Need help reducing noise of Amp!

[tommy1]

Hi everyone!
Please help me to reduce noise from my amp even the Vol. is down completely, the noise"U` u` u`" from the speaker is still there.

Thank you!
PD

 

[AndrewT]

Hi,
what's the amp? What is connected to it?
Have you measured anything?

 

[Iain McNeill]

are we talking mains hum or white noise?

a picture of the amp innerds would help, a schematic would be even better.

 

[tommy1]

Hi Andrew!

2sc5200, 2sa1943(output Transistors) . 2sc669, 2sb649, 2sc2705, 2sa1145.
Only speakers connected to the Amp .
PD

 

[tommy1]

This amp belongs to a small company(HOMEbusiness) I bought it a long time ago. I call them ,they said that they won't provide anything unless send it in for repair. And I did fix it but the only problem is the noise.
thanksss!
PD

 

[Mooly]

It's not enough to go on...
If it all works and nothings blown as such, then it might be a power supply fault... maybe an open circuit cap etc or a regulator fault.

Need to see a circuit really... no idea at all what the amp is. Is it stereo (2 channels) are both channels faulty ? etc etc

 

[tommy1]

...the thing is that I took the broken part out(UPC1237HA: audio circuit protector for the speaker relay, and I've been waiting for the part). I am getting the audio output signals before the relay. The sound is normal, except the noise even I turn the VOL. down completely.

 

[tommy1]

An externally hosted image should be here but it was not working when we last tested it.

I cannot send the pic. from my email. Please help!!!

 

[PhaseLockLoopy]

hummmmmmmmmmm

Hum likes it when nV/√Hz gets converted into V/√Hz Hum likes a ground loop to have a different potential

It’s so nice to hum

 

[tommy1]

...how to fix this problem??

 

[5th element]

...how to fix this problem??

This is still not enough to go on. What type of noise is it you are getting.

Iain McNeill asked this right at the start.

Hiss, hum, buzz, squeals like tuning through the AM band?

 

[tommy1]

This is HUM, 5th element.

 

[Iain McNeill]

well why didn't you say

It could be that the reason the protection module failed is because some other low power circuit has shorted, or got taken out in the process and the resulting higher quiescent current is producing more 50Hz mains stimulus.

Have a look around the sense circuits in the output stages to look for burned components - or in fact anywhere. Do you know why the protection module failed?

 

[Mooly]

Have a look around the sense circuits in the output stages to look for burned components - or in fact anywhere. Do you know why the protection module failed?

Or if indeed it has failed... maybe it's reacting to the AC noise on the output and doing it's job.

I asked earlier. Is this a two channel amp ? stereo. Are both channels humming ?

 

[Mooly]

Does this help regarding posting a picture,
read post #254 make sure you "go advanced" when typing a message you want to add a picture to.
http://www.diyaudio.com/forums/troubleshooting/148984-bugs-13.html

 

[tommy1]

Thank you so much for your times! I am now waiting for the part UPC1237, and as soon as I put it in, I will let you know the result.

*Both channels are humming.
*The sound is ok. I am getting the audio output before the relay.

PD

 

[Mooly]

That IC will not cure the hum... it's a DC offset protection circuit.
Data sheet here,
UPC1237 Datasheet pdf - PROTECTOR IC FOR STEREO POWER AMPLIFIER - NEC