Transformer noise Marantz MM7025 power amplifier

[Dollso]

Hi,

I recently added a Marantz MM7025 power amplifier to my SR8015 AV receiver to take some of load off the SR8015 as it could get hot, my speakers are Monitor Audio Gold 300 5G.

The MM7025s transformer makes an audible hum and you can feel the vibration when you put your hand under it.

There is also a buzzing/hiss with a clicking sound from both speakers midrange driver.

I have switched everything else off and disconnected from mains and it still remains, the SR8015 on its own is dead silent.

Is this normal or is there something interfering with the MM7025? or is the unit defective? Is there anything else I should try to resolve this?

Thanks,
Gerry.

 

[DVDdoug]

That sounds like a DC offset (asymmetrical AC) on the power line. There have been a few discussions about it and I found one here.

The noise coming out of the speaker is probably unrelated to the mechanical noise/vibration. That sounds like a defect if you can hear it from your normal listening position. All active analog electronics generate SOME noise that you MIGHThear with your ear up to the speaker or with headphones.

 

[Dollso]

That sounds like a DC offset (asymmetrical AC) on the power line. There have been a few discussions about it and I found one here.

The noise coming out of the speaker is probably unrelated to the mechanical noise/vibration. That sounds like a defect if you can hear it from your normal listening position. All active analog electronics generate SOME noise that you MIGHThear with your ear up to the speaker or with headphones.

I thought DC offset was mostly something that effected toroidal transformers? the MM7025 has a EI transformer, and it's the one with the hum vibration from the transformer, and the buzzing and clicking on the mid range driver, but yes it's only audible when your ear is closer than say 1ft to the driver.

The SR8015 on the other hand has a toroidal transformer, and is dead silent, no hum, if you put your ear right up to the midrange driver you can just about hear a slight hiss, but from saying 1ft you can hear nothing, which is normal I thought.

Thanks

 

[Dollso]

So, the hum from the transformer was being made more noticeable by the unit it was sitting on, the low hum/vibration from the EI transformer was resonating through the stand and making it seem louder, I isolated the MM7025 from the stand and the hum is barely noticeable now.

The clicking and buzz are still coming through the midrange driver, which is audible up to several inches from the driver, all my other systems and speakers only have a barely noticeable sound of air blowing/faint white noise, and your ear has to be right up to the driver to hear it.

I have isolated everything, tripping all the mains trips bar the one with the room the mm7025 is in, then switching off and unplugging everything on that circuit, bar the mm7025, also disconnected everything bar the speakers.. the buzz/clicking is still the same.. only thing I can think off is there is a plug socket with usb charger built into it on the wall in the same room, and sometimes it makes a buzzing sound.. or maybe this is just how the MM7025 is?

 

[DVDdoug]

I thought DC offset was mostly something that effected toroidal transformers?

No. I have an amplifier with a regular-old transformer that used to vibrate/hum pretty badly when the TV was turned on. I knew it was some kind of "interference" on the power line because it happened with no audio connections but at the time I didn't know about the DC problem.

Now that I have a different TV it doesn't happen anymore.

I have isolated everything,

It could be the power coming-into the house. If possible, try it somewhere else. There might simply be something wrong with the amplifier.

 

[Speedskater]

Take the amp to a friend's house in a different neighborhood and see if it hums there.

 

[Dollso]

I've decided to return the MM7025 as don't see the point in something that is adding noise to my system that wasn't there before.

 

[RPoitou]

Does the noise go away when you turn off the front panel illumination? We have a Sherwood receiver which needs the display dimming to shut it up but only at certain times of the year! - I assume it's dirty mains caused by something a neighbour plugs in.

 

[Dollso]

Tried that, didn't make a difference, the MM7025 doesn't have a display as such, just the blue ring around what looks like a porthole display, makes it match the AVR, but you can turn the blue ring off, which I tried, even used a line conditioner which also had no effect