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-   -   Mains Noise Suppression (http://www.diyaudio.com/forums/everything-else/851-mains-noise-suppression.html)

Seeker 2nd October 2001 09:08 AM

Hi I'm having a real problem with whitegoods appliances putting noise (spikes/pops) on the mains and it being reproduced on my HiFi. Does anyone have a solution? Thanks for any help you can give!

GRollins 5th October 2001 06:02 AM

Spikes and pops, huh?
You can approach the problem from any number of directions. It may take a combination of things to get the noise under control. A couple of things occur to me off the top of my head:
--There have been at least two threads where we were talking about various strategies for filtering noise from the AC lines. You might want to look those up.
--Your system might be on the same circuit breaker as the noise-producing equipment. Try putting your system on an outlet that you know to be on a different circuit breaker. In particular, there's a trick that works for 120V AC lines--switch to an AC line that comes from the *other* side of the incoming 240V, as all the 120V lines on that side of the AC may be polluted by the hash.
--Indulge in a little fiddle factor on the power supply in your system. More capacitance in the main bank. Regulated rails. Small capacitors (.01-.1 uF) across the AC line before and/or after the power transformer.
Experiment a bit with some of the cheaper options, then proceed in whatever direction seems most promising.

Grey

Geoff 5th October 2001 11:51 AM

Seeker

Grey is right in his response about minimising the pick-up of mains borne noise. However, you should also consider eradicating it at source as far as possible. The main culprits are switches and thermostats on things like fridges and central heating systems. The noise generated when the contacts make or break can be suppressed fairly easily if you can get access to the switch/'stat terminals, by wiring a contact suppressor across the contacts.

The contact suppressor can be purchased as a single device or can be made from a 120ohm resistor in series with a 0.1uF capacitor. If you make your own, ensure that the capacitor has a suitable voltage rating. The switch/'stat will be handling mains voltages so the capacitor must be rated for an rms voltage at least equal to your mains voltage (there are special types designed specifically for this purpose). Also ensure that all connections (eg capacitor to resistor) are insulated and cannot make inadvertant contact with any earthed metalwork. If in doubt, employ a qualified electrician to do the work for you.

In particularly difficult cases, a VDR (voltage dependant resistor) in parallel with the contact suppressor may be needed.

Geoff


tinitus 23rd July 2010 02:50 AM

Hey, I need mains filters on my PC components

My hifi is picking up noise through mains
I have tried a "hifi" mains filter on my PC, and it helped
But that filter burned a while ago
Since then I have wound my PC mains wire on a small toroid core
It helps too, but not enough

I want to BUY some small simple filters
And not too expencive

Any suggestions which, and where (EU) ?

Or are there other options, like those to put on signal interconnects etc ?

Any experiences what really works here ?

Brian Oshman 23rd July 2010 03:02 AM

Ensure that your neutral conductor is properly connected all the way out to the service entrance and transformer.

tinitus 24th July 2010 12:12 AM

We only have 2pin connectors here
Im not sure its even allowed to do what you suggest

gootee 24th July 2010 04:02 AM

If your system is solid state, the pops and cracks are probably from the broadband RF burst (from switch or relay opening or closing) getting rectified by some p-n junctions. While eliminating or mitigating the problem at its source might be best, you could also try a simple low-pass RC filter on each audio input, with a cutoff frequency of 200-300 kHz or so. To come up with the simple filters, see my two posts at http://www.diyaudio.com/forums/pass-...ml#post2228277 . Also see point number three in my post at http://www.diyaudio.com/forums/chip-...ml#post2245928 . If your power amplifier doesn't already have such filters, they should be installed in any case, probably as close to the first amplifier components as possible. If the bursts are getting in through the DC power rails, you might have to experiment with different decoupling/bypass capacitors, and possibly an additional small series resistance or a series inductance, depending on what stage is being affected most (small signal or large).

tinitus 24th July 2010 04:05 AM

hey gootee, please note that I have used a VERY old thread

not too clever that I did, it seems

jean-paul 24th July 2010 06:32 AM

Quote:

Originally Posted by tinitus (Post 2252329)
We only have 2pin connectors here
Im not sure its even allowed to do what you suggest

No wonder that you have/had noise problems. What you do is not allowed and the suggestion to check the earth/ground connection is the right one ( except that is was called neutral by Brian which is not the correct name ). All computer power supplies are designed with a noise filter in them so no need for an extra filter. They do need safety earth/ground for filtering and safety. That is why all normal computer power supplies use the euro 3 pin connector with safety ground/earth and that is why a 3 pin euro cable with safety earth/ground contacts is supplied. Standard 3 pin connectors with safety ground should always be used in 3 pin "earthed" wall outlets. That way a connection from the computers safety ground/earth will be made to the safety ground/earth of the domestic installation that is properly "earthed" as described by law.

If you use any desktop computer unearthed you will not only have noise problems in for example your sound card but the computer will pollute the mains too because of its SMPS. And if you touch the metal case you will "feel electricity" or you will even experience a shock when touched with moist hands as it will carry half the mains voltage because of the resistors/caps in the mains filter connected from L and N to the (now not to safety ground connected) earth connection + case. Please check up how mains filters work, they do need an earth/ground connection to loose the noise to.

Only devices that have 2 pin connectors from the factory don't need safety earth/ground. These are nowadays so called "double insulated" devices. This system is often misunderstood in various european countries that insist every mains connected device should be "earthed" but this is not the case as the device is double insulated. The requirements can all be found on the web.

Some problems aren't problems but just severe user errors that start simple from an ignorant action but often cause problems later. Just connect the gear as it should be connected and it will be safe and the noise problem will be gone.

AndrewT 24th July 2010 09:32 AM

Quote:

Originally Posted by tinitus (Post 2251290)
I need mains filters on my PC components

My hifi is picking up noise through mains

Quote:

Originally Posted by tinitus (Post 2252329)
We only have 2pin connectors here

Quote:

Originally Posted by jean-paul (Post 2252471)
connect the gear as it should be connected

All 2pin double insulated equipment must never be converted to use the third pin Protective Earth (PE) for extra safety nor filtering.

All 3pin equipment must use a 3pin mains connection with the third wire (PE) and must never be modified to remove that PE purpose.

It is always better to reduce interference at source, i.e. in the fridge/washing machine/"Hoover"/in the workshop.


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