By Semab
I am a budget-conscious audio enthusiast. My main system is powered by a class AB amplifier I built about 15 years ago. I had a strong emotional attachment to it and never really had a desire for an upgrade.
In 2022, I wanted to set up a secondary stereo system. I discovered the Fosi Audio TB10D, which was sold for NZ$120 from Aliexpress. Class D, yikes! I thought, but I heard good things about the TPA3255 chip. I was curious. For the price, why not?
Oh boy, I was pleasantly surprised by the quality of sound it was pumping out. Only a week or two passed, and Fosi Audio released another product, the BT20A Pro, which looked like a refined version of the TB10D, again based on the TPA3255 chip, but with Bluetooth, tone control defeat (with a little “click” at the centre knob position), and the capacity to upgrade the default NE5532 op amp. I don’t know why I bought it when I was already perfectly happy with the TB10D. Perhaps I wanted a little personal challenge. I happened to have a bag of unused op amps from my old DIY audio hobby projects, so I played with a variety of op amps to see if I could hear the difference. The difference was very subtle, sometimes not quite discernible. I thought the original NE5532 was not bad at all, but I ended up selecting the OPA2604 as the permanent replacement. It was very subtle, but I think it made the sound a bit more mellow, and the female vocals from the little amplifier were almost unbelievable.
I have been closely following Fosi Audio since then. They have been busy rolling out new products like the V3 and ZA3 amps. I had to restrain myself from clicking the “buy now” button on a few occasions, as I didn’t want to end up with too many amplifiers at home.
However, when the MC351 was released, I knew I had to buy it. I saw the ad and drooled over it. It was a beauty—a beautifully crafted aluminium chassis with the golden recipe, the TPA3255 chip, and an integrated DAC, meaning I could get rid of an RCA input selector box. On the spec sheet, the DAC looked pretty decent. Minimal cable visibility has been a thing since Apple brought their iMac into this world, and I knew this little box was going to add that slick character to my lounge. Yes, my lounge. I was ready to say goodbye to my old faithful DIY class AB amp. I have three inputs: Google Chromecast Audio, a Sony LX310 turntable, and a TV. Nothing special. Chromecast Audio can handle a few not-so-fancy streaming services well enough (e.g., Spotify, YouTube Music, etc.) and can support Qobuz up to a 96kHz sampling rate. My three inputs beautifully connected to the MC351: Chromecast via optical, turntable via RCA, and TV via Bluetooth. If your turntable has no integrated phono stage, you will have to add a phono preamp to connect to the MC351.
One thing I noticed was the nice implementation of input selection. It remembers the last input it used. If you switch it off and switch it back on, it will stay at the same input. It is a nice touch. I have seen many cheap audio products revert to the default option when turned on.
Bluetooth was also implemented very well. After my TV successfully paired with the MC351, I switched to Bluetooth, and the TV sound came out of the audio system as expected. If I switch
the input to something else, for example, optical, the amp quickly unpairs from the TV, letting the TV sounds come out of the TV speakers. (If it was poorly implemented, it could have held up the Bluetooth connection, inadvertently muting the TV sound.) It saved me from having to fiddle with the remote control and navigate TV menus to unpair the amp, which was great. When I switch back to Bluetooth, the amp immediately pairs with the TV again and plays the TV sound seamlessly. I have seen many products fail to do this simple thing!
Another thing I liked is the automatic standby feature. It automatically goes into standby mode after 2 minutes of no audio signal - it will help my power bill as I often forget to turn off the amp. There is a “mode” button to switch between different inputs. It is functional, but it was a little difficult to change the input in a dark room. Input labels are not illuminated, and the little dot LED next to the label was not bright enough to help me read the label.
The VU metre is a nice touch. It is mesmerising to watch the movement of the needle. However, the volume has to be reasonably high to see most of it. Imagine yourself sitting alone at night, a glass of whiskey in hand, and your favourite jazz track playing. But you don’t want to wake up the family, so you set the volume low. Sadly, the VU metre is not working as hard when you kinda want it the most.
I opened up the case to examine the quality of components and upgradability. Most components are surface mount, except for the electrolytic capacitors. One thing I instantly noticed was the beefy 4700uF reservoir capacitors. The inductors appear to be from Sumida. Unlike Fosi’s other recent products (e.g., V3, ZA3), I wasn’t able to see premium brand components like Nichicon and WIMA capacitors.
I wanted to see if it allowed opamp upgrades, but it didn’t look promising. I spotted 8 NE5532 op amps, directly soldered onto the surface of the board.
A separate board appears to be the DAC and Bluetooth. I was unable to see what lies under this board as I failed to undo the screw.
The Fosi Audio MC351 is probably not intended to please critical audio connoisseurs. In comparison to the highly regarded V3 and ZA3 amps, I can see Fosi made some compromises to add more features and convenience. It is an all-in-one compact amp that pleases your eyes and ears. The magic of the TPA3255 chip continues, and it is a formidable audio engine. I don’t have a passive sub, but I am planning to get one to see if I can pull out the full potential of this little amp.