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Old 31st March 2013, 08:01 PM   #1
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Default AC Line Filter

I am considering adding AC line filter in my CD player and tube amps.
The one I have in mind is Corcom 3EAH1. See picture.

I got the idea from this thread:
heater wiring - the Good the Bad and the Ugly

What are the pros and cons of this device ?

Are there better options ?
Attached Images
File Type: jpg 3EAH1.jpg (83.2 KB, 308 views)

Last edited by HP8903B; 31st March 2013 at 08:24 PM.
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Old 31st March 2013, 08:21 PM   #2
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Corcom was used in a lot of industrial machinery (Woodman bagging machines) and test equipment, so unless the brand name has new owners after a fast buck, they should be industrial strength.
I have had trouble with lamp dimmer hash and driveby CB radios in an op amp mixer, but not my tube preamp or amp. Something about the heavy 60 hz iron power transformer, and the double steel box, perhaps. One steel box around AC wiring, another around the signal parts. Small disc capacitors to ground on inputs don't hurt, either. Your results may vary. It is all in the details of the design.
The only thing that got into the dynakit stuff was the Navy Extra Low Frequency communication, back when. Beep Boop Bupp. Beep Boop Bupp. I wonder if they still do that, now that they have satellite downlinks.
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Last edited by indianajo; 31st March 2013 at 08:23 PM.
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Old 31st March 2013, 11:35 PM   #3
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Just remember that those filters are only good for HF and above. Below 1MHz the attenuation drops off rapidly.
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Old 31st March 2013, 11:42 PM   #4
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I have used those very same Corcom units in several projects and always with good results. It has just become my standard practice now. Usually whenever I see an old computer on the curb I will snag it and keep only the fans and those nifty Corcoms. (The small CPU fans are perfect to put directly on a power trafo for a little quiet air flow.)
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Old 1st April 2013, 02:31 AM   #5
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What are the disadvantages of this device ?

Does it degrade the sound ?

What are the benefits of this device ?
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Old 1st April 2013, 03:30 AM   #6
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Your sound doesn't run on 1 mhz power. It runs on 60 hz. That is if it has a 60 hz transformer. Corcom filter out the 1 mhz and above, on your 60 hz entry. IMHO if your amp has a switcher supply, the design could have to be more advanced. I've never seen a switcher supply with one of these in it, not even in an Ishida weigher. Of course the wizards of the orient would never use anything designed in the USA, except to make the prototype work.
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Old 1st April 2013, 04:04 AM   #7
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Quote:
Originally Posted by HP8903B View Post

What are the disadvantages of this device ?
The disadvantage is that it is physically larger than an IEC connector without the filter. In a tight box, that could be a problem.

Quote:
Originally Posted by HP8903B View Post

Does it degrade the sound ?
The power-line filter itself should have no direct effect on the sound. As pointed out up-thread, the power transformer is a magnificent filter on conducted noise (which the Corcomm filter is also designed to block).

Quote:
Originally Posted by HP8903B View Post

What are the benefits of this device ?
The benefit is that it will keep high-frequency energy from entering your amplifier box. If you are using a metal chassis with a metal bottom plate, you have a good shielded enclosure that prevents stray radiation from getting into your circuitry.

However, if RF energy is conducted into the amplifier chassis enclosure on the power lines, it can (and likely will) re-radiate into other wires inside the box and cause mischief. Remember, many of the tubes used in audio amplifiers have gain well into the VHF and UHF spectrum, and RF energy (from a local radio station, for instance) can easily create intermodulation noise or (worse) be detected. AM radio stations are particularly nasty, if you live in the vicinity of the transmitter...

In general, the Corcomm will help block RF energy (>1MHz) from getting into your box on the power-main lines. Same idea with putting small capacitors directly to the chassis on the input/output audio lines to keep unwanted RF energy from getting into the enclosure.

You may not need a filtered power-entry module, but on the other hand if you have room for it it will certainly keep unwanted high-frequency noise out of your box.

Hope this helps a bit.

~ Sam
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Old 1st April 2013, 04:12 AM   #8
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BTW - for the case of a switching power supply, especially the offline switchers used in computer power supplies, the filtered IEC connector keeps noise from getting out of the enclosure!

This is important to keep radiation from a device from interfering with other pieces of equipment, and is usually required to secure government agency approval of a particular device.

Since we don't worry about government approval of our DIY amps (well, usually ), this isn't an argument for using the filtered connectors. And for the tube amplifiers in particular, switching power supplies are not common (although they are showing up with greater frequency in new designs).

But if your amplifier is messing with TV programs your significant-other is trying to watch, maybe it's cheap insurance to maintain a peaceful home?
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Old 1st April 2013, 06:15 AM   #9
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Thank you guys for the input.
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Old 4th April 2013, 01:15 AM   #10
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More than everything you need to know about AC filters.

'RFI, Ferrites, and Common Mode Chokes For Hams'
http://www.audiosystemsgroup.com/RFI-Ham.pdf

Don't let the title fool you! Jim Brown is the AES committee chair on EMI/RFI.
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