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Old 20th October 2002, 08:34 PM   #1
biff584 is offline biff584  United States
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Question IEC power filter- EMI/RF- for power amp

I am building a 100 watt stereo power amplifier (the Elliot P3A). I know that it is important to get the purest possible power supply to get good audio quality. I was planning on using an IEC connector for the power cord (like those on the back of computers) - I found a few that include ac EMI/RF power filters. Anyone know if these are a good idea? I was planning on getting a 10amp power filter- doesn't cost much and I figure it won't hurt anything. Any ideas? The filters I'm looking at are at:

http://www.mouser.com/index.cfm?hand...12&pdffile=410

Thanks alot.

Brian Anderson
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Old 20th October 2002, 09:19 PM   #2
jwb is offline jwb  United States
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I always use a corcom filtered IEC input on everything. Gets rid of a fair amount of crap on the mains.
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Old 21st October 2002, 12:17 PM   #3
trwh is offline trwh  United Kingdom
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biff584,

You say you want to use a 10A filter - you should use a filter with a smaller current capacity. I use a 3A filter for a 500VA transformer in my P3A variant amp. The filters with lower current capacities use high value inductors, and generally offer more effective filtering when compared to higher current capacity units of similar cost / size.

Hope this helps,
Tim.
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Old 21st October 2002, 12:30 PM   #4
ALW is offline ALW  United Kingdom
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Default Filters

Personally I feel they ruin the sound when used on power amps, and none work as intended since they all are mismatched when terminated to the mains.

A.
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Old 21st October 2002, 01:57 PM   #5
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Default Cleaning AC

...And what works then? Is there anything that doesn't impair dynamics or whatever, but cleans up AC?

Is there something we can build and be effective?


Carlos
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Old 21st October 2002, 03:36 PM   #6
jwb is offline jwb  United States
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Default Re: Filters

Quote:
Originally posted by ALW
Personally I feel they ruin the sound when used on power amps, and none work as intended since they all are mismatched when terminated to the mains.

A.
Give me a break...

Class A amps, which are all anyone builds around here, draw constant current from the mains. Filtering out the non-60Hz components of the AC input is a good thing. The sound will be much improved, and the noise floor lowered.
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Old 21st October 2002, 03:47 PM   #7
ALW is offline ALW  United Kingdom
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Quote:
Class A amps, which are all anyone builds around here, draw constant current from the mains. Filtering out the non-60Hz components of the AC input is a good thing. The sound will be much improved, and the noise floor lowered.
I bet they don't (draw constant current that is). Unless you're using power factor corrected PSU's, I guarantee they don't!

You're confusing the DC current drain (which at some level will also be non-constant) with the AC power drain which is definitely non-constant.

You could try a simple experiment - try your power amp with different current rating fuses, just temporarily.

If you can hear no difference then there's something wrong, if you can hear a difference, tell me why

The other point is that none of these filters do what is asked of them properly, since they are designed for a 50R line impedance, and mains is never 50R.

Andy.
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Old 21st October 2002, 06:25 PM   #8
ALW is offline ALW  United Kingdom
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Default Another relevant experience

My preamps are class A, and also draw nominally constant current, each circuit is also fed, currently, via an RC filter.

Lowering the impedance of the PSU feeding these circuits improves the sonics dramatically - discuss.

A.
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Old 21st October 2002, 07:49 PM   #9
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Default Re: IEC power filter- EMI/RF- for power amp

Quote:
Originally posted by biff584
I am building a 100 watt stereo power amplifier (the Elliot P3A). I know that it is important to get the purest possible power supply to get good audio quality. I was planning on using an IEC connector for the power cord (like those on the back of computers) - I found a few that include ac EMI/RF power filters. Anyone know if these are a good idea?
Correct me if I'm wrong but isn't the main reason for a input filter to stop generated noise going out in the mains, not to stop incoming noise? Switched power supplies generates much noise therefore you must stop it. These filters also demands functioning protetive earth also.

My advise is to use MuRata filter in strategic places.
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Old 22nd October 2002, 07:29 AM   #10
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I don't want to sound too negative but I think it's better to use sufficient amount of transient suppression instead, VDR's and/or tranzorbs, tranzils plus of course MuRata-filter together with groundplanes.

I don't know if you, Biff584, have "polluted" mains or not. Maybe you have. Here in Sweden there is usually no need for filters because of "dirty" power. We don't have any LW, MW or SW transmitters of stronger sort.
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