Fosi Audio Class D amp - model 3V review - TPA3255 

NOTE: The component at 7:06 is an inrush current limiter, not a resettable fuse.

I adore simple designs ! What a beauty!

Yesterday received my unit of V3, I must admit that I'm really really surprised how good it is. Best results you will get if you use it as a power amp with dedicated preamplifier. Just set the potentiometer to 3 a clock and use a preamplifier for volume regulation. I am using old Yamaha C40 preamplifier and the result is just amazing!!!

Finally, someone mentioned the pop free on/off - volume. My main concern with vintage, efficient speakers.

Occasionally with these relatively unknown cheapies you get a real happy surprise, very occasionally it is just mind blowing.. The early Tripath amps that were 30 dollars were pretty mind blowing at the time and started class D acceptability trend. This was a great review. Like the Tripath, this IS all about about the chip, the makers followed TI's basic application notes and did a nice job of packaging it. I have to get one I think. The Texas Instruments data sheet shows we have one of those mind blowing things.. The specifications for this chip. I couldn't believe it. I hadn't looked at what was available for a fairly long time and good grief, every parameter was beyond anything I thought possible not so long ago. Texas say the power rails can accept up to 53V for 315W in stereo or 600W mono! The Texas site is a goldmine for engineers. This chip has data and application notes and technical articles - You could be reading for days. Amazing product amazing site, literature and data. Well done TI. Though I am a member..But I think its available to everyone. Remarkable product.

Amazing how much power one can control through a tiny box!

Thanks John!

Fosi makes great amps I have the BT30D thanks for the review.

Thank you. Looks like I'll pick up a few for around the house.

Thanks John & Snickers....

I just received a SMSL SU-1 over the weekend and paired it with the Fosi V3 with the 48v power supply and it sounds really good. Using optical cable from TV and speakers are a pair of old Andrew Jones designed Pioneer tower speakers.

You are one of the few youtubers that i would listen to when buying a product, due to your truthful reviews. Looks ad sounds like a great amp, guess the lack of a power switch is easily resolved and i like the idea of socketed chips. Reaching for the plastic as I'm writing this comment.

Good review.

thanks. I received a TPA 3255 2.1 amp with 32v5a adapter a few hours ago and noticed that the subwoofer sounds to be clipping above 80watts power meter at the wall. Turns out I was correct.

I hope you'll get the 48 volt power supply that Fosi Audio sells (you can buy the V3 with either PS) and retest. I did and it does improve results. If I were Fosi I'd only sell it with the better power supply.

I am new to this channel. Now I realised Cheap Audio Man's review is the cheapest in terms of review quality

Several things here. Yes, so far, the V3 is the best of the budget class D models and Fosi is leading the pack with their developments (subjective, I know. I got the 48V power supply and made sure to swap out the Op Amps with the absolutely superb Sparkos Labs SS3602 discrete Op Amps. The result was a sound level that I hadn't - up to this point - experienced with these budget class D models. In fact, mine now sounded closer to a Class AB amplifier than I had envisioned beforehand. Be careful though, because if you are going to invest in Discrete Op Amps (especially the much larger Sparkos Labs versions), not only will you need a riser, but you will have to slightly bend back some of the ELNA capacitors that border the Op Amp receptacles so that the Op Amp will fit. In the end, you'll enjoy the sound (most of you will). Also, I'd like to point out that the V3 enclosure can get quite warm - actually as warm as one of my hybrid tube amps, which surprised me. I guess that's why they gave it a vented top and bottom (not as a special feature as they advertise, but as a requirement due to the heat).

I bought a Fosi V3 along with a 48V 5A power supply. I'm using the amp right now. The V3 is OK but, as with a lot lower-end Class D amps, I find that listener fatigue sets in early when listening to music. I guess I prefer the warmer tonality of Class AB amps. Btw, the V3 will run quite warm when used with a 48V power supply, compared to the included 32V supply.

This is an amazing amp and paired with a good preamp like my Vincent Audio starts entering audiophile territory. I'm using the 48 v power supply. It does run warm but so what.

Can’t wait to get mine, I hope Fosi found my email with my shipping address!

Try using 2 lithium drill battery to equal 40v or a 40v drill battery should do some justice for the out put levels. 🎶💯🍻 good work as always

Specs are a little better then the Aiyima a07 but looks basicly the same amp with some upgraded components. Will you hear the difference? I run a tube A03 Aiyima pre amp to warm up the sound, to two 07 amps, one for 8 ohm 90 dB tower speakers on 26v 10A PS, and one for a subwoofer 2 x 4 ohm on a 48v (sett to 44v) 10A PS. Works great. Letts see the reviews about the V3, looks a great amp.

Would you be able to provide or share the test results when utilizing a 48V 5Amp configuration? That specific data is of primary interest to many who buy that adapter for an upcharge!

With a fixed output filter you have to choose which impedance to target, 2, 4, 8 or 16 ohms. If the actual impedance doesn't match what the output filter was designed for then you can get some extreme peaks in the high frequencies.

Does the Fosi v3 has better components under the shell than their upgraded versions viz BT20A Pro and BT30D Pro ?

I noticed (online) that the AC cord on the power supply on this amp has no ground prong. Would it be possible/easy to find a replacement for this AC cord that has the ground prong present?

There is some heat when using 48V power, will this affect the life or performance of the product?

I like my v3, wish it had a 12 volt trigger

So much talk from everyone on heat my a07 runs 12hrs a day for over a year now and heat is never an issue. The chip in any PC runs very hot. Chips are made to run at a high temp. On the other hand I did get my fosi v3 and it sounds very good and it's very hard to tell the difference between this and the A07 maybe at loud volumes the V3 will be better. Specs and graphs are nice but just use your ears that all that matters. The base power supply gets very loud why would anyone need 400watts from a larger supply

Thanks for the complete test but im skeptical for fosi audio because the bt20 i have its the worst amp i ever heard and i listen music a lot even with a good dac the sound was muddy fool off distortion. Maybe because i test every amp with very good speakers. I will rather wait a while for this v3 amp. Appreciate the test keep up the good work.

RE: PSU: A Philippine guy who has worked a lot with TPA3255 found out that the optimal supply voltage for TPS3255 is around 43v. Voltages above that generates a lot of heat. I suppose that is correct. I had a Fosi BT20A Pro with a 48v PSU, and that got very hot. The BT20A have 3 design flaws: Bad heat design, tone controls, and 2 SMD mounted LM5532 to give the chip a balanced input signal, the last 2 took all the details out of the amp. I had mine for just one week.

@ 7:07 - this is not a fuse. It is a Negative Temperature Coefficient Thermistor.

@ 6:47, looks like the chokes are Sagami 7G14D/J, 10µH. @ 11:44, the amp's filter is tuned for 4Ω. So for 8Ω load, it will be under-damped for high frequencies. Apart, wish you can test the power output with the maximum supply voltage for this amp (50-53V). Also, have you noticed the temperature of amp's case at the end of the power test? If yes, is it at acceptable level?

It comes alive with a 40v 10ah lithium battery bank

Any chance youd measure it with Sparkos op amps?

Wouldn't it been a good idea if an 'Optical Toslink' connections too existed along with the RCA Line in ?

I have some 16ohm 75w rms speakers I wish to use with an amp like this, do you know what sort of undistorted output power I would be able to get out of this setup?

John I am not sure how to reach you but you seem to have some very sharp people reading and responding. My question has nothing to do with this amp. Its more to do with building generic class a and class a/b amps. I like the PCBs with two halfs on one board like the Rod Elliot P3A. As a hobby I pickup these PCBs and then build them as per schematic. Then I start to make changes and see if that change improved the music or not. I get some friends over and we do blind tests to see if they can spot the difference between sides. And then we see which side is more popular in terms of votes. The only gear I own is a 100 Mhz scope 2 channel. How can I use this analyze and pick which mod or part improved the amp and which did not. My scope has a FFT function but its very basic. It does not give me any numbers. One idea I was thinking off was put one channel on input and the other on output. Then do a Ch1-Ch2 and see which side gives me less variation in signal. Am looking for ideas that will help me speed up my testing. My objective is to have the best amplification while still being true to the input signal. I know your super busy with the move but think about how much this would help us DIY guys who are constantly tinkering. Right now P3A says use BC546 I want to test BC547, 549c, 560 and see what changes. Thing is Im not even sure what to monitor and how.

Your amp can only be as good as your power supply. You tested the upper limit of your power supply, not the amp.

7:55 I wonder how much of an impact spreading some thermal compound on that metal slab would make... I will do that with mine and see how it goes

I wish it had normal RCA pre out and not 3.5 mm.

its a nice amp but the thing is with this amp is $69 with 1 input.. You can get a 200W Sony strdh190 or a yamaha a-s301 for $99 to $150

Would the output wattage increase at all by using a 48v 10a supply?

I’m using the better 48 volt 5amp power supply. Can you give me an estimation of power outputs with that unit?

Hi, Can it be used as a mono block (PBTL)? Thanks!

I hate tone controls. Well not really, bass boost for low volume listing is okay, but thats it 😊

В разных видео Fosi audio v3 наблюдаются разные версии, ревизии плат. Например ранние за март месяц, а здесь более новая за апрель месяц. Также разные версии катушек индуктивности наблюдаются. Почему так?

At 4 ohms. Your curve has a lot of zigzags inside the curve. Which was not there when you were testing 8 ohms. Can you explain that

I see a potential problem with this amplifier, it's flat and wide frequency response is fantastic but herein lies the problem... Eventually someone is going to play a piece of music with a lot of heavy bass content and this amplifier is going to try and give you everything you asked for all the way down to 10Hz if not lower and the supply capacitors fitted to this amplifier are not going to cut it! I think that it would have been interesting to scope the supply voltage for sag and also at the speaker output for clipping at the same time... I know that you have some great bass test tones to complete the test... I expect to see it become quickly apparent that tone controls would benefit this amplifier, currently you don't have any means to cut back on the bass when you want to play it a bit louder... I have run into this problem before, I had the sound as I wanted it but I could only manage to get to a certain amount of volume before the amplifier would cut out and need a restart... But by having a bass control, I realised that if I cut back on the bass, I could get it to play louder and remain stable... Those supply capacitors are rated for 63V at 2200μf, they could have been a bit larger in capacity... The voltage rating suggests that you can use the amplifier at a decent amount of input voltage... I think that I saw up to 48v... That would change the output power of this amplifier, having the extra voltage might mean that the amplifier won't need to consume more current for the lack of voltage at the level of volume you require... So yeah, that bass test I mentioned above would make a great video.... It's a nice amplifier no doubt and at lower levels it's going to put some depth into the music especially if your speakers can punch that low, you might even have no need for a subwoofer... I really like this amplifier from what I have seen thus far but I would definitely have to check and see if the supply can keep up with the current demand...

Thanks John ... Fosi has been bugging me to test their stuff ... I think you just did it for me. For me this amp has two deal breakers in it ... 1) The power switch on the volume control was a mistake. It means you can not use the amp at fixed gain behind a pre-amp or any other device that has it's own volume controls. You would have to reset the gain every time your turned it on. 2) The line out is coupled to the inputs at fixed level making it useless to control a subwoofer. Also... I suggest you test those NE5532 chips and see if they're fakes... if they are replace them with RC4558 chips (about 75 cents each). Aside from that it looks very impressive.

I was interested in the V2 that was doing the rounds recently. Regarding the heat spreader, I would think be better to mount on top side, under vents?

Hey anyone know what the input impedance is on this amp? would highly appreciate an answer!

What amplifier chip does it use?

What was wrong with your previous method of showing distortion. It did have the advantage of being visual and simple.

I think a budget class A/B amp is still better than any class D amp that I have heard.

Using Old fashion measuring techniques.

To really test the max power output, it would take about 3 (or even 4 for 48VDC) large 12V lead acid batteries in series. How about 3 12V, fully charged auto batteries.

i Have 2 different TPA3255 Based Amps and the bass on these are non-existent , how is it when lessening to bass on that one? Anything......

i received mine also... I'm not that blown away!... 😂

Notice for not technical viewers especially the ones not familiar with electronics: This review up to today( 29 July 2023) is the only competent technical review of the amp. The other reviews unfortunately are made by people with no engineering background whatsoever, youtubers who don't know the difference between subjective feelings and actual measurements and facts.

36 volts are You sure ? Not 32 volts

So, could you get more power out of it by using your own power supply?

I’m surprised it has Through Hole components with sockets. That’s a selling point for me.

From what I have seen, usually those cheap class D amps are noisy because they are using a volume pot with too high of a resistance. Like 100k when it should be more like 20k. No excuse for that other than using the cheapest pot available.

Which is better for v3, swap an op amp or just add a dac. Anyone?

You make very good educational videos, the problem is you cannot evaluate sound with a mobile phone and the junk speakers you have in your workshop. Build a new set of good speakers. This amps does not sound good at all. It has a much to soft sound, without any details, it is totally uninspiring to listen to. I hope the new V3 sounds better.

hi,can you help us do a review on youtube

🙋👍🫂

Cost less than $5 to make in China lol