Annoying Hum

[greatracks 0]

hello guys.................

need your help again!. sure one of you experts can come up with something (hopefully!).

i have an annoying hum coming out of my speakers. as soon as i turn power on on the amp it hums through speakers even without turning amp volume up. can i add it even hums without mixer and laptop connected. this has been happening for a couple of weeks now. have even changed amps to no avail, and also tried different speaker cables etc but nothing i can do or nothing i can think of will stop it.......................help!!

[Gary (GDK) 0]

Buy a ground loop isolator!

 

Gary

[greatracks 0]

Buy a ground loop isolator!

 

Gary

 

gary..............

thank you for that. i have one although i have never used it as until a few weeks ago i never had a hum!. i cannot get my head around why it suddenly started humming after being perfect and hum free for over a year!. can you think of any reason why it would start humming all of a sudden?.

mark

[superstardeejay 0]

So what's the least you have connected when it hums? Tell us. With anything like this it's best to start with the basics (just amp and speakers, nothing else) and then add the other bits till the hum starts.

[banginbeats 0]

It will be a problem with the earth somewhere along the line. maybe in the amp or if not, it will be on the socket you are using. mite be worth getting amp re pat tested, just a thought :)

[greatracks 0]

It will be a problem with the earth somewhere along the line. maybe in the amp or if not, it will be on the socket you are using. mite be worth getting amp re pat tested, just a thought :)

 

 

i appreciate your comments. had a brand new 1600 amp in use last night and i have to be honest and say i hardly noticed the hum although it was there.

in response to s/s dj it hums with nothing connected other than amp. laptop and mixer are turned off. ground loop isolator didnt make a deal of difference. will get everything tested and take it from there i guess!.

[Keith 0]

To trace the faulty piece of equipment should be very easy. Do the following: -

 

1.Plug speakers in to amp and power up. If there is a hum check the mains lead and if you have a mains lift switch on amp activate that.

 

2. If no hum plug in mixer and power up. If hum then check leads between mixer and amp ensuring earth is connected.

 

3. If no hum continue plugging in gear until you get the hum.

 

4. Do not plug gear in when testing and leaving turned off and this will give a false test.

 

 

Hope this is of help.

 

PS Sounds like a faulty cable to me

 

Keith

[greatracks 0]

To trace the faulty piece of equipment should be very easy. Do the following: -

 

1.Plug speakers in to amp and power up. If there is a hum check the mains lead and if you have a mains lift switch on amp activate that.

 

2. If no hum plug in mixer and power up. If hum then check leads between mixer and amp ensuring earth is connected.

 

3. If no hum continue plugging in gear until you get the hum.

 

4. Do not plug gear in when testing and leaving turned off and this will give a false test.

Hope this is of help.

 

PS Sounds like a faulty cable to me

 

Keith

 

 

 

keith................

thanks for the advice. dont think its anything serious, but still, its annoying at times!. will check all my cables one by one and take it from there.

mark

[Keith 0]

Did you ever trace the fault?

 

Keith

[supersound dj 0]

I had an annoying hum once.

 

I got rid of the roadie

[Paul's Karaoke 0]

It could be the Power supply to the Laptop. If it has an earth in the Power Plug from the wall to the PSU disconnect it. If its a moulded plug remove it and replace plug with new one and cut the earth back so it isn't in the way.

 

Hope you get it sorted

 

WARNING - Earth conductors are there for a reason, they should NOT be removed.

Edited November 11, 2009 by Dream Catchers

[Keith 0]

It could be the Power supply to the Laptop. If it has an earth in the Power Plug from the wall to the PSU disconnect it. If its a moulded plug remove it and replace plug with new one and cut the earth back so it isn't in the way.

 

Hope you get it sorted

What!!!!!!!!!!!!!!!!!!! Are you really saying what I think. Removing the earth is not only dangerous but irresponsible. Never never remove an earth it is there for a reason.

 

Original post said the hum was there with nothing plugged in so it cannot be the laptop.

 

Keith

 

[vokf 0]

Sorry Paul - I agree with Keith. This is could be dangerous, and if a problem did occur due to this mod, the person who did the mod would be negligent.

 

Some Laptop PSU's are double insulated, so have no earth - but this is by design.

 

 

I've problems today - I needed to isolate an oscilliscope, but would get my ass kicked if I lifted the earth wire and had to find another work around.

 

Jason

 

 

[Dukesy 0]

I never interfere with electrics - not qualified, and wouldn't state as such online either! smile icon

[Keith 0]

I never interfere with electrics - not qualified, and wouldn't state as such online either! smile icon

To be honest I am surprised that the moderators have left the comment on. Hint Hint

 

Keith

[Dukesy 0]

To be honest I am surprised that the moderators have left the comment on. Hint Hint

 

Keith

 

Where have you been????????? Hint Hint

 

Don't have to be Isaac Newton to predict that Halley's Comet passes by more often! :lol2:

 

Call that an astronomically funny if you want! smile icon

 

So how many mods here do you know?!

[Paul's Karaoke 0]

What!!!!!!!!!!!!!!!!!!! Are you really saying what I think. Removing the earth is not only dangerous but irresponsible. Never never remove an earth it is there for a reason.

 

 

Keith

 

A power transformer is a Class 2 unit and does not require an earth to the Insulated Plastic Unit. All new power leads are now only Live and Neutral with a plastic earth prong. Older Laptop Power units were fitted with an earth lead and because the units were a Class 2 unit did not do anything and caused white noise when connected to certain equipment such as Mixers Amplifiers etc which are Class 1 unit's. To combat this effect it is advisable to replace the Power lead with a modern one or if your able to fit plugs remove the earth from the unit. I guess my 3 years as an electronics technician came in handy.

 

You should never remove earth leads from Class 1 units to prevent risk of electrocution. The units have metal housing and must be earthed for electrical safety regulations.

 

If in doubt, Do nowt

[Paul's Karaoke 0]

To be honest I am surprised that the moderators have left the comment on. Hint Hint

 

Keith

 

If someone puts on a comment that is deemed to be wrong then removing the comment would not be helpful.

 

The responses must be advantageous so as to insure that it is noticed. even when a post is wrong then a polite response to highlight their view is adequate. Rather than a rather uneccesary rant. After all are we not supposed to be here to help each other as Professionals

[Dukesy 0]

After all are we not supposed to be here to help each other as Professionals

 

Fair point Paul, but I'm going to have a necessary rant!

 

Appreciate that for many, DJ'ing is a second job / hobby, and that there is more to life than sitting in the comfort of a chair in front of a screen putting a few words together in a space of a couple of minutes when logged on.

 

I sometimes get the impression that DJs would probably prefer teenagers to be hanging around on street corners dealing drugs as long as it didn't encroach on DJU Members' ego's and have to cause them the inconvenience of giving advice when newbies did ask intelligent well thought out questions which deserved a reply from the older role models and self proclaimed professionals.

 

Of course I'm referring to newbie posts going unanswered, or unanswered for l-o-n-g periods of time....it really made my sides split when it was suggested recently about giving something back! Ha ha!

 

Bottom line, there are a lot of lazy oiks in the industry, who don't give a toss about anybody else other than themselves.

[Paul's Karaoke 0]

Good points Dan. I keep forgetting that it's not just Full time and Part Time DJ's. I was Just trying to help, but will think twice in the future what I actually offer as advice.

 

Lesson Learned

 

....it really made my sides split when it was suggested recently about giving something back! Ha ha!

 

 

 

 

Just realised who this was aimed at.....lol :stu:

[Dukesy 0]

Just realised who this was aimed at.....lol :stu:

 

Really?

 

Don't take my general comment / observation personally Paul!

[Paul's Karaoke 0]

Don't take my general comment / observation personally Paul!

 

I'm not Dan....Just making light of it :lol2:

[superstardeejay 0]

A power transformer is a Class 2 unit and does not require an earth to the Insulated Plastic Unit. All new power leads are now only Live and Neutral with a plastic earth prong. Older Laptop Power units were fitted with an earth lead and because the units were a Class 2 unit did not do anything and caused white noise when connected to certain equipment such as Mixers Amplifiers etc which are Class 1 unit's. To combat this effect it is advisable to replace the Power lead with a modern one or if your able to fit plugs remove the earth from the unit. I guess my 3 years as an electronics technician came in handy.

 

Paul, with due respect, what you've said is nonsense, and the advice may endanger the life of anyone following it.

 

Laptop power supplies (PSU's) are just that..power supplies. They arent power transformers. They take the mains, turn it into DC at 345V, apply it to a high frequency chopper oscillating at anywhere between 18-100kHz or so, step it down via a ferrite-cored choke, regulate it via PWM, then rectify and smooth it before putting it out to the laptop.

 

Laptop PSU's sometimes require an earth because their design dictates it for approval in the country of sale. The oscillator can cause HF interference back into the mains (or airborne) which may breach the RFI emissions regs. So heavy filtering is included inside the PSU, part of which involves components connected between the L,N and E conductors of the mains. The filters cause leakage current down the earth lead and back into the wall socket and provide a low-impedance path for any unwanted harmonics emanating from the PSU or indeed from the mains into it. Similar components are often fitted from the low voltage output rail back to the mains earth conductor to remove harmonics before they reach the laptop. It follows that if you remove the earth wire in this case, your laptop low voltage lead will by way of the filter components be connected to the L&N mains supply! In certain cases this can cause the casing of the laptop and anything metal connected to it (mixer, mic, cd player, flightcase) to also be live.

 

As manufacturers strive to make smaller PSUs for laptops, (and yet laptops become increasingly power hungry) so the problems of safe isolation of the high and low voltage components becomes more problematic. Many manufacturers gain approvals for safe isolation not by inserting extra insulation or fresh air between the components (since this takes up room) but by using earthed screening. This usually consists of copper tape or shim, connected to mains earth, and inserted at various points inbetween the PSU components and in many cases actually in between the windings of the switchmode choke. So, removing the mains earth here will negate any safety isolation in the PSU, meaning that in the event of a component failure, (eg..a blown transistor or capacitor) the full mains (or its DC equivalent..remember..345V) may contact your LV output to the laptop and audio equipment. This is not folly, it's reality, many laptop PSU's fail by going bang when something fails inside and the packed conditions in there make safe isolation/insulation/screening very important indeed.

 

Sound system noise generated by a PSU are usually either mains hum ( a low-note hum loop caused by the mains earth forming a loop with another earthed object in your system) or audible harmonics (hissing/warbling) caused by the switchmode action of the PSU circuitry which is being picked up through the low voltage output and into the laptop.

 

So either buy a 2-pin PSU (where the isolation, oscillator frequency and filtering is designed for 2 pin use) or buy a 3-pin PSU and leave the earth in place with a loop isolator... as it WILL NOT BE SAFE IF IT'S CUT OFF.

 

Kevin

 

 

[vokf 0]

^^^^

 

Good tech stuff from Kevin (superstardj).

Been checkout out a very noisy switch mode power supply today (3v3... so not anything too scary!)

 

Probably the best description I've seen for ages. :Thumbup:

 

 

 

[Paul's Karaoke 0]

You obviously know what your talking about Kevin. I understand the points made and accept that I was wrong. As I have said I will think seriously about what I post in the future.

 

A very indepth explanation and deserves credit