What is the subwoofer frequency crossed at?

According to the Fosi site, the 'sub freq' knob does exactly what you would expect, acts as a variable crossover point control. ""...adjustable 40-300Hz cutoff frequency for subwoofer... It doesn't say what the slope of the cutoff is.

Are they screw fasteners for the speaker wires?

The unit has a set of combination binding pot/RCA connections. So it will accept bare wires or RCA connectors for your speakers.

has any one used this with a non powered sub, and did it sound OK ?

William, I have this Fosi amp for a small patio sound system. I do have a sub speaker but it is powered and not passive. I am 100% satisfied with the sound of my system. The Bluetooth works great as well as the aux input. This however does not answer your question but I may give you something to consider. According to Fosi specs, the rated output is 50 watts + 50 watts + 100 watts. I deduce that to mean 50 watts for each left & right speaker and 100 watts for sub speaker. That should be a sufficient 2 to 1 ratio for output division. Fosi also states that the output can be increased with an option 8 amp power supply, but they don’t state exactly how much the output increases. Whether or not a passive sub speaker would “sound ok” has many other variables, ie: size of speaker, sensitivity of speaker, speaker material, type of enclosure that houses speaker, if the enclosure is ported and if the port is tuned properly, if speaker is front firing or down firing, acoustical environment, etc, etc. It is possible a passive mode that the sub speaker may not “sound” satisfactory but may not be the fault of the Fosi amp. I hope this was helpful.

I see in some reviews that there should be a bluetooth/rca switch on the back , but no switch exists on mine. how do i switch to bt and pair it?

For the BT30D theres a power switch on the front. When you turn it on it activates the Bluetooth, but uses the RCA jacks until you actually pair a device via Bluetooth. Just unpair the Bluetooth if you want to use a turntable or DAC.

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🎧 Elevate your sound game—because your ears deserve the best!

POWERHOUSE PERFORMANCE - Unleash crystal-clear sound with 165W x2 + 350W subwoofer power driven by premium TPA3255 chips.
BUILT TO LAST IMPRESS - Sleek all-metal chassis with premium controls and ClimatePartner certification for eco-conscious audiophiles.
TAILORED BASS EXPERIENCE - Fine-tune your bass with dedicated SUB FREQ and SUB VOL knobs for immersive, personalized audio.
SEAMLESS WIRELESS FREEDOM - Bluetooth 5.0 ensures stable, drop-out free streaming up to 15 meters—perfect for indoor and outdoor vibes.
VERSATILE 2 1 CHANNEL SETUP - Effortlessly connect desktop, bookshelf, or outdoor speakers for a rich home theater or HiFi soundscape.

The Fosi Audio BT30D Pro is a compact yet powerful 2.1 channel Bluetooth amplifier featuring Texas Instruments TPA3255 chips delivering 165W per channel plus 350W subwoofer power. It offers precise bass and treble controls, stable Bluetooth 5.0 connectivity up to 15 meters, and a durable all-metal design, making it ideal for desktop, bookshelf, or outdoor speaker setups with premium sound quality and eco-friendly certification.

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Color	Black
Item Weight	1.5 Pounds
Wattage	165 watts
Number of Channels	2
Output Wattage	165 Watts
Output Power	50 Watts
Audio Output Type	Speakers
Format	WAV, WMA
Wireless Technology	Bluetooth
Control Method	Remote
Connector Type	RCA, 3.5mm Jack
Audio Output Mode	Stereo
Number of Audio Channels	2.1 Channel
Connectivity Technology	Bluetooth
Controller Type	Android
Additional Features	Built-In Bluetooth
Compatible Devices	Speaker

Fosi Audio Bluetooth Subwoofer Amplifier 2.1, BT30D Pro Subwoofer Amp with TPA3255 Chips 165W x2+350W & Bass Treble Control, 2.1 Channel Sub Amplifier for Desktop/Outdoor/Bookshelf SpeakersClimatePartner certified

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