Fosi Audio BT20A Pro Amplifier Review

[Maiu95]

Cheap class D amps tend to be unstable with certain loads, and that sometimes manifests itself in overly prominent highs. My A07 sounds fine with my ATC SCM19v2, but not so good with my Mission LX-.3 MKII.
If you get an opportunity, borrow a class AB amp from friends or buy one. You may find that they sound a lot better with your particular load.
A friend of mine in the US got a Yamaha R-S700 for $120 recently, he said his speakers sounded different to him now, more bass, more body, less harsh. It's a very solid amp, even at $200. If you are in Europe, 160€ to 220€ is realistic for the R-S700.
If you are interested in AB amps, we have a thread called "Inside Yamaha amps" where you can look inside them. Denon, Marantz, Rotel and other AB amp manufacturers look very much the same.

I was looking for a Yamaha A-S 301. Will be ok with DBR62? Low/medium volume (85db max)

 

[TheBatsEar]

I was looking for a Yamaha A-S 301. Will be ok with DBR62? Low/medium volume (85db max)

I think so, yes. But remember that eventually you might want to go to different speakers, i would go for a the A-S 701 right now.
Check out Hifishark for used deals, only fools pay retail.

 

[Fosi Audio]

What is a good RCA input switcher for this amp?

We are developing a switcher Fosi Audio LC30.

 

[MrOtto]

We are developing a switcher Fosi Audio LC30.

Perfect.

 

[TonyJZX]

isnt a 'switcher' essentially a preamp?

stick a vol. knob on it and you're done

 

[SWSL]

....
But none of the Fosi products that I own and have also used extensively have ever failed, even in very small cases, so again, why insist on solving a non-problem?
At the moment this version, as far as we know, responds more to a marketing need, in satisfying some users who would feel reassured by greater heat dissipation which at the moment does not seem justified by overheating problems of any Fosi unit. my acquaintance.
If beyond this the measurements will also show good benefits in terms of audio quality then it will be a different matter, but at the moment we don't know it (nor should we assume it)

Audio quality is important but keeping the amp running comes first. I suspect that you run your devices in a cool indoor environment at a comfortable volume for a personal listening stage. In our use, we run our Fosi BT30 pro (a dual 3255) at high volume in an outdoor humid 29-30 c setting near the ocean for hours. In our situation, heat is an issue. We drilled out the case to avoid problems with extended play. Besides avoiding heat shut down we also want the amp to last and prefer not to cook the components any more than necessary.

I also wonder how long you have used Fosi 3255 based devices that have not ever failed. That is, are you concluding that after 16 months of medium volume use in a cool environment that you have good enough idea of longevity over years in high volume high heat environment? Sufficiently robust testing to criticize Fosi for improving their approach to cooling?

I appreciate your perspective overall but question if these are not assumptions based on somewhat ideal usage over relatively short time period.

 

[Talisman]

Audio quality is important but keeping the amp running comes first. I suspect that you run your devices in a cool indoor environment at a comfortable volume for a personal listening stage. In our use, we run our Fosi BT30 pro (a dual 3255) at high volume in an outdoor humid 29-30 c setting near the ocean for hours. In our situation, heat is an issue. We drilled out the case to avoid problems with extended play. Besides avoiding heat shut down we also want the amp to last and prefer not to cook the components any more than necessary.

I also wonder how long you have used Fosi 3255 based devices that have not ever failed. That is, are you concluding that after 16 months of medium volume use in a cool environment that you have good enough idea of longevity over years in high volume high heat environment? Sufficiently robust testing to criticize Fosi for improving their approach to cooling?

I appreciate your perspective overall but question if these are not assumptions based on somewhat ideal usage over relatively short time period.

Forgive me if my answer is trivial.
But what are your reasons for inferring with absolute certainty that we need precautions against the heat?
Fosi audio in this same thread to a specific question replied that tests were performed at high volume for a long period of time without problems (sorry but I don't want to go looking, you can check yourself if you feel like it).
As long as there is no feedback indicating possible issues there is no reason to assume there will be any.
Still on the Aiyima a07 3255, despite the thousands of units sold, there do not seem to be any major reports of failures due to overheating.
So again. You are trying to remedy a problem that simply does not currently exist.

 

[SWSL]

I just received my BT20A Pro with the 48V supply. After playing for 2 hours at full volume on the BT20 at about 83 dBc with B&W 602s, the power supply was at 63 degrees F and the amp case was at 81 degrees F. The room temperature was 61 degrees F (my cellar). Hope this helps.

Would love to see similar test @ 80 F.

 

[SWSL]

Forgive me if my answer is trivial.
But what are your reasons for inferring with absolute certainty that we need precautions against the heat?
Fosi audio in this same thread to a specific question replied that tests were performed at high volume for a long period of time without problems (sorry but I don't want to go looking, you can check yourself if you feel like it).
As long as there is no feedback indicating possible issues there is no reason to assume there will be any.
Still on the Aiyima a07 3255, despite the thousands of units sold, there do not seem to be any major reports of failures due to overheating.
So again. You are trying to remedy a problem that simply does not currently exist.

Hi- Yes I saw that Fosi said they tested for overheating. Rather than a general statement I would prefer to hear "We tested this product at this power output for this long at these ambient temperatures and measured these temps here and here" So that the testing would include full acceptable range ambient temp usage and not just optimal or typical temps as a skeptic might suspect.

Here are my two reasons I applaud Fosi's steps toward superior cooling:

1) We have had our Fosi dual 3255 amp shut down on us when using in our public situation as described before. Very embarrassing. The case was very hot. A short wait with the amp turned off allowed it to return to operation. For the next event, we blasted a fan on the closed case and had no problem. I decided to drill ventilation holes and have not had an issue since.

2) I am no electronics engineer, but from what I have read, there are components that deteriorate more rapidly under higher heat conditions. I understand that capacitors especially absorb heat when near a radiating heatsink and more so in a small closed case. Perhaps I am misinformed and it's only time/usage and not heat that causes aged amplifiers to develop bad capacitors that must be replaced?

I don't think it's quite correct to consider taking a small protective measure as requiring absolute certainly of need. To the contrary, protective measures with low cost tend to work the other way, don't you think? As a philosophy, a company that pursues a reputation for quality might consider how the cost/benefit ratio works out. Cost to ventilate for 90% of user conditions that will never see a difference vs reliability benefit for the 10% who might see failure over x years due to accumulated heat buildup? Invented numbers here of course, just for consideration of design philosophy. Of course real numbers do matter if you can get them. I suppose that if it takes 15 years for components to fail, then for a cheap item in today's culture that's not worth any cost at all. But if 5% fail in 5 years, then that is significant and maybe worth implementing a superior cooling strategy that costs very little for your premium line.

cheers

 

[Talisman]

1) We have had our Fosi dual 3255 amp shut down on us when using in our public situation as described before. Very embarrassing. The case was very hot. A short wait with the amp turned off allowed it to return to operation. For the next event, we blasted a fan on the closed case and had no problem. I decided to drill ventilation holes and have not had an issue since.

In our use, we run our Fosi BT30 pro (a dual 3255) at high volume in an outdoor humid 29-30 c setting near the ocean for hours. In our situation, heat is an issue

I believe that the problem is not the thermal resistance of a small 100 euro domestic amplifier.
I think the problem is that you intend to use this little amp as if it were a professional power amp for outdoor parties, it is not and you shouldn't expect it to for 100 Euros.
I suggest you orient yourself on the excellent Behringer A800, which is certainly much more suitable for your use case.
https://www.audiosciencereview.com/...behringer-a800-stereo-amplifier-review.10499/

 

[TonyJZX]

its amazing to me that people would push a $100 amp outside of its operating design

if you want a cheap commerical rated unit:

the t.amp E-400

Stereo Power Amplifier Low installation depth of just 308 mm, Power: 2x 310 W at 4 Ohm, 2x 155 W at 8 Ohm, 1x 450 W at 8 Ohm bridged (@1 kHz, THD 120, Inputs: XLR, jack (balanced) and RCA, Outputs: Speaker Twist and binding posts, Protected circuit...

www.thomann.de

 

[SWSL]

its amazing to me that people would push a $100 amp outside of its operating design

Hey - the $100 amp (Fosi BT30D pro) works great in our application ! All we had to do was ventilate it. But I'm not supposed to use it? Maybe I can clarify.

There is no money in our projects nor any need to get into professional equipment. Our events are 15-25 friends on a patio for a weekly non drinking dance. No money is involved. Few have much. We previously put out computer speakers which were just not loud enough, so I organized a small system for a bit over $300 US. Brought bookshelf speakers from US to Mexico in my suitcase to keep cost down. Built a heavy sealed sub box using a $40 10" car audio driver that matches well for lower wattage amps and adds some bottom end.

Blasphemy, right?!

Everyone appreciates how good it sounds, big difference. Glass half full. Perhaps you would hate it and walk away.

Loing ago I was in commercial audio and video production as a professional. I did sound recording on film sets a few times but mostly produced tiny projects. Dabbled in live sound as well, organizing and operating a budget sound system (think Peavey Shure, etc.) for a local rock band for a few years making sound listenable and danceable in clubs to big parties. I made it work with just enough. I also went out a few times to do live sound with a friend who worked for a fine little company called Meyer Sound out of San Francisco. They had the gear.

Doesn't mean much but I'm no fool. I am also not an audiophile but like it to sound pretty good and can't tolerate the distortion that many do.

Wrong profile for this site? I was attracted by the science part I admit. I like an engineering approach to things. And the best reviews for the gear I was buying are here.

So to sum up this little line of discussion, Talisman insists that Fosi should not take any cooling measures of any kind in their products to assure function and durability because no user will ever be any different than you, and... well, if some users are different then that use is not legitimate. Tonyzdk agrees that our use is not legitimate and by extension users like us should not have any consideration in product design. Indoor users only?

Clearly, for some audiophiles, even passive cooling of a class D amp is a bad idea that should be avoided. Go figure!

 

[trivium]

Just got the blue (which looks more grey) BT20A Pro with the orange knob. Im extremely satisfied, also glad I went with a Class D as my onkyo receiver was getting some interference from my computer. Running the hitmakers off these with the 48VDC, it sounds beautiful with just enough headroom, the volume knob is usually at 50% but will increase to 75% or so for some classical or older recordings with less gain. It has the power, the biggest issue is the gain is a bit low paired to a Asus Xonar U7 which only has 1.1V pre out. Ideally this would be paired with something closer to 2V. it's fine for my desk, though if you wanted more volume just be careful what Dac you pair it with. If I had one complaint, it would be the that the bass/treble pots are somewhat cheap/grainy feeling but now im just being picky. The volume pot feels to be better quality, though Pots are expensive and they had to cut cost somewhere in an effort to focus on sound.

 

[Jedi2155]

I recently purchased both this and the BT30D Pro and ended up sticking with this unit as I definitely can hear the differences between the two. My main listening comparison was on a Triangle Borea Br03 pair of bookshelf speakers being fed either through Bluetooth and on my PC via Soundblaster Zx soundcard as my DAC. Music source was via Tidal "Master" quality audio tracks (FLAC)

My main experience came from a Denon AVR-X6500h powering a Klipsch RP-8000F in my Home Theatre and trying this out gave me a pretty impressive feel for what $80 could do although my Denon ($2000+ MSRP) undoubtedly significantly sounded better with its class AB amplifier vs class D on the BT30D Pro.

Combinations Tested (ranked from best sounding to least):
Denon X6500h -> Triangle Borea Br03
Soundblaster Zx -> BT20A Pro -> Triangle Borea Br03
Denon X6500h -> Klipsch RP-8000F (Bi-Amped) + 2x SPL-120
Soundblaster Zx -> BT30D Pro -> Triangle Borea Br03
Bluetooth -> BT30D Pro -> Triangle Borea Br03
Bluetooth -> BT30D Pro -> Klipsch RP-8000F

I set both units to Tone Controls at flat (12 o'clock) and volume at (3 o'clock or 75%), gave it the best sound. Comparing the BT30D Pro to the BT20A Pro, the BT20A was less boomy, and more clear sounding giving me a feeling closer to my Denon AVR (about halfway better). The difference could be best described as better low end bass response and more "warm". Despite both units utilizing a TI TPA3255, the BT20A also has replaceable Op-Amps (NE5532) which may be a differentiator. The BT30D Pro can push 2x175w into 4 ohms with a THD of 0.04%, while the BT20A can do up to 300Wx2 into 4 ohms with a THD of 0.005%.

The BT30D pro definitely sounds like an excellent value but it felt it definitely gave up some sound quality compared to the BT20A so if you don't need the passive subwoofer output I'd stick with the 20A which has a pre-out for an active subwoofer as well. I'm glad I went this setup over a Klipsch Fives, Sevens, or Nines although I haven't heard those speakers but if they're like my RP-8000F the Triangle's definitely sound better for music.

Other key improvements on the BT20A Pro over the BT30D Pro include:
- Tone knobs have an indent for a "flat response"
- Volume knob can be used to reset "bluetooth pairings"
- Upgradeable Op-Amps

In addition the points brought up above:
- Better sound over BT30D Pro (more power, less harmonic distortion)
- Flatter response

This is now really making me think again about switching my setup to a Marantz Cinema 70s / NR1711 for my Desktop PC since this Fosi is much closer to my Denon in terms of performance.

 

[TheBatsEar]

@Jedi2155
Welcome at ASR.

 

[baron-samedi]

Hello. I just got my BT20A Pro. It makes obnoxiously loud sound when I turn it off, so I am thinking of actually leaving it on at all time. And volume knob feels kind of flimsy. Also it was probably discussed here, but bluetooth connection is always on? You cannot switch it off?

 

[Maiu95]

I think so, yes. But remember that eventually you might want to go to different speakers, i would go for a the A-S 701 right now.
Check out Hifishark for used deals, only fools pay retail.

I tried the AS 301. I can tell that I really don't like it. Yes, with class AB the tweeter sounds better and the voices are better, but the bass is dry and if I raise it with the potentiometer it becomes just boomy (elac debut reference). With Fosi TB10D is punchy and fast, just perfect. To get the same bass with a class AB I think I should spend at least double what I paid for the AS 301.
The equalization of both is slightly different. The Fosi got much more upper-mid. To get the same result I have to decrease the 4khz by about 2-3db and the 2khz by 1db. The highs are a little dirtier but that's okay. Years ago an amp like this would have cost no more than $200.

 

[Talisman]

I tried the AS 301. I can tell that I really don't like it. Yes, with class AB the tweeter sounds better and the voices are better, but the bass is dry and if I raise it with the potentiometer it becomes just boomy (elac debut reference). With Fosi TB10D is punchy and fast, just perfect. To get the same bass with a class AB I think I should spend at least double what I paid for 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

 

[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.