Amplifier, speaker, DAC, and audio-system specifications explained with source-checked data and calculations.
Short answer Do not assume the BT30D Pro SUB FREQ knob controls a powered subwoofer connected to PRE OUT. Fosi’s current product page says the 3.5mm PRE OUT can feed a powered subwoofer, powered speaker or another amplifier. But its current user-instruction page describes SUB FREQ specifically as adjusting the frequency output of the passive…
Data Dossier: The Fosi Audio BT30D Pro is a compact 2.1-channel amplifier with Bluetooth/RCA input, stereo passive-speaker outputs, a separate passive-subwoofer output and a full-range 3.5mm pre-out. The buying challenge is that “subwoofer support” means two different signal paths, and the current product page and user-instruction page do not completely agree about allowable DC input…
Data Dossier: The Fosi Audio MC331 combines a compact stereo amplifier, DAC, Bluetooth receiver, headphone output and tube-buffered presentation in one small box. The useful buying question is not whether it has "105 watts." It is whether its inputs, outputs, power supply and speaker range fit the system you are actually building. This is a…
A source-checked Fosi Audio ZA3 data sheet that reconciles conflicting output ratings, explains the 32V/48V power-supply ceiling, stereo/mono modes, dimensions and buyer FAQs.