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Old 8th May 2003, 03:48 AM   #1
dxg is offline dxg  Australia
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Default Really bad interference... how to fix?

Hi all.. im new here, so take it easy anyways, on with it...

I have two seperate amps suffering the same problem.
One is LM3876 based, the other is not worth mentioning.

Problem is this: Whenever someone turns on/off the light switch in another room, or whenever someone is turning on the gas stove (its got an inbuilt spark-based lighter, connected to power..) both my amps make a very anoying *click* sound. Sometimes this noise is VERY loud...

The power supplies of the amps are just basic transformer/bridge/capacitor combinations.

I tried running a smaller amp of a power supply that has some voltage regulators, but same thing.

I have also bought an IEC line filter (TSC EMI FILTER 06AE1) seen here: http://www1.jaycar.com.au/productVie...Max=&SUBCATID=
(excuse the long link)

It didn't help.

I also tested a panasonic hifi in my room, and it suffered the same fate.


Everything that was tested was running off my computer (SB Live! 5.1). When i connect earphones to the sound card, there is no noise. Computer has a switching mode PSU, hence its immune to this noise...

Also if I run the the amps off a walkman (isolated from mains...) the same thing happens.

And so i am really confused as to what could be causing this. Ive had someone recommend I use a switching mode power supply, but a) not really keen on building one.. seem kinda complex, b) havent been able to find any schematics for a decent Mains 240VAC -> ± 35VDC

Another thing worth mentioning, amps are NOT in an enclosure of any sort.. havent got around to making/buying one. However I doubt this could be the problem, as turning on the lights in the bathroom (approx 10 meters/30 feet away) has same effect as turning on a lamp 1 foot away.

[Something extra i just checked/observed now whilst writing this]
The stove, and bathroom are on same mains line as the amps/computer

BUT I have another power point in my room, on a seperate mains line. If I run the lamp thats 1 foot away from the amp off the same mains line as the amp, and turn it on and off, i get bad interference. IF however I run the lamp off a seperate mains line, it causes no inteference to the amps at all.

So any ideas?
I dont really want to run amps off other powerpoint due to convinience... however it might have to be done.

Is the mains line somehow stuffed?
Can I add something to the amps power supplies to counter/fix it?

Any help greatly appreciated
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Old 8th May 2003, 07:30 PM   #2
moamps is offline moamps  Croatia
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Hi,

You really put some effort into studying this problem. You have eliminated most of my ideas about its sources, but I still have a few of them left Did you measure voltage fluctuation in the mains outlet when you switched the light on and off? That is, I'm suspecting a bad contact (and high internal resistance) on these main line contacts in the distribution wall rack. Also, are you sure you have the ground point (third contact) on the main outlet properly wired? I'm slightly surprised that the IEC line filter hasn't resulted in any improvement whatsoever.

I'm convinced (like you) that the disturbance comes through the mains line. What type is your power transformer (toroid or EI)? Do you have any snubbers on primary or secondary windings or bridge?

(Too many questions and no answers, sorry)

Regards
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Old 8th May 2003, 08:05 PM   #3
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sounds like the plug is wired backwards..LOL
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Old 8th May 2003, 09:02 PM   #4
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Lightbulb clicks and pops

Hi,
Check if your preamp has not a too high bandwith. Same applies for poweramp. Very often a very simple lowpass filter at the input, comprised of a resistor and/or ferrite bead and a small cap to ground after that, will do wonders.
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Old 8th May 2003, 09:34 PM   #5
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Have you tried to connect a VDR across the mains input?

Use size K10 and bigger, 250 V AC if you have 230 Volt mains voltage or 150 V for 120 V in

(VDR = voltage dependent resistor, varistor)
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Old 8th May 2003, 11:30 PM   #6
dxg is offline dxg  Australia
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moamps:
Voltage fluctuation... how would I measure it?
I'll (try) check the ground point when I get home.
Transformer is EI. No snubbers.

JOE DIRT:
Backwards? you mean it would matter?

Elso Kwak:
lowpass filter at the power input? will investigate...

perandes:
I was actually thinking of adding a varistor in the future, but guess I can try add one now, see if it helps.


Thanks for replies, will try suggestrions and go from there.
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Old 9th May 2003, 07:48 AM   #7
moamps is offline moamps  Croatia
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Quote:
Originally posted by dxg
moamps:
Voltage fluctuation... how would I measure it?
I'll (try) check the ground point when I get home.
Transformer is EI. No snubbers.
Hi,

Measure AC voltage on mains outlet with hand multimeter with and without light switched on. If AC voltage will drop (few volts or more) than check wires and connection of that mains line. Be careful.

Regards
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Old 9th May 2003, 09:18 AM   #8
MadMax is offline MadMax  New Zealand
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You could have bad connection in your mains, if neutral is bad and exsess curant flowing in earthing system could cause funny things to happen, do lights dim exessevly when turning on high load, turning on lights should cause very low volt drop, oven should cause 5% max. AC power is always noisy but normaly caps smooth this out. I dont think your problem is amp, try amp in other outlet with light. Do check outlet connections for losseness and spread contacts. If not sure get electrican to do this, as this stuff bites.
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Old 9th May 2003, 01:49 PM   #9
DRC is offline DRC  United Kingdom
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Exclamation Problem with mains ....

Check the earth continuity, maybe there is a break and you audio gears' ground is floating.
Isolate the supply and check resistance to ground at the distribution point (using a long piece of wire).

Take care - all usual disclaimers apply
Dave
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Old 4th June 2003, 05:51 AM   #10
dxg is offline dxg  Australia
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Ok, a few things I tried:

Connected varistors, and didnt help. Atleast my stuff is somewhat protected now...

I did however try something completely different:
The amp for the front speakers can run of a wide voltage range. So I ran it off a battery. I connected the input to a walkman. At this stage, the amp was completely isolated from the mains.

I still get interference from mains equipment located some 8 meters away.

There is a desk lamp next to the amp, which causes exrteem interference even if the amp is running off batteries. I tried putting a different lamp right next to the amp and switching it on and off, and it caused almost no interference at all.

Its as if the interference is coming from crappy switches, and somehow propogating along the mains, even though the amp is running off batteries. Theres really not much else it could be...

So would building a nice shielded enclosure fix this?


======
Elso Kwak:
Hi,
Check if your preamp has not a too high bandwith. Same applies for poweramp. Very often a very simple lowpass filter at the input, comprised of a resistor and/or ferrite bead and a small cap to ground after that, will do wonders
------
Anyone know of any schematics for this type of filter?
======

======
moamps:
Measure AC voltage on mains outlet with hand multimeter with and without light switched on. If AC voltage will drop (few volts or more) than check wires and connection of that mains line. Be careful.
------
Was going to measure that, but found this disclaimer on my multimeters:
WARNING: This meter must not be connected to high energy sources which have transient voltages greater than 1000V. This includes the 240V mains.

======
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