TPA3118 SANWU noise problems

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meira007

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Joined 2012
#1
Hello Everyone

I am building a Bluetooth speaker with 2 x TPA3118 Mono Sanwu.

Everything is powered from a battery pack with a step up voltage converter.

Even without the Bluetooth powered on, as soon as I Plug the power there is hiss coming from the speakers.

Could anyone give me a help on what could be the reason and how to solve it?

Thanks in advance to all!!
 
#4
This is the Picture of the pre build and testing the speaker:

oGHprz.jpg
 
#11
Got your PM. First things first. Gain mod. Did you do it? These boards often come with 32dB configured. You can remove R2 (R27 on Sanwu Boards) to lower gain to 20dB.

Secondly. Powering from batteries you combine gnd from bluetooth board and sanwu amp. This would create a groundloop if there is no circuit preventing this. You can buy a cheap seperator on ebay for usb if it is 5V

Third thing. Sanwu board come with 10uH filter inductors. This is suited for 4 ohms. If speakers are 8 ohms use 33uH
 
#12
Why is it that cable ferrules, standoffs and connectors seem to be forbidden these days ? Every PCB should be mounted mechanically with standoffs or the like to a case to avoid short circuits and safety issues. It looks very sloppy too and you can be sure someone will comment on it. Any mechanical work needs to be done first to avoid damage, dust etc. Drilling , tapping thread and such after soldering is quite foolish as chances are likely something will break or get damaged. Mounting stuff us not expensive when bought in numbers. I recently paid 5 Euro for 100 pieces 12 mm Torx M3 screws/bolts...

Gentlemen, it really is not standard anymore to solder wires to PCBs directly (except in China but they will learn too in a few years). If wires were soldered directly to boards in the past then wires were soldered in the holes not laying on top of them. Stranded cables should be used with crimped cable ferrules when screw connectors are used.

You think I am exaggerating ? I am not, there are safety regulations and mechanical design rules for a reason. You learn fast when the first PCB goes boom when a loose stranded wire touches another contact in the connector. Learning the hard way 🙂
 
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#13
A bit harsh but some valid points. 18650 cells pack a lot of punch and can be dangerous. I don't recognize the pcb on the left wall, is that something to control charging? Does the 3s battery pack have any protection beyond what the cells themselves have?
 
#14
Hey Everyone!

Thank you very much for your inputs. Being harsh or not you are completely right that this is not the safe way to connect anything... shame on me, but it is still on the prototyping phase 🙂 I promise I will clean it up and send a Picture afterwards.

I started with the gain mod by removing the R27 and the noise is noticeably lower, but still audible. Curiously, the noise is higher when no audio input cable from the Bluetooth board are connected to the amplifiers. When connecting and powering on the Bluetooth board the noise in the speakers decreases... (?)

Yes the Bluetooth board and amplifiers have the same ground connection on the - of the DC-DC boost converter... The Bluetooth is rated 12V, Is there any isolator for 12v?

The speakers are 4ohm - SBAcoustics 2,5" fullrange

The battery pack has a dedicated protection board with balanced charging.

The tiny PCB you see on the left wall is a very interesting device to monitor the battery status, check it in the link. At the moment is not connected to the battery pack still:

LED Battery level voltage monitor meter indicator Alkaline Nicad NiMh LiPo L - Gammatronix

Thanks once again for all your help!
 
#15
Very clever little board, thank you for sharing the link.

Not sure exactly the device Mortenhoe was suggesting, but there is a 12v isolator available from Mornsun: B1212S-1W. You can't always find it on ebay but it is on AliExpress. I haven't tested it with the specific Bluetooth board you are using (on my list of things to do) but it fixed a noise problem I was having with this board:

APT-X Bluetooth 4.0 Audio Receiver Board Wireless Stereo Music Module iPhone PC | eBay

Be sure to use a 12.6v "smart" charger and not a generic SMPS to charge your pack.
 
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#20
I think you are right, same board with and without connectors. I was wrong in my assumption of which board you have, the other one I have and need to test is this one:
Bluetooth 4.0 Audio Receiver Board Wireless Stereo Sound Module 12V/24V Car | eBay

Thanks for the YouTube link. I have not done the mod. Perhaps I have been working around the distortion without realizing it.

The noise I fixed with the Mornsun device was classic Bluetooth/ground loop noise. I am driving a "Verst" 2.1ch board.
 
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