hi all. As a complete novice to electronics I’m hoping for any help possible.

I’ve been trying to build a speaker using a class D amp I’ve bought from eBay. I’ve tested the amp while completely free standing and it sounds great.

It’s got 3 potentiometers for the volume etc. soldered directly on to the PCB, originally I wanted to de-solder the pots and extend the wires for better asthetics on the speaker box. After re-wiring the pots with about 20cm of 6 wire ribbon the static it picked up was incredible. So I’ve re designed the speaker to use the pots in the original arrangement from the PCB. But still it was picking up static although a lot less. Originally I had attached the PCB through the wooden box by the potentiometers. I noticed the static would increase when I put my hand on the wood. I figured it’s some form of “signal/voltage” in the wood being amplified? Like I said I’m a complete novice. So anyway I’ve isolated the PCB from the wood by fitting a plastic insert and attaching the PCB to the plastic, this has helped but still the static is there. That’s the best I can do. Eventually I want to design my own Class d amp. But for now I’m trying my best to use an off the shelf part to make life a little easier.

One thing I have noticed in the process, whilst the amp is on if I make any contact with the circuit ie. touching a pot or an inductor it completely eradicates the static, unfortunately I don’t know why. Also I know it’s probably not a good idea to handle a live PCB. It was an accident...

Does anyone have any idea as to where the static is coming from? Possibly a bad ground somewhere on the PCB?

Also the static is the same no matter what position the pots are in.

Hope this isn’t in the wrong thread. I’m very new to forums.

I have pictures if anyone needs to see but I’m not sure how to upload/attach

Thanks to anyone kind enough to help

 

What does this "static" sound like?
What is powering the circuit?
What is the source of the audio signal?

 

Its like a hum.
It’s a 24v power supply brick for cctv, I’ve tried different supply’s with the same result
And it’s a Bluetooth audio signal, the board has phonos on it as well. It has a mosfet on the board which I believe switches the supply from phono to Bluetooth and there is static before and after the mosfet switches. So I don’t think it’s the audio supply.

 

This started after you removed the pots and continued after you replaced them? If so, I would suggest that you either broke a connection or shorted something with s solder bridge.

Bob

 

This started after you removed the pots and continued after you replaced them? If so, I would suggest that you either broke a connection or shorted something with s solder bridge.

Bob

It was a previous amp that I removed the pots from. I’ve not touched this one. It’s as it came out of the box.

 

Do you get the hum with no inputs connected?
If so, try connecting the negative of the power supply to the AC safety ground.
If not, then you likely have a ground loop.

 

Do you get the hum with no inputs connected?

And it’s a Bluetooth audio signal

Bob