Help with Buzz Noise

Hello Everyone,

I'm having some buzz noise issues from my power amp just out of the blue, and need some advice to solve this.

The problem may be from the TIP31 transistor at the driver stage.
When I use my fingers to hold the casing of the transistor, the buzz noise greatly reduced to almost not audible (still there unless I place my ear right next to the speaker driver), but once I let go, the buzz noise comes back.
This problem happens to both channels.
The buzz noise stays at the same level even when I turn the volume to max, and don't seem to be bad soldering as the amp still plays apart from the buzz noise.

The complementary TIP32 don’t seem the have the same issue.

Anyone had similar problem before?
 
Last edited:
Thank you Mark,

Would not be the electrolytic caps. The only electrolytic caps I have in the setup are 2 x 10,000uF on the PSU which are brand new, none on my amp board.

The buzz sound is like (between 1:04 - 1:18 sec in this video):
The video seem to suggest that noise pickup at the input. I'll probably have to check my input signal cabling and route. The cables are non-shielded twisted pair, running from the RCA at the back of the chassis to the front where the volume pot is, then to the amp boards.
They do cross the speaker out cable a little, and perpendicular to the VDC cables with approx 1/2 inch distance.

Will the input signal cable to shielded ones.
 
Thank you Mark,

I just used a piece of copper sheet to separate the signal cables and power cables, and the buzz noise reduced significantly (still a little).
Will go get some of those 2 core double shielded cable (with a drain wire) to change out the existing signal cable and see how it goes.

I know there are different opinions on how the cable shield should be connected to the ground, but I will try out different arrangements and see which gives the best results.
 
Received the double shielded cables I ordered online, turned out there is one layer of tin foil with some strands of thin wire as the second shield instead of a proper layer of braided shield. A bit disappointed.

Nevertheless, I replace the twisted pair (PTFE solid core) and put in "double shielded" cable, from the RCA connector to the ALPS, then from the ALPS to the board. The shield are all connected at one point only then connect to the chassis ground.

The buzz noise still there..........................o_O extremely frustrating.
 
Hi Ctrlx,
Been on a loooong work assignment.
See picture with some notes. No schematic as the boards were given to me from a friend.
Let me know your thoughts.
Thanks.
 

Attachments

  • IMG_5134.jpg
    IMG_5134.jpg
    588.8 KB · Views: 54
Thanks Ctrlx,
Yes, I was thinking that it could be the big film caps mounted vertically could be picking up some noise. I have just ordered some electrolytics to replace them and see.
Not sure what you mean by cross channel loop, can you elaborate a bit more?
I don't think it is the input connections as I disconnected the input cable from the board, I still get the noise through my speakers.
Will trouble shoot a bit more and update later.
 
Just a quick update, as Ctrlx suspected, the large film caps mounted vertically were picking up the noises.
Have changed them to electrolytics now and hums are gone. However DC offset increased a little from ~30mvdc to ~50mvdc.

It was the film caps on the board nearest to the transformer that were giving problems, I changed those out first and noise were immediately gone even when the other board was still having the large film caps. But after spending some time listening for a few hours, I noticed that the channel from the board still with the film caps sounded a little brighter, my son thought so too without knowing what changes I made. So I changed out the remaining ones and all good now.

Thank you Mark and Crtlx(y)