Fosi Audio BT20A Pro Amplifier Review

[Maiu95]

Maybe yes for the treble, ok. But I'm sure the bass is dry compared to that of the Fosi set flat. I don't listen to electronic music, I don't need that bass. But with the Fosi the bass sounds like a couple of Presonus Eris E5 I own (studio monitors), punchy and fast. I spent a day doing an A/B comparison. And then I didn't talk about the AB class in general, I'm referring to the comparison with the AS 301.

You need to understand that these differences you've perceived are very unlikely to be real, either the treble on Class D or the "boomy" bass on Class AB.
Consider the possibility that your expectation shapes your perception

 

[Talisman]

Maybe yes for the treble, ok. But I'm sure the bass is dry compared to that of the Fosi set flat. I don't listen to electronic music, I don't need that bass. But with the Fosi the bass sounds like a couple of Presonus Eris E5 I own (studio monitors), punchy and fast. I spent a day doing an A/B comparison. And then I didn't talk about the AB class in general, I'm referring to the comparison with the AS 301.

The point is that clearly hearing a different bass response indicates an equalization of the frequency response which would show a frankly broken design. I doubt you hear the -0.7 db of the fosi at 20hz. And I equally doubt that an amplifier like the yamaha a301 could have a swollen response on low frequencies, that would be an unacceptable mistake.

 

[Jimi Floyd]

Did somebody swap the grey volume knob with a copper tinted one? I have the replacement ready, but as strong as I pull (within some "safe" limit) I am not able to remove the original one. Is it glued, maybe? Anybody can help from experience? Thank you!

 

[Doodski]

Did somebody swap the grey volume knob with a copper tinted one? I have the replacement ready, but as strong as I pull (within some "safe" limit) I am not able to remove the original one. Is it glued, maybe? Anybody can help from experience? Thank you!

First things first. Is there a set screw in the knob holding it to the shaft? Can you get a V shaped tool(s) in there to pry the knob out/off with? Can you show a exact image of what you see?

 

[Jimi Floyd]

First things first. Is there a set screw in the knob holding it to the shaft? Can you get a V shaped tool(s) in there to pry the knob out/off with? Can you show a exact image of what you see?

Unfortunately no set screw and the knob is recessed in the amplifier body

 

[Doodski]

Unfortunately no set screw and the knob is recessed in the amplifier body
View attachment 289672
View attachment 289673

Splined teeth on the shaft. From where I'm looking at it appears it's a press fit but adhesive could have been applied @ assembly. What's your gut feeling on using two blade type screwdrivers and prying on that plastic and anodized metal(s). I would not. LoL> It's a gong show waiting to happen. I leave it up to you to determine if you wanna go for the gustO.

 

[Jimi Floyd]

Splined teeth on the shaft. From where I'm looking at it appears it's a press fit but adhesive could have been applied @ assembly. What's your gut feeling on using two blade type screwdrivers and prying on that plastic and anodized metal(s). I would not. LoL> It's a gong show waiting to happen. I leave it up to you to determine if you wanna go for the gustO.

The knob might be glued, I quit. Breaking the amp for a knob color change does not seem a wise move.

 

[Holdt]

The knob might be glued, I quit. Breaking the amp for a knob color change does not seem a wise move.

They are very seldom glued on splines like this. Typically they are pressed on with no force to speak of. The following would be the process. I know it sounds a bit wrong but it should only be applicable for the context of knob-pulling.

I'd gradually start pulling harder and harder (on my knob) while wiggling (my knob) a bit. Hopefully it's a happy ending and it eventually gets loose. If it doesn't I'd just leave it be.

 

[TheBatsEar]

I say pull it and pull it good. No shame in using both hands either.
Let it rip, but some backbone into it, don't forget to grunt.

 

[Holdt]

I say pull it and pull it good. No shame in using both hands either.
Let it rip, but some backbone into it, don't forget to grunt.

But you sometimes can get too violent. Remember the lyrics from this old banger;

"Don't go breaking my knob
I couldn't if I tried
Honey if I get restless
Baby you're not that kind

Don't go breaking my knob
You take the weight off of me
Honey when you knock on my door

Ooh, I gave you my key
Woo hoo
Nobody knows it
When I was down
I was your clown
Woo hoo
Nobody knows it.."

 

[Hiten]

if you still want to remove the knob; you can insert strong soft thread around the knob pushing it in with pointed forcep in the tiny gap as shown in the picture. Two on opposing side. (somewhat like gallow/harness) then tie the two ends and pull. If possible open the amp and hold the potentiometer soldered to the pcb firmly*. Usually chinese amps have metals knurled shaft and plastic knobs. This looks like metal and galling may have occured making it difficult to removing.

* a link to video of teardown. LINK

You will be the best judge how much force to safely apply and if it is worth the risk.
regards

 

[Kimbrough Xu]

What are the differences with the bt20a potentiometer? In terms of sound, I mean

Because of the taper A potentiometer, you can hear a more linear sound change when you adjust the volume.

 

[MrOtto]

Can I use this OP amp?

TI LM4562NA/NOPB Dual Operational Amplifier OPA DIP8 (Unit) - Audiophonics

The Texas Instruments LM4562NA/NOPB is a high-performance 2-channel operational amplifier (OPA) integrated in a PDIP8 enclosure. This ultra low distortion, low noise and high speed AOP is optimized for high fidelity audio applications.

www.audiophonics.fr

 

[Fosi Audio]

Unfortunately no set screw and the knob is recessed in the amplifier body
View attachment 289672
View attachment 289673

@Hiten @Holdt

Sorry for not having shared a demonstrative video on swapping the volume knob earlier.

I'd like to share a simpler way to pull out the knob. Just use a piece of polishing cloth like this to wrap the knob and pull it out!

You can search for the words "apple polishing cloth" on Amazon and find it.

 

[Jimi Floyd]

@Hiten @Holdt

Sorry for not having shared a demonstrative video on swapping the volume knob earlier.

I'd like to share a simpler way to pull out the knob. Just use a piece of polishing cloth like this to wrap the knob and pull it out!
View attachment 289888

You can search for the words "apple polishing cloth" on Amazon and find it.

Thank you!

 

[Holdt]

@Hiten @Holdt

Sorry for not having shared a demonstrative video on swapping the volume knob earlier.

I'd like to share a simpler way to pull out the knob. Just use a piece of polishing cloth like this to wrap the knob and pull it out!
View attachment 289888

You can search for the words "apple polishing cloth" on Amazon and find it.

Thanks. In due time, you will make every customer a knob-pulling expert.

 

[Kimbrough Xu]

I am so proud of myself, I just pulled it out with my hands

 

[GjBrennan]

Anyone able to hear a very faint flapping noise coming from the tweeter when their BT20A Pro is idling, when the volume knob is set between 12 o'clock to max?

Yes, Fosi audio support asked me to try different power supplies, RCA cables, turning wi-fi off, using different speakers. I did all of this and the flapping is still there. Fosi asked asked me to send the circuit board back for testing. Its in transit at the moment I will let you know what they say after testing.

 

[MatB]

First of all, thanks amirm for the review!

Finally, I've got my blue BT20A Pro with the orange knob 45 days after purchase.
Overall, I like it very much!

Unfortunately, my device gets pretty hot. Even if I place the BT20 elevated, with free airflow around, the metal body gets very warm.
I've measured 43 °C/109,4 °F on the top of the case!
If I place it in my normal living room shelf it gets unbearable hot. I cannot stack it there, where my WiiM Pro and SMSL D-6 are staying at cool temperatures.

The crazy thing about this is that the device gets this hot only by turning it on. When playing music, it gets barely hotter than that. After shutting the device off, the case gets back to normal levels.
I have the version with the 48V power supply. The power supply itself stays cool.

Does anybody else get these temperatures?
@Fosi Audio is my device malfunctioning?

For reference: none of my other Class D Amps/DACs gets noticeably above room temperature.

 

[nickaigi]

First of all, thanks amirm for the review!

Finally, I've got my blue BT20A Pro with the orange knob 45 days after purchase.
Overall, I like it very much!

Unfortunately, my device gets pretty hot. Even if I place the BT20 elevated, with free airflow around, the metal body gets very warm.
I've measured 43 °C/109,4 °F on the top of the case!
If I place it in my normal living room shelf it gets unbearable hot. I cannot stack it there, where my WiiM Pro and SMSL D-6 are staying at cool temperatures.

The crazy thing about this is that the device gets this hot only by turning it on. When playing music, it gets barely hotter than that. After shutting the device off, the case gets back to normal levels.
I have the version with the 48V power supply. The power supply itself stays cool.

Does anybody else get these temperatures?
@Fosi Audio is my device malfunctioning?

For reference: none of my other Class D Amps/DACs gets noticeably above room temperature.

I've had the BT20A pro, 48V power supply for about 5 days, and I too have noticed that the amp is warm to the touch... It doesn't get unbearably hot though.
Even at idle, the metal enclosure is warm to the touch.
Playing music through a pair of KEF Q350 and running a REL Subwoofer via the Pre-Out.
The amp doesn't get warmer while playing music... just maintains the warm temp... same as when idle.

That aside, I really enjoy listening to music via this amp. I bought this after my Cambridge Audio AXR85 developed a problem.The AX85 sounds boring compared to the BT20APro. The BT20A Pro has super clean vocals, and the instruments really come alive. I love it.

Its my second Fosi amp (I also have a Fosi Audio TDA7498E)