Fosi Audio BT30D 2.1 amplifier - the awesome little amp I returned
I'm a bit of a fan of the small chip amps made by Fosi Audio, at my desk I've got the ZK-502T powering a set of 4 speakers, 2 giant floor standing speakers with 12" drivers wired in parallel with a set of KEF Q150's and at pretty much all volumes, this little amplifier delivers awesome sound. For house parties I'll wire that same amp with a subwoofer on one channel and speakers on another - which works well but limits me to mono and doesn't have much in the way of subwoofer frequency controls and is limited to 50 watts. Enter the Fosi Audio BT30D...
This little chip amp is a tiny powerhouse, pushing out 100watts to the sub channel and 50 watts a piece to the left and right. Build quality out of the box was solid, and definitely a more complete experience than the ZK-502T that it was replacing.
It's pretty rare for an amp to have speaker terminals for a sub, most expect you to have an active sub. Active subs with 15" speakers are pretty uncommon in the budget price range but you can easily pick them up, box and all, second hand for about $100. There's something awesome about a huge speaker driving bass through a ported enclosure. When compared to the Sonos Sub (which is basically an engineering masterpiece) the sound just sounds bigger coming out of the Kicker 15" - but with the caveat of being a lot less accurate (flabby). I prefer flabby when I'm trying to create bass fill for a party or for movies but I know a lot of people who prefer subwoofers to punch them in the gut.
Sound
Sound wise there wasn't any static, distortion or anything to be heard, music was clear and unadulterated. There's a bunch of information online about how amplifiers don't really affect sound quality that much and I think for this little amplifier that much is true, it pretty much puts out what you give it with no processing or anything interesting going on.
Is 100 watts for the sub channel enough? It easily drove the Kicker ES 15" 150w RMS Sub to volumes that filled our garden during a house party and it's more than most people need. Ultimately it depends on how efficient your subwoofer is but if you're looking to fill your house with bass than I reckon it's easy enough. The amp also goes down to 2 ohms so you could technically wire 2 4-ohm subwoofers up in parallel to fill more of the room. The left and right channels pushing out 50 watts a piece is more than enough for the KEF floor standing and bookshelf speakers I've got around. With wattage a 10x increase = a 2x increase in loudness so if you were pushing 100watts per channel instead of the 50 the increase is only going to be about 3db anyway. This amp is plenty powerful for most situations.
Connections
Around the back of the device we've got some RCA inputs, a line level output for an active subwoofer and then the active speaker terminals for left, right and sub channels. There's an antenna for bluetooth and awesomely this device takes DC voltages ranging from 12 to 24 volts - perfect if you're thinking of adding this to an RV or offgrid setup without inverter overhead. It's got slightly less voltage range than the ZK-502T which goes down to 9 volt input but I'm guessing you wouldn't want to drive this thing with a subwoofer at such a low voltage because the power draw looks like it tops out around 4.5 amps.
Connectors are pretty solid, speaker terminals and antenna connector are screwed on to the metal chassis but unfortunately the line level connectors go straight through to the board.
Controls
Control knobs feel great, made of metal, grippy and have a convincing amount of resistance. The power switch is tactile. There are no capacitive buttons to be seen which is super exciting to me, the only issue is that the knobs are pretty close together so there's not much room for fingers to grab on to them. That said the Volume control has more room than the others and is the one you'll be using the most, but I wish the sub volume knob wasn't squashed against the power switch.
Sub Volume and frequency controls are awesome, having an active crossover you can modify and play with means you can experiment with different subs and use them differently in different circumstances. When we're watching movies I crank the sub frequency up because I prefer the sub to act as an audio fill to compliment our front speakers but with music I turn the sub frequency down so it's only responsibility is kicking low notes out. My favourite thing about this amp is that the sub frequency does not affect the main speakers. On the Sonos Amp for example, the crossover frequency for the sub actually cancels out the low end for those speakers (with no way to turn that feature off) so if you have a pair of full range speakers and you're just looking for a bit more bass to fill the room, the Sonos Amp will actually cancel out the low range of those speakers to feed it to the sub.
Bluetooth
Fosi has the cleanest, easiest to use and most insecure implementation of Bluetooth I've seen on any product. There's no passcodes, you just go to the bluetooth menu and connect. Boom done. The only issue comes when you want to connect different devices, sometimes you need to find the one that's currently connect it, and disconnect it in order to connect another one. There's no pairing mode or anything on the amp itself to cancel current bluetooth connections. I actually really love this implementation of Bluetooth but I can imagine it wouldn't be great in public settings or places where you have close neighbours - but in our home it's quicker to connect than Airplay or Spotify connect devices.
Power efficiency
Bundled in the box is a 4.5a 24v power adapter which peaks you out at 108watts. But it's a 200 watt amp I hear you saying - you can read about input power vs output power here.
But here's where it started to go a bit south for me. In standby I didn't record any power consumption, and during music playback power consumption was pretty modest but then when I stopped playing music standby power was left at 3.5 watts. From there I left the amp overnight, no bluetooth connected and no audio source, and it continually consumed 3.5 watts during that whole time. That's not a lot of power, but it's about on par with a Sonos One's idle consumption, and that has a computer + wifi connection running inside. One of the advantages of these chip amps is that they tend to draw super low amounts of standby power (<0.5 watts) when at idle so I'm not sure if I had a defective unit or something strange is going on in this amp to idle it so high.
Depending on where you live in the world, 84 watt hours a day might not equate to much, even on an off grid setup that's pretty low, but in my project to move away from Sonos devices and move to an ultra-low standby draw audio setup it was a deal breaker. To Fosi's credit the return was super quick and easy and it could have just been the unit I got or the way I was measuring - so if this is the only thing holding you back then maybe try your luck and report back!
Conclusion
This little amp is a total powerhouse and pretty unique in that it can drive a subwoofer on its own. It can run on 12 - 24 volt making it a really great amp for off-grid and RV setups. It's let down by its standby power draw but there is a power switch to take care of that - so if you're fine with turning your amp on and off to use it then and you're looking for a simple chip amp to power some speakers and a passive sub the Fosi Audio BT-30D is a pretty unique and solid option.