Post by MartinT on Sept 10, 2020 20:09:29 GMT
Plug-in Mains Noise Filters Review
I decided to purchase a mains noise sniffer to see for myself how effective (or not) my collection of plug-in mains noise filters are in reducing mains-borne noise pollution. Cleaning up mains power quality is one of my key tenets to good sound quality and I’ve probably bored most members rigid with it!
The test unit is a Chinese LHY Audio ‘Line EMI Meter’ costing around £75 with import duty and VAT. It measures noise in mV as well as line voltage. It also has a bar meter at the top and plays the noise as sound, getting louder the worse the noise. It’s a fascinating instrument and I learned a lot more about what creates noise in my household than I had ever known before.
The maker suggests these noise ranges versus ‘goodness’:
The main barn ‘resting’ noise, with all filters plugged in, is around 20mV. The music room is a little noisier at 26mV. However, see later on for just how much this can vary.
Filter Test Results
The results rather shocked me, and I did a couple more rounds of each plug-in to verify my findings, using different sockets for the meter and test subject with all the other filters unplugged.
Yes, you’ve read that right. Most of the plug-in filters ADD noise! The two stars of the show are the Kemp SNS and, top of the pile, the Sercal NoNoise SE, which did their advertised job of reducing mains-borne noise. Possibly most disappointing are the ifi AC Purifier and PS Audio Noise Harvester, which are active devices and which I expected to perform a lot better.
Other Sources of Noise
This is where I got a real shock. The ‘resting’ noise of the main barn, if you remember, is around 20mV. While I was looking at the meter, Ruth turned on the TV. The noise immediately went up by +40mV and it started wailing. Then I turned on the dimmed LED lights above our dining table and the noise shot up by +200mV with the meter screaming. Wow! I also found the CFL lights in the music room, an upright lamp and table-top lamp, each added about 12mV of noise. Luckily, my LED uplighters contribute nothing. So I’ll be looking to replace both CFL bulbs with non-dimmed LEDs.
Conclusions
Test Limitations
I decided to purchase a mains noise sniffer to see for myself how effective (or not) my collection of plug-in mains noise filters are in reducing mains-borne noise pollution. Cleaning up mains power quality is one of my key tenets to good sound quality and I’ve probably bored most members rigid with it!
The test unit is a Chinese LHY Audio ‘Line EMI Meter’ costing around £75 with import duty and VAT. It measures noise in mV as well as line voltage. It also has a bar meter at the top and plays the noise as sound, getting louder the worse the noise. It’s a fascinating instrument and I learned a lot more about what creates noise in my household than I had ever known before.
The maker suggests these noise ranges versus ‘goodness’:
<50mV | Excellent |
<100mV | Very good |
<800mV | Good |
<1,000mV | Average |
>1,500mV | Poor |
The main barn ‘resting’ noise, with all filters plugged in, is around 20mV. The music room is a little noisier at 26mV. However, see later on for just how much this can vary.
Filter Test Results
The results rather shocked me, and I did a couple more rounds of each plug-in to verify my findings, using different sockets for the meter and test subject with all the other filters unplugged.
Model | Noise Reduction (dB) |
Russ Andrews The Silencer | +4.9 |
Tacima SC5723 | +4.3 |
Isotek Isoplug | +3.8 |
Isotek Neoplug | +3.5 |
ifi AC Purifier | +3.2 |
PS Audio Noise Harvester | +2.6 |
VertexAQ Jaya | +0.9 |
Harmonix Enacom | 0 |
Isotek Protek | 0 |
Kemp SNS | -2.0 |
Sercal NoNoise SE | -2.2 |
Yes, you’ve read that right. Most of the plug-in filters ADD noise! The two stars of the show are the Kemp SNS and, top of the pile, the Sercal NoNoise SE, which did their advertised job of reducing mains-borne noise. Possibly most disappointing are the ifi AC Purifier and PS Audio Noise Harvester, which are active devices and which I expected to perform a lot better.
Other Sources of Noise
This is where I got a real shock. The ‘resting’ noise of the main barn, if you remember, is around 20mV. While I was looking at the meter, Ruth turned on the TV. The noise immediately went up by +40mV and it started wailing. Then I turned on the dimmed LED lights above our dining table and the noise shot up by +200mV with the meter screaming. Wow! I also found the CFL lights in the music room, an upright lamp and table-top lamp, each added about 12mV of noise. Luckily, my LED uplighters contribute nothing. So I’ll be looking to replace both CFL bulbs with non-dimmed LEDs.
Conclusions
- The meter is a wonderful new way for me to understand what’s going on with mains noise and correlate it with performance.
- I cannot explain why so many of the filters appear to add noise. However, that’s what I’ve measured so they’re coming out of circuit.
- I have left only the Sercal and Kemp in circuit in the music room, with the Protek plugged in for protection as it contributes no noise.
Test Limitations
- The meter only tests for noise across Live and Neutral. No considerations of noise on the Earth (Ground) side are taken into account.
- Some of the filters interact with each other and are sensitive to how far away they are from each other and from the meter. I used the best readings in each case and tested them alone.
- The meter measures noise in the band 10kHz to 10MHz. Noise is known to exist further up the spectrum so take these measurements as guidance only.
- The ears don't necessarily hear what the meter measures. I have some more experimentation to do.