This video is basically my first real tube amp experience, and it’s with the Fosi GR40. I walk through the unboxing (simple purple box, tubes not pre-installed), the build (aluminum, dark blue finish), and the I/O (3.5mm out, RCA/coax/optical/USB-C in, Bluetooth antenna, 12V power). It’s running an ES928Q2M DAC, does up to 32-bit/384kHz and DSD256, and it also supports a bunch of Bluetooth codecs like AAC, SBC, aptX, aptX HD, and aptX LL. For sound, I’ll keep it straight: the GR40 is unexpectedly warm, rounded, and super immersive. It doesn’t hit you with “clinical detail”—it hits you with personality. The bass/treble knobs are actually useful, and in my testing I usually had treble dialed down a bit more than bass (roughly bass around 12:00, treble around 10:00–11:00 depending on the headphone). What surprised me most is the treble: it’s powerful but not fatiguing, and with brighter headphones like my Audio-Technica ATH-A500, it was an absolutely amazing, chill pairing. I also talk about limitations: this is not an IEM-centered amp. Sensitive, low-impedance IEMs can get noisy (my Moritz Paradise was a noisy mess), so if you’re trying IEMs, stick to higher impedance/lower sensitivity sets. Versus Fosi’s SK2, the SK2 is more technical and detailed, while the GR40 is smoother and more relaxing—different flavors, and the GR40 isn’t for everybody.