The Fosi Audio MC331 Tube Integrated Bluetooth Amplifier is a compact yet feature-packed system that brings vintage tube warmth and modern versatility together at an entry-level price. Equipped with a built-in DAC, VU meter, multiple digital and analog inputs, and Bluetooth connectivity, the MC331 aims to be more than just a budget-friendly tube amp; it’s designed as a complete hub for your audio setup. In this review, we’ll explore its design, build quality, sound performance, and how it pairs with a variety of headphones.
What You Get
- MC331 amplifier
- Bluetooth Antenna
- 2 5654W Vacuum Tubes
- 2 Tube covers
- Remote control
- Power supply unit
- User manual
Build
The Fosi MC331 is one of the most inexpensive tube amps on the market, but its design and build quality stand on its own. It’s a smaller system, but that works to its benefit. Also, I’m kind of a sucker for anything that has a VU meter, so being able to not spend much on one garners a lot of goodwill from me. It’s not just its vintage aesthetic that’s appealing to me, though; it’s the compact size and overall construction. For inputs, it supports Bluetooth (SBC/AAC), USB, optical (TOSLINK), coaxial, and RCA analog sources; outputs include passive speaker terminals, a 3.5 mm pre-out, and a 3.5 mm headphone jack.
Design
Powered by an internal Fosi-designed DAC chipset (TPA3221 + FS-2348B-2F), the MC331 delivers up to 105 W × 2 into 4 Ω with ≤ 0.03% THD and ≥ 100 dB SNR. It combines multiple audio functions into one compact unit—serving as a DAC, preamplifier, power amplifier, and headphone amp.
Sound Impressions
Along with its treble and bass EQ knobs, the Fosi MC331 can significantly enhance or detract from the performance of some headphones, especially the i5. Other headphones I tested, such as the HiFiMAN Ananda Unveiled and Focal Hadenys, performed as I expected them to. The Fosi MC331 has some colorful qualities thanks to its EQ and vacuum tubes, but most of these characteristics are better suited for the i5 compared to the others.
When listening to the i5 with the MC331, the sound signature is super thin without significantly increasing bass and treble. The i5 usually doesn’t sound like this with any other amplifier, so turning up the bass and treble is pretty much a requirement for the headphones to sound good. As a result, you will be given a larger mass of tone from the lows and highs. The i5 gains a ton of warmth, but I was more impressed with its height from the top end. High frequencies have a lot more sizzle, and they hover over you, showcasing more depth and shimmery tones. It acts like a coating of gloss more than natural detail, but it’s very satisfying to listen to.
With the Ananda Unveiled and the Focal Hadenys, the MC331 held a similar warmth, but the shimmer of the highs was never as prominent. The amp did more to increase the separation and width of the soundstage, though, especially with the Unveiled, which opened up the headspace quite impressively. Listening to the Hadenys with the MC331 revealed a tighter sound that was true to its natural accuracy, but with more separation and shape.
Summary
The Fosi MC331 tube amplifier is a surprisingly capable all-in-one unit for its price, offering DAC, preamp, power amp, and headphone amp functionality in a single compact package. While its sonic character can be colored, especially when paired with sensitive headphones like the i5, its warmth, soundstage expansion, and vintage charm make it a compelling choice for those looking to experiment with tube sound without spending a fortune. For budget-conscious audiophiles and newcomers to tube amps, the MC331 provides an accessible entry point into high-fidelity listening with plenty of flexibility and personality.
The Fosi MC331 is available at Audio46.
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