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DIY: Mains Line/Noise/EMI Filtering

amirm

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#1
This is probably too technical for most people here but if you are into DIY work this is by far the best video I have seen on basics of line filtering. It explains for example why there are multiple capacitors put in parallel. Why different devices like chokes are used, etc. And he does this in a very intuitive way. Nothing like the obscure college classes one takes. Likely even if someone is an engineer, this video would be a great watch for them.


It is a very long video but is reference material on the topic. English is Roger's second language but he does a better job on this than any native English speaker I have seen!

If you are at all an electronic hobbyist or into DIY audio, this is a must watch. As an aside, he is covering this in the context of a power supply for a tube amp!

There are more parts to this video which you can watch but I found this one episode to be all encompassing enough to watch by itself. Click on the Youtube symbol in the above player and then go to his channel for the rest.
 

Speedskater

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#2
Is there any printed documentation? An hour and twenty minute video is rather hard to deal with (alone) on a technical subject. Don't have time today to watch it, but that schematic looks strange.
 

amirm

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No printout. He speaks slow so one way to get through it faster is to go in the settings menu and set the speed to 1.5X.

You can also do as I did which is to watch in three parts/occasions. There are actually independent circuits within that larger circuit and he goes through them in that manner.
 
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#6
I NEED HELP PLEASE !
I recently bought a Rotel RB-990BX amplifier. It will power up, but has no output. It stays in "Protection" mode even without having a load (speakers connected) to it. No fuses have blown. ANY SUGGESTIONS ???
 

NorthSky

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#7

amirm

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#9
I NEED HELP PLEASE !
I recently bought a Rotel RB-990BX amplifier. It will power up, but has no output. It stays in "Protection" mode even without having a load (speakers connected) to it. No fuses have blown. ANY SUGGESTIONS ???
Unfortunately that usually means the output stage is shorted out, producing DC output that causes the protection circuit to kick in. So it would need to be taken to a repair shop.
 

DonH56

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Hmmm... I tend to agree, and wrote a similar but longer response in another thread, perhaps they could be consolidated instead in so many different threads?
 
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#11
I wouldn't recommend people try to build AC main's filters from watching this video just like I wouldn't try to build a Koenigsegg after watching one of their videos. But if you want a DIY option, I have a GB going. It's meant to be about as easy as you can get, but still only meant for those than understand the risks - and I still recommend people that are unsure check in before use.

 

restorer-john

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#12
What about effective DC blocking? I have DC blocking in my Squeeky clean test bench feed filter and the effect on toroids in terms of silence is easily demonstrable.

Our mains is pretty ugly looking these days.
 

DonH56

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#13
What caps do you use for blocking (assuming that's what you are using)?

Curious - Don
 
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#14
DC blockers don't really improve sound unless you had a lot of DC. However if you have DC that's bad, you sure as hell want to get rid of, it's loud when it goes to the transformers.

They use electrolytic capacitors (in a way that doubles their voltage rating using two at a time), but they are slightly more complicated than that. Here's a google image search with several variance in schematic and pics of working ones.

By and large enoise is the worst enemy, but if you got bad DC by all means a DC blocker is going to be your good friend.
 

DonH56

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#15
Thanks, forgot about the diodes to ballast the caps and limit reverse bias. The caps need to handle a lot of current, which usually leads to high-value and physically large components, and the diodes let you get away with low-voltage capacitors. Getting UL approval for something like that could be a challenge.

DC generally causes more problems with toroidal transformers than standard EI types (no field gap in the toroids) and IME tends to be not so much actual DC offset per se but the result of noise and distortion on the lines (often from other things in the house) leading to (causing) a non-zero-mean waveform.
 
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#16
It's unlikely to see UL approval since no large company makes them. Van Alstine makes a "humdinger" or something like that. If I'm not mistaken Bryston uses DC blockers in their amps, but they are CE approved, not UL.
 

Speedskater

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#17
In residential areas, I wonder just what is creating all this DC offset? Is it 24 by 7 all year? Major appliances and HVAC systems don't run all the time. More likely it's high line voltage that makes the transformers unhappy.
 

DonH56

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It's unlikely to see UL approval since no large company makes them. Van Alstine makes a "humdinger" or something like that. If I'm not mistaken Bryston uses DC blockers in their amps, but they are CE approved, not UL.
Emotiva and Furman among others sell power strips/filters that claim to block DC. have not looked for a UL approval sticker (do not have either). Have not seen Frank in ages, and he would not remember me, but another one of those icons like Arnie who was less tolerant of B.S.

In residential areas, I wonder just what is creating all this DC offset? Is it 24 by 7 all year? Major appliances and HVAC systems don't run all the time. More likely it's high line voltage that makes the transformers unhappy.
Maybe... A lot of replacement light sources like CFLs and LEDs, many dimmer circuits, and a lot of the SMPS (switch-mode power supply) units in almost all electrical/electronic stuff these days kick back charge into the line and cause distortion that leads to what can look like DC to a transformer. We live in a rural'ish area and power delivery is not great, but I was surprised at how much noise there was at the wall outlets of a number of places down in the "big city" as well as around home. That said I am not sure I ever saw any impact at the output of the power supply after rectification and filtering, but in several places adding a DC blocking filter did fix some transformer hum. I've forgotten the details, but IIRC the magnitude of common-mode offset needed to induce hum in a toroidal transformer was a lot less than I expected (led to me doing a little more research to find out why).

YMMV - Don
 

Wombat

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