50hz hum when audio cable is connected

Ok if i short buzzing signal to the ground it gets a little bit qmore quiet but than the silent channel starts to buzz if i short both channels together the silent shannel pops and remain silent. If i desolider the input wire both channels are quiet if i touch the input it react like normal and start to buzz 50hz as long as i touch either of the channel. It wasnt a case until i replaced the chip last one died when i touched back of the pcb.
Circuit diagram is here
Simple Amplifier Stereo HiFi Circuit with TDA7377_Circuit Diagram World
The photos of real amp pcb is here
Postimage.org / gallery - IMG 20160124 235453, IMG 20160124 235508, IMG 20160124 235522
 

rayma

Member
2011-04-29 8:37 pm
Ok if i short buzzing signal to the ground it gets a little bit qmore quiet but than the silent channel starts to buzz if i short both channels together the silent shannel pops and remain silent. If i desolider the input wire both channels are quiet if i touch the input it react like normal and start to buzz 50hz as long as i touch either of the channel. It wasnt a case until i replaced the chip last one died when i touched back of the pcb.

If it started when the chip went bad, check all the solder joints, then the tantalum/electrolytic capacitors.
 
I'd just replace the polarized caps, one at a time. The others are likely ok.

I reccon you know more than me in electronics im looking forward to learn more about analog electronics in general.
Can you tell me what c8 do is it some kind of filtering maybe this could be the issue? But if it is it should affect all channels so there is only film caps left witch could affect one of the channels right?
 

rayma

Member
2011-04-29 8:37 pm
I reccon you know more than me in electronics im looking forward to learn more about analog electronics in general.
Can you tell me what c8 do is it some kind of filtering maybe this could be the issue? But if it is it should affect all channels so there is only film caps left witch could affect one of the channels right?

It's SVR, supply voltage rejection (filtering).