Noise reduction on simple amplifier

[SimonTHK]

Hello
Ive bought an mp3 player module and a cheap amplifier module. I put the output from mp3 player to the amplifier and it works.
But Im picking up a lot of noise.... Ive twistet the signal wire with ground wire but it doesn't help much. Also I have pulled the signal to ground with 10k, I dunno if this should change anything.

Im constantly getting a high beep sound from the amplifier board. I don't get this noise when using headphones, so I guess the amplifier mainly is the problem. What else can I do to reduce noise?

 

[Nigel Goodwin]

For a start you should use a screened cable between player and amplifier, not an unscreened one - unless it's exceptionally short?.

 

[SimonTHK]

it is ~25 cm, Ill find a screened cable ofcourse

 

[SimonTHK]

In a screened cable, do you have ground running in the outer line? or nothing?

 

[MikeMl]

The Audio-Output Sleeve connection on the MP3 player (the common between Right and Left) may not be tied to 0V of the MP3's battery pack. If you are running the MP3 on an external plug-pack (AC power supply) AND you are running the external amplifier on the same plug-pack, you may be introducing a ground-loop.

Try running the MP3 player on its internal batteries WHILE feeding the amplifier. If that cures the problem, write back, and I'll tell you how to fix it.

 

[dr pepper]

You say a high beep sound, you mean a whistle, the amp board could be oscillating, you need a good connection to ground from the mp3 ( and screened cables as mentioned) and the power supply (as well as a decoupling cap), is the amplifier rated for the impedance of the speaker your using?

 

[SimonTHK]

I added a link to the mp3 player module on my page https://simonelectronics.weebly.com/mp3-player-module-with-uc-and-uart-tx-rx.html
Though you don't need to read it it is a module and it shares power with the amplifier from a 12v DC transformer (plugged into wall).
They do share ground as it is now. Do you want me to try use 2 different power sources?

 

[SimonTHK]

You say a high beep sound, you mean a whistle, the amp board could be oscillating, you need a good connection to ground from the mp3 ( and screened cables as mentioned) and the power supply (as well as a decoupling cap), is the amplifier rated for the impedance of the speaker your using?

Yes it is more like a whistle sound than a beep sound. The amplifier and speaker came in the same package, I believe they should work together

I have not added any decoupling capacitors on the MP3 player. I will do that aswell, together with the screened cable. I guess you want the decoupling capacitor on the MP3 power input, and ground?
Thank you.

 

[dr pepper]

Thanks for the linky, some cool stuff, I know someone who converts old valve radios to dab and mp3 players, his source for bits is a guarded secret.

You could try 2 seperate supplies just as a test, in reality however they ought to work off 1, try a large cap close up to the power supply input to the power amp, like a 4700uF, and put a 100nf disc ceramic accross it too.
Have you tried another speaker?, or maybe 2 speakers in series to lighten the load just as a test.

 

[SimonTHK]

Thanks for the linky, some cool stuff, I know someone who converts old valve radios to dab and mp3 players, his source for bits is a guarded secret.

You could try 2 seperate supplies just as a test, in reality however they ought to work off 1, try a large cap close up to the power supply input to the power amp, like a 4700uF, and put a 100nf disc ceramic accross it too.
Have you tried another speaker?, or maybe 2 speakers in series to lighten the load just as a test.

I only have that speaker. But I did try headphones, and that seems to work better.... though it is some time since Ive been testing that, and I am a lot further in the project right now, so I wont put anything into that.

I will add some capacitors on the transformer output

 

[MikeMl]

...
They do share ground as it is now. Do you want me to try use 2 different power sources?

Try running the MP3 player on its internal batteries WHILE feeding the amplifier. If that cures the problem, write back, and I'll tell you how to fix it.

 

[SimonTHK]

Try running the MP3 player on its internal batteries WHILE feeding the amplifier. If that cures the problem, write back, and I'll tell you how to fix it.

Sorry I don't think I understand what you mean, English aint my mother language.
The MP3 player has no internal batteries, it just get power from a transformer.
What do you mean with "while feeding the amplifier?" feeding it with signals? feeding it with power? Power from same batteries or from transformer?
I might be dumb here, but I honestly don't understand what you want me to do.

 

[Nigel Goodwin]

Can you post a picture of how you've built it?.

 

[SimonTHK]

I hope I can get in with it tomorrow, and get a picture aswell.

 

[MikeMl]

... English aint my mother language.

That's ok, it isn't my native language either.

The MP3 player has no internal batteries, it just get power from a transformer.
What do you mean with "while feeding the amplifier?" feeding it with signals? feeding it with power? Power from same batteries or from transformer?

Ok, I had visions of it being a small, portable, battery powered MP3 player, like this one.

If these are powered with a wall-wart charger/power pack, they sometimes have horrible noise on the audio as long as the AC is plugged in. I was trying you to run the MP3 (with no AC plugged-in) on its own internal batteries while connecting the audio output to a separately powered amplifier to make a test to see if that eliminated the noise...