Hi I just purchased this item cheap second hand, but as soon as switch on and touch the volume control it emits a load hum through the speakers has any one heard of this problem with this amp before? Or know what it might be? Thanks.
If you touch the knob and it hums, i would ground the pot first.
Step-by-Step Assembly Guide
step 10.
Step-by-Step Assembly Guide
step 10.
Obviously it shouldn't hum when touched... so I would look for damage such as cracked print possibly caused by being dropped etc.
Doesnt matter what the pot is, you could have said chassis, foot, handle, its metal and should be grounded. If you touch the metal bottom and no hum, attach the pieces of metal that do hum to the bottom of the chassis.
While I am trying to solve this, could it damage my speakers I don't really have a cheap pair to try it out on.
Maybe i should explain that as soon i change the volume it starts to hum loudly not just touch the volume nob which is made of plastic.
Yes that entirely different...
Sorry its a dolby digital receiver, trouble shooting is above my head without a schematic and the unit.
Sorry its a dolby digital receiver, trouble shooting is above my head without a schematic and the unit.
By just taking the top of... no.
But did it all work before you did ?
Without seeing and hearing first hand I would say yes, its possible.
Does it only hum while the volume is being altered... in other words once adjusted is it OK ?
As soon as you move the volume up or down it starts to hum, and continues to hum until I switch off. Also if you switch it on and then change the input it starts to hum until I switch it off.
The person who sold it to me from you know where, said it was dead and would not power on.
So the first thing I do is take the top to inspect it visually I always do this then with nothing connected switch it on there was a switch at the back set to off so I turned that on and the unit powered up, thinking I’ve been lucky I then connected my speakers.
That’s when I noticed the hum.
The person who sold it to me from you know where, said it was dead and would not power on.
So the first thing I do is take the top to inspect it visually I always do this then with nothing connected switch it on there was a switch at the back set to off so I turned that on and the unit powered up, thinking I’ve been lucky I then connected my speakers.
That’s when I noticed the hum.
I had a cambridge audio unit where the PSU caps had blown, it made the supply rails droop, check for bulging caps anywhere on the power supply or the main pcbs.
I changed 3 or 4 caps and it was good as new for many years after that.
Wrinkle
I changed 3 or 4 caps and it was good as new for many years after that.
Wrinkle
How loud is this hum ?
If you turn the volume to back to zero does the hum reduce ?
Is it a "pure" deep tone or is it harsh and rasping ?
Are both channels left and right affected ?
Is it still the same if you have no inputs connected ?
If you turn the volume to back to zero does the hum reduce ?
Is it a "pure" deep tone or is it harsh and rasping ?
Are both channels left and right affected ?
Is it still the same if you have no inputs connected ?
Moving the volume up or down does not increase or reduce the hum.
Yes it is a pure deep tone.
Yes all channels are affected.
How load not sure what to say quite audible.
I really do suspect cracked print somewhere or, some form of physical damage... it doesn't sound sound like a normal failure mode of a component that would occur in normal use.
A pure deep pure tone indicates 50 cycle "mains" related hum... ripple on rails etc is at twice that frequency and is not a pure tone.
Also, and hard to explain but just a feeling, is the fact its not (by your description) extremely loud or causes damage... and that make me suspect a signal grounding issue (again caused by physical damage rather than component failure) somewhere in there.
Impossible to diagnose really without doing some quick basic checks with a scope.
A pure deep pure tone indicates 50 cycle "mains" related hum... ripple on rails etc is at twice that frequency and is not a pure tone.
Also, and hard to explain but just a feeling, is the fact its not (by your description) extremely loud or causes damage... and that make me suspect a signal grounding issue (again caused by physical damage rather than component failure) somewhere in there.
Impossible to diagnose really without doing some quick basic checks with a scope.
Yes i think you right this unit must have suffered a large impact not the reason he said just stopped working one day.
So i'm thinking i should get a cheap speaker and connect to the centre channel make it hum and go around the pcb's with some thing plastic slightly flexing them and see what happens.
What do you think?
What do you think?
You could do... or add a series resistor to your existing speakers.
A good visual inspection is best first, of top and bottom of PCB's
A good visual inspection is best first, of top and bottom of PCB's
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