• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Fosi Audio BT30D


Active Member
Oct 7, 2022
I was recently on the hunt for a simple 2 channel amplifier with some sort of subwoofer control for a 2.1 setup (the subwoofer in question only has an LFE input). I decided to buy a Fosi Audio BT30D - the original version, not the 2nd "Pro" version. The newer Pro seems to have better amplifier specs, but according to posts on this forum the subwoofer RCA output doesn't have crossover or volume control (only the internal sub amp does). So I purchased the older model which does have a variable LPF for the sub out RCA.

I was uncertain if the "sub freq" knob was also a HPF for the speakers, or if they had a fixed HPF? In room measurements of the speakers only (attached below) suggests it does not have any HPF for the speakers. I also wondered exactly what the speaker treble and bass controls were doing, and this is evident in the measurements (I tested at min, max, and 12-o'clock = mid)
bt30d adjustment knobs.jpg

Anyway, I don't have the equipment or skills to test the amp properly, but it sounds find for what it is. One problem is that it makes a loud thump out the sub when it turns off. And as noted in one of the threads for the Pro version, the bluetooth receiver is always on and "open", plus it overrides the RCA inputs, which is an annoying "feature".

BTW, the speakers are B&W 685 S1 with the ports stuffed and being tested at ~2m distance in a ~6x6m room with hard floors (seems to have lots of reverb).


Apr 24, 2023
The tone and subwoofer controls were a big selling point when I decided on this amp. The BT, while always open, without the antenna it’s pretty much useless and doubtful it could be hijacked by someone not in the same room. I would love to see a version of this amp with a second line in and defeatable BT.
Top Bottom