Audio noise

[KSwitzer]

Please read carefully, because I think I've addressed all the obvious issues and may answer a lot of questions in this description.

Also, if you think there is a better thread or another more appropriate forum I could post in, please let me know.

The attachment is a video(audio) of noise from my Klipsch Forte II midrange when connected to a Cambridge Audio 851W amp. You may need to turn it up a bit to hear, but it's a rythmic pulsing buzz with a pulse about every second in case that's relevant.

20230112_185931_1_1

• KSwitzer
• Jan 15, 2023

Audio-no video

I've simplified the setup as much as possible to remove variables:

*The amp has no inputs connected except 110V AC power.
*The power is from an outlet that is connected with a single run to the circuit breaker box. There is only this one outlet on the circuit.
*Every other circuit breaker in the box is switched off, so the only device in my entire house (single family home) that is powered on for this test is the amplifier.
*I have tried another amplifier (Cambridge Audio and two other sets of speakers (Klipsch RB-5 and Infinity SM125). All combinations produce this same noise.
*I've also tried plugging into a different circuit with the same results. That circuit has multiple outlets, but nothing else was plugged in at the time of testing.

So at the time of testing, there is only one circuit open with only one device powered (the amp), and I'm still getting this noise. Doesn't seem like it could be ground loop, because I don't see a loop in this simple scenario. Also, the pulsing nature of the noise puzzles me.

I'm about out of my mind with this, so I hope someone has an inkling of what I could do or try to do to resolve this.

 

[RichPA]

A ground fault tester is only about $5. I'd check that on both outlets you've tried.

 

[rothwellaudio]

*The amp has no inputs connected except 110V AC power.

Does the noise go away with shorting plugs in the inputs? Is it the same with both the balanced and the unbalanced inputs?

 

[cpt_paranoia]

The buzzing sounds more like some RFI breakthrough than a ground loop. Are there any devices with displays or wireless comms nearby? Or wired digital comms?

 

[gadget73]

the pulsing is awful weird. Does the amp pulse the output with a normal input signal? Just wondering if we actually have two problems here, a buzz, and something wonky in the amp that makes the output level pulse up and down.

 

[KSwitzer]

Thank you all for the excellent replies. I'll try to follow up on everyting.

I'll get the ground fault tester tomorrow., but another interesting data point is this... I tried a little Sherwood amp with an ungrounded plug. I didn't shut down the other circuits, just plugged it in the dedicated 2-channel outlet and wallah! No buzz. Interestingly when I use a cheater plug to avoid the ground pin on my Cambridge 851W, it doesn't stop the buzz. Does this make sense?

Does the noise go away with shorting plugs in the inputs?

I don't have shorting plugs. Would I be shorting just the RCA inputs? I'm not using balanced inputs now as the AZUR 651A doesn't have them.

Are there any devices with displays or wireless comms nearby? Or wired digital comms?

Nothing is plugged into the circuit or the amp. All other power to the house except the one outlet is off at the circuit panel. If everything has no power and isn't on this circuit, do I still need to worry about it?

Does the amp pulse the output with a normal input signal?

When connected to the amp, the pulsing/buzzing is attenuated but still there. It increases when I turn the volume up. I have not observed it pulsing the audio signal itself though.

 

[cpt_paranoia]

If everything has no power and isn't on this circuit, do I still need to worry about it?

Do you have any battery-powered appliances? A mobile phone, for instance? A laptop? A tablet?

Do any of your neighbours have (electrically) noisy electrical equipment?

 

[Bill Ferris]

Do you have your wireless smart, or otherwise, phone nearby to the audio system ?
They have been known to inject cyclic pulsing noises when powered up near some operating audio equipment.

As an example, I have a inexpensive wireless temperature outside located battery powered transmitter to send to the battery powered receiver display in my workshop that`s placed on one of my 2 electronic repair benches.

Several yrs. back when the outside transmitter`s battery died, it was brought into the workshop to have the battery changed.

When my housekeeper/ caregiver opened it up to replace the 2 AAA batteries, as soon as she replaced the batteries my perfectly operating music playing Mc MA-6100 integrated amplifier that was playing my WAV. ripped music that`s hardwired fed from my living room`s music sourced A/V rack, the startling unexpected nasty sounding pulsing racket that came out of the MA-6100`s speakers made me think that the 24/7/365 powered up integrated HQ Mc. amplifier was for some reason blowing up !

As I jumped up and was freaking out about the pulsing buzzing racket coming out of the system, as my housekeeper/caregiver continued to walk to the door leading outside to put the wireless temperature transmitter back outside where it resided, the racket started subsiding as she walked further from the ~ 6 ft. away located operating integrated amplifier, so it was then I realized what was happening, and relaxed, as I was about to turn off the MA-6100 and pull it for service.

My point here is sometimes puzzling & annoying audio interference can come unexpectedly from the most benign battery powered wireless digital based RF sources, when the low powered operating wireless transmitting device is in close proximity to some perfectly operating audio equipment.

Just an suggestive thought.

 

[Lavane]

I even had a new refrigerator cause RF noise. I turned off my internet router, cell phone, TV, etc., and finely found the fridge causing the problem when it was going through some cyle.

 

[KSwitzer]

A ground fault tester is only about $5. I'd check that on both outlets you've tried.

Both circuits check fine with my new circuit tester (as I would hope, since I wired them myself ).

Do you have your wireless smart, or otherwise, phone nearby to the audio system ?

I will check for battery powered stuff tonight, but I'm still finding it strange that an older Sherwood 2-channel amp with a 2-prong plug is not picking up this interference. Could the torroidal power supply in these Cambridge units make them susceptible to that?

 

[Bill Ferris]

I will check for battery powered stuff tonight, but I'm still finding it strange that an older Sherwood 2-channel amp with a 2-prong plug is not picking up this interference. Could the toroidal power supply in these Cambridge units make them susceptible to that?

Don`t know, just conveyed my totally unexpected interference experience from the digital based low output battery powered wireless temperature transmitter when near to my standard type power transformer vintage Mc. ungrounded (2 prong power plug) integrated amplifier that is plugged into a recently manufactured HQ Panamax brand rack mount surge/spike/conditioner that`s plugged into a grounded outlet.
I don`t know of the path of the interference into the integrated, as once I became aware of it, I chose not to repeat it by replacing the transmitter`s batteries outside away from the workshop in the future.

Sorry, I`m unable to provide any more helpful information concerning this situation, KSwitzer, Sir.

 

[cpt_paranoia]

Could the torroidal power supply in these Cambridge units make them susceptible to that

You seem only to be considering conducted susceptibility. You also need to consider radiated susceptibility: RFI.

 

[KSwitzer]

You seem only to be considering conducted susceptibility. You also need to consider radiated susceptibility: RFI.

I'm trying to consider everything, I guess. How do I sort out the RFI? I thought shutting down the power grid in my house except for that one outlet would isolate any interference noise, but still need to rule out battery wireless. And why do you think its only showing up with these Cambridge Audio units?

 

[cpt_paranoia]

And why do you think its only showing up with these Cambridge Audio units?

Units? I thought it was just one amp.

Different designs have different susceptibilities. There may be a fault. I wouldn't expect different equipment to behave the same way, because the circuits are not the same.

 

[gadget73]

I will check for battery powered stuff tonight, but I'm still finding it strange that an older Sherwood 2-channel amp with a 2-prong plug is not picking up this interference. Could the torroidal power supply in these Cambridge units make them susceptible to that?

hm thats an interesting data point. So both of the amps that make noise are 3 prong cords but a 2 prong cord amp does not? That makes me wonder if you're getting noise riding in on your ground. If this is all fresh home run to the panel, maybe its worth having a gander at the connection at the ground rod itself, and where the ground rod wire comes into the service entrance. Also depending on the soil where you are, maybe dump some water on the ground rod to see if that does anything. If you're on sandy soil and its dry it makes for a fairly high resistance ground.

also I'm assuming this is to the main service entry, not a sub panel? If its a sub, check the grounds at both ends of the feed to it as well. Checking the ground to neutral bond screw at the service entrance not a terrible idea either. Just make sure its all tight.

 

[KSwitzer]

Units? I thought it was just one amp.

I started by troubleshooting just the 851W amp. Then I tried with just an AZUR 651A integrated amp under the same conditions.. There the buzzing got louder when I turned up the volume, but it was much quieter with the volume down. When I added the amp to the integrated amp it had the same behavior, where the volume knob would attenuate that really obnoxious sound in the attached video.

With the Sherwood Int. amp I had no buzz at all. I'll try another Sony AV unit tonight and see what it does, but I expect it's going to be quiet.

I also have a Cambridge 851N that has an integrated amp mode, so I'll give that a try too. Don't know why I didn't think about that.

I hate to bail out on this CA equipment after a $2000 investment. I'll lose my shorts reselling it.

 

[KSwitzer]

I hate reading threads without closure, so I'll try to bring some here. I realized that chasing the amplifier pulsing/buzzing noise was irrelevant if, when properly connected to a preamp, it wasn't audible. So I put everything back together, Azur651 to 851w, and 851n to Azur 651. It sounds great, even though at higher volumes I know that buzzing is there.

In the meantime I ordered a Schiit Freya + to replace the 651, and that will give me balanced outputs to the 851w (for what it's worth). I'm hoping the Freya can perform like the 851n does in preamp mode and eliminate the buzzing altogether.

Worst case, I can return the Freya for $50 restocking fee.

Thank you everyone that commented and offered suggestions. This is a great community.

 

[El Rubio]

For future reference, if you want to rule out RFI, get one of those mylar emergency blankets and wrap around your gear. The blanket will shield it from RFI and help you locate sources. You can hold it up and shield from one side at a time. Now, this isn’t an inch of lead and will not totally block everything, but I have noticed about -20dB of attenuatiin when wrapped around a source. That should be an audible change. The blankets are pretty cheap and can be found in the camping section at walmart.