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I am trying to wire up an audio amplifier circuit using the Kemo M031N 3.5W amplifier:

enter image description here

I have connected the wires from the amplifier to a terminal block. With a suitable 10V power supply and a 2W 8Ohm speaker but no input signal (ie nohing connected to the input wires at all), there is no or very low noise (which is a good start). I have connected one of the input wires to the PSU ground, which is also connected to the speaker.

The problem I have is that whatever I attach as an input signal (even when there is no actual signal), I get a lot of noise from the speaker. The noise is a mixture of bursty static noise (every 2-3 seconds) and a louder fast clicking. This noise appears at a low level even if I just touch the input wire at the terminal block with a screwdriver.

I have tried using a 10V regulated (home brew) PSU, the 5V from a Raspberry Pi and a PP9 battery. All have the same noise effect, to varying degrees (the battery was best but the noise still audible).

If I connect good quality (unscreened) speaker cable to the inputs on the terminal block, the noise is slightly louder. When I touch the other ends of the speaker cable together, the noise is very loud.

I have tried adding a 10k and a 2k2 resistor across the inputs with no change. I have also tried a 330uF capacitor across the supply at the terminal block.

Does anyone have any ideas on what I could try next?

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  • \$\begingroup\$ Try a different power supply. If the noise is the same from every source, then it can't be the source. That leaves the amplifier or the power supply. The amplifier shouldn't make the kind of racket you are describing, so that leaves the power supply. It's probably a switching power supply with a really nasty, unclean output. \$\endgroup\$
    – JRE
    Nov 12, 2020 at 16:39
  • \$\begingroup\$ Those things tend to be unstable as ****. You can try adding decoupling, and screening the inputs, but to be honest I'd look for a better amplifier. \$\endgroup\$
    – user_1818839
    Nov 12, 2020 at 18:20
  • \$\begingroup\$ As the previous comment said, your circuit is most likely oscillating. You have to be very careful when building stuff with this kind of module. Make all wires very short and direct. Make sure the inputs and outputs are separated. Especially keep the grounds short. \$\endgroup\$
    – user69795
    Nov 12, 2020 at 19:16
  • \$\begingroup\$ Thanks for the comments. I'll try a different (better?) amplifier and shorter/screened cables on the input. \$\endgroup\$
    – WhyNine
    Nov 13, 2020 at 15:58
  • \$\begingroup\$ So did that work cause I'm having same problem \$\endgroup\$
    – Dan
    Jan 18 at 10:09

1 Answer 1

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I can't post comments yet so I am adding this is the (an?) answer.

I tried a different power supply, including using a battery, so I know that's not the problem. I tried adding some extra decoupling as well.

In the end I gave up with this amp and went for a BlueTooth amp instead. This had the advantage that it eliminated any ground loops and the signal was going into the amp in digital form. Now there is no noise at all from the speaker unless I am actually playing something.

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    \$\begingroup\$ Hi, You are not using the same account as you used to ask the question (despite the same username) - that is why you are currently unable to write comments here. However as this sort-of does conclude the question (i.e. no solution was found as you went with a different approach instead), then it is effectively an answer, so I won't convert it into a comment. Unfortunately, unless you can find and use your original login credentials, you won't be able to accept this answer, to actually mark this as the (effective) end of the question. (We can't "accept" it for you.) \$\endgroup\$
    – SamGibson ♦
    Jan 19 at 12:32

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