Nobsound Hifi Mini Bluetooth Music Audio Stereo Receiver and Stereo Power Amplifier (Black)

I an audio enthusiast and love fiddling with gadgets. I also used to build audio amplifiers. The primary reason for choosing this product was the small form factor and low cost. I also saw a reviewer of this product on Amazon who use this product mounted inside a speaker cabinet.This product works but has one fatal flaw which I think should be pointed out. I have enclosed some pictures that I took when testing this receiver. I used a laboratory power supply set to 24 Volts. Apparently in order to save cost the designers of this receivers failed to provide an output filter. The second picture shows the measured output signal with no speaker load attached while streaming silence. The output is a square wave signal at around 320 kHz. I have also enclosed a picture of the output waveform with a 4 Ohm load connected to one of the outputs when driving the amplifier with a sine signal.Apparently the designers of this product in order to save cost have adoped the so-called filterless Class-D approach. Class-D amplifiers work by switching the output between ground and the supply voltage at a high frequency. Normally tyhere is an output lowpass filter which removes those switching components and only leave the audio signal. All Class-D amps that I have used in the past have such a filter. Not having an output filter in effect uses the speaker itself as the lowpass filter. However, this approach which is used by this product has some serious implications.First of all, every speaker handles high-frequency signals differently since a speaker is designed to be driven with signals at frequencies below 25 kHz. The fact is that most speakers will exhibit fairly high eddy losses at those switching frequencies used by Class-D amplifiers. In other words you are likely to damage the speaker voice coil by driving a speaker with such a signal. Further, depending on the speaker there likely will be distortion inside the speaker. When manufacturers measure amplifier dirtortion they usually measure distortion by adding a low-pass filter after the Class-D amplifier. This is usually acceptable since the Class-D amplifier itself provides for a low-pass filter. However, in this case it is safe to assume that the actual distortion that occurs inside the speaker will be magnitudes higher than the specs shown on the Nobsound data sheet since it is lacking the output filter. So the distortion specifications shown are essentially useless. After all a speaker voice coil behaves a lot differently than an ideal load resistor.Another major problem with filterless Class-D designs such as this Nobsound Bluetooth amplifier is EMI which stands for electromagnetic interference. When connecting long speaker wires, there will be lots of unwanted EMI radiated since this receiver is outputting the high-frequency signal without any low-pass filtering (except for some small ferrite beads). As such I would bet this amp does not meet the FCC Part rules section 15B which is a requirement by law and as such most likely is even illegal to distribute in the US.Filterless Class-D amps for the above reasons are usually only used in amplifiers of less than 5 Watts and also designs where the amplifier is mounted directly onto the speaker to avoid EMI issues.I would not recommend this product if you want to keep your speakers safe and avoid having massive EMI issues.

These are fantastic little amps and super easy to use. Bring some life back to an old set of speakers.I just leave mine on all the time and connected to my TV. It uses VERY little power - might be good for an off-grid home or RV even. Since flatscreen TVs have such horrible speakers, and I refuse to use a sound bar, I can just plug this guy in, set volume up halfway or so, and still use volume control on TV through mini-jack output.Also has bluetooth, but I don't use it as much as I thought I would since it is disabled when you are using the line input.

I bought one these for a friend as a birthday present. We tried every out the bluetooth, the AUX port, the headphone amp, & the stereo amp. They all worked great. The amp stayed cool & it produce a good amount treble & bass output that was well balanced. I liked & he liked it, so maybe I'll be getting more soon.We only tried it on a 12volt car battery so, running this on a 24 volts would be even better. Well worth there cost.

First of all, this Bluetooth amplifier is the least expensive I found. It does not have a power supply bundled which I think is an issue. A decent power supply costs around $15. I do not recommend buying the one that is offered by Nobsound but instead get another one with a higher voltage.Setting this up was quick. I also like the large volume knob. I also like that this unit is small.One the negative side, I find that the sound quality is not as good as any of the audio amplifiers I have used in the past. Especially the bass response is rather muddy. The other issue of concern is the short wireless range as already pointed out by some other reviewers. I wish that there was an external antenna but the designers of this unit decided to integrate the antenna which turns out to be a short trace on a circuit board. As a result I am getting spotty reception in most cases. Of course if I have my phone right next to the amp the signal is steady.

I got this for my garage and patio speakers to replace the Airport Express I was using to stream music. I didn't want to be limited to using iTunes and wanted to stream Amazon music from my Kindle. It works very well so far. You do need to leave the device nearby as it has a pretty short range, It didn't come with a power supply so I used one from an old IBM Thinkpad. It's 14V 4.5 Amp which is well above the minimum required.No hiss between songs like other bluetooth devices I tried and it doesn't cut out frequently like Apple Airplay did. I'm no expert audiophile but I'm happy with the sound quality of the music I'm listening to on my back porch as I write this.

This device is plenty powerful (driving a pair of Boston CR67s) and has very good fidelity. For me, having no tone controls is actually preferable since my Bluetooth devices are all running some sort of equalizer themselves.The little power up tune can be somewhat annoying (as other folks have mentioned). My fix for that was to wait until after my player of choice connects to the amp to turn up the volume.I highly recommend this product

I was generally pleased with this unit. It is connected to a pair of bookshelf speakers which I owned for 2 years. I never had much use for these speakers ever since we remodeled our home. After I got this, I was able to stream sound from my Blueberry. Sound was decent and volume loud enough for my needs. However after approximately 1 week one of the 2 channels started developing some static. It would be intermittent. Now after another 2 days both channels are totally dead.

Great little amp... I've been using this since first day hooked up with my Polk 300 watts 12" sup and 4 satellite speakers, sounds wonderful.. very happy, the bluetooth works well with my laptop, been gaming with this.. just love volume nob on the top of it.