It is a good idea to isolate the capacitors from the chassis with some foam rubber or something similar.2 But I am seriously wondering if the input decoupling caps are not shielded enough. When i touch them the hum gets louder.
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This can also happen when things aren't grounded properly too.
Isolate the caps first.
Touching the caps and the hum increasing is a positive verification that you DO have a grounding issue.
I agree.
This is a very common effect to a grounding issue.
Measure resistance from 0V on Meanwell psu to chassis.
no reading discontinued
Touching the caps and the hum increasing is a positive verification that you DO have a grounding issue.
should i resolder everything on the board, especially the caps?
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no reading discontinued
should i resolder everything on the board, especially the caps?
Hope you got the information above.
Try fixing this
Sorry about the delay. My basement AC drainage pump was spitting water all over the place. It took me a while to wipe the water from the floor. So I am here.
yes.
Are you using metal standoffs on your pcb?
yes.
Measure resistance from 0V on Meanwell psu to chassiscorrection...O ohm
Attachments
Also how is the Meanwell psu 0V connected to chassis?
I did not connect PSU 0V to the chassis. Should I? Just to be sure, 0V is the negative side of PSU?
I just did a chemo-therapy on B1, resoldering, rewiring, and did everything you suggested. The hum is reduced! I touch the caps, no noise. But the faint hum is still there. Faint but I hear it, even from a few feet away. May be I am CDO!
It's demonic! I can't get rid of the hum.
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Yeah negative side of supply.
Just temporarily make a direct connection between PSU 0V and the chassis of the preamp (not chassis of supply).
Usually this connection is made via the standoffs or possibly the volume pot. TIGHTEN EVERYTHING nice and tight.
If you make these connections super tight you can break through the oxides on the surface of the aluminium. Otherwise get sandpaper and sand the chassis around these areas?
A starwasher can also be useful to bite through oxides.
Just temporarily make a direct connection between PSU 0V and the chassis of the preamp (not chassis of supply).
Usually this connection is made via the standoffs or possibly the volume pot. TIGHTEN EVERYTHING nice and tight.
If you make these connections super tight you can break through the oxides on the surface of the aluminium. Otherwise get sandpaper and sand the chassis around these areas?
A starwasher can also be useful to bite through oxides.
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Just the other day, I fixed someone's PA rig.
They had an annoying hum problem.
It was due to the pots not making a solid electrical connection to the chassis.
I had to TIGHTEN the volume pots nice and BLOODY tight, and the hum completely disappeared
So try the things mentioned earlier regarding making sure you remove oxides and paint.
AND just cause you can't see oxide doesn't mean you don't have it. YOU HAVE IT
They had an annoying hum problem.
It was due to the pots not making a solid electrical connection to the chassis.
I had to TIGHTEN the volume pots nice and BLOODY tight, and the hum completely disappeared
So try the things mentioned earlier regarding making sure you remove oxides and paint.
AND just cause you can't see oxide doesn't mean you don't have it. YOU HAVE IT
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