Hi everyone,
I have a power amp that has ground hum coming through the speaker of one channel, even with nothing connected. It’s not loud, just about audible from listening position. I have attached a picture of the inside. The channel that’s humming is the speaker output nearest to the power input.
I’m not an electronics expert, but I have tried a few things. I removed some zip ties and moved the power cable away from the audio output cable. I have also used a chop stick to check for any loose components but found none.
Do you have any other ideas to try? I recognise that playing around with certain aspects of the amp can be dangerous, and I will be sure to discharge caps and anything else you suggest.
Thanks.
I have a power amp that has ground hum coming through the speaker of one channel, even with nothing connected. It’s not loud, just about audible from listening position. I have attached a picture of the inside. The channel that’s humming is the speaker output nearest to the power input.
I’m not an electronics expert, but I have tried a few things. I removed some zip ties and moved the power cable away from the audio output cable. I have also used a chop stick to check for any loose components but found none.
Do you have any other ideas to try? I recognise that playing around with certain aspects of the amp can be dangerous, and I will be sure to discharge caps and anything else you suggest.
Thanks.
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Did this just start recently, or come on gradually?
Often, those large electrolytic capacitors on the board wear out, and cause
the power supply voltage ripple to increase.
Often, those large electrolytic capacitors on the board wear out, and cause
the power supply voltage ripple to increase.
Any more thoughts on possible causes of this issue?
It was suggested by the manufacturer that these could be tried (my feelings in parentheses):
It was suggested by the manufacturer that these could be tried (my feelings in parentheses):
- Install a ground-loop killer, typically based on a diode bridge. (Seems like a "band aid" rather than fixing the problem)
- Rewire the audio signal with a different wire. (Seems unlikely to make a difference)
- Move the mains wiring loom away from the signal wires. (Done)
from the above image,
the secondary ac supply wires go to one channel and then used three copper wires to connect to the second channel,
( is it possible that the ac phrase are 180 degrees different to one another. )
suggest to use three Y cables to connect the secondary power rails to the two channels at the same spot.
this will make sure the two amps receive same power source, same phrase at the same time.
under the same environment. it might help the ground issue.
will you try to make a star grounding in this amp
will you provide the picture of the copper side, a whole picture of the amp.
and the model of the amp so that we know more about it.
*
the secondary ac supply wires go to one channel and then used three copper wires to connect to the second channel,
( is it possible that the ac phrase are 180 degrees different to one another. )
suggest to use three Y cables to connect the secondary power rails to the two channels at the same spot.
this will make sure the two amps receive same power source, same phrase at the same time.
under the same environment. it might help the ground issue.
will you try to make a star grounding in this amp
will you provide the picture of the copper side, a whole picture of the amp.
and the model of the amp so that we know more about it.
*
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Thanks Alexchoi. I've attached some better quality photos. You will probably see on these that the power supply does in fact seem to be connected using Y cables.
Please could you tell me more what you mean by this: "will you try to make a star grounding in this amp." Considering I have various other amps that have no grounding issue and that the ground hum is only on one channel on this amp, I assume there is a faulty component on this channel. It's a TeddyPardo ST 60.
Thanks for the help.
Matt
Please could you tell me more what you mean by this: "will you try to make a star grounding in this amp." Considering I have various other amps that have no grounding issue and that the ground hum is only on one channel on this amp, I assume there is a faulty component on this channel. It's a TeddyPardo ST 60.
Thanks for the help.
Matt
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The bottom PCB in the last photo has its input circuitry right next to the toroidal power transformer. Is this the channel that hums?
Well-spotted--yes it is, and looking at it in person, it does look very close compared to any of my other amps that are working fine. Any ideas what to try on this? Heat-shrink insulation around it?
Great--I'll try that, thanks.
It seems that the circuit boards are attached to the case with tape (presumably with thermal properties), so I may also try moving the boards away from the transformer, unless anyone thinks this could cause any problems.
It seems that the circuit boards are attached to the case with tape (presumably with thermal properties), so I may also try moving the boards away from the transformer, unless anyone thinks this could cause any problems.
in the first image, the ac power cable blocked my view of the connections,
caused me to make a wrong survey, Pardon me.
star grounding is suppose to have all the ground wires joint at one point,
in the image , only the power grounds jointed.
later I knew its the factory design. so it must be ok,
upon your new images, I found the ac power cable is placed the other way round, would it cause the hum?
caused me to make a wrong survey, Pardon me.
star grounding is suppose to have all the ground wires joint at one point,
in the image , only the power grounds jointed.
later I knew its the factory design. so it must be ok,
upon your new images, I found the ac power cable is placed the other way round, would it cause the hum?
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the image in #1,
the ac power cable is parallel to the input cable and above the input circuitry,
could it induce the hum?
the image in #11
the ac power cable is close to the case and far from the input circuitry,
will it help?
the ac power cable is parallel to the input cable and above the input circuitry,
could it induce the hum?
the image in #11
the ac power cable is close to the case and far from the input circuitry,
will it help?
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The 'tape' is actually silicone rubber pads which are there to transfer heat from the transistors to the heatsinks. Metal bars are used to clamp the transistors tight against the silicone pads.
It may be that the proximity of the transformer wiring and the circuit boards is the problem, in which case rotating the transformer to move the wires away from the circuit board could help.
If the problem is the magnetic field from the transformer, which I think is more likely, then rotating it won't help because being a toroid the field will be the same all the way around.
You could flip the circuit board upside-down so that its input is orientated to the other end the same as the other channel. The fact that the components will face downwards, not upwards, shouldn't matter at all.
It may be that the proximity of the transformer wiring and the circuit boards is the problem, in which case rotating the transformer to move the wires away from the circuit board could help.
If the problem is the magnetic field from the transformer, which I think is more likely, then rotating it won't help because being a toroid the field will be the same all the way around.
You could flip the circuit board upside-down so that its input is orientated to the other end the same as the other channel. The fact that the components will face downwards, not upwards, shouldn't matter at all.
The point where a winding ends and wires are brought
to the outside is a strong source of stray field and even
more so if the transformer is cheaply made in a way so
that all winding ends exit in the same "window".
It is easy to check this by using a tape head and amp as
detector - or by rotating the transformer.
to the outside is a strong source of stray field and even
more so if the transformer is cheaply made in a way so
that all winding ends exit in the same "window".
It is easy to check this by using a tape head and amp as
detector - or by rotating the transformer.
Moving the transformer over a little seems to have basically made the hum inaudible, with some remaining minor hiss only audible within about a foot of the speaker. The other channel (and other amps) have a bit of noise, so this is a great result, and most importantly, seems to indicate there’s nothing wrong with the amp.
To top it off, the transformer fastenings had enough play that I could just screw it down in its new position. Thanks very much for all the help everyone--much appreciated.
To top it off, the transformer fastenings had enough play that I could just screw it down in its new position. Thanks very much for all the help everyone--much appreciated.
What do you mean by "moving the transformer over a little" ?
Twisting the three secondary wires together may be a good idea.
Twisting the three secondary wires together may be a good idea.
I took off the nut/bolt/top plate from the transformer, moved/rotated the transformer away from the boards, checked through speakers for optimum position, put the nut/bolt/plate back on, and the hum seems much better.
I will indeed carefully play around with wire positioning before I put the lid back on.
Thanks.
I will indeed carefully play around with wire positioning before I put the lid back on.
Thanks.