Mains filter - made things worse?

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Thermionic Idler
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Mains filter - made things worse?

Post by Thermionic Idler » Mon Dec 16, 2019 11:02 pm

So here's a rather interesting thing that I thought I would share.

I have a Kemp Elektroniks power strip which I've owned for about 10 years or so (this one: http://www.kempelektroniks.nl/en/222/ke ... ower-strip ) which incorporates (allegedly) a noise filter, the details of which I know nothing about (as it's proprietary).

I didn't have enough space to have it in place after we moved recently, so instead I used the Mark Grant power strip I have instead, which doesn't have any kind of filtering - just a good low-impendance hard-wired connection to the mains. (I think it's this one: https://www.markgrantcables.co.uk/uk/ma ... ins-block/ ).

The Mark Grant unfiltered strip was still in use when I connected in the new Beast power amps recenrly - all my sources were connected with it.

Last weekend I reconfigured the rack so that I could get my turntable set up again, and put the Kemp Elektroniks power strip back in circuit with its filtering. I should note that the Beast monoblocks were not connected to it - they were plugged into raw mains, but all my sources (server, DAC and preamp) were powered through the Kemp mains filter.

For a few days, I wondered to myself where all that harshness and congestion had come from. I wondered if something was going wrong with the Beasts. Tonight I took the filtered power strip out of circuit and put the non-filtered strip back. And I got the music back - everything went back to sounding as musical and as good as before.

I would have expected that at the bare minimum, I'd have heard no difference, but it was most interesting that something that was supposed to improve things actually resulted in a backward step, and it wasn't exactly subtle. Has anyone else added something which was supposed to be an improvement but proved to be the exact opposite? Wondering if there’s an unexpected interaction between the filtering and the power supplies or something.
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Re: Mains filter - made things worse?

Post by izzy wizzy » Tue Dec 17, 2019 12:50 pm

I'm sure there are good filters but I don't think it's easy. I've heard some people gain advantage from isolating the digital/computer stuff from the analog stuff. If the filter presents a highish Z to HF rubbish, then maybe it was isolated from the lowish Z mains and so circulated the computer noise into the DAC and other things you had connected to the strip coz no where else to go.

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Re: Mains filter - made things worse?

Post by Wolfgang » Tue Dec 17, 2019 3:06 pm

I only got/get really good results with PS audio power plants.

https://www.psaudio.com/perfectwave-p5-power-plant/

The next best results was with the Furman IT Reference 20 with a huge isolation transformer with high power outlets and balanced ones for less power (ideal for phono section).The Furman also uses some passive filtering but it doesn't affect the power transfer/low impedance. With these units I can also hear a real difference when using high quality power cables.

https://www.furmanpower.com/product/dis ... -REF%2020I

All power strips with passive filters or surge protectors degrade audio quality. It sounds a lot better to use a dedicated power line (10gauge) for the sound system right out of the breaker box without any filtering. Ideally -but I guess that works only with a 120V/2 phases power system like in the US- one would hook up additionally all the "dirty" power consumers (dishwasher, computers, dimmers, etc) on one phase and the "cleaner stuff" on the the phase to which the audio system is connected. This is not just theory, I tried that practically and it really was a big improvement. I still use a dedicated power line with high quality power outlets in addition to the PS audio and Furman.

However, for hindering noise from the audio computer/monitor to be fed back into the power line (despite separate isolated outlets of the Furman/Power Plant) I use in addition simple passive filtering (filters need to be used in reverse direction).

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Re: Mains filter - made things worse?

Post by jack » Tue Dec 17, 2019 6:01 pm

Wolfgang wrote:
Tue Dec 17, 2019 3:06 pm
...All power strips with passive filters or surge protectors degrade audio quality...
That's a very sweeping statement! Very subjective too, I suspect.

My understanding is that standard good quality mains passive line filters, e.g. the Schaffner FN 2080, have an identical forward and reverse transfer function, i.e. they are omni-directional. I've certainly never heard any differences whichever way round they are - I did a lot of work on this when I was doing a load of Tesla coil stuff, and had a load of RF hash around.

As much as anything, the quality of the GND/Earth is significant. Due to the impedance of the outlet wiring, especially if you're on a ring final circuit (ring main), any crap that is put onto the GND by a noisy unit is generally not filtered out and can use that route to get into your HiFi. If you are radially wired, then there should be a "common ground" back at the consumer unit - this makes it harder (but far from impossible) for noise on one circuit to affect another.

An "audio ground" (completely separate ground spike) really does help (measurably so) in cases when the normal ground return is contaminated - I have a separate low-impedance ground for all sensitive kit (not using the normal mains ground from the socket at all), including for the ultra-sensitive test equipment in my lab. Be warned that you must understand fully the earthing arrangements of your property otherwise you may place yourself and others at risk!
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Re: Mains filter - made things worse?

Post by Mike H » Tue Dec 17, 2019 8:36 pm

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Re: Mains filter - made things worse?

Post by mainscablesrus » Tue Dec 17, 2019 8:57 pm

Power amps usually sound best plugged straight into the wall socket in my experience.
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Re: Mains filter - made things worse?

Post by jack » Tue Dec 17, 2019 9:47 pm

mainscablesrus wrote:
Tue Dec 17, 2019 8:57 pm
Power amps usually sound best plugged straight into the wall socket in my experience.
...and yet they may contain a passive filter in the incoming IEC socket and have a massive low pass filter in the form of the transformer.

Just as a thought experiment, why would a mains input filter adversely alter the reproduced sound of an amplifier?
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Re: Mains filter - made things worse?

Post by Wolfgang » Wed Dec 18, 2019 4:39 pm

Just as a thought experiment, why would a mains input filter adversely alter the reproduced sound of an amplifier?
From the PS audio website:
"Traditional power conditioners can only affect a portion of incoming noise and are unable to compensate for over or under voltage. Furthermore, power conditioners raise the impedance of the power going to your system, which can bleach your sound and drain away dynamics. "

PS audio uses different techniques than regular filters in the Dectet Power Center. Might be an interesting alternative to the expensive power plants or cheap mains input filters at still affordable price.

"Filtration is handled through large core high permeability magnetic devices wound with heavy gauge OFC providing both common mode and differential mode filtering you can both measure and hear. Protection is through both microprocessor controlled over/under voltage surge guard and MOV spike that will always make sure your equipment is fully protected."

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Re: Mains filter - made things worse?

Post by jack » Wed Dec 18, 2019 5:31 pm

That sounds like an absolutely standard two-stage mains filter, but with oversized inductors to lower the Rdc. Typically, a 20A good quality filter has an insertion loss of about 15 ohms at DC, so that could be lowered a bit. However, the combination of differential mode and common mode inductors is completely standard.

So, I wonder what else they've done to justify the price? OFC copper is a bit silly as it's almost certain that the wiring to the utility outlet is not OFC, and from the property to the utility company is certainly not.

PSaudio also go on about the "Harvester" - that looks like a pretty standard capacitive filter network (LNE).
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Re: Mains filter - made things worse?

Post by Wolfgang » Wed Dec 18, 2019 6:46 pm

So, I wonder what else they've done to justify the price?
They use hospital grade outlets with isolated ground, separate zones, star wiring "that provides similar benefits to having individual dedicated lines feeding each piece in your high-end audio system."

Don't know how good their "power center" sounds and how much it will improve a system. I just know what the power plants can do to a sound system and that every word they say about it is true.

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Re: Mains filter - made things worse?

Post by chris661 » Sun Dec 22, 2019 11:20 am

Something to consider - most of the equipment that's used in HiFi has a really low power factor. ie, the mains current draw is actually over a very short part of the cycle. Via Fourier, that means it's got a lot of high-frequency components.

Since a power conditioner will present a high impedance at high frequencies, it seems entirely possible that it'll limit (perhaps quite severely) the peaky current draw of most HiFi equipment.

One way to fix that would be to apply PFC to the HiFi gear, meaning it'll draw mains current over the whole cycle. I haven't built an amplifier for years, and likely never will (the Cambridge CXA80 is nice and easy to use at home, and I can't build anything that'll compete with the Powersoft amps), so there'll be some reading to do for anyone that's interested.

Another way to fix the issue is to ditch the power conditioner.

My bet would be that adding the power conditioner would directly affect the rail voltages and PSU ripple in the connected equipment.

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Re: Mains filter - made things worse?

Post by Nick » Sun Dec 22, 2019 2:12 pm

Or just use choke input supplies.
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Re: Mains filter - made things worse?

Post by Neal » Mon Dec 23, 2019 11:16 am

Yup, in MJ book he measured current peaks 5~6 times the stated draw using a cap input supply...
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Re: Mains filter - made things worse?

Post by rowuk » Mon Dec 23, 2019 3:00 pm

I have always wondered what the problem is that those filters are supposed to cure. Could it possibly be that the golden eared engineers that design our kit do not hear the problems? Are typical power supplies on premium gear so primitive that we need filters?

Granted, less is more and if we live in a location with inherently clean AC, why add filters? On the other hand, maybe we DIYourselfers need to figure out what to do with high and low power devices. I would prefer each device to extract clean power and be immune to environmental problems. Surely this is not rocket science. Ferrites, common mode rejectors, optimal caps (not too much or too little), chokes are all available.
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