Hello,
i recently bought a Greenwave AC EMI measurement device and made some interesting observations while testing to find the best spot for the filters i wanna share and talk about
1. Noise searches the shortest path
this got specially obvious as in my listening room the AC comes in at the door light switch, plugging filters directly into the socket at the door reduces EMI levels in the whole room from that point on, where in comparison filters plugged into the last sockets of the circuit barely filter any noise, as the whole noise still travels down the whole line to the last socket
i guess this is only a really good tip if your main concern is incoming EMI from outside AC, as filters plugged between devices will effectively isolate the two devices somewhat noise-wise
2. Know your filters
Power filter with included 1/2/3 stage emi filter might not be "the solution" as these will not only block incoming EMI, but also block EMI that wants to flow out of the system, now if you close one drain the noise either searches another path or stays "floating" in the (with filters) isolated system
imagine following scenario i measured:
before power strip with filter with 2 greenwave filters : 400mV
after power strip with filter: 1600mV with PC running
after power stirp with filter AND and additional greenwave parallel filter: 400-600mV
i can really only explain the measurements like this:
the power strip filter essentially blocks noise in both ways making the devices after the power stirp somewhat "floating" noisewise, pluggin in one parallel filter gives the majority of noise again a path to flow out of the system trough the unfiltered ground connection
imo this is really important to understand, as i dont think its a good idea to only isolate a system without giving the noise a path to flow out of the system, making the issue potentially worse than it was
there are these filters that somewhat differeniate from your usual ones: https://auth-nt.de/produkte/netzfilter/adapter/1/netzfilter-emd-503?number=EMD503 in that they have also the ground connection fitlered, essentially really isolated all paths for noise, so even a parallel filter afterwards wouldnt help much
like i said before, not really sure if its a good idea to "contain" the noise
what i draw from this is that with your usual power strip you want to use parallel filters additionally, the power stirp filter isolated outside noise and the parallel filter gives the noise from inside a connection to flow out of the system trough ground path, to me it makes logically sense at the measurements i saw with the greenwave ac meter also support this but its really never talked about, so what do you think?
i recently bought a Greenwave AC EMI measurement device and made some interesting observations while testing to find the best spot for the filters i wanna share and talk about
1. Noise searches the shortest path
this got specially obvious as in my listening room the AC comes in at the door light switch, plugging filters directly into the socket at the door reduces EMI levels in the whole room from that point on, where in comparison filters plugged into the last sockets of the circuit barely filter any noise, as the whole noise still travels down the whole line to the last socket
i guess this is only a really good tip if your main concern is incoming EMI from outside AC, as filters plugged between devices will effectively isolate the two devices somewhat noise-wise
2. Know your filters
Power filter with included 1/2/3 stage emi filter might not be "the solution" as these will not only block incoming EMI, but also block EMI that wants to flow out of the system, now if you close one drain the noise either searches another path or stays "floating" in the (with filters) isolated system
imagine following scenario i measured:
before power strip with filter with 2 greenwave filters : 400mV
after power strip with filter: 1600mV with PC running
after power stirp with filter AND and additional greenwave parallel filter: 400-600mV
i can really only explain the measurements like this:
the power strip filter essentially blocks noise in both ways making the devices after the power stirp somewhat "floating" noisewise, pluggin in one parallel filter gives the majority of noise again a path to flow out of the system trough the unfiltered ground connection
imo this is really important to understand, as i dont think its a good idea to only isolate a system without giving the noise a path to flow out of the system, making the issue potentially worse than it was
there are these filters that somewhat differeniate from your usual ones: https://auth-nt.de/produkte/netzfilter/adapter/1/netzfilter-emd-503?number=EMD503 in that they have also the ground connection fitlered, essentially really isolated all paths for noise, so even a parallel filter afterwards wouldnt help much
like i said before, not really sure if its a good idea to "contain" the noise
what i draw from this is that with your usual power strip you want to use parallel filters additionally, the power stirp filter isolated outside noise and the parallel filter gives the noise from inside a connection to flow out of the system trough ground path, to me it makes logically sense at the measurements i saw with the greenwave ac meter also support this but its really never talked about, so what do you think?
Don't think of the filter like shoving a potato up your exhaust and making the muffler explode. Good noise filters are usually lossy and convert noise to heat. Albeit such a small amount as to be nearly unmeasurable, but that's what lossy really means. They also short noise to ground. A good rule is that it's easier to stop noise at the source, than after it conducts or radiates elsewhere.
Something I always tell people when it comes to cleaning products, but it also applies to filters, is, "Identify the enemy!" Unless you know what kind of dirt you're trying to remove, or what kind of EMI you need to filter, you'll probably choose a sub-optimal solution.
I know nothing about the Greenwave device but today you need to consider wifi and cell phones and I don't know if the Greenwave goes that high. A useful tool is the TinySA Ultra spectrum analyzer as it covers most of that stuff. Another thing to consider these days are inverter driven heat pumps. They can mess up your line. Also, no filter will fix a non-sinusoidal AC waveform. I like to rely on good power supply and grounding design that isn't bothered by dirty power. Equipment using less than great ground strategy tends to be more susceptible to EMI.
Something I always tell people when it comes to cleaning products, but it also applies to filters, is, "Identify the enemy!" Unless you know what kind of dirt you're trying to remove, or what kind of EMI you need to filter, you'll probably choose a sub-optimal solution.
I know nothing about the Greenwave device but today you need to consider wifi and cell phones and I don't know if the Greenwave goes that high. A useful tool is the TinySA Ultra spectrum analyzer as it covers most of that stuff. Another thing to consider these days are inverter driven heat pumps. They can mess up your line. Also, no filter will fix a non-sinusoidal AC waveform. I like to rely on good power supply and grounding design that isn't bothered by dirty power. Equipment using less than great ground strategy tends to be more susceptible to EMI.
There's conducted EMI and radiated EMI and looks like the OP's talking about the conducted type. A good solution for that would be an online UPS or sinewave inverter for the delicate things alone.
True, but unfortunately, most PFCs in the market are passive and they only improve the displacement power factor (DPF) by widening the conduction angle, but never get anywhere close to the sinusoidal waveform.
True, but unfortunately, most PFCs in the market are passive and they only improve the displacement power factor (DPF) by widening the conduction angle, but never get anywhere close to the sinusoidal waveform.
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I disagree with your assertion that an EMI filter is a one-way deal. A CLC style EMI filter absorbs EMI on both sides. That is the most-common type of line filter.
More common AC power line problems are:
1] Switch turn On/Off clicks & pops.
2] Failing hardware arcs & sparks.
Well designed audio components should be able to deal with steady state conducted noise.
1] Switch turn On/Off clicks & pops.
2] Failing hardware arcs & sparks.
Well designed audio components should be able to deal with steady state conducted noise.