ZK-MT21 2.1 Channel Bluetooth Audio Power Amplifier Board 50W×2+100W with Treble and Bass Control for DIY Bluetooth Speaker Home Theater

I'm more impressed with this one over the larger 36v $36 one of a different brand I was using that cooling fan crapped out. This one sounds better more dynamic and seems to have as much power at 24v also I had to unplug the 3.5mm jack to use the Bluetooth this one you can just link to it even while using the jack as input and it was half the price and no fan to crap out. I'm using for my tv I boxed in the stud cavity's in the wall under my tv and cut in a 6.5" component set and an 8" subwoofer, it's pretty sweet, I also used PVC pipe to install a port into the subwoofer cavity I had to replace the sheetrock with plywood and mud it in like drywall also the sheetrock couldn't support the pressure good even with a wood ring glued on.

I'm actually surprised that this works as well as it does. I hooked it up to the speakers in an old Samsung TV soundbar and subwoofer. I usually connect via Bluetooth from my laptop. It sounds much better than anything this cheap has a right to sound. Everything functions, the Bluetooth is reliable. I can't figure out if this is the amp, but I have to keep turning down the subwoofer, probably because the speaker I hooked it up to is cheap. Otherwise, it's loud and clear.

I have a couple of these. Bluetooth sounds better than using the cord. Use an appropriately powerful DC laptop brick or anything similar if you want the biggest sound. The one connected to my PC uses a 200w 20v DC brick to drive 4 speakers (2L and 2R in parallel) plus 2x 12in subs (also in parallel). It will shake things off the walls in my house. You won't believe the performance from such a cheap device. Pros: Easy to assemble, wire, and connect power. Bluetooth setup is simple. With the right power and speakers/sub, your neighbors will think there's an earthquake. Cons: Slight hiss if you leave the main volume knob turned up to max with nothing playing. If you're listening to something with pauses at low volume, it may not play the next spoken syllable or noise. This does not happen at medium volume or if the movie you are watching has birds chirping etc in the background. It's almost as if it goes to sleep for a fraction of a second.

Works is great for my simple PC audio setup. No noise or anything via AUX or Bluetooth.

This amp provides a lot of bang for your buck! You havento do a little minor assembly, which I wasn't expecting, but it's simple and a screw driver is provided. I'm powering it with a 20v DeWalt tool battery to drive no less than seven speakers in a custom enclosure - 1ea 10" Klipsch sub, 2ea 10" Ashdown mid/woofers and 2 pairs of 2.5" Klipsch high frequency drivers with 1" poly dome tweeters. And it effing rocks! After pairing it in my phone, the Bluetooth connects quickly every time I power the rig up. The fidelity is excellent. Crisp highs, detailed mids and plenty of power to drive the sub, especially with the sun frequency set higher. At lower settings where it rolls off more mid-lows its power does drop off, but, with a tiny plate amp like this that's to be expected. I'm honestly blown away with how much bass thin amp can produce. With more use I will have more info on longevity (and battery life, but,that's not related to this review). Well worth the money for what you get!!

I'm seriously impressed with the sound quality this amp produces. I purchased the zt21 about a month prior to this one. But the zt21 kept popping while playing music. Thought it was capacitor so swapped it out but still the same issue. Then I noticed if I blew on the heat sink when it started to pop, it would stop. Placing a fan on top solved the problem. So that's why I chose the HT21, because of the built in fan, but was surprised at how much cleaner it sounds. And the knobs to control the Frequency, Bass, Treble, and Volume are much more accurate & smoother than the zt21. Bluetooth sound quality is significantly better as well. I use a 24V 5A LED Driver power supply for good clean power, but I also use ~ 30V high amp 18650 lithium battery packs I make, when I want my system to be portable. Overall, this is a much better amp than the zt21, it may be more expensive, but well worth the price. Just remember to use a good quality power supply or battery pack for a nice clean sound. This one can take up to 36V/ ~10-12 Amps I believe.

For an amplifier, it's a great price point and has great output power. Fan is a little loud, but I unplugged the fan and it stays cool when not driven hard (running at 19V). BT audio processing time is a bit frustrating. Unlike most of my other bluetooth audio devices, there is a delay. While it's not significant, it's enough to drive you crazy when watching a video of someone speaking (slow speaking is not as problematic). For music however, or any other source that does not require audio and video to be perfectly synced, it's fine. Aux input does not have this delay, only bluetooth. UPDATE: Changed from 4 stars to 3, due to what seems to be an input threshold required to output sound via bluetooth (kind of like a a subwoofer amp that turns on/off automatically when it detects input). Listening to some classical music, I noticed it cutting out between notes. Tested on two different devices (phone and laptop) the same piece sounds perfect via aux input, but the quietest parts are missing when playing via bluetooth. As a note fades toward silence, it suddenly cuts the output completely, and restores output just AFTER the next note starts. This is a MAJOR flaw that means I'll be using a separate bluetooth adapter for this amp, rendering all onboard bluetooth functions useless.

Perfect little amplifier. I’m using a 24v 240 watts power supply and this little amp puts it down beautifully among the dual subwoofers and quad array speaker systems I have. Volume nobs may not be perfectly adjusted but you can always adjust it to your needs. Clean and powerful sound for a reasonable price.