Hum in Anthem MRX 700

[TLS Guy]

So if I understood right, sound quality is not affected, just that a power frequency related (e.g.120 Hz in the US) noise is somehow superimposed to the audio signal. In that case, it is most likely a connection (usually connections to "ground" related issue. If there are nothing visibly loose or opened, such as wires coming off, then it could be some bad solder joints that have gone from weak to poor, and could be hard to find by the naked eyes.

Yes, it certainly does sound as if there could be a break in the internal ground plane. However failing power supply caps can cause this issue also, so there is excess ripple from the power supply. A scope on the power supply rails would show this problem fast.

 

[Verdinut]

So if I understood right, sound quality is not affected, just that a power frequency related (e.g.120 Hz in the US) noise is somehow superimposed to the audio signal. In that case, it is most likely a connection (usually connections to "ground" related issue. If there are nothing visibly loose or opened, such as wires coming off, then it could be some bad solder joints that have gone from weak to poor, and could be hard to find by the naked eyes.

You are referring to the 1st harmonic of the 60 Hz AC power in the US which is the frequency that is mainly heard with hum on AC lines all across North America?

 

[PENG]

You are referring to the 1st harmonic of the 60 Hz AC power in the US which is the frequency that is mainly heard with hum on AC lines all across North America?

2nd, no such thing as 1st, because that would be called the fundamental right?

 

[MVW]

I think something, solder joint, component, or ground became defective inside the Anthem MRX 700. The hum is very steady and consistent.

 

[Verdinut]

2nd, no such thing as 1st, because that would be called the fundamental right?

I didn't know. So a first harmonic does not exist. Isn't that weird that some chain starts by the second? I always thought that a harmonic was a mul;tiple of a fundamental frequency. Really weird!

 

[TLS Guy]

I didn't know. So a first harmonic does not exist. Isn't that weird that some chain starts by the second? I always thought that a harmonic was a mul;tiple of a fundamental frequency. Really weird!

And so it is. If 40 Hz is the fundamental then 40Hz X 1 is 40Hz. So that is the fundamental frequency. So 40 Hz X 2 is 80 Hz which is the second harmonic.

Here are the modes of a vibrating string.

An open string can produce all harmonics, as can an open organ pipe.

A closed pipe, that is a pipe closed at on end will produce the fundamental and only the odd harmonics.

 

[AcuDefTechGuy]

I would hope fot the money I paid it would last longer than 7 years.

My AVP-A1HDCI was $7,500. It lasted 8 YR. I was upset too. But these things might not last as long as we hope, especially when they keep on cramming all kinds of parts into theses things.

 

[Verdinut]

And so it is. If 40 Hz is the fundamental then 40Hz X 1 is 40Hz. So that is the fundamental frequency. So 40 Hz X 2 is 80 Hz which is the second harmonic.

Here are the modes of a vibrating string.

An open string can produce all harmonics, as can an open organ pipe.

A closed pipe, that is a pipe closed at on end will produce the fundamental and only the odd harmonics.

Thank you for the explanation. I however knew that a closed pipe only produced odd harmonics.

I am sure you can answer the following questions with regard to organ pipes:

One of the wood pipes of the 10,000 pipe Wanamaker Grand Court Organ at Macy's Center City in Philadelphia has a Graviissima resultant pitch equivalent to a 64 foot stop. It is described as follows in the booklet that came with Gothic label CD featuring it:
It consists of 25 Sub Quint pipes + 32 Open Diapason I + Independent 21 1/3 (Sub Quint)
Would you know how the 64 foot equivalent pipe is configured?

With regard to the Grand Organ at the Royal Albert Hall, in the booklet which came with the disc that you had recommended I purchase, the 64 foot pipe is described as an Acoustic Bass (fr. 32). How would that pipe be built?

Thank you for any additional info which I believe you would be able to provide on the above.

 

[WMH]

- I have the very same issue with an MRX500. It is definately a 60hz hum and it varies in amplitude no matter what volume is set to. With mine, if I turn it ON/OFF repeatedly it will eventually go away. I thought it might be an intentional software virus(so you had to send it in to get it fixed) because it always seem to happen about the same day every month. Now it does it randomly and way more often.
- It is most likely a bad or cold soldered capacitor in the power supply circuit.
- Has Anthem given you an estimated repair cost?
- Have you come up with any answers?
- I'm going to check the circuits with an oscilloscope and see what I can find, I wish I had schematics it would be a lot easier. The problem is, I never know when it will start to hum.
- I'll let you know if I find anything.

 

[mgood]

I have a similar issue with my MRX 710, but in my case the hum is coming from the unit itself. It is constant regardless of volume setting, and started being a real pain when I installed an LG OLED TV in my system. Whenever the TV is turned on and a dark image is displayed the hum from the unit is excessive. Turning off the TV results in a receiver that is quiet for the most part. It seems clear to me that the issue is mains noise, and I'm suspecting that the TV and other units are polluting the mains with DC current. What do you guys think?

I have ordered a DC blocker from the Swedish company Supra cables which will hopefully remedy the problem. Unfortunately I will have to wait until March for delivery.

I did send the receiver in for service on account of this issue a couple of years back. The shop found no issues with the unit..

 

[TLS Guy]

I have a similar issue with my MRX 710, but in my case the hum is coming from the unit itself. It is constant regardless of volume setting, and started being a real pain when I installed an LG OLED TV in my system. Whenever the TV is turned on and a dark image is displayed the hum from the unit is excessive. Turning off the TV results in a receiver that is quiet for the most part. It seems clear to me that the issue is mains noise, and I'm suspecting that the TV and other units are polluting the mains with DC current. What do you guys think?

I have ordered a DC blocker from the Swedish company Supra cables which will hopefully remedy the problem. Unfortunately I will have to wait until March for delivery.

I did send the receiver in for service on account of this issue a couple of years back. The shop found no issues with the unit..

This is not DC. That is nonsense. You could I suppose get DC offset on an AC line but even that would be next to impossible and I have never seen it. It would not cause hum anyway.

Your problem is resonance. Now new loads like LED light bulbs, computer and TV switching power supplies and now a host of other things, are what are known as discontinuous loads. That is that they do not draw power evenly throughout the AC cycle like say a toaster does. They favor the peaks of the waveform. This results in chopping. I suspect you have an older home. This is significant as until recently houses could be wired with the neutrals of circuits daisy chained. Because these discontinuous loads cause neutral gauging this is no longer allowed. However having older wiring makes you problem worse.

So when your TV is drawing the amount of power that has just the right amount of chopping of the peaks, it is resonating with the core of the transformer in your Anthem unit.

So your solution may be to run your Anthem off a UPS power conditioner like a suitable powered unit from APC.

Buzzes around homes from LED bulbs, especially those connected to dimmers are an increasing problem.

I can be certain that your TV is not sending DC down the line. A DC blocker is total snake oil.

I can give you no certain method that will solve your problem. You will have to experiment. A new TV might make it better or worse. I had this problem slightly with my previous TV acting in this way with the APC power conditioner. The new OLED does not. That previous TV is now in another system and does not affect the different APC conditioner in this way. So unfortunately this is all very hit and miss. So I can not give you a definite solution for your situation, just tell why it is happening.

 

[PENG]

I have a similar issue with my MRX 710, but in my case the hum is coming from the unit itself. It is constant regardless of volume setting, and started being a real pain when I installed an LG OLED TV in my system. Whenever the TV is turned on and a dark image is displayed the hum from the unit is excessive. Turning off the TV results in a receiver that is quiet for the most part. It seems clear to me that the issue is mains noise, and I'm suspecting that the TV and other units are polluting the mains with DC current. What do you guys think?

I have ordered a DC blocker from the Swedish company Supra cables which will hopefully remedy the problem. Unfortunately I will have to wait until March for delivery.

I did send the receiver in for service on account of this issue a couple of years back. The shop found no issues with the unit..

There are different kind of hum. If it is resonating with other things that injects large amount of low frequency harmonics it would likely sound more like 120, 180 or higher Hz but not 60 Hz. Can you attach an audio file?

Some amps are more prone than others to the same kind of excitation. Luckily you already know the source is the TV so now you just have to figure out what to use with the Anthem. You can try contacting Anthem for suggestion. If you are still within the return window for that TV, you should do so and try another one.

 

[Pogre]

You know this past weekend when I did some tweaking I had to change inputs for my pc to aux 1 in order for the mic cord to reach my seat and it caused a hum. When I put everything back the way it was no more hum. I don't have any explanation or anything, just thought it was a bit odd. Glad it went away when I put things back.

 

[mgood]

This is not DC. That is nonsense. You could I suppose get DC offset on an AC line but even that would be next to impossible and I have never seen it. It would not cause hum anyway.

Your problem is resonance. Now new loads like LED light bulbs, computer and TV switching power supplies and now a host of other things, are what are known as discontinuous loads. That is that they do not draw power evenly throughout the AC cycle like say a toaster does. They favor the peaks of the waveform. This results in chopping. I suspect you have an older home. This is significant as until recently houses could be wired with the neutrals of circuits daisy chained. Because these discontinuous loads cause neutral gauging this is no longer allowed. However having older wiring makes you problem worse.

So when your TV is drawing the amount of power that has just the right amount of chopping of the peaks, it is resonating with the core of the transformer in your Anthem unit.

So your solution may be to run your Anthem off a UPS power conditioner like a suitable powered unit from APC.

Buzzes around homes from LED bulbs, especially those connected to dimmers are an increasing problem.

I can be certain that your TV is not sending DC down the line. A DC blocker is total snake oil.

I can give you no certain method that will solve your problem. You will have to experiment. A new TV might make it better or worse. I had this problem slightly with my previous TV acting in this way with the APC power conditioner. The new OLED does not. That previous TV is now in another system and does not affect the different APC conditioner in this way. So unfortunately this is all very hit and miss. So I can not give you a definite solution for your situation, just tell why it is happening.

Thanks for the detailed response. I'm mainly guessing the source of the hum based on what I've read online.

My house was completed in 2018 so the wiring should be good. It's in Norway however, so not sure about the neutrals issue you mention. I do have plenty of LED bulbs and also Z-wave dimmers etc.

I'm not entirely sure the DC blocker is snake oil. Here is a link to the product:
http://www.jenving.com/products/view/dc-blocker-md01-16-eu-3024000378

Here is a DC blocker thread on ASR in which Amir M chimes in:
https://www.audiosciencereview.com/forum/index.php?threads/a-dc-blocker-to-help-stop-transformer-hum.948/

Still, mostly guesswork on my part so I do appreciate the information and tips.

 

[mgood]

There are different kind of hum. If it is resonating with other things that injects large amount of low frequency harmonics it would likely sound more like 120, 180 or higher Hz but not 60 Hz. Can you attach an audio file?

Some amps are more prone than others to the same kind of excitation. Luckily you already know the source is the TV so now you just have to figure out what to use with the Anthem. You can try contacting Anthem for suggestion. If you are still within the return window for that TV, you should do so and try another one.

Thanks Peng. I'll see if I can't get a recording of the hum. The Anthem does seem to be more sensitive than the Marantz SR8001 I had previously.

 

[TLS Guy]

Thanks for the detailed response. I'm mainly guessing the source of the hum based on what I've read online.

My house was completed in 2018 so the wiring should be good. It's in Norway however, so not sure about the neutrals issue you mention. I do have plenty of LED bulbs and also Z-wave dimmers etc.

I'm not entirely sure the DC blocker is snake oil. Here is a link to the product:
http://www.jenving.com/products/view/dc-blocker-md01-16-eu-3024000378

Here is a DC blocker thread on ASR in which Amir M chimes in:
https://www.audiosciencereview.com/forum/index.php?threads/a-dc-blocker-to-help-stop-transformer-hum.948/

Still, mostly guesswork on my part so I do appreciate the information and tips.

I say it is snake oil because the grid has to be protected against DC off set. DC off set would produce no back EMF in inductors. So that would mean that any significant DC off set in the grid would cause current to flow in the primary coils of transformers of the distribution system, and the power transformers of your electronics. It would not cause a buzz or any noise, just burn out your power transformer. Power distribution systems have to have robust protection to stop DC getting into the grid, as it has the potential to do a lot of damage.

I have test gear and have looked a lot of grid wave forms. I have never seen any DC offset coming off the grid anywhere were I have lived. Not ever.

I say this is snake oil, as there are always people willing to sell you expensive stuff for non existent problems. Selling DC blockers is in that category. Significant DC off set is something no power company can allow to occur.

 

[WMH]

The problem is definitely a hardware issue with the Anthem unit. All this harmonics and DC offset info is irrelevant, it would be filtered out by the units DC power supply circuits. If you have a ground loop problem with an input or output, the hum will ALWAYS be there. This is an internal DC power supply INTERMITTANTLY not working correctly and allowing 60hz noise on the DC supply voltage/s.
My problem is identical with a MRX500.

 

[PENG]

The problem is definitely a hardware issue with the Anthem unit. All this harmonics and DC offset info is irrelevant, it would be filtered out by the units DC power supply circuits. If you have a ground loop problem with an input or output, the hum will ALWAYS be there. This is an internal DC power supply INTERMITTANTLY not working correctly and allowing 60hz noise on the DC supply voltage/s.
My problem is with a MRX500.

Don't forget such filter effects you mentioned are on the secondary side of the transformer not the primary on the incoming side.

The OP's transformer hum seems activated when he turned on his new OLED TV, if I can hear an audio clip I would be able to tell if it is due to harmonic resonance so hopefully he would make a recording for us to hear. It does not sound like grounded loop related kind of 120 hz (in NA) hum.

 

[TLS Guy]

The problem is definitely a hardware issue with the Anthem unit. All this harmonics and DC offset info is irrelevant, it would be filtered out by the units DC power supply circuits. If you have a ground loop problem with an input or output, the hum will ALWAYS be there. This is an internal DC power supply INTERMITTANTLY not working correctly and allowing 60hz noise on the DC supply voltage/s.
My problem is with a MRX500.

No you have not understood. This is not an electrically produced noise directly. I can be certain from the OP's description that this is mechanical noise from the laminated core of the power transformer. It just happens that the electromagnetic forces generated by the magnetic flux of the coils in the transformer are generating a mechanical resonance in the coil which is audible. This is nothing unusual. Mechanical sound radiation from power transformers is actually quite common.

 

[Verdinut]

Don't forget such filter effects you mentioned are on the secondary side of the transformer not the primary on the incoming side.

The OP's transformer hum seems activated when he turned on his new OLED TV, if I can hear an audio clip I would be able to tell if it is due to harmonic resonance so hopefully he would make a recording for us to hear. It does not sound like grounded loop related kind of 120 hz (in NA) hum.

Here I see the advantage of a switching power supply using a small transformer with a very unlikely risk of getting humming noise, and an additional advantage of consuming less power because of higher efficiency.