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

Test audio component: an ultra-low impedance power conditioner brand Y without any  power outlets on back of the unit. The unit includes an attached dedicated proprietary power cable from the same manufacturer. The unit doesn’t include any active circuitry whatsoever. Accordingly, one might not expect this unit to generate any EMI noise into the line as a result of being connected to a wall outlet. The unit includes a toggle switch on the front panel to enable the user to select from two different “flavors” of ultra low impedance provided from the unit. 

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

EMI Noise Level: 37.1 mVp-p AC

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

EMI Noise Level: 37.5 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with ultra-low impedance power conditioner brand Y connected to wall outlet 1 of 2 via the unit’s dedicated power cable and front panel selector “A” setting selected. 

EMI Noise Level: 40.1 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with ultra-low impedance power conditioner brand Y connected to wall outlet 1 of 2 via the unit’s dedicated power cable and front panel selector “B” setting selected. 

EMI Noise Level: 43.3 mVp-p AC

My conclusion: It’s clear from the measurements that the ultra-low impedance power conditioner brand Y isn’t an EMI noise generator. The de minimus  increase in EMI noise is likely due to the dedicated power cable acting like an antenna. Based on these measurements. I see no reason for excluding the ultra-low impedance power conditioner brand Y from use in a high-end audio system. 

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celander OP
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@steakster Regsrding the presence of a transformer inside the power conditioner brand X, I have no doubt that one is present. I don’t know its physical size and electronic properties. That said, I suggest it might be difficult to justify including a large transformer-based power conditioner into one’s audio system to reduce EMI noise if the same power conditioner is also introducing an additional layer of EMI noise into the system. Savvy audio designers should and do offer products that mitigate or altogether eliminate EMI noise from their designs. Those are the ones I’m trying to include in my system to the exclusion of others that are contributing more EMI noise than they remove.

Don't you agree?

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

Test audio component: a Class D monoblock amplifier brand Z with detachable, independent 300W GaN power supply. 

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

EMI Noise Level: 22.6 mVp-p AC

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

EMI Noise Level: 22.2 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with Acoustic BBQ power cable connected to wall outlet 1 of 2. 

EMI Noise Level: 23.7 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with only 300W GaN power supply connected to wall outlet 1 of 2 via the Acoustic BBQ power cable. 

EMI Noise Level: 25.3-25.8 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with Class D monoblock amplifier brand Z connected to 300W GaN power supply connected to wall outlet 1 of 2 via the Acoustic BBQ power cable. 

EMI Noise Level: 54.8-61.9 mVp-p AC

TriField EM100 connected to wall outlet 2 of 2 with Class D monoblock amplifier brand Z connected to 300W GaN power supply connected to wall outlet 1 of 2 via the Acoustic BBQ power cable. (XLR input closed by XLR-RCA adaptor with RCA EMI/RFI blocker cap.)

EMI Noise Level: 67.0-81.2 mVp-p AC

My conclusion: While the 300W GaN power supply didn’t significantly increase EMI noise in the power line, the full Class D monoblock amplifier brand Z with the 300W power supply increased EMI noise by over 2-fold. I’m not certain whether such an increase in EMI noise will necessarily be audible, but it is present. 

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