Fosi Audio BT20A Pro Amplifier Review

[potfur]

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)

32V here, just lukewarm (much cooler than a typical AB amp with a similar power rating). At idle, power consumption around 4 watts. Playing music at reasonable volume, ca. 5 watts. I suspect it runs much cooler with the 32V PSU.

 

[Luminair]

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.

That's actually not hot for the hardware! For context, the maximum Junction temperature of the TPA3255 chip used in this amp is 150 °C according to its spec sheet. The recommended Junction temperature is 125 °C. The ambient heatsink temperature used in various tests in the spec sheet is 85 °C. And the chip has temperature self-protection features. Not that we know the temperature of the stuff in the box, but you get the drift.

This goes to show why common amplifiers have huge cases with huge heatsinks and lots of airflow -- they do use a lot of power, and they do need some cooling! But these modern little amps are very efficient, and they're probably getting cooled "well enough" by their aluminum boxes because so many of these little things continue to be made.

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

Unfortunately that doesn't mean anything because it's a GOOD thing for the case to get hot on the outside because it's acting as a heatsink. A worse product could seem cooler but actually have a higher temperature inside cooking the components.

 

[Jimi Floyd]

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.

32V PSU here, 26°C room temperature. The Fosi BT20A Pro played all day at good volume and it is still playing, case temperature 35°C.

 

[SaltyCDogg]

Mine seemed to get a lot hotter when connected with Bluetooth. When just using RCA it seems fine.

 

[MatB]

Thanks for all the replies!

I've investigated a little further on this.
When the power-switch is off, the amp consumes about 0.5 Watts. When power is on, without playing any music, it consumes about 7.5 Watts in idle mode.
Yesterday, I've switched the amp on without RCA/Speakers connected/playing for testing purposes and the temperature got up to 47°C/116,6°F within 1-2 hours! It stayed at this temperature.
After 3 hours of no changing temperature, I connected my RCA/Speakers and played at about modest 65 dbA (with low sensitivity speakers) and it didn't go up in temperature at all.

What surprises me that much is that the amp gets this hot without playing any music. 47°C doesn't sound very much, but its quite uncomfortable touching it and it feels like a little heater in my room, even though I don't really "use" it.

@SaltyCDogg: Thanks for your hint. I will investigate on this. Haven't connected bluetooth yet.
@nickaigi: Thanks for your experience with the 48V power supply. Would be interesting what the real temperatures are.
@Luminair: Thanks for your explanations. I'm just surprised that the device is that hot, without playing any music at all. I like the sleek look of the BT20A, but now I'm thinking about drilling holes, applying outside heat sinks or even installing a fan - this seems kind of ridiculus to me, let alone losing on guarantee.

Would be great if anybody else with the 48V power supply could reply in terms of idle case temperatures.

 

[nickaigi]

Thanks @MatB for digging deeper.

After reading @Luminair reply, I went and read the data sheet (Section 7.4: Thermal Information and 9.4.1.5 Overtemperature Protection OTW and OTE) from Texas Instruments.

TPA3255 has a two-level temperature-protection system that asserts an active-low warning signal (CLIP_OTW) when the device junction temperature exceeds 120°C (typical) and, if the device junction temperature exceeds 155°C (typical), the device is put into thermal shutdown.

Like @Luminair said, my Cambridge Audio being a class A/B is massive, has holes/perforations on the metallic top cover, massive heatsink + a fan that would turn on/spin 99% of the time that I used it even at very low volume. With all of that, the amp would still get warm and would routinely shut itself down. I had kept it at the top of my TV console where it received enough air flow (see picture). I live along the Equator, average daily temp is about 25°C, So the 47°C wouldn't really be that much of a problem for me.

With all this in mind, I am satisfied that the heat that I described coming from the BT20A Pro is not a cause for alarm. As @MatB has said, the temperature doesn't change when playing music... it just holds constant in my use case. I believe that if the heat became an issue, the amp would go into thermal shutdown. The amp has not once shutdown on me.

 

[GjBrennan]

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 have had the same problem with this amp getting really hot. I was testing the pre-amp stage connected to my Nad C 352 when i noticed. Plus the bass and treble don't work when using it as a pre-amp stage to a power amp. Another problem I noticed is when the volume is turned pass 12 there is an annoying ticking coming through the tweeters.
I have contacted Fosi and they have asked me to send the amps circuit board back to them for testing. I have the 48V power supply.
I have seen that other folks are experiencing the same problems.

 

[Luminair]

I'm thinking about drilling holes, applying outside heat sinks or even installing a fan

You should just return it and find an amp that suits your needs. That might mean lower power, more efficient, more heatsinking, or a power-saving mode so it's cooler while idle. But again, the device itself doesn't care that it's hot; it's working as intended.

 

[guddu]

I asked Fosi here in some thread about heat efficiency with their 3255 amp using 48v psu and he said they have had enough testing or something like that.
But I have had a bit higher heating issues with Fosi TB10d kept on TV table in open space with all the air flow around it and so had to send back the unit to Amazon.
OTOH, I have 2 Aiyima A07 Pro units running with 48v psu without any heating observed.

Is it unreasonable for these little 3255 amps with such closed enclosure to run a little bit hotter ??? Probably not!!!
But it’s annoying.

 

[nickaigi]

You should just return it and find an amp that suits your needs. That might mean lower power, more efficient, more heatsinking, or a power-saving mode so it's cooler while idle. But again, the device itself doesn't care that it's hot; it's working as intended.

@MatB @Luminair After about 5hrs of watching movies and listening to music (Bluetooth and RCA), I used an infrared thermometer and found that the BT20A Pro (with 48V PSU) stayed constant at 40°C

 

[alvigg]

Has anyone replaced the opamps? Is so, what difference do you hear?

Has Amir tested that?

 

[ClassicGuy]

If you can't stand the heat ...

don't get the 48V power supply

 

[Fosi Audio]

Perhaps wait for Fosi Audio V3, venting holes on both sides.

Here it comes

Fosi Audio V3 Amplifier Review

This is a review and detailed measurements of the Fosi Audio V3 stereo amplifier. It was sent to me by the company and costs US $89.99 with stock 32 volt supply. Price goes up to $109.99 with the 48 volt supply. There is a $10 discount coupon right now. Despite its budget price, the V3...

www.audiosciencereview.com

 

[idex]

Is the Pre-Out affected by the volume control?

 

[TheBatsEar]

Is the Pre-Out affected by the volume control?

It doesn't seem to be in the Fosi A3: https://www.audiosciencereview.com/...-audio-v3-amplifier-review.45757/post-1633203
However, it's not confirmed, it could be a translation error.

So this is a good question, can anyone answer this for the BT20a?

 

[TheBatsEar]

Is the Pre-Out affected by the volume control?

Welcome to ASR

 

[Jimi Floyd]

Is the Pre-Out affected by the volume control?

Yes, it is

 

[NoxMorbis]

Is it just me or is this thing pretty impressive? Too bad almost none of these have AUX/Sub outs. If you need that it really limits one's choices.

 

[geauxwandering]

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.

 

[NoxMorbis]

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

Noice! I'm sure you did, but did you connect the capacitor negative to negative and positive to positive?