Need Advice on How to Eliminate Low Level Hum from Transformer inside a CD Player

[Wooferhead]

This is the interior of a typical entry-level CD Player I have.

This is a close-up shot of the transformer with a label on top that reads "NPT-1451D, ONKYO, SN2301640C, PEHH005DB, TAM M1624".

I had it plugged in to a typical wall electrical receptacle when I first received it just to test out all the buttons and functions. It wasn't connected to any components at the time, just the CD Player alone. I put a CD in it for test. Everything worked fine. It was quiet. There was no hum or any strange noise.

I then proceeded to connect the CD player to a receiver and used it only a couple times. One day, I noticed a low level hum coming from the inside of the player the moment I turned it on with no disc in it. The hum stopped the moment I turned it off. I assume it came from the transformer. I was hoping the hum would go away after a short time but it persisted ever since. The hum is not loud at all but definitely audible in close proximity, say two to three feet away.

The CD player and the receiver share a power bar with a surge protector. The power bar is plugged in to a typical wall electrical receptacle. Nothing else is on the power bar except the two components. There is a coaxial audio cable connecting the CD player and the receiver. Apart from the CD player, a pair of small bookshelf speakers is connected to the receiver.

I have attached a ferrite bead on the power cord of the CD player near its plug. Some say it would work. Unfortunately, it doesn't solve the problem in my case.

I am no audiophile and don't possess any knowledge regarding electrical engineering or electronic design. I am hoping some knowledgeable members of this forum could help identify the root cause of the hum and advise ways to eliminate it. I understand it is a rather common problem many have experienced.

Really appreciate any advice and suggestions you might have.

 

[DVDdoug]

That can caused by DC offset on the power line.

Try another outlet on a different circuit to see if it makes a difference. (If you are in the U.S., with split-phase power, the other phase might be OK.) Or you could try unplugging things to see if there's something else causing the problem.

I think I used to have that problem, although I didn't know what was causing it at the time... When I turned-on my TV, my power amplifier would hum & vibrate. (I had assumed that it was caused by high-frequency interference (even though the result was a low-frequency hum) and now that I know about the DC issue I no longer have that TV so It's no longer a problem.)

 

[Sokel]

Also try it's mains plug the other way around if you're in a country that allows that.

 

[Wooferhead]

Thanks for the replies.

I did try to plug in the CD player to a different receptacle but the result is the same.

There is only one way to insert the plug due to the different sizes of the prongs.

 

[antcollinet]

What happens if, while hearing the noise, you disconnect the coax between them. Or disconnect the power from the reciever.

If etiher of these eliminate the problem, do you have the option of an optical/toslink connection instead of the coax?

 

[Wooferhead]

What happens if, while hearing the noise, you disconnect the coax between them. Or disconnect the power from the reciever.

If etiher of these eliminate the problem, do you have the option of an optical/toslink connection instead of the coax?

I don't have an optical/toslink connection on the CD player.

The hum starts the moment I turn on the CD player while the power of the receiver is off. Turning the receiver on and off doesn't effect the hum in any way.

What would disconnecting the coax while both components are turn on do?

 

[JustJones]

I did try to plug in the CD player to a different receptacle but the result is the same.

Was the receptacle in the same room? Try running a long extension cord from somewhere like the kitchen or bathroom. If it's DC offset You can also try flipping off breakers until the offending one is found but that's a lot of hassle.

 

[antcollinet]

I don't have an optical/toslink connection on the CD player.

The hum starts the moment I turn on the CD player while the power of the receiver is off. Turning the receiver on and off doesn't effect the hum in any way.

What would disconnecting the coax while both components are turn on do?

You can turn them both off, disconnect the reciever, then turn on the CD player and see if there is still hum.

It is a long shot - but Im thinking of current carried by ground connections - I've not heard of that impacting transformer noise before though.

 

[Wooferhead]

Was the receptacle in the same room? Try running a long extension cord from somewhere like the kitchen or bathroom. If it's DC offset You can also try flipping off breakers until the offending one is found but that's a lot of hassle.

I ran an extension cord from the kitchen and plug in the CD player but with same result.

I don't know how to do the other method with the breakers. Do you mean flipping the breakers on and off?

 

[Wooferhead]

You can turn them both off, disconnect the reciever, then turn on the CD player and see if there is still hum.

It is a long shot - but Im thinking of current carried by ground connections - I've not heard of that impacting transformer noise before though.

I unplugged the receiver from the power bar, disconnected the coax from the receiver, and turned on the CD player. Same result.

 

[antcollinet]

I unplugged the receiver from the power bar, disconnected the coax from the receiver, and turned on the CD player. Same result.

Ok - then it has nothing to do with the receiver connection.

Most likely as pointed out above, a DC offset on your mains supply.

I think you can buy devices to eliminate this - but I'm not aware of any specifically and have no personal experience. Perhaps worth trying an isolation transformer?

 

[fatoldgit]

The cheapest DC blocker that I know of that has been proven*** to be effective is the AUDIOLAB DC BLOCK.

Comes in a single outlet version as well as a multi outlet.

Peter

*** proven as in measurements and also end user reports.... which in this case is non-snakeoil... if you had a hum before use and now you dont... it works.

 

[Wooferhead]

I tried the GLI-200 Hum and Buzz Kleaner by Earthquake Pro but it didn't make a difference.

I haven't tried a DC blocker. Does it work the same way?

Is this the one for $159?

 

[computer-audiophile]

It could actually be that the transformer is humming mechanically. Sometimes the vibrations are also transferred to the housing plate, which then acts as a soundboard. If this is the case, only mechanical measures will help. Tinkering skills are required. You can place damping materials underneath, change the mounting, etc.

 

[Wooferhead]

It could actually be that the transformer is humming mechanically. Sometimes the vibrations are also transferred to the housing plate, which then acts as a soundboard. If this is the case, only mechanical measures will help. Tinkering skills are required. You can place damping materials underneath, change the mounting, etc.

That's possible but I don't have the skill required to fix it.

But there was no hum when I first tested it on its own. Hum started only after I connected it to the system.

 

[antcollinet]

I tried the GLI-200 Hum and Buzz Kleaner by Earthquake Pro but it didn't make a difference.

I haven't tried a DC blocker. Does it work the same way?

Is this the one for $159?
View attachment 335244

The GLI is intended for killing noise from your speakers, not from a transformer. Completely different problem.


Regarding your picture - I have no idea what it is - a link would help.

 

[computer-audiophile]

That's possible but I don't have the skill required to fix it.

If that is the problem, external power conditioners will be of no use and would also be too expensive in combination with an inexpensive CD player. In that case, I would rather buy a different player.

 

[antcollinet]

That's possible but I don't have the skill required to fix it.

But there was no hum when I first tested it on its own. Hum started only after I connected it to the system.

Of course it is mechanical vibrations - nothing else can make a sound. DC offset is a common cause of mechanical vibrations.

Transformer hum

From the Naim Amplifier manual: A hi-fi system usually shares a mains circuit with other household equipment some of which can cause distortion of the mains waveform. This distortion can in turn lead to mechanical hum from mains transformers. Some Naim transformers are large in size, making...

community.naimaudio.com

 

[computer-audiophile]

DC offset is a common cause of mechanical vibrations.

... mostly on toroidal transfomers.

 

[antcollinet]

Assuming you are in USA something like this might help. Worth trying it if you can return it if it doesn't help.

Amazon.com