Introduction: Building a 2x25W Bluetooth 4.1 Amplifier TDA7492P

About: Electronics enthusiast, vlogger on youtube.

In this project we are going to build a bluetooth speaker amplifier based on the TDA7492P class D audio amplifier coupled with a Bluetooth 4 module. We are not actually going to build the amplifier module because we can get that from China, very affordable, it only costs around $12 shipped which is way less that it would cost us to buy the bluetooth module and the TDA7492P individually not to mention the cost of fabricating a PCB of this size.

So we are actually going to use this module and build the final product with a nice enclosure and a suitable external power supply.

Step 1: Checkout the Video!

The video describes the entire build so I recommend watching the video first to get an overview of the project. Then you can come back and read the following steps for more detailed explanation.

Step 2: Parts List

Here you can find a list with links to all the parts I used in the project. Feel free to adjust and make changes according to your own needs.

Step 3: Working on the Enclosure

One thing I’m concerned with this enclosure is the bluetooth signal strength. Remember this is an aluminium enclosure and might block our bluetooth signal entirely. Even the end caps are metal though on one end I’m going to use the plastic output speaker terminals so the signal might pass through there. If needed I will also replace the remaining end cap with a plastic or fiberglass one.

Using my drill press I drilled 4 holes, 3mm in diameter, required for mounting the pcb to the bottom of the enclosure. Next I also drilled the required holes for the side panel that holds the power switch, the dc power jack, the power led and the line in jack. For the rocker switch slot I drilled a couple of bigger holes and then filed the remaining parts until I had the required slot size. This was fairly easy to do because the panel is made out of soft aluminium.

Here is a template in PDF format that you can use for drilling as long as you use the same model of enclosure.

For gluing the two standoff for the speaker terminal panel I used some two part epoxy. I carefully aligned the standoffs so that they fall right under the two holes of the panel and then I applied the epoxy around them and left it to dry for about 1 hour before attempting to apply any force on these standoffs.

Step 4: Wiring

Before doing the final wiring I removed all the conectors from the PCB and was left with bare pads to which I could solder wires going to connectors on the side panel. For the speaker output I used 24AWG wires, for the power input I used 22AWG and for the remaining connection I used some light wires, something like 30AWG since they don’t carry any power. Extra care should be taken here to avoid making any mistake like reversing the polarity on some connection.

Before installing the PCB inside the enclosure I used a piece of 0.5mm thick thermal silicone pad on the bottom side of the PCB. This will help transfer the heat from the pcb to the aluminium enclosure and at the same time it will insulate the pcb electrically. I also installed a small heatsink on the main amplifier chip, I’m not sure if this is necessary or not but I think it’s a nice addition and it can’t do any harm

Step 5: Testing & Final Thoughts

With the power switch off, I connected the dc power and the speakers. Then I turned the amplifier on and searched for the bluetooth device on my tablet. After connecting to the device which appears as “Sanwu audio” I was able to play music. It seems the quality is nice, like I said not audiophile grade but certainly good enough for me and it can also go quite high in output power, certainly seems like enough power for these two speakers that I have.

I did a range test and I can play music without any interruptions from up to 2 or even 3m away with a line of sight between the amplifier and the phone. I did however notice a decrease in signal when I try to connect or reconnect to the bluetooth module, it does take longer for a connection to be established. This could be improved by replacing the remaining aluminium side panel with a plastic one or by adding an external antenna so you should do that on your build if you need the extra range.

So I’m pretty happy with how the project turned out, it’s a nice compact, bluetooth amplifier, capable of delivering up to 25W for two speakers and that power is more than enough for my usage. There are also ready made versions that you can purchase, complete with enclosure, they’re not very expensive and I have placed a link in the parts list right above but I like to make stuff myself and I hope you do too.

You should checkout my Youtube channel for more awesome projects:

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