Audio amp noise reduction - help

audioguru said:

There is a connector with 2 thick wires and another connector with 3 thick wires. One connector has AC from the transformer and its wires must be kept away from the volume control.

The rectifier diodes might be radiating a buzz into the nearby opamp wiring.

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too much trouble with that amp huh? sorry... atleast maybe i can learn something.

the connector with the two yellow wires is the AC power... the next connector with the three white wires is the L+R output and the other three wires on the back of the PCB are the input wires... none of them bother the volume
control, the sub-woofer wires aren't visible on these pictures sorry if the photos aren't clear enough, they are from my mobile phone.

what do you propose for the diodes?

Some of the soldering on the circuit board looks horrible. Resolder the rectifier diodes and big 3300uF filter capacitor.
The circuit board has a nice "star" ground point at the big filter capacitor which is good.

A bit solution for your problem/education purpose, temporarily connect 12v dc battery to filter capacitor to see which one produce the humming . if humming is still present then The IC might be defective, on the other hand, if it is clear no humming then circuit are poor in grounding /filter.




regarding on aljamri post
place insulator in between metal(aluminum) plate and soldered side of the board. then connect the metal plate to ground.
You can use also new PCB board as replacement to metal plate,

jumides said:

regarding on aljamri post
place insulator in between metal(aluminum) plate and soldered side of the board. then connect the metal plate to ground.
You can use also new PCB board as replacement to metal plate,

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nice...what it does? forms a capacitor?

it act as shield from noice , think of shielded wire(coaxe cable), small wire are on the center surrounded by bigger wire , In microphone wire plugged onto mic input then cut the ground wire(outside wire) you will hear humming.

on your PCB layout, ground are to small , usually on older amplifier they use bigger grounding, and all free space they use it for grounding.

yeah i know... at fisrt i thoughted it could be as easy as replacing a capacitor but i guess it's not easy at all...

thanks ppl!

aljamri said:

I've been adviced to do the following by a great fellow in this forum:

bring a metal sheet, put your device on it and connect a peice of wire to the ground of your dc side. This will eleminate any noise exist due to poor grounding.

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Sorry I did have not come here since I post my first thread. Yes as our friend said it is easy take any metal sheet and of course put insulator in between plastic or even cardboard and use a piece of wire to connect it to the negative of your supply ( no need to solder it ).