How can I measure the noise on my AC mains with a 2ch oscilloscope?

I’m not an EE so although I have some nice test equipment I need help. Here is the problem, the AC Mains are 120 vac but I’m trying to measure the noise on the AC signal , millivolts. I’d like to answer two questions how bad is my power and second  does my isolation transformer make a difference.


thanks for the help 


I went through a similar exercise a few years ago, and after getting a zillion contradictory opinions from well-meaning audiophile buddies, finally brought in the big guns -- the electrical contractor who managed the replacement of Michael Fremer’s house wiring (see Mikey's YouTubes & Stereophile articles for the blow-by-blow) and Audioquest guru Garth Powell himself. I also wrangled sessions with engineers from our local power utility and from Tesla, which installed my rooftop-PV system. I figured that, with my engineering & electronics background, all I would need would be a little direction in order to analyze and address any noise issues by myself.

However, they all agreed that what you & I want to do would require tens of thousands of bucks worth of specialized analyzers. To my amazement, even my utility’s engineers didn’t have access to such devices. A simple scope and 10X probes, or even one of these PC/phone-based spectrum analyzers, doesn’t provide all the information you need to fully understand power-line anomalies. There are many types of noise (including 2d-order FX produced by the interaction of noise components with each other & with an audio signal) that are relevant in this type of use case that even a top-notch amplfier’s internal power supply isn’t designed to address.

For example, as Garth has demonstrated so effectively, even high frequency noise -- hundreds of KHz, I presume -- can create low-amplitude sidebands that aren’t filtered out by a conventional component PS, and that leak into the audio path to compromise the resolving power and transient response of even a modest audiophile-class stereo. Analyzing & mitigating the FX of line noise is not as simple as measuring an amplfier’s THD or filtering 60-cycle hum.

Despite all this, I still didn’t give up & picked up a prosumer "line-noise analyzer" that gave me a ballpark idea of aggregate noise levels within different frequency bands. I was then able to at least qualitatively understand how the levels of certain bands of noise fluctuated as a function of time-of-day. Surprisingly regular. But again, not real useful, beyond confirming that the relatively inexpensive inverters in my PV system produced more noise than did my power utility.

So I finally, finally! gave up and sunk $7-10K into a Garth-designed Audioquest Niagara conditioner and complementary power cords. A lower-end version of what Fremer himself was using with his Dartzeels & Chronosonics.

Happy ending. The Niagara produced one of the most dramatic improvements in SQ -- imaging, soundstage, detail, physicality, air, you name it -- I’ve ever experienced in a system I’ve owned. Beyond anything I’d expected. And I’ve been building systems from Stereophile-class components for almost 50 years.

When it comes to power, as with cables or anything else audiophile, the devil is of course in the details. What worked for me might be ineffective for you, especially if power quality is not your weakest link. But I can say this with the authority of personal experience: Once I started interviewing people who really knew what they were talking about, it quickly became obvious that trying to fully quantize a typical home’s line noise before taking corrective action is neither necessary nor sufficient -- and would require pricey, specialized gear that cost more than a full-blown, top-of-the-line conditioner.

My 2c.

Gents your experiences are extremely helpful. I’m using a Core Power Technologies DEEP=CORE 1800. And with my AMT tweeters it’s quieter. But not sophisticated as your solution. I do believe the Honda inverter is cleaner power ! 

I’ve heard the same comment from a friend that switched from PS Audio P20 to a Shunyata he never looked back .

i have a High freq current probe for the o scope that I might look at up stream and dwn stream of the power conditioner? 

thank you all for your contributions




Are you really interested in answering the questions posed in your starter post, or are you interested in your system sounding more like live music?

I'm definitely sold on the Audioquest Niagara solution at this point, but Shunyata, despite a very different design philosophy, also makes superb gear.  Just be sure that you deploy comparable power cables on your amplification components.  The conditioner is only part of the story.

Good luck.  Hope I was able to help even a little.