Karaoke Forums

Hello, When I set up my Mackie sr1530's I get a bad hum. I think it is power related, but not sure. I have tried diff outlets and in some cases the hum get lower.

The hum is a low range hum, it is not to bad but still you hear it bad when the music is low.

Thanks for the help.

Sounds like a ground loop...

Did you make any changes recently to your setup?

BTW, ground loops can be tricky to troubleshoot and most ppl recommend using cables w/ one end of the shield disconnected to resolve the problem but that would require modifying the cable. Fortunately, I haven't had this problem - yet.

Use a prococess of elimination to find the source of the hum. If it is hum caused by an external culprit such as a neon sign transformer a cheapie transistor radio will have the noise and can actually be used to trace the location of the source. Usually a low frequency (power hum) is generated internally but in either case is is important when dealing with low inputs and high power outputs to plug all the units into a grounded outlet with a common ground to all.
Turn the Sr1530's on with no inputs and check for hum (I have had 2 or 3 cases with the Jbl Eon speakers on the inputs with nothing attached and the levels turned up picked up local radio stations) Next try it with the cables hooked up to the speakers but not to the mixer..If clean at this point then the hum is coming out the mixer. In certain cases it is possible to unconnect the shield on one end of the audio cables to break a stubborn ground loop but then they are subject to RFI(picking up music and noy yours)Then the next test is with the mixer hooked up does the hum vary with main level faders? If not then the mixer power supply is probably developing leaky or bad filters. If you are running high input or high output levels it will cause noise but usually background type (frying eggs) Disconnect all inputs to mixer and turn all the levels up... All inputs with nothing coming in should be fully attenuated. It can be a problem but it's nothing like the good old days when we were using tube type stuff with 60 cycle (yes it used to be cycle not hertz) filaments to heat the tubes and great big power supplies to provide all the heat....

You mean in the olden days when 100 watts would do what 1000 watts cant do today. I was in the guitar center last weekend looking at amps and a tube type 100 watt guitar amp goes for over $1000 now can you believe that?!

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I'm Not Dead yet...... But every day Im getting Closer !

Yup.... You got that right Dr D If you powered up a 150 Watt Bogen P A System and and had the speakers to do it you could talk to the people in the next county... At least get their attention and make 'em wonder what was goin on .....

Then at one time when solid state rectifiers came out we started putting in higher voltage filters and replacing the tube rectifiers with solid state top hat rectifiers . This boosted the B+ voltage about 30 - 50-% Then we really started bouncin speakers off the tail gates.. Ahh the good old days...

Most of the time when I get hum..it is usually a grounding issue. And..at least in my case, it is esily solved by getting rid of the ground plug, I plug all my equipment into the same power strip...then plug the power strip into a 3-prong to 2-prong converter then plug it into the wall....works4me

While that does usually work as a VERY temporary fix, it is VERY dangereous to get rid of the ground plug. This was a trick of sound techs years ago but the problem was that people were getting shocked yielding minor burns to death.
There are better and safer ways to eliminate a ground problem.

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I figured someone would say that. ground plugs in most cases are an overkill (pardon the pun). Ground isolation is a tried and true technique.

Ok, but I'd make sure your liability insurance is paid up.

In case you didn't know, it takes very little current to kill someone - less than 1/10 of an amp. I'll stick with isolation boxes, modified cables, troubleshooting, and local grounding points long before I go to removing the ground plug.

The scene in 'The Commitments' when the guitar player gets shocked is not that hard to recreate - even with modern sound equipment.

Tried & true yes - I have done it myself for a night if I don't have the proper piece. It does work, but has it's drawbacks too. This is from experience as well. I played guitar in a band that the soundman dropped the ground plug & my lips hit the mic & I got shocked BIG TIME - still have a scar on my lips.
Ground isolation is a tried & true technique but there are SAFE ways to do it now!!!!
If I got shocked at a karaoke show because of a ground tab being pulled off, trust me, i'd probably own your equipment AFTER the lawsuit!

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There is a product out called the "HUM ELIMINATOR" . I bought mine at the guitar center. Use it on a computer that has a hum when plugged ito a mixer and it does work. I cant tell you a brand name, but Several companies make them. Some of them are optoisolators and dont lift the ground they merely isolate. The system still remains grounded.

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I'm Not Dead yet...... But every day Im getting Closer !

I use a soundblaster mp3 device which is totally usb... converts directly to rca connections. No hum!

It's from Ebtech. I had the web site listed but it was removed, obviously a site to show someone how to safely remove a ground loop hum by not removing the ground tab plug isn't allowed. Anyone want to know the site, PM me! It also explained the dangers of removing the ground prong as well.
Sheesh, don't get that at all!

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I'm glad I saw the URL before it was pulled and bookmarked it. I'm learning and they have a great document on eliminating ground loops.

After working on high voltage equipment in military radar, and having a variety of things happen with grounds were pilled for whatever reason I'm pretty hardcore paranoid about grounding - especially on my audio equipment. I've seen too many things go horribly wrong and people get hurt when grounds are lifted. Thanks but not every company ties chassis, electrical and/or signal ground together. I'll stick to tried and true - AND SAFE.

Ok reading up on this. When I get it right I will post it.

Thx all

okay... you know, I've had enough.

I could understand the problem with hyperlinking... but having either the software or an admin remove urls without the http is just ridiculous!

Phil... this really needs to be explained once and for all. We're trying to help people here.

Two of the biggest interference causing things in a bar environment are neon lights and light dimmers. Keep trying different plugs, several plugs may be on the same circuit (all tied into the same circuit breaker) If the offending item is on that circuit you'll have problems. Try an extension cord to another room if possible. I have 3 seperate 20 amp circuits on our stage, works great! (Oh yea, it helps if your son-in-law is a master electrician)

If your system is hooked into a TV with cable TV, try unhooking the cable that provides the cable TV. That solved the problem for me. It is sometimes a very simple thing that is causing the problem. Maybe this will help. Worth a try at least.

Ok tried some stuff. I hooked the equipment and speakers to another outlet and it seems ok. But most of the noise comes from when I hook up my computers sound card to my mixer. anyone know what to do?

Thx for all the great info