LM1875 hum

[xecluded]

Anyone have any experience with this amp from ebay.

2 X LM1875+NE5532 class A Audio Amplifier Board

I bought one recently. It was very easy to hook up and it worked on my first try - yeah!!!

While it works OK and sounds pretty decent, there is a loud hum on both sides and I am hoping someone can give suggestion to get rid of the hum. Since I will be using it with a preamp, perhaps bypass the preamp section on this board with alleviate the hum somewhat????

Thanks.

[petemoore]

Two of the best sources are input and power supply.
Input is easy to isolate, it can be tested for not being wrongly connected, disconnect it, still hum ?
Look at the power supply, what kind of filtering, regulation?
Still a wrong board connection or turned around filter cap [reverse polarized] might do that, missed ground connection could too.

[gootee]

The thread linked below should have the answer. There are some helpful diagrams of system interconnects etc, in the first few pages, that might be all you need.

http://www.diyaudio.com/forums/chip-...grounding.html

[nigelwright7557]

Originally Posted by xecluded

Anyone have any experience with this amp from ebay.

2 X LM1875+NE5532 class A Audio Amplifier Board

I bought one recently. It was very easy to hook up and it worked on my first try - yeah!!!

While it works OK and sounds pretty decent, there is a loud hum on both sides and I am hoping someone can give suggestion to get rid of the hum. Since I will be using it with a preamp, perhaps bypass the preamp section on this board with alleviate the hum somewhat????

Thanks.

Have you tried earthing or unearthing the input zero volt line ?

An earth is required or not required depending on what is driving the amp.

[xecluded]

The amp is prebuilt. All for me to do is hook up the input, speaker outputs and the power transformer to it. I disconnected the inputs and the hum still there. Not sure if grounding would be the issue as the unit came to me completed.

[AndrewT]

Hi,
since the PCB is pre-built, then the Hum problem is almost certainly a wiring error.

[xecluded]

I followed the wiring instruction from the seller and made sure it is correct. I will try to move the power transformer further away from the board to see if that would help any. Thanks.

[gootee]

A photo of how you have connected things to it would probably be very helpful.

You should have tightly twisted together all wire pairs that go to it, such as the input signal and ground pair, and the power supply or transformer pair, as well as the transformer input pair. You would also want to keep AC wiring and components and power supply wiring well-away from sensitive signal paths and components.

Also, grounding could definitely still be the main problem. There is a ground from the board to somewhere. And if you have it in a case, there are possible ground connections at your input jacks. And your speaker jacks. And your source has some ground connection. And there is an AC power ground. If you can post a good photo or diagram of all of that, it might enable someone here to spot the problem. You should be able to have almost no hum.

[xecluded]

Great idea. I will take picture and post it here tomorrow afternoon.
Right now, it is sitting on a piece of wood as I want to make sure that it is working as it should before i migrate it onto a case. Thanks.

[xecluded]

Here is how i hook it up. Thanks.