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Fosi Audio BT20A Pro Amplifier Review

Rate this stereo amplifier

  • 1. Poor (headless panther)

    Votes: 3 1.0%
  • 2. Not terrible (postman panther)

    Votes: 31 10.3%
  • 3. Fine (happy panther)

    Votes: 177 59.0%
  • 4. Great (golfing panther)

    Votes: 89 29.7%

  • Total voters
    300

Doodski

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@geauxwandering if you don't mind let me know when you have those measurements that I suggested for you. They are critical to starting the process.
 

Jimi Floyd

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Let me preface, I’m new to anything audio. Looking for any advice on what this capacitor’s purpose is and input on what went wrong. As you can see, there are only remnants of the original capacitor. To be fair, I was running it pretty hard at 48v. I replaced the capacitor with a same spec Nichicon and I am still not getting any sound output. Any input on where to check for other possible collateral damage is greatly appreciated.

View attachment 295835View attachment 295834
If you value your time, cheaper to buy a new one, I fear
 

Doodski

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If you value your time, cheaper to buy a new one, I fear
In this case it might be beneficial to determine and get a idea of what blew up and or fried. A example situation is that it might have been reverse polarized and then plugging in a new one would result in the same issue. Additionally there might be a simple fix requiring a simple inexpensive part to complete and confirm a repair.
 

Doodski

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@geauxwandering we need to move this to a dedicated thread so as to not disrupt @amirm's review thread. If you ask the MOD nicely you might get the comments from this thread moved to the new thread. I apologize to the MODs for not suggesting this earlier. When a repair situation arises my technician instincts kick in and I go into troubleshooting mode and I focus on the repair and never focused on what kind of review thread that this is. Hence I commented here.
@AdamG247 and @BDWoody
 

AdamG

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@geauxwandering we need to move this to a dedicated thread so as to not disrupt @amirm's review thread. If you ask the MOD nicely you might get the comments from this thread moved to the new thread. I apologize to the MODs for not suggesting this earlier. When a repair situation arises my technician instincts kick in and I go into troubleshooting mode and I focus on the repair and never focused on what kind of review thread that this is. Hence I commented here.
@AdamG247 and @BDWoody
Start the new thread and send me a pm with a link and we can move them out. Thanks
 

Doodski

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@geauxwandering the MOD very nicely advised that starting a new thread is required. Thank you to @AdamG247 for being so understanding. So get that going and then post for @AdamG247 in that thread so he can find it and knows where to relocate all this off-topic commentary.

LINK for posting a new thread.>>>
 
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Kimbrough Xu

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Let me preface, I’m new to anything audio. Looking for any advice on what this capacitor’s purpose is and input on what went wrong. As you can see, there are only remnants of the original capacitor. To be fair, I was running it pretty hard at 48v. I replaced the capacitor with a same spec Nichicon and I am still not getting any sound output. Any input on where to check for other possible collateral damage is greatly appreciated.

View attachment 295835View attachment 295834

I presume you are running it very hard because you need to turn the volume knob to the end, if so, it is just becuase of the Taper A potentiometer!
 

Martinvb

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Just got my amp from Amazon.nl. I noted that the volume knob is rather loosely connected to the pot, even rattles a bit when shaken. One other member also noted this and was informed by @Fosi Audio that this was normal. Not sure about this. What is the experience of other users? Anyway, sound quality is as expected and the bt20a Pro form factor exactly fits my use case, so one happy owner here. For regular use, the 32V adapter seems more than what I need to drive my 8 ohm speakers.
 

hoguga

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hello



Is the audio quality better than a Denon 3800h or 4800h? amplifier only, of course.
I'm thinking of using the pre out of the 3800h for the front speakers.
 

Martinvb

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Sorry, I haven’t compared the two side by side. SNR and THD of the Fosi seem to be slightly better (if specs are correct), but I would not bet on it that in a fair contest such differences are actually audible.
 

KaeliKoo

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Just got my amp from Amazon.nl. I noted that the volume knob is rather loosely connected to the pot, even rattles a bit when shaken. One other member also noted this and was informed by @Fosi Audio that this was normal. Not sure about this. What is the experience of other users? Anyway, sound quality is as expected and the bt20a Pro form factor exactly fits my use case, so one happy owner here. For regular use, the 32V adapter seems more than what I need to drive my 8 ohm speakers.
I can verify what you're saying - it is funky and not attached tightly. I have a TB10D which is essentially the same front and the same size knob. It is firm and tight with no play or looseness.
I'm wondering if that looseness is because that knob can be be pressed in to clear the bluetooth on BTA20 Pro.
 

Martinvb

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I can verify what you're saying - it is funky and not attached tightly. I have a TB10D which is essentially the same front and the same size knob. It is firm and tight with no play or looseness.
I'm wondering if that looseness is because that knob can be be pressed in to clear the bluetooth on BTA20 Pro.
Ok thanks. I’ve decided not to worry about it too much, as like you say the knob has a double function and its play may be related to that. For me it is not justifiable to demand the same QC of electronics in this price range as you would expect from more established audio brands with much larger profit margins. You simply can’t have it all. I was lucky though with a 100% good working Topping PA5, which is still going strong. That’s life ;).
 

pseudo

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I'm considering one of these to drive a pair of Monitor Audio MR2s (6 ohm, 100W rms, 90db). Do you guys think the 48V power supply is worth the upgrade in my case? Will it make much difference to sound quality and how loud it'll go without distorting?

Also bear in mind I like to listen at high volume and live in a hot climate. My current Aiyima D03 gets scarily hot to the touch.. (the amp itself does at least, the power supply not so much)
 

pseudo

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I received yesterday my Fosi BT20A Pro with the 32V power supply and I have it connected to a pair of Klipsch Cornwall speakers. It is amusing to hear this very small and very light amplifier push two giant speakers with their 15" woofers to loud sound levels.

View attachment 280067

Anyway, using the RCA input or the Bluetooth input does not give the same sound quality, the Bluetooth being brighter. In wireless mode I am comfortable dialing 60° counterclockwise the treble knob. Out of curiosity I decided to measure the frequency response of both input modes. I don't have refined lab equipment. As a signal generator I used a MacBook pro running Audacity, set to produce sine tones, 31 in total, spaced by 1/3 octave. The computer was connected to the amp 1) through a Topping D10s DAC and RCA cables to the RCA input, and then 2) via Bluetooth. The amp was connected to the speakers and the output voltage of the right channel was measured by a multimeter for each frequency. 0dB was set at 2V amplifier output (1 kHz).

RCA input

View attachment 280070

More or less flat, with a rise in the treble reaching +2dB at 20 kHz. My ears arrive to 12-13 kHz, so I hear a +1dB rise at most, that is perfectly tolerable. Amir measured a +0.5 dB rise at 20 kHz with a 8 ohm load. I don't know the high frequency impedance of the Klipsch Cornwall, It may be higher than 8 ohm or have a phase different from 0, that would explain the difference.

Bluetooth input

View attachment 280071

I didn't expect this result. Bass frequencies are rolled off below 63 Hz, then there is a minimum at 315 Hz, then a rise up to almost +3dB at 10 kHz followed by a drop at 20 kHz. Now I understand why the sound feels light and bright with Bluetooth. I googled "Bluetooth audio frequency response" but I could not find any single plot, so that I don't know if all Bluetooth devices have this problem or it is codec related or it is just my amp. I hope somebody here can help me to better understand what is going on.
Also, did this get addressed at all? Haven't read through the whole thread yet but was this just a one off or is bluetooth not that great on this thing?
 

Guyvxt

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I purchased the BT20A and BT20A pro on offer during Amazon Prime day.

Has anyone else had issues with the BT20A pro giving a very feint beeping sound out of the speakers when the amp is on but there is no music playing? It is independent of the volume setting. It sounds like years ago when you would get some noise out of speakers when your phone is nearby. It's more noticeable in the left speaker (which is closest to the Bluetooth antenna) When I press and hold the volume button to turn off the BT the issue disappears. But when I power cycle the amp the BT is back on and so is the noise.
I don't actually have a need for the BT so I am tempted to return it and get the TB10D instead as their website says it has the same components but without the bluetooth.

The BT20A does not have this same suspected BT noise, but unfortunately the BT20A does a pop in the speakers when switched via a smart plug so that one doesn't fit my requirements either and will need returning.
 

Martinvb

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I purchased the BT20A and BT20A pro on offer during Amazon Prime day.

Has anyone else had issues with the BT20A pro giving a very feint beeping sound out of the speakers when the amp is on but there is no music playing? It is independent of the volume setting. It sounds like years ago when you would get some noise out of speakers when your phone is nearby. It's more noticeable in the left speaker (which is closest to the Bluetooth antenna) When I press and hold the volume button to turn off the BT the issue disappears. But when I power cycle the amp the BT is back on and so is the noise.
I don't actually have a need for the BT so I am tempted to return it and get the TB10D instead as their website says it has the same components but without the bluetooth.

The BT20A does not have this same suspected BT noise, but unfortunately the BT20A does a pop in the speakers when switched via a smart plug so that one doesn't fit my requirements either and will need returning.
The noise is not present in my unit. It should not be there: I would return it.
 

Guyvxt

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I've been exchanging some emails with Fosi support (very quick to respond).
I don't use BT so it was always in 'RCA Mode' with this noise present

I powered the amp on and the noise was there.

I paired my phone and the noise disappeared. I 'disconnected' my phone (but still paired) and the noise came back. When I turned the amp power on and off the noise came back briefly but then stopped once it had automatically connected to my phone by BT.

I unpaired my phone and the noise did not come back.

I have tried several power on/off and the noise is still not there.

I've paired my phone to the amp for further testing. The only time the noise is present now is for approximately 5seconds when I pair/connect/disconnect. When I unpair the noise is present for approximately 2 seconds
Very strange but seems to be working ok for now.

Interested to hear if anyone else hears any noises close up to the speaker when they pair/unpair


[update] after leaving the amp off a while now when I put it on the noise is back and I get a message on my phone that it wants to pair, I hit block or ignore it. Noise continues. Will be returning and exchanging for a V3. Have an EQ on the wiim devices I am using with them so not sure I need the treble/bass knobs. If I needed the knobs the only option would be the TB10D.
 
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Holdt

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Just some extra information that may be useful to some. This guy tests mostly car audio components but has some interesting tests of HiFi as well. He tested the BT20A Pro as well.

Regular test-->

Test with different power supplies-->

All tests of mini amplifiers-->

Explanation IR to how more power can be drawn from the outputs than the power brick ratings imply-->
 
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