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Old 18th February 2011, 03:05 AM   #1
Roushon is offline Roushon  India
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Default Mains filter for audio equipments

I had this problem with the remote control receiver in my
audio amplifier. It was false triggering whenever the fan
regulator or switches were operated. The thread where
I discussed this problem is here:

Remote control receiver unit problem

Although the problem is not there anymore in my new
home as the wiring and the switches seems to be
better. But the weakness in the remote receiver circuit
is there if there was any. So I decided to add the mains
filter circuit suggested by Mooly in the above thread
from the following site:

Audio Mains Filter DIY | DMS Audio

Now that I am getting the 2mH coils done Aucosticraft
told me to be cautious before adding the filter without
much discussion here.

This is the reason I start this thread to ask the audio
community if adding the filter will harm in any way
to any audio equipment. Although Mooly gave me a
go ahead to add the filter. For convenience the circuit
is attached.

Regards
Roushon
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Old 18th February 2011, 03:50 AM   #2
AEIOU is offline AEIOU  United States
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Why would a mains filter in any way harm your audio equipment?
If anything, you would expect it to help. Along with the circuit you have, I'd add a few MOVs Metallic Oxide Varistors for surge protection.

As long as your audio equipment has fuses, is fused you're good to go.
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Old 18th February 2011, 07:17 AM   #3
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Hey Roushon,

Now I got your exact problem.
1) In other thread you said you are using you will be connecting to the filter to 15V ie the secondary of transformer. If so please connect it to primary of transformer( guess you are not using smps.) Let me know if you are using smps.

if you are using smps I would recommend you to go for small transformer. the core of transformer itself help in suppressing spikes to some extent. as it cannot respond to spikes of small width.

A simple solution would be buy readymade RFI/EMI suppressor from market. there each costs around 250 to 200 Rs. ( where as you are going to get coil wound for 195 Rs each.)

Try using one such filter available in market. that should greatly ease your job.

a simple solution can be using an X2 cap of 100nf parallel with mov close to primary of transformer should be enough in most cases. if you are using metal chassis don't forget to ground it.

now I have a question, if you make rectification how would you check if the solution works ? you have already shifted.

Do let me know for further discussion.

EBF Series
a typical one.... dont forget to add MOV here.
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Old 18th February 2011, 10:16 AM   #4
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Default filter

use this
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Last edited by QSerraTico_Tico; 18th February 2011 at 10:40 AM. Reason: pict too big
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Old 18th February 2011, 11:25 AM   #5
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I agree, buy a screened off the shelf unit. It will be more effective and probably cheaper than you can make one yourself.

I do wonder if the problem is due to radiated emissions though, in which case a mains filter won't help.
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Old 18th February 2011, 12:10 PM   #6
macboy is offline macboy  Canada
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IR receiver modules are extremely sensitive to power supply noise, and will give off spurious signals when noise is present. The power supply to the IR receiver module should be filtered, but much of the time, it is not. All you need is a series resistor (in the 10's to 100's of Ohm range) on the + supply followed by a bypass cap from + to Gnd. The acutal values are not critical because the module uses very little power (usually << 1 mA) and the noise you are filtering is quite high frequency. Check if your amp has such a filter and if not add one.
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Old 18th February 2011, 02:30 PM   #7
Pano is offline Pano  United States
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Great answer Macboy, thanks for that. Goes right to the heart of the matter

As to this question:
Quote:
Originally Posted by Roushon View Post
This is the reason I start this thread to ask the audio community if adding the filter will harm in any way to any audio equipment.
Not harm the equipment, but you may end up with more noise than you started with. Why?

Most line filters present a high impedance path to noise, that's how they keep it out. But that goes both ways, it can keep it in, too. I know, I've measured it. On a device with a noisy power supply it can be quite dramatic. And anything plugged into the filter with the noisy device it will also see all this trapped noise.

Worse case scenario: You have a noise sensitive device like a phono preamp plugged into the same line filter as a very noisy device like a Class-D power amp. The power filter makes it hard for the noise to drain back out the mains so it backs up into the phono preamp. Without the higher impedance path for noise, at least it would have drained away.
Obliviously, you would not want those two devices to share a filter. But the filter can cause more noise on the AC for just a single device, because the noise can't drain well back into the low impedance mains.

Now I know what you are going to say. "The noise is drained off to ground." Well, yes, it "should" be. But often it ain't. Or if it is, it just ends up polluting the ground - the same ground used by other equipment. So you have to be careful and not assume that the filter is automatically going to kill noise. It may, or it may not. Depends on the filter, your equipment and your mains & ground.

My
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Old 18th February 2011, 04:16 PM   #8
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Roushan, Should have asked you before. are you keen on DIY or you are ready for ready buy?
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Old 19th February 2011, 12:07 AM   #9
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Quote:
Originally Posted by AEIOU View Post
Why would a mains filter in any way harm your audio equipment?
If anything, you would expect it to help. Along with the circuit you have, I'd add a few MOVs Metallic Oxide Varistors for surge protection.

As long as your audio equipment has fuses, is fused you're good to go.
Some manufactures of high power amplifiers recommend plugging the amps directly into the wall outlet.

Why, because the filter acts as a series resistor limiting maximum current (this is the simplified version).
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Old 19th February 2011, 12:09 AM   #10
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Jim Brown has several papers on filters.

Audio Systems Group, Inc. Publications
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