger than the v3 banana sockets, the same as the LC30 banana sockets. They are better because they are big enough for your fingers to comfortably reach and tighten well, but unfortunately they do not fully accept the standard banana plugs. Only about half.
AudioQuest SureGrip 100 BFA banana plugs:
They are not deep enough. In any case, the connection is stable. The sockets are not loose. They hold the plugs tightly. I think this may change in the future if possible. It would be nice if they were made of copper and gold plated. These banana jacks are similar on several of their devices. I recommend that in the future we use a jack that accepts standard plugs along their entire length, and is also big enough to comfortably reach and tighten them if we are not using the plugs, but clamps or a fork. Let's move on. Next is the trigger input. There is no output, so further chaining (stitching) with a trigger is not possible. (This is not a problem, because it is not needed at the end of the chain, just an option) Below it we find a high-pass filter switch, which, when using a subwoofer, cuts off the bass from the main output at 80 Hz and sends it to the subwoofer output so that we can use the 2.1 system. Next to it are the bluetooth antenna and the power supply input.
Top vent hole „MAX”
From the external dimensions it is clear that we cannot really pair this amplifier (on top of each other) with any other Fosi product. If it had been a little wider, it would have matched the members of the za/zd/zh series and then there would have been room for a balance button on the front panel, which would be a great help for those listening to music in an asymmetrical room, and perhaps an additional RCA input and a trigger output on the back panel. This is just my imagination. But this way, it would have fit into the family of existing devices with its dimensions. But it was not designed for an existing device family. This is a new device. Used separately, it is a very nice device. It should be treated as such.
Side vent holes:
Motorized volume controll. Well, it is not my favorite. I do not understand what this method, which was widespread in the 90s-2000s, is doing in today's devices. It is not accurate, it never was unless it is very, very subtle, slow. It should be much slower than it is now. In this specific case, it is also disturbing. Because if we use the zd3, zh3 with a fixed output, it overdrives the bt20a max. In practice, this means that the volume control goes from zero to a comfortable listening level in the room too quickly. Usually, physical potentiometers are not accurate in the lowest position. One side often sounds earlier. When we turn the potentiometer a little higher, this normalizes, but that is exactly why a slow and long-travel volume increase would be important. Here, unfortunately, we barely move the volume knob and we reach the normal volume. This is too fast. I encountered the same problem when pairing the p4 preamp and the v3 monos. There, I also reached the listening level too quickly. However, this volume control is completely fine when using CD players, turntables or tape recorders. With a normal 75-85db output signal, the motorized control works well from the remote control. This is a small anomaly caused by the high output signal level in the case of the zd3 and zh3 and of course when using any other company's 110 – 120+db output source, dac or streamer. This can be easily remedied if when pairing the BT20a max with, for example, the ZD3, ZH3 (or other high output sources), they are used in preamp mode. Not on the fixed (full volume level) output. By setting the bt20a max to maximum volume, we adjust the volume on the preamplifier. But this anomaly could have been avoided with a volume control like the long way, very slow, infinite volume control used in the zh3.. For me, this is very annoying.
Usage:
We don't have much trouble with the assembly. We just wind up the antenna, connect the speakers, the sources, the power supply and the fun can start!
Yes, it's fun, because the sound quality is very good! The performance is light, spacious, airy. The stereo space is very good. The Bluetooth connection is stable. The signal processing is good!
The sound is also very good in Bluetooth mode. We get very good detailed sound that is true to the instrument. This is a really good little compact device that will definitely be a success. I wrote my little complaints only because of my habits and my own expectations. You don't have to take it seriously because there are people who will love it for exactly the same reasons I complained about it. It is very important to me and many users that we like the devices. It should have features that we really like in daily use. That's why I write personal reviews and personal expectations about them. Next products should always be better and better..
Controls and connectors:
I usually never use the Bluetooth connection. Regardless, this is a very useful feature. If you need it, it's there. Of course, it provides convenient use, there are those who will love it just because of the bluetooth connection. But I don't play music from my phone at home. I did it just now for the sake of thorough testing. I like to use my reliable cables and my playback devices or the PC player software. During the test, I played many high-resolution files with the full version of the Poweramp application used on my phone. Every detail sounded very good. Whether it was a hi-res or a plain flac file in the phone's player, it was always sufficiently detailed and true to the instrument. The space is very good. It has the same good quality as my v3 monos, and in fact better. Although in the past I have modified my V3 monoblocks with a few extra capacitors, better banana sockets and op amps. In addition, I use them with better quality and double-priced xlr cables than the rca cables of the new comer bt20 max . I don't want to exaggerate the sound again, which is why I compare it to the v3 monoblocks. What can be said about the mono sound quality of the v3 is also here, and even a little better. The Bt20a max provides a very pleasant listening experience. In a home environment, it can easily hold its own in the main hi-fi system. It won't have many other challengers or real competitors in your office thanks to Bluetooth 6 connectivity, two analog inputs and excellent sound quality, as well as its compact size and remote control.. The sound quality is great, very good space, large power reserve which is more than enough for anything. I paired it with large floor-standing speakers. This small amplifier has the power needed to deliver a punchy sound. The equalizer can be turned off, but it does not introduce noise that can be heard by ear into the sound even when used. The equalizer effect is correct. Good remote control. Unfortunately the ZH3 is not one of the devices that can be controlled with a remote control. This would have been really good.
Distortion: 0,003%. Very good! Of course, at high volume, you should not expect the factory-specified distortion value (this varies similarly with all amplifiers) But even this is fine with the BT20a max. At normal volume, its sound is really very nice. There is no noticeable distortion or noise when listening to loud music. It could certainly be measured with measurements, but I didn't hear anything..
Since I already took it apart because of the fan, I also updated the op amps, although the ne5532 is a very good op amp, but I hear it as thin and digital to sound, so since I had many opa1612 and opa1656 and oracle II 02 at home in reserve, I put the opa1612 in it.
Note: The factory ne5532 is in a socket by the way. The possible versions for modifying the op amps are limited because the integrated cooling fan reduces the space, so only normal height I.C. s can fit without removing the entire fan. Since the op amps are under the fan and a little further in, some manual dexterity is required.
I spent days doing a/b testing using the lc30 so that there would not be a momentary pause in listening when switching. I have to say that (I repeat) everything that can be said about the v3 monos in terms of sound quality is also present in the BT20, even the stereo space is slightly better, and I really like my monoblocks and I think the op amps are better in them (akliam LC5). That's why I'm going to get negative comments because according to the measurements there's nothing audible between the op amps. But I feel like these aren't expensive op amps, and some of them I can't hear better because I spent too many dollars on them. Even among the similarly priced ones, there are some that I've thrown away because I liked one and not the other. For example, the opa1656. For me, this sound is not right. That's all for now. Let's skip on this theme..
Another positive observation: The buffer capacitors in the BT20A Max are larger than those built into the V3 Mono.
Inside BT20A MAX:
Summary: Versatile, three-channel compact amplifier with very good sound quality, stable, high-resolution bluetooth 6 connection, two analog inputs and a high-pass filter, as well as a sub output for 2.1 use. With switchable equalizer, built-in cooling, motorized volume control and remote control. Due to its excellent sound quality, it may be a favorite of many users, and may also be popular due to the high-quality Bluetooth connection. Fosi engineers deserve a lot of praise for achieving such sound quality. In the A/B test, I do not hear the advantage of monoblocks. Despite the fact that they were V3 monos powered by a 48V 10A GAN power supply, the BT20A Max 48 V5 A GAN was driven. Neither in sound quality nor in spatial representation. My objections described at the beginning arise from my own habits and expectations. I feel that my small complaints are realistic, but I did not find any fault with the sound quality. Excellent! They have built a serious rival to the V3 mono. Since the sound quality is the same or better in favor of the newcomer, the new amplifier also plus that we have to use a single amplifier, a single power supply, plus there is a volume control, equalizer, and the use of a remote control. High-resolution bluetooth, less heat generated, more inputs, subwoofer output for 2.1. High-pass filter. The overall user experience is high.
Let's enjoy it because it's good.. :
pros:
High-resolution and stable bluetooth connection
Excellent sound quality!
Switchable equalizer
High-pass filter and subwoofer output for 2.1 use.
Good build quality
3 input chanel
High user experience
cons:
The motorized volume control does not work well with a high input signal. It adjusts itself too quickly, the volume control knob reaches the room listening volume with minimal movement. (This is not a fault at all with a lower input signal!)
The remote control does not control the ZH3.
The sound of the cooling and flowing air is too loud for me. Perhaps an even larger ventilation opening on the roof without a built-in fan would have been enough. Or a temperature sensor control to turn on/off the active cooling.
Due to its unique size, it cannot be stacked directly with other Fosi products.
Let's not wait any longer, unpack and see what's in the box:
Contents: BT20A MAX
48v 5a Gan power supply
Remote control
Bluetooth antenna
User manual.
Before we start, let's take a quick look around, front panel:
It's immediately clear that the design is new, obviously I'm mainly thinking of the front panel here. It's different from what we're used to. It has a designer, rounded front panel. With a plastic decorative strip on top. This is the first device with all four edges of the front panel rounded. We find a power button on it, which is also the channel selector. Here we can see that we have 3 input channels. We see a series of LEDs that indicate the currently used input, the remote control sensor, an equalizer and a motorized volume control. The layout is very logical, I like it too.
The device has very good parameters. I don't usually fill my reviews with specifications, I prefer real-world usage reviews. If you want more details, you can find everything on the manufacturer's website. I'll mention a few:
Hi res Bluetooth Audio, With Bluetooth 6.0, the BT20A MAX supports a wide range of high-quality codecs, such as LDAC, aptX and aptX Lossless, Qualcomm chip: QCC3095. PFFB (this is Fosi's first stereo amplifier with PFFB) 2x300 watts on 4Ohm, Hi pass filter, snr 112 pcs. distortion 0.003%. Separate power supply for digital and analog sections. Elna capacitors. Built-in cooling.
Factory data:
The housing is reminiscent of the v3 mono design. We also find the round side ventilation openings. It finally got a top opening where the heated air can escape. This is the MAX inscription itself. We know from physics that the flow of hot air rises upwards. It got a significant help for ventilation: a built-in fan, which is relatively quiet. The ventilation MAX inscription visible on the top of the housing is equipped with a perforated orange insert plate like the side vents. We can hear a discreet rustling (and airflow) from close up during operation. Since I sometimes listen to music very quietly, I hear it, and during the break between two songs can hear, which bothers me. A basicnoise during the break. After a few days of use, I couldn't get used to it, so I took it apart and pulled off the fan's contact lug because it can still ventilate through the slots and checked if it overheats. I don't encourage anyone to do this, but there was no significant heating. After a few hours of use, without active cooling, I measured 33-34 degrees Celsius. I've been using it for two days now without active cooling, with normal room volume, and there is no significant heating. So far, it has never exceeded 34 degrees Celsius. Unfortunately, I haven't measured it with the fan running before, but when I touched it with my hand, the heating was very similar. It may be that the change is only minimal. I don't want to disassemble it again for accurate measurement, I will obviously monitor the temperature in the long term and if necessary, I will restore the active cooling. If I ever notice overheating, and I need to reset the factory cooling. I will report it in the article or in a comment.
I couldn't get used to the sound of the cooling fan.
Many people are reassured by the fact that it has active cooling. It bothers me. We are not all the same...
Backside:
From left to right we find two RCA inputs. Then a bypass button to turn the equalizer on and off. Below that we find a sub output, then the speaker outputs. These are easy to use with your fingers, not too small. They are larger than the v3 banana sockets, the same as the LC30 banana sockets. They are better because they are big enough for your fingers to comfortably reach and tighten well, but unfortunately they do not fully accept the standard banana plugs. Only about half.
AudioQuest SureGrip 100 BFA banana plugs:
They are not deep enough. In any case, the connection is stable. The sockets are not loose. They hold the plugs tightly. I think this may change in the future if possible. It would be nice if they were made of copper and gold plated. These banana jacks are similar on several of their devices. I recommend that in the future we use a jack that accepts standard plugs along their entire length, and is also big enough to comfortably reach and tighten them if we are not using the plugs, but clamps or a fork. Let's move on. Next is the trigger input. There is no output, so further chaining (stitching) with a trigger is not possible. (This is not a problem, because it is not needed at the end of the chain, just an option) Below it we find a high-pass filter switch, which, when using a subwoofer, cuts off the bass from the main output at 80 Hz and sends it to the subwoofer output so that we can use the 2.1 system. Next to it are the bluetooth antenna and the power supply input.
Top vent hole „MAX”
From the external dimensions it is clear that we cannot really pair this amplifier (on top of each other) with any other Fosi product. If it had been a little wider, it would have matched the members of the za/zd/zh series and then there would have been room for a balance button on the front panel, which would be a great help for those listening to music in an asymmetrical room, and perhaps an additional RCA input and a trigger output on the back panel. This is just my imagination. But this way, it would have fit into the family of existing devices with its dimensions. But it was not designed for an existing device family. This is a new device. Used separately, it is a very nice device. It should be treated as such.
Side vent holes:
Motorized volume controll. Well, it is not my favorite. I do not understand what this method, which was widespread in the 90s-2000s, is doing in today's devices. It is not accurate, it never was unless it is very, very subtle, slow. It should be much slower than it is now. In this specific case, it is also disturbing. Because if we use the zd3, zh3 with a fixed output, it overdrives the bt20a max. In practice, this means that the volume control goes from zero to a comfortable listening level in the room too quickly. Usually, physical potentiometers are not accurate in the lowest position. One side often sounds earlier. When we turn the potentiometer a little higher, this normalizes, but that is exactly why a slow and long-travel volume increase would be important. Here, unfortunately, we barely move the volume knob and we reach the normal volume. This is too fast. I encountered the same problem when pairing the p4 preamp and the v3 monos. There, I also reached the listening level too quickly. However, this volume control is completely fine when using CD players, turntables or tape recorders. With a normal 75-85db output signal, the motorized control works well from the remote control. This is a small anomaly caused by the high output signal level in the case of the zd3 and zh3 and of course when using any other company's 110 – 120+db output source, dac or streamer. This can be easily remedied if when pairing the BT20a max with, for example, the ZD3, ZH3 (or other high output sources), they are used in preamp mode. Not on the fixed (full volume level) output. By setting the bt20a max to maximum volume, we adjust the volume on the preamplifier. But this anomaly could have been avoided with a volume control like the long way, very slow, infinite volume control used in the zh3.. For me, this is very annoying.
Usage:
We don't have much trouble with the assembly. We just wind up the antenna, connect the speakers, the sources, the power supply and the fun can start!
Yes, it's fun, because the sound quality is very good! The performance is light, spacious, airy. The stereo space is very good. The Bluetooth connection is stable. The signal processing is good!
The sound is also very good in Bluetooth mode. We get very good detailed sound that is true to the instrument. This is a really good little compact device that will definitely be a success. I wrote my little complaints only because of my habits and my own expectations. You don't have to take it seriously because there are people who will love it for exactly the same reasons I complained about it. It is very important to me and many users that we like the devices. It should have features that we really like in daily use. That's why I write personal reviews and personal expectations about them. Next products should always be better and better..
Controls and connectors:
I usually never use the Bluetooth connection. Regardless, this is a very useful feature. If you need it, it's there. Of course, it provides convenient use, there are those who will love it just because of the bluetooth connection. But I don't play music from my phone at home. I did it just now for the sake of thorough testing. I like to use my reliable cables and my playback devices or the PC player software. During the test, I played many high-resolution files with the full version of the Poweramp application used on my phone. Every detail sounded very good. Whether it was a hi-res or a plain flac file in the phone's player, it was always sufficiently detailed and true to the instrument. The space is very good. It has the same good quality as my v3 monos, and in fact better. Although in the past I have modified my V3 monoblocks with a few extra capacitors, better banana sockets and op amps. In addition, I use them with better quality and double-priced xlr cables than the rca cables of the new comer bt20 max . I don't want to exaggerate the sound again, which is why I compare it to the v3 monoblocks. What can be said about the mono sound quality of the v3 is also here, and even a little better. The Bt20a max provides a very pleasant listening experience. In a home environment, it can easily hold its own in the main hi-fi system. It won't have many other challengers or real competitors in your office thanks to Bluetooth 6 connectivity, two analog inputs and excellent sound quality, as well as its compact size and remote control.. The sound quality is great, very good space, large power reserve which is more than enough for anything. I paired it with large floor-standing speakers. This small amplifier has the power needed to deliver a punchy sound. The equalizer can be turned off, but it does not introduce noise that can be heard by ear into the sound even when used. The equalizer effect is correct. Good remote control. Unfortunately the ZH3 is not one of the devices that can be controlled with a remote control. This would have been really good.
Distortion: 0,003%. Very good! Of course, at high volume, you should not expect the factory-specified distortion value (this varies similarly with all amplifiers) But even this is fine with the BT20a max. At normal volume, its sound is really very nice. There is no noticeable distortion or noise when listening to loud music. It could certainly be measured with measurements, but I didn't hear anything..
Since I already took it apart because of the fan, I also updated the op amps, although the ne5532 is a very good op amp, but I hear it as thin and digital to sound, so since I had many opa1612 and opa1656 and oracle II 02 at home in reserve, I put the opa1612 in it.
Note: The factory ne5532 is in a socket by the way. The possible versions for modifying the op amps are limited because the integrated cooling fan reduces the space, so only normal height I.C. s can fit without removing the entire fan. Since the op amps are under the fan and a little further in, some manual dexterity is required.
I spent days doing a/b testing using the lc30 so that there would not be a momentary pause in listening when switching. I have to say that (I repeat) everything that can be said about the v3 monos in terms of sound quality is also present in the BT20, even the stereo space is slightly better, and I really like my monoblocks and I think the op amps are better in them (akliam LC5). That's why I'm going to get negative comments because according to the measurements there's nothing audible between the op amps. But I feel like these aren't expensive op amps, and some of them I can't hear better because I spent too many dollars on them. Even among the similarly priced ones, there are some that I've thrown away because I liked one and not the other. For example, the opa1656. For me, this sound is not right. That's all for now. Let's skip on this theme..
Another positive observation: The buffer capacitors in the BT20A Max are larger than those built into the V3 Mono.
Inside BT20A MAX:
Summary: Versatile, three-channel compact amplifier with very good sound quality, stable, high-resolution bluetooth 6 connection, two analog inputs and a high-pass filter, as well as a sub output for 2.1 use. With switchable equalizer, built-in cooling, motorized volume control and remote control. Due to its excellent sound quality, it may be a favorite of many users, and may also be popular due to the high-quality Bluetooth connection. Fosi engineers deserve a lot of praise for achieving such sound quality. In the A/B test, I do not hear the advantage of monoblocks. Despite the fact that they were V3 monos powered by a 48V 10A GAN power supply, the BT20A Max 48 V5 A GAN was driven. Neither in sound quality nor in spatial representation. My objections described at the beginning arise from my own habits and expectations. I feel that my small complaints are realistic, but I did not find any fault with the sound quality. Excellent! They have built a serious rival to the V3 mono. Since the sound quality is the same or better in favor of the newcomer, the new amplifier also plus that we have to use a single amplifier, a single power supply, plus there is a volume control, equalizer, and the use of a remote control. High-resolution bluetooth, less heat generated, more inputs, subwoofer output for 2.1. High-pass filter. The overall user experience is high.
Let's enjoy it because it's good.. :
pros:
High-resolution and stable bluetooth connection
Excellent sound quality!
Switchable equalizer
High-pass filter and subwoofer output for 2.1 use.
Good build quality
3 input chanel
High user experience
cons:
The motorized volume control does not work well with a high input signal. It adjusts itself too quickly, the volume control knob reaches the room listening volume with minimal movement. (This is not a fault at all with a lower input signal!)
The remote control does not control the ZH3.
The sound of the cooling and flowing air is too loud for me. Perhaps an even larger ventilation opening on the roof without a built-in fan would have been enough. Or a temperature sensor control to turn on/off the active cooling.
Due to its unique size, it cannot be stacked directly with other Fosi products.
As I'm listening this morning with the 32v5a FOSI power adapter, one thing I like is that the amp sounds powerful/full even with that lowest brick. On the Aiyima A04 and A07, for example, dropping to lower power was very noticeable.
And, as noted above, the lower power does not really change the ability to use the volume pot to get very very quiet playing. The volume pot is just not as accurate to the extreme far left. You can listen quietly, just not super-quietly.
Interesting how much the fan seems to bother some folks. It's behind me in my setup, not in front of me, and I really can't hear it unless I really strain when no music is playing. It just dissapears into the base room noise level.
So, for people with very sensitive hearing, this might not be something to use for a nearfield system if the amp will be near you/in front of you due to placement.
And, as noted above, the lower power does not really change the ability to use the volume pot to get very very quiet playing. The volume pot is just not as accurate to the extreme far left. You can listen quietly, just not super-quietly.
Interesting how much the fan seems to bother some folks. It's behind me in my setup, not in front of me, and I really can't hear it unless I really strain when no music is playing. It just dissapears into the base room noise level.
So, for people with very sensitive hearing, this might not be something to use for a nearfield system if the amp will be near you/in front of you due to placement.
unfortunately I can hear it from three meters away in silence. In three days I got to the point where I really like its amplifier sound but I simply can't stand the sound of the fan. I have to turn it off. I think the hearing threshold may be the difference between those who are bothered by it and those who are not.. We are not the same. What makes you think the op amp can't be replaced? I replaced it because they are really in a case. and one more question. would anyone measure its amplifier temperature after, say, two hours of listening to music? I'm just curious because mine doesn't go above 34 degrees Celsius. Unfortunately, I didn't measure how many degrees before I turned off the cooling. I don't know how efficient the fan is. I've been using it with the cooling off for two weeks now. My speakers are Heco Victa 700 floorstanding speakers in which I replaced the capacitors with Jantzen. new capacitors original factory capacity.
I corrected my review, I guess the op-amps can be replaced (they are socketed), there just isn't any room for the taller discrete ones, just chips like the 5532.
I am glad that I do not have your sensitivity of hearing - normal life would drive me crazy, I think!
I personally think disconnecting the fan is probably OK with a 32v or 36v brick, and driving efficient speakers at normal volumes, but I'd be more concerned about unplugging it if using the 48v brick and driving power-hungry speakers at loud volumes.
I also did write to Fosi with feedback that many initial reviewers are bothered by the fan sound, and they may want to develop a PFFB stereo amp that is better suited for desktop/close up use. I'll be interested to see what they develop in regard to these types of concerns. I also hope they can develop a unit that has very precise volume control for lower levels (like the wonderful 64-step relay attenuator in the Schiit Saga 2 preamp).
I received the factory 48v 5a gan. I took out the two v3 monoblocks two weeks ago and I'm now using the bt20amax with one of the v3 power supplies. This power supply is 48v but 10a gan. My speakers are big. Fan off and 33-34celsius. Of course at normal volume. Not quiet. But not concert volume. There's no overheating with this big brick. I like to try everything thoroughly and of course carefully. Just thinking about something is not enough. I need certainty.
Well, Fosi amps seem well built overall and they use good components. If your caps & chips get a little hotter, but there's still passive venting, it probably won't shorten the product's life by too much...
putridspecies
New Member
- Joined
- Jan 8, 2026
- Messages
- 4
- Likes
- 7
One thing I’ve noticed is the Fosi seems to have higher input sensitivity than on my topping pa5 II plus. My turntable/external phono preamp (Pluto 2) is much louder (and noisier) on the Fosi at relatively lower volume than on the Topping amp. Not necessarily a bad thing, just taking a little time to get used to as the background noise of my pluto 2 was practically silent with the topping. I am also in agreement that low level volume isn’t perfect on the amp, it goes too quickly from very quiet to loud quiet. Currently routing the turntable/phono preamp through my wiim pro plus and that has helped dial in the pregain and low volume quirks. Aside from that, no complaints . Really enjoying the BT20A max
- Joined
- Dec 12, 2019
- Messages
- 16,160
- Likes
- 36,617
i.e., by 3 dB (or maybe 4)
saberger0357
Active Member
- Joined
- Oct 25, 2018
- Messages
- 251
- Likes
- 227
How might this compare to the 3e Audio A7 which I like a lot?
I don't own any 3e amps, alas...so to compare specs and feature-set...Fosi is a little cheaper in price, two RCA inputs instead of one RCA and one balanced...with the A7 you get that gain level switch and the volume pot bypass, both of those are nice to have. Power wise, and FR-response-wise, I think they'd be about the same using a similar power brick.
So I'd say it comes down more to use-case and needed features rather than power/sound quality...
Has anyone considered adding a resistor to the fan wires to slow it down rather than unplugging? Should be quieter while still maintaining active cooling. Seems there are some EE types here to give it a go…
Also I’m considering hooking it up to my tv via an arc hdmi audio extractor and then using a usb to 12v step up into the trigger port to turn on from the tv power on. I would have to modify the step up adapter to have a mono 3.5 end but should be easy.
Also I’m considering hooking it up to my tv via an arc hdmi audio extractor and then using a usb to 12v step up into the trigger port to turn on from the tv power on. I would have to modify the step up adapter to have a mono 3.5 end but should be easy.
Guddu
Major Contributor
- Joined
- Feb 10, 2020
- Messages
- 1,855
- Likes
- 1,915
Let me chime in as 3e A7 is my daily amplifier and I absolutely like it.
If BT20A MAX has flat req. response like A7 and published specs then there may not be any SQ differences to talk about.
BT20A MAX seems to more like a lifestyle product than a plain dedicated power amplifier like A7. You can BT20A MAX as
If you desire balanced input and/or auto ON/OFF then A7 is your option.
Otherwise, BT20A MAX has multiple RCA inputs, triggered input, HPF with subwoofer out, Bluetooth, Remote [+Active Cooling] - Quite a lot to like about it.
I would like to get BT20A MAX simply for ease of connecting 2 different DACs for quick blind test or comparison.
or, One set of RCA for pre-out from my AVR and another for input from DAC/streamer.
Last edited:
putridspecies
New Member
- Joined
- Jan 8, 2026
- Messages
- 4
- Likes
- 7
Following up on this, turns out it was a grounding issue. Once I switched over to a 3-pronged power supply, a 48v gan from Fosi I had laying around, the hum was gone. External phono preamp back to being completely silent, and back to being connected directly to the amp. Not sure if it’s an issue with the Fosi amp as I had the exact same issue when testing out the ampapa d1, or something else in my upstream/downstream chain, so YMMV, but wanted to put it out there in case anyone else experiences this.
With that said, after trying the ampapa d1 for a few days I am enjoying the Fosi a lot more. Sounds better right out of the box (personal opinion) and It’s perfect for those that don’t want or need the extras like digital display or balanced input. I was not a fan or in need of those and the Fosi fits my use case perfectly.
