Noise from Powered Speakers when Connected to AVR via RCA

[Danaxus]

Hey all,

I am pulling out what precious little hair I have left trying to figure this out and could really use some help. I have a pair of powered speakers (KEF LS60W). They work wonderfully, dead quiet when using AirPlay, or HDMI inputs, even when connected to the AVR (Denon x4800h), using RCA cables. However as soon as I select the AVR as an input, there is insane noise coming from them (see below video).

The problem is ameliorated when I connect an HDMI between the AVR and the primary speaker. I still hear noise, but it’s way quieter and sounds like it’s only a single frequency (I think 317Hz).

Things I’ve tried and did nothing:
- Plug the AVR and Primary speaker into the same wall outlet using a multiplug (tried two different ones)
- Plug them into separate wall outlets connecting to separate fuses in the fuse box
- Plug them into separate wall outlets that share a fuse
- Disconnect the primary and secondary speakers, using wireless transmission instead
- Using different RCA cables
- Disconnecting all other devices and speakers from the AVR, ensuring no other cables were even close, and only connecting a single RCA cable to the primary speaker (depending on which RCA was connected, the noise came from either the primary or secondary speaker, even if wirelessly connected to each other).

The only thing I can think of that might be important is that I have 3-phase power in my house, though as far as I know, wall outlets are single phase only? I’m no electrical engineer - this stuff is as mysterious as voodoo to me.


If anyone can help, I’d greatly appreciate it. I spent months designing and building my audio room, and it’s really disheartening to have it fail on me due to electrical gremlins.

 

[AnalogSteph]

The problem is ameliorated when I connect an HDMI between the AVR and the primary speaker. I still hear noise, but it’s way quieter and sounds like it’s only a single frequency (I think 317Hz).

What happens if instead of using the HDMI cable, you connect an RCA cable between the LS60 sub out and an unused (assignable) audio input on the Denon (any but Phono)?

1. If that does exactly the same as connecting the HDMI, the LS60s are probably trying to be clever with the RCA inputs and it's backfiring in your situation. I'm seeing a 3-pin mains power connector indicating an IEC Class I device, so some mitigation for ground loops would be required.

2. If that does not work nearly as well, then odds are both of your RCA cables stink when it comes to shield resistance.

3. If that solves your problem entirely, well, all the better.

- Disconnecting all other devices and speakers from the AVR, ensuring no other cables were even close, and only connecting a single RCA cable to the primary speaker (depending on which RCA was connected, the noise came from either the primary or secondary speaker, even if wirelessly connected to each other).

So to confirm, the only things connected to the AVR at this stage were:
* mains power
* RCA to LS60?

You can also try explicitly providing a ground connection to the AVR via the screw terminal at the phono input from known-good PE (your outlets are all grounded, right?), or via the network connection if you happen to have a rackmount switch and shielded Ethernet cables.

Another question - why do you have to use the analog input for the AVR to begin with? What about HDMI?

 

[Danaxus]

What happens if instead of using the HDMI cable, you connect an RCA cable between the LS60 sub out and an unused (assignable) audio input on the Denon (any but Phono)?




So to confirm, the only things connected to the AVR at this stage were:
* mains power
* RCA to LS60?

You can also try explicitly providing a ground connection to the AVR via the screw terminal at the phono input from known-good PE (your outlets are all grounded, right?), or via the network connection if you happen to have a rackmount switch and shielded Ethernet cables.

Another question - why do you have to use the analog input for the AVR to begin with? What about HDMI?

First of all, thank you, thank you for the response! I’m more grateful than you probably realise.

Here are the results of your suggestions:
By removing the hdmi cable and using an RCA from the speaker sub out to the AVR instead, the noise completely disappears. Unlike with the hdmi, there is no persistent tone at 317Hz (or any other frequency for that matter). Just for the sake of curiosity, I plugged the hdmi cable back in (so both the sub out RCA and the hdmi were running to the AVR), and when I did so, the 317Hz hum returned.

So as of now, the system seems to be running perfectly!!

To answer your other questions:
- yes just having mains power and RCA to LS60 was enough to produce that really loud noise.
- I’m not sure if the outlets are grounded; I will ask my electrician when he returns in a few days.

- I have a rack mounted router/switch. Short Cat.8 cables run from there to the rack-mounted patch panel right below it (same rack obviously), and from there Cat.8 cables run throughout the home (so insanely well-shielded). None of my media devices are currently connected via Ethernet however, as I’ve run out of switch ports. I’m making do with WiFi until I sort that out. Is the idea to use the rack as a common ground for the speakers and AVR?

- Finally, regarding HDMI. I have a surround sound system, and the AVR is powering the remaining speakers (they’re all passive). In order to incorporate the LS60 as the front L and R, the AVR demands I use the RCA preouts, and won’t accept hdmi (or optical for that matter). I’m guessing because it needs to use its own internal crappy DAC, and then send each channel out analog? I honestly wish I could use a separate better DAC, but as far as I understand, that’s not an option if I want to have my Auro3D, Dolby Atmos, etc.


Thanks again!
Niko

 

[AnalogSteph]

By removing the hdmi cable and using an RCA from the speaker sub out to the AVR instead, the noise completely disappears.

Score!

Then I suspect that the RCA input is more or less balanced (as previously suggested e.g. by Bruno Putzeys) and its CMRR is struggling with the common-mode voltage between receiver and speakers in your setup.

So as of now, the system seems to be running perfectly!!

Then I'd just leave it like that.

- Finally, regarding HDMI. I have a surround sound system, and the AVR is powering the remaining speakers (they’re all passive). In order to incorporate the LS60 as the front L and R, the AVR demands I use the RCA preouts, and won’t accept hdmi (or optical for that matter).

Ah, OK, that makes sense then. They are the only outputs post volume control.

I’m guessing because it needs to use its own internal crappy DAC, and then send each channel out analog?

The DAC isn't so much the issue, but the analog PGA volume control that follows.

Fundamentally it shouldn't be too hard to provide a volume-controlled digital output for an AVR manufacturer, but it's just not a common feature in the consumer audio world to date. (And I don't know what the odds of it being implemented any time soon are, given that the industry seems to be busy collapsing.) I've heard of professional gear having this, but then it can still be buggy.

 

[Kal Rubinson]

- Finally, regarding HDMI. I have a surround sound system, and the AVR is powering the remaining speakers (they’re all passive). In order to incorporate the LS60 as the front L and R, the AVR demands I use the RCA preouts, and won’t accept hdmi (or optical for that matter).

Do you realize that by using the RCA preouts into the LS60 you are introducing an A/D conversion, DSP and a D/A conversion that is not in the other channels and whose additional latency is neither fixed nor consistent? In my system, I use the LS60 for LS/RS while the rest are passive speakers but I use the S/PDIF (RCA digital) input which, according to KEF, offers a fixed latency.

Of course, you would need a volume-controlled S/PDIF output from the AVR but...............................

Fundamentally it shouldn't be too hard to provide a volume-controlled digital output for an AVR manufacturer, but it's just not a common feature in the consumer audio world to date.

 

[AnalogSteph]

Do you realize that by using the RCA preouts into the LS60 you are introducing an A/D conversion, DSP and a D/A conversion that is not in the other channels and whose additional latency is neither fixed nor consistent?

Good point. But why neither fixed nor consistent? I would assume that the KEFs would be defaulting to the same sample rate every time when using the analog input. (Which could be wrong, of course.) In that case it would be consistent and can be compensated as long as the AVR provides enough leeway in terms of delay.

KEF LS60 Wireless loudspeaker Measurements

Sidebar 4: Measurements

www.stereophile.com

The KEF's output arrives at 13.75ms, implying 10ms of extra latency from the loudspeaker's DSP. The Phase Control adds an additional 4.5ms of latency,

>10 ms strikes me as quite a lot. That being said, the maximum distance handled by this AVR should be 60 ft (~20 m), or 50+ ms.

 

[Kal Rubinson]

Good point. But why neither fixed nor consistent? I would assume that the KEFs would be defaulting to the same sample rate every time when using the analog input. (Which could be wrong, of course.) In that case it would be consistent and can be compensated as long as the AVR provides enough leeway in terms of delay.

?? KEF did not recommend using the analog input in this mixed application.

>10 ms strikes me as quite a lot. That being said, the maximum distance handled by this AVR should be 60 ft (~20 m), or 50+ ms.

From KEF regarding use of S/PDIF input:
Here's the latency info from end-to-end using acoustical measurements:

I am using cable mode.

 

[Danaxus]

Do you realize that by using the RCA preouts into the LS60 you are introducing an A/D conversion, DSP and a D/A conversion that is not in the other channels and whose additional latency is neither fixed nor consistent? In my system, I use the LS60 for LS/RS while the rest are passive speakers but I use the S/PDIF (RCA digital) input which, according to KEF, offers a fixed latency.

Of course, you would need a volume-controlled S/PDIF output from the AVR but...............................

I wonder if that’s why Audyssey was complaining my LS60s were out of phase.

During the denon setup process, it was very clear that I had to hook up each speaker to specific outputs. I’m aware of all the extra conversion stuff, but not sure how to get the x4800h to let me use a digital output (coaxial, toslink, hdmi), instead.

How did you get your system to work? Is it just a more flexible AVR?

 

[Kal Rubinson]

How did you get your system to work? Is it just a more flexible AVR?

It is not an AVR. I use a Merging Hapi II for its analog and digital outputs.

 

[Danaxus]

It is not an AVR. I use a Merging Hapi II for its analog and digital outputs.

I took a look at that product, I’ll be honest, I’m not exactly sure what it’s supposed to do, or whether it could fill my needs (I.e. take music from Apple TV, like a Spatial Audio track, and play it out of my surround system that’s configured as Auro3D).

I’ll keep my eye on the market, as I view the Devon x4800h as a mediocre solution, but one of the few available in today’s market.

 

[AnalogSteph]

I wonder if that’s why Audyssey was complaining my LS60s were out of phase.

They may literally just be overall inverting on top of that. The Stereophile review mentions something about

Without the Phase Control, the Uni-Q driver's tweeter and midrange sections can be seen to be connected in inverted acoustic polarity,

Have fun reversing the polarity on all your other speakers.

 

[Danaxus]

They may literally just be overall inverting on top of that. The Stereophile review mentions something about

Have fun reversing the polarity on all your other speakers.

omg, why? Eh, easily doable I suppose. I’ll mess with the phase control on the kef speakers, and if that doesn’t work, I’ll spend 5 minutes grumbling as I reverse every other speaker as you say. As long as it works, I can live with it

 

[Kal Rubinson]

I took a look at that product, I’ll be honest, I’m not exactly sure what it’s supposed to do, or whether it could fill my needs (I.e. take music from Apple TV, like a Spatial Audio track, and play it out of my surround system that’s configured as Auro3D).

None of that. Just a 16 channel DAC and network interface.