XH-M548 Bluetooth Amplifier review

I recently bought this board for a personal project for my house. I thought it will be helpful for some folks out there that are planning to buy one. The board specs are impressive but you’ll be disappointed when you learn the actual figures. It turns out, those specs are just for marketing reasons.

The BAD things about this module

Wrong Output Power Claims

It claims 120W x 2 output power but in reality it only can handle 50W x 2 output max. Why? It only have 1 TPA3116 Amplifier chip on board which is only capable of delivering 50Wx2 power output. The large heatsink made me think that it have 2 TPA3116 chip but I was wrong. Looking at the bottom it will become obvious that it is only using 1 IC.

Aux input not Working

The aux input circuit is wrong. It is connected to the output of the op-amp which is a bad idea. Although this connector is not labelled “input”. But I know most of us will assume this is an Aux input as most bluetooth amplifier have. Based on the schematic, it will work as an Aux output rather than input.

Muting the Main Amplifier when no music is Playing

The bluetooth module is programmed to automatically mute the TPA3116 amplifier chip when nothing is playing on the bluetooth receiver or it is not paired. This is the reason why there is no audible hum even if I am touching the amplifier inputs.

Annoying Power on sound

It is not an issue if you are only using it with small speaker but it is very annoying for a 100W speaker. Or maybe its just me. The power on sound is a 3 note melody if I remember it right.

20W Audio Amplifier LM1875

LM1875 is an old yet reliable Audio amplifier IC. It is very common and you can get it for very cheap price. With this IC you can get up to 30W power output with 33V supply using 8 ohms speaker.

It has very simple circuit and very easy to build because it requires few components. This design is for single supply application. You can find more information about this IC on its Datasheet on this link.

PCB Design

This time around I am playing with Kicad. It’s is very different from what I used to but it has more feature and best of all its free! The layout is not yet optimized(i.e. size of the trace) because i am still learning. But you can download the project file so you can edit it for your own project. The size of the capacitors are just assumed.

3D render

The best about Kicad is that it has built-in 3D rendering feature for your board at no cost. This is a very useful tool for visualizing your project.


You can download the Kicad project here:

Download page


Simple USB powered Guitar Amp

Here’s a simple guitar amp that is USB powered. It only has gain control and nothing else. The amp is based on LM386 IC and can only give up to around 200mW when powered via USB. But you can get as much as 700mW when powering it with 9V and using an 8 ohm speaker. There is no volume or tone controls to make the circuit simple but I am planning to to design a USB powered guitar amp with tone controls in the future. But for now, here is the simple version.

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TDA7498 – 200W class D audio amplifier

Many years ago, it is not easy to build a powerful audio amplifier. You will need big power transistors with massive heavy heatsinks plus a heavy transformer too. It will also require a lot of efforts to build it, from drilling the heatsinks and connecting those wires. It is a very tiring task. Today a 200W amplifier can be as small as your mobile phone. Thanks to the evolution of Class D audio amplifiers. Smaller and more efficient amplifiers are now possible.

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DIY Loud Bluetooth Speaker for your car

Building a bluetooth speaker nowadays won’t require so much technical knowledge. You just need to know how and where to connect wires. You can now buy a bluetooth receiver with a built in amplifier online and make your own audio system for your car for cheaper price.

WHY DIY(Do it Yourself)?

Some cheap car amplifiers on the market is not honest on their advertised power, these are very common to cheap and not so known brands. By doing it yourself, aside from getting cheaper, you can also be sure that your amplifier has the right power you need.

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3W x 2 class D amplifier

In case you wan to build an small amplifier for your small speaker, here’s a 3W per channel amplifier for you. Take note that this can only operate up to 5.5V. You can’t use USB to power this circuit as USB can only provide up to 2.5W power. If you will use 8 ohms speaker, it can only provide up to 1.4W of power.

Minimum value of Ri is 18k. Minimum speaker impedance is 4 ohms.

3W x 2 Class D amplifier

Here’s a simple amplifier that I used for my speaker project. The IC operates at 5V. Note that although it runs on 5V, it can’t be powered via USB because USB can only deliver 2.5W. Ri minimum value is 18k which will give you 24dB voltage gain. The voltage gain is computed by equation : 20 log(2*(142k/Ri))