How to cheaply measure AC power noise

[Roger22]

Hi all - I recently developed what sounds like distortion which is occurring at varying degrees with any track I listen to. Through bypassing and swapping I've ruled out any equipment or cable issues so my next thought was maybe I'm having a dirty power problem. Rather than buying an expensive conditioner that may not help I was curious if there was a way to measure or see the state of the power. Would a simple oscilloscope do the job? Could also be grounding potentially but nothing changed that I'm aware of which is why I'm suspecting AC noise.

 

[wwenze]

Why not measure DC power noise inside your equipment? The equipment needed for that is much cheaper.

 

[DVDdoug]

What is your sound source? Have you tried other sources/inputs?

Have you tried headphones and speakers?

Does it happen at all volume levels?

If power line noise causes a problem it's usually literally noise... Buzz, hum, or whine, etc., in the background. It would be worse (most noticeable) at low volume or with no signal. You won't confuse noise with distortion.

If you're getting audible distortion from some kind of defect (under "normal conditions"... not overdriving your amplifier, etc.) it's usually in only one channel and that can often help to track it down... Switching the left & right connections to the speakers or at other connection points.

 

[Roger22]

What is your sound source? Have you tried other sources/inputs?

Have you tried headphones and speakers?

Does it happen at all volume levels?

If power line noise causes a problem it's usually literally noise... Buzz, hum, or whine, etc., in the background. It would be worse (most noticeable) at low volume or with no signal. You won't confuse noise with distortion.

If you're getting audible distortion from some kind of defect (under "normal conditions"... not overdriving your amplifier, etc.) it's usually in only one channel and that can often help to track it down... Switching the left & right connections to the speakers or at other connection points.

I've tried 3 different sources, even using the same tracks for consistency. I've used two different preamps, two amps, and even connected my Ifi Neo streamer to an amp directly. The amp conveniently has gain controls. I swapped speakers and even got desperate and changed speaker cables. None of it made a difference in the noise which is present in both channels. It's definitely not 60 cycle hum, I'm just running out of ideas.

It sounds like distortion. Similar to the sound of an electric guitar with an overdrive pedal. The type of buzzy noise caused by a bad driver but it's not. It's present at all levels but tracks with the volume, not a static background noise. It's worse on poorer quality recordings for some reason but even on newer high quality material it's present, just to a much lesser degree.

The only recent change was new speakers, Tekton Ulfberhts, which I've have about a month. Everything was fine until about a week ago when this noise started out of the blue. At first I thought perhaps a couple of drivers in the speakers failed but I hadn't been pushing them hard and it was both channels. Swapping the speakers confirmed they weren't the culprit.

Having run out of things to try I've ordered a cheap Fosi BT20A. Figured I'd stream Bluetooth from my phone just to eliminate literally everything in the current system except the speakers.

 

[MaxwellsEq]

Mains noise is unlikely to cause something like this. Can you listen to any of the chain with headphones, since that will eliminate the speakers' behaviour?

 

[Roger22]

Mains noise is unlikely to cause something like this. Can you listen to any of the chain with headphones, since that will eliminate the speakers' behaviour?

Good suggestion but the only thing with a headphone jack is the AVR and I don't have a set of wired headphones. Depending how this goes I may be buying a cheap set for testing. I have a little Fosi integrated arriving sometime today I'm going to connect directly to the speakers. I can much more easily change the power source via extension cord with that as well. I'm hoping It will help with isolating the cause.

 

[Ricardus]

I bet it's the speakers. Like someone said up there, it's VERY unlikely it's noise in the mains. If the gear you're using has decent enough power supplies, they should be taking care of that.

 

[sam_adams]

Any cheap 6VAC transformer will allow you to 'observe' the AC mains signal on an oscilloscope. While the transformer may contribute some minor level of distortion to the signal, it will be swamped by the noise inherent in the AC mains. As others have already mentioned, it probably is not noise from the AC mains.

 

[Prana Ferox]

Agreeing with others that this doesn't sound AC power related. I am curious if you get noise (that you can characterize isn't hiss) from the speakers with the source paused and the volume turned reasonably up.

 

[fpitas]

Any cheap 6VAC transformer will allow you to 'observe' the AC mains signal on an oscilloscope. While the transformer may contribute some minor level of distortion to the signal, it will be swamped by the noise inherent in the AC mains. As others have already mentioned, it probably is not noise from the AC mains.

And at 6V you're less likely to electrocute yourself

 

[sam_adams]

And at 6V you're less likely to electrocute yourself

It's always a good idea to use a properly grounded AC test lead when doing testing:

 

[Audiofire]

It's always a good idea to use a properly grounded AC test lead when doing testing:

Don't create ground loops through an oscilloscope. They can really ruin one's day. Isolation transformers break ground loops.

EEVblog #279 - How NOT To Blow Up Your Oscilloscope!

 

[BDWoody]

Don't create ground loops through an oscilloscope. They can really ruin one's day. Isolation transformers break ground loops.

EEVblog #279 - How NOT To Blow Up Your Oscilloscope!

That made me think of the label on the QA100 digital scope:

Careful out there.

 

[Cbdb2]

Or use both scope channels in A-B and let the probe grounds float. No isolation transformer needed.

 

[Cbdb2]

Have you tried a frequency sweep to see if its at all freqs? There easy to find on Spotify etc.

 

[Speedskater]

Still, the only place that AC power line noise matters is in the signal-to-noise ratio at your audio equipment's output.

 

[Timcognito]

Do you have any old light dimmers on that circuit. Those things can create havoc though the line or sometimes the air with RMI.

 

[Speedskater]

Much of the AC power line noise is generated by your audio system's components!
Heck, if you look at a big power amp's power line waveform with a current probe, you will see that the amp's power supply id a great harmonic distortion generator. The current waveform will look much like a square wave. (Unfortunately power line current probes are pricey)
So if your audio components can deal with the noises that they generate, most external noises are trivial.

 

[antcollinet]

It sounds like distortion. Similar to the sound of an electric guitar with an overdrive pedal. The type of buzzy noise caused by a bad driver but it's not. It's present at all levels but tracks with the volume, not a static background noise

As others have said - noise doesn't cause distortion like that. Mains supply noise - even less so.

 

[sam_adams]

Isolation transformers break ground loops.

Not really.

Best to use a differential probe:

As a note—and a warning to viewers at home—the test lead pictured here is called a "suicide cord" for a reason. If you can't figure out why it's called that, then you shouldn't be using it. Ever.