Evaluating Equipment-induced EMI noise in one’s audio system


Audiophiles have long recognized power line noise as the bane towards enjoying one’s audio system since at least the 1970’s (if not earlier). Folks appreciate their rigs often when the power grid has lower traffic during off-peak hours, such as late into the evening. More recently, perhaps beginning in the mid-1980’s or so (please don’t hold me to dates here, as I’ll stipulate I might be off on time), audiophiles have employed numerous devices such as power conditioners, power line filters, power regenerative devices, even battery-driven gear as a way to reduce power line noise getting into one’s system. And many of these devices actually work as claimed. But in this thread. I want to explore the extent to which the audio equipment, itself, whether a power line noise treatment device or an essential or auxiliary piece of audio electronics component introduces EMI or RFI noise into one’s system. I’ll describe a simple, inexpensive tool and method to evaluate any component’s inherent line noise. And whether one should use that as a guide to accept or reject a given audio component in one’s system. I will present my findings for two well known components familiar to most folks here in the forum. One will be a power conditioner that regenerates a corrected AC power signal. The second component will be a Class D amplifier and external power supply. Buckle up and let’s have some fun! 

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So let’s begin!

My journey into this arena begins with my confounded findings of certain power line noise introduced into my audio system. In one instance, I did not understand how much EMI noise entered my audio system and the source of that noise. I had used a lot of AC power line conditioners and elaborate power line filters from a variety of reputable companies over the years. And a times, following the eventual equipment upgrade path many audiophiles find themselves suffering through, the power line noise would fluctuate to higher or lower noise levels with each reiteration of my audio system.

At a point in my last recent reiteration, I decided that I had enough of my ignorance. And so I developed a simple and effective test to evaluate specific components for their inherent noise level. First, the tools needed. I obtained an EMI noise measurement device. Many companies make decent ones. I went with a TriField model EM100.
 

Second, the method. I evaluated the audio component of interest on a conventional duplex wall outlet. I first measure the baseline power line noise on each outlet using the EMI measuring tool. That is essential because any deviation. from those baseline levels provide insight into the added (or reduced) EMI noise on the parallel line circuit when the audio equipment is connected to the second wall outlet of the duplex outlet. Based on the levels of elevated EMI noise my EMI tool measures above baseline measurement with the audio equipment item is connected and turned on can serve as a guide for one to assess whether one should accept or reject that equipment item into one’s audio system. Secondary measurements can be done with the equipment in the audio system in a similar manner using the EMI measurement tool, tho different test configurations might be required.

I’ve tested this method with four different audio equipment items to validate the approach to my satisfaction. I’ll share my data with two or three of these items below. 

Conditions with conventional duplex wall outlet; EMI Noise Level measurements from TriField EM100. 

Test audio component: power conditioner brand X with multiple power outlets on back. Majority of the “source” outlets are for providing power to source gear components; a secondary set of “power” outlets are for providing power to equipment like amplifiers. 

Two different power cables were used to provide power to the power conditioner brand X. This was done to rule out any possible EMI noise artifacts introduced by a given power cable that provided power to the power conditioner brand X. 

TriField EM100 connected to wall outlet 1 of 2 with nothing connected to wall outlet 2 of 2. 

EMI Noise Level: 72.4 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with inothing connected to wall outlet 1 of 2. 

EMI Noise Level: 70.0 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with power conditioner brand X off and connected to wall outlet 1 of 2 via BBQ power cable. 

EMI Noise Level: 61.7 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with power conditioner brand X on and connected to wall outlet 1 of 2 via an Acoustic BBQ power cable. 

EMI Noise Level: 172.5 mVp-p AC

TriField EM100 connected to power conditioner brand X output source outlet with power conditioner brand X on and connected to wall outlet 1 of 2 via an Acoustic BBQ power cable. 

EMI Noise Level: 389.9 mVp-p AC

TriField EM100 connected to power conditioner brand X output power outlet with power conditioner brand X on and connected to wall outlet 1 of 2 via an Acoustic BBQ power cable. 

EMI Noise Level: 388.0 mVp-p AC

TriField EM100 connected to power conditioner brand X output source outlet with power conditioner brand X on and connected to wall outlet 1 of 2 via generic power cable. 

EMI Noise Level: 401.9 mVp-p AC

TriField EM100 connected to power conditioner brand X output power outlet with power conditioner brand X on and connected to wall outlet 1 of 2 via generic power cable. 

EMI Noise Level: 395.9 mVp-p AC

My conclusion: It’s clear from the measurements that the power conditioner brand X is an EMI noise generator that shouldn’t be used in a high-end audio system. 

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