Fix for bluetooth audio amplifier board XH-M314 TPA3118 2x45W from China

The purpose of this article is to help audio enthusiasts, who decided to buy bluetooth audio amplifier board XH-M314 TPA3118 2x45W from China. It was not designed properly and as it seems I found the fix.

One day I decided to make my own small powered speaker and one of the requirements for it is to be bluetooth connected as nobody likes wires these days.

First attempt to buy off the Aliexpress went with total fiasco. Seller sent me the wrong model- much cheaper non- bluetooth board. I couldn’t even get my money back because of Aliexpress changed their attitude for foreigners.

In parallel to that buy I bought much cheaper bluetooth version, XH-M314 TPA3118 2x45W, which was around $7. After 3 moths of waiting it finally came. After testing it with a quick connection to one of the older speakers I immediately saw a terrible problem. The bluetooth board would make terrible noise at around 120dB, which would resembles English sentences about powering up and bluetooth connection. This nonsense I would describe as horrendous noise molestation at the screaming level  for about 15-20 seconds. You could imagine, dealing with that at every power on and connection to your phone would be impossible to bare.

Researching the web didn’t give me any good solution. One Russian man suggested to put variable resistors instead of capacitors C19 and C31. Those capacitors parts of input feed from the bluetooth to power amplifier. Another solution was proposed as of some kind of delay board for the speakers to be turned on.

Both of them did not appealed to me for multiple reasons.

I have done some research about chipset and found the following:

AS19AP24256 bluetooth receiver (U2) was used for bluetooth part and it was made by not well known company from China (jsxingheng.com). It wasn’t well documented and explained. Please take a look at their supposed datasheet in one picture file:

I failed to change anything on that part of design, although their the one who originated the problem.

The power amplifyer U1, TPA3118D2 on the contrary was easy to find and it was made by TI.

Part of the schematics from the datasheet presented here:

From this we can see two or three ways to deal with the problem.

a. I tried to put power governor by connecting pin 6 on the TPA3118D2 to the ground. Before we do that, we have to cut the trace, leading pin 6 to positive voltage on the pin 7, generated by power amp for it’s internal use. Doing that will drastically reduce the volume and screaming of this Chinese lady became just a loud noise, but it wouldn’t get it down to 0 volume.

b. I attempted using pin 8, which is supposedly the Gain. It didn’t work for me or at least using variable resistor instead of R11 and R12 on the TI schematics didn’t do any changes.

c. Pin 12 is the Mute. Getting it connected to Pin7, which is about 3.3.V and it is generated by Power Amp internal conversion does work like a charm. It muted any sound.

Now it was a time to make a simple R-C circuit to make sure high level given from pin 7 would be present for about 15 seconds during power up. It came as a very simple solution after truing 3 different capacitors and looking at RC fallout.

Here is the actual mod:

Resistor R9 on the board is originally 100K. I changed it to 240K.

Solder 30uF, 16v (I had 25V in my bin) capacitor with positive connected to Pin 7 and negative goes to resistor R9, side closer to U1 (see the picture).

If you don’t care about bigger capacitor size (about 60-70uF), you could leave the R9 unchanged and try to come up with different capacitor size. The combination of R and C here give time delay for mute function during power on.

Here what the final installation of the XH-M314 looks like:

You are welcome to ask questions in the Visbis forum or shoot me a message on this website. Due to constant attacks on the forum, the posting of your messages is temporary going through the screening and approval. Sorry, but we are tired of fighting the pornographic facilitators and had to implement draconian measures.