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The Magic Cafe Forum Index » » F/X » » DI box/AC conditioner question (0 Likes) Printer Friendly Version

biff_g
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Canada
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The sound system that I've been using consists of two 12" powered speakers and an unpowered mixer.

https://www.carvinguitars.com/products/s......=LM12A-2
https://www.carvinguitars.com/products/s......ct=C844U

The problem is, there is always this hum/white noise that comes out of them. The amount of noise goes up and down with the volume, and it doesn't seem to be associated with any particular channel. I can sometimes reduce it a little bit by plugging into different outlets, but I can never get rid of it completely.

Does it sound like something like a DI box or an AC conditioner might work? Or is there anything else that might help?
ClintonMagus
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Southwestern Southeast
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Is it hum, white noise, or both? I assume that the problem occurs regardless of venue. Does it occur only when the mike or other components are plugged in, or is it constant, regardless of connections?

If the problem is hum with nothing connected, it sounds like there may be a problem with the amp's internal grounding. If you bought it new and you haven't had it very long, I would take it back to the dealer. If nothing else, see if a new one at a dealer has the same problems. Take yours with you and, if there are no problems with the dealer's amp, plug yours into the same outlet, verify that all of your settings are the same as those on the dealer's amp, and see if the problems persist.

In similar situations I have had noise issues if the preamp levels were significantly higher than the "Main" levels.
Things are more like they are today than they've ever been before...
Dan McLean Jr aka, Magic Roadie
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Biff_g (if that is your real name),
Part of what ClintonMagus is saying is that "hum" and "white noise" are words typically used to mean very different noises.

"White noise" is very specific indeed. You can hear it
here
.

"Hum" often refers to something more specifically called "ground hum", and you can hear it here.

There are other possibilities, too, so you probably need to take it to someone who deals with audio electronics, who will probably be able to sort it out for you.

Good luck!
Dan McLean Jr
g0thike
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Bliff,

You got to troubleshoot.

Several things comes to mind that will cause problems:

1) Faulty mixer, hum.
2) Your plugging in a cd/ipod to a microphone input, it will cause hum.
3) Plugging in a microphone into a line (audio) input, hum.
4) Faulty powered speaker, plug them in one at a time.

Connect your components one by one and see which part causes hum.

You might also have to borrow someones mixer.

Without physically being with you in person, this are my guesses.

G0THIKE
biff_g
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Thanks for your help guys. Dan, thanks for the audio samples... I definitely have both white noise and hum. It does occur regardless of venue. I have tried plugging things in one by one, and into different outlets, but it doesn't seem to matter which components I have plugged in, or where/when I plug them in. Even when just a speaker is plugged in the noise is still there, but I called the Carvin tech guys, and they listened to one they had in stock, and apparently that one was like that too.

I thought that I was just going to have to live with the level of noise, but I was just at a school where the noise/hum were almost completely gone!

The guy at Carvin suggested I try an AC conditioner, but it looks like they are thousands of dollars? I'm not sure if I want to spend that much just to try something that might not work. What do you think?
Starrpower
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Goth, could you explain the line input vs. mic input situation?

I have been dealing with hums in my sound system for years. It's usually not bad enough to cause a problem but I can hear it and it is annoying.
g0thike
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Star,

A Line Input would be a connector for audio such as an IPOD, mp3 player, laptop, basically any music signal. You plug the device into the Line In. They are mostly 1/4 and rca plugins.

A Microphone Input is where you connect a microphone to the mixer.

If you connect a ipod or any music signal to a microphone connector you might get problems such as static, hum and so on.

If you can tell me about your set-up I might be able to help with the hum.

G0TH
Eldon
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Virden, IL
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This is just one more thing to try. People have a tendency to set the master gain to high and the channel gains low. Try turning down your master volume and turning up your channel volumes. This will give you a better SNR.
Donald Dunphy
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Victoria, BC, Canada
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I might be out of my leagues giving this advice, but have you considered that it might be a "dirty power" issue?

Something like a Monster Powerbar (to provide "clean power") might be the solution... for only a couple hundred dollars, or less. Look for the ones that isolate each outlet.

More here about "clean power": http://www.monstercable.com/power/Monster_Power.asp

(This could be the same thing as an AC conditioner, just in different terms.)

- Donald

P.S. A few years ago, when I worked PT for The Source by Circuit City (formerly Radio Shack in Canada), we had a bit of training about Monster products, and their power bars which can eliminate "dirty power" problems for home theatres / home stereos. You have to get the right product to do this. You aren't looking for a simple "surge protection" powerbar.
Donald Dunphy is a Victoria Magician, British Columbia, Canada.
miscoes
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Allariz, Spain
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Hello.

A DI box will help you, for instance, when connecting a laptop to an audio system. If is a DI with isolation transformer it will eliminate almost any hum from laptop's power source.

If you're using Ipods or other devices battery powered the DI box will be of little help, otherwise than converting line level to balanced mic inputs.
Dan McLean Jr aka, Magic Roadie
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Hi, biff_g (if that is your real name)!
Rather than spending money on solutions that may or may not be directed at your specific problem(s), I suggest touching base with g0thike, who has graciously offered to help by first trying to get a handle on the specifics of your system, and the specifics of your symptoms.
Cheers!
Dan McLean Jr
FingerlakesFreelance
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Wow! Does this topic catch my eye! I've got a similar problem (for sure it's "white noise" (thanks for the sound sample MagicRoadie!)). I can "hide" it if I keep the master turned down, but then I lose the 'oomph' I need to keep 'em dancin...

In the past I was sometimes able to eliminate it by cycling power to the mixer, but that 'fix' has seemed to stop working.

I'm using the Gemini PMX1600 w/ a PV 500 amp.

Another problem I'm having - I get 'bleed thru' from an iPod or laptop source. Either of these devices will leak through the cross fader selector switch. Only way to 'hide' it is to turn the source output way down, but I need to bring it back up again to match the other sources.

Help?
g0thike
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Finger,

Some of us can provide a possible solution but need more info.

1) Are U connecting the IPOD into the microphone input?

2) Are U switching to line and not phono?

3) Have you tried Gemini Customer Service at 1 (732) 738-9003?
rattman
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Don't know if this helps any - One thing to be aware of is all amplification devices produce a degree of hiss (White Noise). this is very common and usually can be eliminated with a equalizer (unless using powered speakers). White noise levels will depend on the sensitivity of your speakers. IF your speakers have a high sensitivity you will often here the hiss more than lower sensitivity speakers. This type of hiss should normally not be heard from over 20' and when you have the music playing at 'normal' levels.

With all that said you still need to look at each item along the path to rule out any other issue
rattman
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P.S. Always use balanaced cables when you have long runs !
miscoes
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Allariz, Spain
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Hello again.

Should you speak spanish I've put two videos on YouTube explaining the use of DI boxes to avoid hum and noise and to safely interface to theaters sound systems.

Tou can see it at:

http://www.youtube.com/watch?v=WzRKzVQI74o

and

http://www.youtube.com/watch?v=qZa4zgb5JHQ
biff_g
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Canada
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Thanks again to everyone that has contributed to this thread! A few weeks ago I may have discovered the solution to the problem that I was having. I've only used the speakers a couple of times since then, so I don't know for sure, but I haven't had the problem since.

The carvin speakers come with three inputs, an RCA input, a 1/4" instrument input, and an XLR input. When the speakers arrived, the volume for each of the three inputs was in the middle, so I'd always just left them there, except for when I was trying to get rid of the noise. Problem was, I'd always turned the volume for the three up or down together, instead of (DUH!) turning up the one that I was using, and turning down the other two. The hum, which is really more of a buzzing noise, seems to be connected with the 1/4" input, but disappears if I turn it all the way down. I'm hesitant to say 100% for sure that that is the problem (wouldn't want to jinx it!), but it sure seems like it.

As far as the white noise goes, that's been less of a problem as well, but I'm not 100% certain about that either. A guy at one of the music stores I went to explained a bit about the noise floor, and showed me how to set up my mic so that it would be less of a problem. So far so good, although the white noise does seem to be especially venue dependent.

Thanks again!
miscoes
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Ok. So the answer is...

Turn down the volume in the unused channels.

In EVERY audio system, unused channels volume should be set to 0. The input circuit of audio channels is an amplifier that amplifies also hum and noises induced in the input (as if it were an antenna)

So, raise only the volume for the input channel desired and lower for everything else.

In professional devices, you have two volume controls for every channel, a GAIN control and a VOLUME control (and possibly a PAD to attenuate 20-40 dB the input) and is a good practise to set both to 0 if the channel is unused.

I guess you have a balanced (3 wire) cable between mixer XLR outputs and speaker input 1, with line/mic switch in speaker set to line and volume in the middle (to start). Channels 1 and 2 in speaker should be set to 0 and equaliser also to middle position.
Then, in the mixer you should also set to 0 all unused channels and start with equaliser in middle position. Listen to some well known music and try to adjust the system to sound the way you like LOWERING the undesired frequency ranges in the equaliser (opposed to raising frequencies as amateurs always do)
Avoid also "smiling face" setups in graphic equaliser (in the mixing board)

Should you have more questions please, detail the connections you have.
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