BT20A MAX
amplifier
$230
Used market: $165*
Specifications
3 of 5 values have a recorded sourceExpert Audio Engineering Commentary
Headroom Notes
Fosi publishes two numbers, 'Max Output Power: 300W x 2 @ 4Ω' and 'RMS Output Power: 180W x 2 @ 4Ω', and names no power supply for either. The unit is sold in three supply configurations on the same page - 32 V 5 A, 48 V 5 A and 48 V 5 A GaN - so the rated output belongs to a machine that does not exist until you choose one, and the choice changes the price by twenty dollars.
Thermal Behavior
'Terminal Impedance: 2-8Ω'. A TPA3255 stage genuinely will run a 2 ohm load, but the figure recorded for power is the 4 ohm one, because that is the only load Fosi rates.
What the datasheet actually says
Quoted verbatim from the manufacturer’s own page, with the date we checked it. We state what is printed, not what anyone intended by it.
«Max Output Power: 300W × 2 @ 4Ω | RMS Output Power: 180W × 2 @ 4Ω»
The rated RMS output is 180 W per channel into 4 ohms, which is 360 W of audio out of both channels together. The power supplies offered for this amplifier on the same page are 32 V x 5 A and 48 V x 5 A - 160 W and 240 W of DC input. Neither figure includes conversion losses. The published RMS rating and the published supply options are both the manufacturer's; they are printed a screen apart and are not reconciled anywhere.
checked 8/5/2026* Estimated with the depreciation fallback (~72% retained value). · checked on 8/5/2026