Усилители мощности стерео — Fosi Audio BT20A MAX

The BT20A MAX is a compact two-channel class D power amplifier from Fosi Audio with a built-in Bluetooth receiver and a dedicated subwoofer output. It sits above the BT20A PRO in the maker's range and is the first Fosi stereo amplifier to use PFFB, a post-filter feedback topology. The maker's list price is USD 229.99, and buyers choose between 32 V and 48 V power supplies, including a 48 V GaN adapter.

Key specs that matter

Continuous power reaches 180 W RMS per channel into 4 ohm, with 300 W per channel quoted as peak power, and the amplifier accepts speaker loads from 2 to 8 ohm. Fosi specifies noise at 112 dB or more below full output and THD at no more than 0.003 percent, with a 20 Hz to 20 kHz band held within 0.5 dB. The amplifier stage uses a Texas Instruments TPA3255 chip, with NE5532 operational amplifiers in the input section. The DC input is rated at 5 A. Two RCA inputs and Bluetooth can be selected, and the outputs are speaker terminals plus a sub out for a 2.1 system. The chassis measures 140 x 148 x 45 mm.

Engineering and use context

PFFB takes feedback after the output filter, so the loop also corrects errors from the filter inductors, and Fosi credits it with the low distortion figure and a flatter response. The power architecture is split into separate supplies for the digital and analogue sections, with Japanese ELNA capacitors used to limit noise. A silent built-in fan improves cooling efficiency by 30 percent over the PRO version, which helps the TPA3255 keep full output during long sessions. The Bluetooth section uses a Qualcomm QCC3095 chip with Bluetooth 6.0 and a range of up to 15 m, supporting SBC, AAC, aptX, aptX HD, aptX Adaptive, aptX Lossless and LDAC at up to 24 bit and 96 kHz. Volume runs through a motorised potentiometer that follows the remote control. The front panel carries bass and treble controls with a bypass mode, and a high-pass filter can be switched in when a subwoofer takes over the lowest octaves. A 12 V trigger input lets the amplifier turn on together with other components.

Pairing

The support for 2 ohm loads and the rated power suit most passive bookshelf and floorstanding speakers, and the higher-voltage supply is the choice for getting the full power figure. Line sources such as a preamp, a network player with adjustable level or a USB converter connect to the RCA inputs, while phones and tablets connect directly over Bluetooth. The sub out and the high-pass filter allow a powered subwoofer to join small satellite speakers in a desktop or living room 2.1 system.

Alternatives

The Fosi Audio BT20A PRO is the earlier stereo amplifier in the same range with the same peak rating and a Bluetooth 5.0 receiver.