Slight hum in my amp. Is this normal?

@gdhal,

An isolation transformer will not pass DC.

oldschool1,

Is this what the inside of the amp looks like?
http://www.studio-22.com/anthem/images/Anthem%20MCA%2050%20-%20Inside1.jpg

If so notice the two toroidal transformers on each side. Pull the top off the amp and check the center mounting bolt and nut for tightness. Make sure the round top plate is seated properly on the top of the transformers. Maybe one of them is loose.

After checking them, to make sure they are secure, power up the amp and listen to the two transformers. If the hum/vibration is still there listen to each transformer individually the best you can. First verify the hum is coming from one or both of the transformers. Is one louder than the other? If so recheck the mounting bolt and nut. Make sure the round top plate is seated properly on top of the transformer.

.

atmasphere

You can have DC on the line and oddly enough, it can be passed through transformers.

Please explain.

atmasphere

But its still an AC waveform and so can travel through a transformer. But the output will still be asymmetrical.

Is it really DC in the true sense/meaning of the word? Does it build to a DC voltage and then fall to zero at each half of the waveform cycle? If so then I could see how it would pass though from the primary to the secondary winding of an isolation transformer.

Sorry for my ignorance. I am just trying to better understand what is going on.
I do know there are people that say that an isolation transformer will block DC offset on the AC mains from the secondary of the transformer. I personally do not have any personal experience whether it will or not.
I believe you when you say it will not. I also believe that to be the case from actual bench testing which you have done.

I know AC and DC can both travel in a circuit at the same time. And yes I know the DC can be blocked using a DC blocker allowing only the AC to pass though the circuit or another circuit.

I know a pulsating DC voltage source, such as a battery, can be transformed, for lack of a better word, but constant DC voltage cannot. (As long as the applied voltage is constant.) If a constant DC voltage could pass through a transformer then an output transformer on a tube power amp would pass DC to the speakers.
Jim

.

The hum in my Prima Luna Prologue Premium integrated sounds like a constant 60hz. It is in both channels equally, Its amplitude is not affected by the volume control and muting the amp does not make it go away.

Now that sounds like a typical ground loop hum.

For the test below feed all the associated audio equipment from only one wall duplex receptacle outlet circuit. You can repeat the test later if you have more than one circuit you are using to feed your equipment and then check for hum again.

First disconnect all the source equipment from the inputs of the amp. With nothing connected to the inputs of the amp check for the hum.
(I assume the amp uses a 3 wire grounded plug and power cord).

No hum?

Add/connect one piece of source equipment to the amp’s inputs. Check for hum.
(In most cases the source equipment will use a 3 wire grounded plug and power cord that may be causing the ground loop hum).

Hum?

Disconnect that piece of source equipment from the amp’s inputs and then try another piece of source equipment and connect it to the amp’s inputs. Check for hum.

Hum?

If yes, good chance it is the integrated amp causing the ground loop hum problem.

If no hum, then it’s a good chance it is the first piece of source equipment you connected to the amp’s inputs.

Try all other pieces of source equipment and check for hum.

If no hum, then start reconnecting the source equipment, that did not cause the hum, back to the amp one piece at a time to the amp’s inputs checking for the hum.

If by chance you have a CATV cable box or a SAT dish box connected to the audio system in anyway start there first. Disconnect the incoming coax cable from the receiver box.
This a prime suspect for a ground loop hum problem. What happens is there is a difference of potential, voltage, from the incoming coax cable shield and the safety equipment ground at the wall AC power outlet. In most cases the coax cable shield is not ground properly outside at the grounding block on the outside of the house.

dweller,

Does the integrated amp hum with nothing connected to any of the inputs?

Does the hum sound like this? 60Hz.
https://www.youtube.com/watch?v=SVZ2P0KsLic
https://www.youtube.com/watch?v=Lnd57eOyesk
.

Or like this? 120Hz.
https://www.youtube.com/watch?v=pC4Uzt0qm2E
.

Check this out. A tube causing a 60Hz hum?
https://www.youtube.com/watch?v=GrVtX0QGNls