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I saw a similar thread about this but it’s closed and no solution was posted. I’m having issues with the line-in on my AMP (which is connected via RCA cables to a preamp, connected to a turntable). There is a constant buzzing sound whenever the line-in is connected that gets louder if I turn up the volume. Also, the music from the turntable is very faint (and not nearly as loud as the buzzing). I’ve tried adjusting the line level but the buzzing is there regardless of the level, and it's always a lot louder than the music. I've tried rebooting the Amp, and switching RCA cables, but nothing seems to work. The amp works for streaming and powering speakers, but there's something up with the line-in.

I submitted a diagnostic: 2147038663.

While you wait on a Sonos rep to look at that diagnostic, a couple of potentially helpful observations. 

Hums are frequently caused by improper grounding. I’d be checking both the pre-amp you spoke of, as well as the turntable to ensure they’re properly grounded. 

The music being faint certainly suggests that the pre-amp in the circuit isn’t doing its job. Could be a power issue, could be as simple as flipping a switch, or making sure it is properly plugged in to a power source (which may help the first issue, too). I’d try removing the pre-amp completely just to see if everything is the same in terms of volume, that would be a good indication as to whether or not it is working.

All indications in your post suggest the issue is before it reaches the Sonos Amp, but the diagnostic should confirm that the Sonos Amp is working as designed.

Always lower AMP’s Volume before changing Line-In connections, power to the pre-amp, or connections to the pre-amp input.

Does the level of the hum respond to changes in the AMP Volume control? If you can, remove input to the pre-amp. Is there any change in the hum? Remove power from the pre-amp. Is the level of the hum similar to when the pre-amp had power? Remove connections to AMP’s Line-In. Is the hum present?

Thanks to both of you for your replies! Let me be a bit more specific about my setup and what I’ve tried already.

I have a pro-ject debut carbon TT → cambridge audio duo preamp (which can double as a headphone amp) → sonos amp → passive speakers. The TT ground is screwed down on the preamp.

When I switch out the Sonos AMP with a tube amplifier, there is no buzz/hum and the music is at the proper volume (the preamp seems to be working). Same thing if I use the headphone output from the preamp.

After reading your posts, I reconnected the ground wires, and all the RCAs, and even tried switching the outlets and surge protector everything is plugged into. The only thing that made any difference was the preamp used to be sitting on top of the Sonos AMP, and I found there was a slight clicking in one ear of my headphones. The clicking in the headphones went away when I separated the preamp and the AMP. But when I tried the whole setup (TT→ preamp→ AMP→ speakers), the buzz/hum was still going strong.

 

Buzz (appropriate name!), answering your questions:

Does the level of the hum respond to changes in the AMP Volume control?

Yes - it is 100% responsive. It gets loud/soft with the AMP volume control, and goes away entirely if you turn the volume all the way down.

If you can, remove input to the pre-amp. Is there any change in the hum?

No. If I remove the TT input to the preamp, nothing happens. The hum is still there.

Remove power from the pre-amp. Is the level of the hum similar to when the pre-amp had power?

No, the hum goes away when you remove power from the preamp or the AMP.

Remove connections to AMP’s Line-In. Is the hum present?

No.

--

In short: The hum is always and only there when (1) the RCA cable is connected to the Sonos AMP and the preamp; AND (2) both the preamp and Sonos AMP have power. If either end of the cable is not connected, or if either the AMP or preamp aren’t connected to power, the hum goes away.

Also, the hum is there even if the preamp is in stand-by mode, and turning the preamp “on” doesn’t change the hum at all.

I’ve also tried with a different set of RCA cables, same result.

…..

Thank you both. Does that help?

 

 

 

 

 

I assume that hum is not present in the headphone output during any of these connection combinations.

When you remove input to the pre-amp is the turntable ground wire still connected to the preamp? If so, disconnect this ground too.

Does the turntable or pre-amp use a grounded mains plug? Is the power plug polarized? (Inserts only one way in the wall outlet) If the power plugs are not polarized, try different power plug orientation combinations for all of the devices.

We need to track down any wire path to anything that is wired to ARC.

Are there any other wired connections to ARC, such as a subwoofer, network connection, or an HDMI input?

By the way hum issues such as this can be very difficult to resolve. There are well paid consultants who systematically work through hum issues for recording studios, broadcast stations, and such. We’ll keep working on this -- we’re not done yet.

Hi @mbarek 

Welcome to the Sonos Community!

Whatever is happening, the software doesn’t seem to be aware of it - no hardware faults are reported by the Amp.

I recommend you connect a device that does not require the pre-amp to the Amp’s line-in and test. A CD player, TV, set-top box, or anything else with RCA connectors for stereo audio, basically. If you don’t get the humming noise when using another device, then I can only suggest you try replacing the pre-amp (assuming all grounding considerations have been taken care of, as described by @Airgetlam).

If, however, you still get the same hum then I first recommend plugging the Amp into a different power outlet and testing again (ideally in another room). If the hum persists, please factory reset the Amp and add it back on to your system and try one more time. If the hum still persists, I recommend you get in touch with our technical support team.

I hope this helps.

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