I'm looking at power entry line filters. Specifically, the Schurter KMF series. They come in a general purpose kind (with both X and 2Y capacitors) and a medical kind that doesn't have the 2Y capacitors (from line, neutral to ground on the "inside" of the filter).
In the medical field, the 2Y capacitors are omitted to eliminate ground current (I believe, correct me if I'm wrong). In audio, one could argue that having the 2Y capacitors would allow the HF line noise would get injected into the system ground, which may be undesirable. But I'm not sure how much this matters - if it's real at all.
Neither type offers that much attenuation at audio frequencies. Some of the best ones have, maybe, 20~25 dB attenuation at 10 kHz. The medical types are generally more expensive but offer worse attenuation above 1 MHz.
So my question is basically, which filter should I choose and why?
~Tom
In the medical field, the 2Y capacitors are omitted to eliminate ground current (I believe, correct me if I'm wrong). In audio, one could argue that having the 2Y capacitors would allow the HF line noise would get injected into the system ground, which may be undesirable. But I'm not sure how much this matters - if it's real at all.
Neither type offers that much attenuation at audio frequencies. Some of the best ones have, maybe, 20~25 dB attenuation at 10 kHz. The medical types are generally more expensive but offer worse attenuation above 1 MHz.
So my question is basically, which filter should I choose and why?
~Tom
Assuming the layout is sane I have never had a problem with a bog standard IEC appliance inlet non medical filter (That said, most of my designs are for balanced line use so a little ground current is not a big deal).
You will find that the higher current ones offer less attenuation, so only go as big as you need.
For valve stuff the real win is generally a transformer with an interwinding screen, far more then the inlet filter.
Dont over think this, a bog standard unit of a couple of amps rating is usually fine.
Regards, Dan.
You will find that the higher current ones offer less attenuation, so only go as big as you need.
For valve stuff the real win is generally a transformer with an interwinding screen, far more then the inlet filter.
Dont over think this, a bog standard unit of a couple of amps rating is usually fine.
Regards, Dan.
what are you trying to filter ?
is the source indeed the line ?
all to many times people are trying to apply line filters to remedy noise sources that aren't coming for the AC line at all
is the source indeed the line ?
all to many times people are trying to apply line filters to remedy noise sources that aren't coming for the AC line at all
You are absolutely right. If the device does not produce garbage to the powering line, and does not need to be certified, Y-caps have to be eliminated. Otherwise when you connect to the setup the device that creates such garbage, and has Y-caps, your filter will cause garbage currents through the ground loop. Typical example is using computers (especially notebooks) in recording studio, frequent topic on gearslutz.com forum.
That is a very good and relevant question, actually. My amp works well without the filter. I'm not trying to address a specific issue. The only thing I've noticed is that sometimes HF switching noise from the fridge, thermostat, etc. will cause an audible 'click' in the speakers. It would be nice to get that out of there, but I can't prove that it enters via the mains.
Part of my desire to use a filter is that I'm designing an amp with about $800 worth of iron in it so the cost of a $20 mains filter kinda pales in comparison. Filtering mains noise out before it enters the amp just seems like a good idea.
So in that scenario you get a voltage differential between the source and the load from the noise current running in the ground loop? Am I understanding you correctly?
~Tom
wavebourn
are you talking about using the laptop as a controller or as an audio source?
because either circumstance must be approached differently
are you talking about using the laptop as a controller or as an audio source?
because either circumstance must be approached differently
I am talking about laptop that has battery charger that produces garbage current in the ground wire from it's ground wire connected to some other equipment and the ground in the outlet. But if that "some other equipment" does not have "Y-caps" there is no current. If it does have, there is garbage in the ground loop.
Simply put: if your equipment does not produce garbage avoid Y-caps. They are not for you. They are for those who needs to get certificate for their equipment.
Simply put: if your equipment does not produce garbage avoid Y-caps. They are not for you. They are for those who needs to get certificate for their equipment.
tomchr
emi sources are a b---- aren't they in the days of old when tube amp where invented many an engineer and tech where driven to near madness by such sources.in your case without knowing what amp we are dealing with either magnetic sheilding or applying the right value caps on suppresor grids to eliminate hf noise or both may be needed
let's not forget that tubes where developed for radios and can have wider bandwidth's than we realize even though we're only running audio through them!
emi sources are a b---- aren't they in the days of old when tube amp where invented many an engineer and tech where driven to near madness by such sources.in your case without knowing what amp we are dealing with either magnetic sheilding or applying the right value caps on suppresor grids to eliminate hf noise or both may be needed
let's not forget that tubes where developed for radios and can have wider bandwidth's than we realize even though we're only running audio through them!
wavebourn
i think you should acquaint yourself with isolation transformers or wideband opto isolators
i think you should acquaint yourself with isolation transformers or wideband opto isolators
Try these. At least the price is right. I got some and added one to an SSE. It quiets the noise generated by plugging an electric drill into the same power strip as the SSE. Doesn't totally kill it, but drops about 10db.
The power strip makes things worse. There is almost no noise when both are plugged into the wall outlet. The inlet filter kills the remaining noise in this case. The green wire should go directly to the star ground point, which is where the red/yellow wire on the power transformer enters the PC board on the SSE.
SALE! - SAE EMI Filter 115/250VAC 3Amp STE8-3-The Electronic Goldmine
The power strip makes things worse. There is almost no noise when both are plugged into the wall outlet. The inlet filter kills the remaining noise in this case. The green wire should go directly to the star ground point, which is where the red/yellow wire on the power transformer enters the PC board on the SSE.
SALE! - SAE EMI Filter 115/250VAC 3Amp STE8-3-The Electronic Goldmine
Thank you; in the 2'nd part of the last century I've acquainted myself with "common wire" approach instead of a "ground" term. It helps. When speaking of "ground" imagine a "common wire" that passes currents, often "common", and has own resistance and inductance.
Wouldn't an isolation transformer be redundant? The amplifier already has an "isolation transformer" with its primary and secondary windings.
Right.
If it has a shield between them it has some kind of "Y-Caps" equivalent. But if fields caused by own rectifying diodes dominate it can be a pus. Each case is different, and has to be calculated. But usage of standard filters where they are not needed causes more harm.
wavebourn
just to make sure where on the the same page the isolation x-former i'm talking about isn't on the power line it's used on the audio line. the situation you mentioned earlier about laptops in a studio or any unbalanced line level sources interconnected can become grief
power ground and audio ground are not always the same
i don't know if you've come across any power amps that have provisions for removable ground straps to isolate power and audio grounds
the other common term for the kind of transformers i am talking about are repeat coils
the other place you would encounter these is in splitter snakes ei foh and monitor fantails
just to make sure where on the the same page the isolation x-former i'm talking about isn't on the power line it's used on the audio line. the situation you mentioned earlier about laptops in a studio or any unbalanced line level sources interconnected can become grief
power ground and audio ground are not always the same
i don't know if you've come across any power amps that have provisions for removable ground straps to isolate power and audio grounds
the other common term for the kind of transformers i am talking about are repeat coils
the other place you would encounter these is in splitter snakes ei foh and monitor fantails
What do you mean, is not called an isolation transformer. It is a line-matching transformer, with symmetrical in, or out. It is a great thing. However, it ruins the sound, but the less it ruins, the more expensive it is.
well if you don't like x-formers what are your thoughts on wide band opto isolators.
my apologies to tomchr for absconding his thread
my apologies to tomchr for absconding his thread
It's always best to isolate noise at source - especially domestic noises such as motors, fridges, which can be noticed by not just the one hi-fi rig. Eg. spend the effort putting a temporary line filter to a suspect item (fridge). Have two in-line filters - one for Line-Neutral, and one for Line/Neutral to earth filtering - so that you can diagnose main problem, and then perhaps deploy an appropriate fixed filter in to problem equipment.
Wavebourne's initial issue is similar to adding line harmonic filters in industrial environments - they act as a 'magnet' to draw currents from any other unrelated equipment in to the part you're trying to alleviate harmonics into/out of.
Wavebourne's initial issue is similar to adding line harmonic filters in industrial environments - they act as a 'magnet' to draw currents from any other unrelated equipment in to the part you're trying to alleviate harmonics into/out of.
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