Weight is a lie. This little box claims to do exactly what a $1,500 amplifier does. This is the FOSI BT20A Max. It’s got a cooling fan, it’s got 300 watts of power, and it fits in my back pocket. But there's a catch—actually, there are three catches.
So today we’re finding out if Fosi is genius... or just full of it. We’re going to talk about the things that aren't in the manual.
For decades, we’ve been told that if an amp doesn’t weight 50 pounds and costs a month's rent, it isn't 'real' Hi-Fi. But this little guy here is really, really interesting, especially if every square inch of your living room is counted. Personally, I would have love to have an amplifier just like that in my first apartment. My living room was super small and I remember that my first amp, I think it was a Marantz 2252 was taking all the space on my tv furniture. I had to put my turntable on top of it. I know, we’re not suppose to do that, but I was young, poor and…..had limited space. And thats why I love technology and how it evolves, cause Hi-Fi should serve your life, not dictate your furniture layout. The BT20A Max is the "Apt Audiophile" manifesto in a box. Let’s talk specs!
QUICK SPECS
What it is: 300w, 2.1 Stereo, Class-D with 2 analogs input and a sub-out
What it ISN’T: Not an integrated amp. No HDMI, No Optical, No Phono stage.
The Build: CNC Aluminum
Regarding specs, I don’t want to read you the full list, I mean, you can go on Fosi website for the full treatment but long story short, its a 300w class-d 2.1 amplifier. So it is purely a stereo system with a subwoofer output ….and two analog inputs.
So right off the bat, this is NOT the same thing as an integrated amplifier. You don’t have any digital input like an HDMI eARC or Optical Input, neither a phono stage or any other outputs besides the speaker terminals. You want to plug your turntable on this thing? You’ll need a dedicated phono preamp.
You want to get the full fat cinema sound out of your tv? You’ll need a dedicated DAC and plug it into one of the analog inputs here.
Where this amp wants you to do is connect it with Bluetooth and stream your music. It supports all the hi-res codec, like LDAC, AAC, APTX, APTX HD, etc, etc. So if you want simplicity, this amp is stupid easy to use. Connect your Bluetooth on your phone, select the BTA20A Max and voilà.
It comes with a remote control that is very easy to use. Its made out of plastic, but doesn’t feel too cheap. I like the simplicity of it and the layout of the buttons. Less is more.
The chassis is made of CNC-machined aluminum. It feels like a piece of lab equipment, not a toy. I don’t mind a plastic remote, but I do mind a plastic DAC, or amplifier.
I really like the motorized analog pot for the volume control. But…. don't expect surgical precision here. That’s the only drawback with this knob I would say.
And talking of volume, here's the first catch regarding the 300w claim!
1ST CATCH : THE POWER LIE
Most budget amps (especially Chi-Fi like Fosi) scream "300 Watts!" on the box. In the real world, this is a half-truth that confuses beginners.
The Physics: Power (Watts) is limited by the Power Supply (Voltage). Most Fosi units ship with a 32V power brick. To actually hit the advertised max wattage, the chip needs a 48V power brick.
So advertising an amp rated for 300W but providing a power supply capable of delivering 70W-100W. It’s like selling a Ferrari with a speed limiter set to 60mph. So you’ll have to spend a little extra for the 48V power brick that will give you approx. 240W-300W depending on the load of your speakers.
People think they need a 100lb transformer to drive speakers in a 12x12 room. They’re buying "headroom" they will never, ever use, and sacrificing desk space for it. So for most people 70W is plenty. I mean, 300W in an apartment would blow your windows out anyway.
SOUND QUALITY
My reference speakers at the moment are the KEF LS50 Meta and I really like the sound quality out of this little box. Does it have the same soul as my big 35 pounds Atoll? No, but the Atoll is over 5 grand brand new, its a dual-mono design, and has a massive transformer inside with very high-grade components. So no, it doesnt deliver the same finesse, but guys…this is not the same category here.
The Tone Control Debate
On the front panel, you have bass and treble control, so you can dial the EQ exactly the way you like it. Ok ok, calm down here purists! I’m already hearing you typing on your keyboard. Real "Hi-Fi" amps should have a "Direct" or "Straight" path because tone controls add noise and distortion to the signal. And…that couldnt be further from the truth on this amp. It does NOT add any distortion or noise to your sound. Actually, this amp gives you a black background.
Most apartments have terrible acoustics. If your room is "boomy," you need to turn the bass down. If your room is "dead" (lots of carpets/curtains, big fat couch), you might need a treble boost. As an apartment dweller, you can’t always crank it. At low volumes, the human ear loses sensitivity to bass (this is called the Fletcher-Munson Curve). So tone controls allow you to add that "fullness" back in so the music sounds rich even when the neighbors are sleeping.
But, if you want, you can completely bypass the EQ section of the amp by switching off the TONE on the rear panel, so you’ll preserve the original audio signal. Personally, I don’t usually play with bass and treble on an amp, I blindly trust the engineer behind it. And to my ears, it sounds really good without any tone adjustment.
Another option on this amp is the HPF, which is set to an 80Hz cutoff frequency to ensure that all the high frequencies are delivered to the main speakers. That’s perfect with my KEF that has a frequency response of 79hz to 28khz, its a perfect match.
I must say, I really prefer the sound with the High Pass Filter On. I thought the sounds had more weight, was more punchy and the integration with the subwoofer was better. But don’t take my words, experiment with YOUR setup.
Overall, it sounds punchy, transients are good. I’m actually really surprised, considering this amp cost 250$. This is one of the biggest surprise I had since I started reviewing gear. It does sound full and meaty!
Don’t say it Charles, don’t say it…please….IT PUNCHES ABOVE ITS WEIGHT! Damn it, I said it. Call the Hi-Fi police right now guys!
Quick album recommendation before we jump into the second catch: The Album Recommendation: James Blake - Trying times
This album is a masterclass in texture. Blake’s vocals are vulnerable and intimate, but the production is surgically clean. It’s such a deep and profound album, perfect for late-night listening and I suggest you bring a box of Kleenex. Its beautiful and sad. Listen to how the BT20A Max handles the sub-bass weight and the silence between the electronic pulses. It’s an album that demands a "black background," and this $250 amp actually delivers it.
Now, let’s catch the ghost in the machine.
Catch 2: The "Ghost in the Machine" (The Fan)
The Truth: The BT20A Max has an active cooling fan which is great. We need that!
But in the manual, it does not mention that the fan runs continuously even when no music is playing (there is no auto-standby mode). It also doesn't mention that in a quiet room, a "near-field" listener (desk user) will hear it.
So yeah, They added a fan to protect the components, but you need to know it makes a sound. You can’t hear it when the music is playing, but if you’re sitting close to it you’ll definitely hear it. Just don’t forget to turn off your amp when you’re done.
Now, the last catch the one you should be aware of.
Catch 3: The "Personality Transplant" (Op-Amp Swapping)
Here’s the catch: if you like modding your amp, well, this is not the right model for you .Everyone told me I could swap the op-amps in this. Thing is, its not like the BT20 Pro where Fosi actually encourages you to swap the op-amp.
Fosi BT20 PRO
If you type “BT20A Max Op-amp replacement”, some people say it’s possible. So I went to the source and Fosi told me: Don't touch it. You’re not supposed to mod this. They confirmed the Max isn't designed for op-amp rolling like its little brother. If you’re a tinkerer who wants to swap 'brains,' you actually want the cheaper Pro model, not this one. The internal layout, including the fan, may obstruct any attempts to replace components like the opamp. It might cause heat issues the fan can't handle.
For those of you who don't know what the hell is an op-amp,imagine that the amplifier is a body. The power supply is the heart, the metal case is the skin, but the Op-Amp (Operational Amplifier) is the brain.
It’s a tiny chip that takes the weak signal from your phone or turntable and tells the rest of the amp how to make it bigger. Just like a brain, it has its own "personality." Some brains are clinical and analytical; others are warm and romantic. By swapping it, you are literally giving your amplifier a personality transplant
So guys, if you attempts the op-amp replacement, you’re own your own, cause it will void the warranty of your amp.
So, who is this for? I would say that this is amp is not only for people on a budget or people living in a small apartment. It is for anyone looking for a small foot print amp that sounds great and gives you the simplicity of streaming your music.
But this amp has its own limitations. No digital output and no phone preamp. Also, no headphone output. So it all depends on your needs.
But I think it is perfect for an office, or as a secondary hi-fi system.
Personally, I will use it as my outdoor system and plug these little KIN One speakers with it. Its gonna be super compact, and will deliver a much better sound than any Bluetooth speakers out there. This amp is so cheap that it frees up your budget for either room treatment or better speakers. An expensive amp into bad speakers is a waste; a budget amp into great speakers is a revelation.
Because speakers are the most important part of your system, beside your room. So for me, spending 250$ on an amp and taking the rest of the money on getting better speakers is a huge win. The snobs are looking at graphs; we’re looking at records.
