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  #1  
Old 08-27-2012, 08:22 PM
shezza shezza is offline
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Default Hum from sound module!

Hi all, when I plug my Yamaha DTX Multi 12 or my Yamaha DTX700 into my combo amp I get a hum from the combo.even when the sound modules are switched off.
BUT when I pull the adaptor lead out off the Multi 12 and the DTX 700 the hum goes!
Any ideas please.
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  #2  
Old 08-27-2012, 08:31 PM
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Garvin Garvin is offline
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Default Re: Hum from sound module!

Sounds like a grounding issue... But being that I am fearful of electricity, I have no idea how to address it.
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  #3  
Old 08-27-2012, 09:15 PM
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skod skod is offline
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Default Re: Hum from sound module!

Either your combo amp or the wall-wart power adaptor has a grounding problem, and there is a ground loop being created through the power supply when you have them all interconnected. This causes fault currents to circulate in the shields of your signal cables, and that shows up as hums in the audio. Wallwarts for audio use almost never have grounding plugs, so my bet is on the combo amp as the source of the problem.

Several possibilities exist for fixing this. First, if the combo amp has a ground switch (or sometimes a "ground lift" switch), try putting it in the opposite position of whatever setting that it is currently in. This is mostly true of guitar amps instead of more modern combo amps, so your amp may not have such a thing- but it is worth a try.

Secondly, and this is a temporary solution only: if your combo amp has a 3-pin (grounding) power plug, you can try "lifting the ground" by using a 3-pin to 2-pin adaptor at the power outlet. This leaves you with no safety ground, and as a result is definitely not for long-term use. But it can be very useful for short term fixes, such as at gigs.

Lastly, the _right_ way to fix ground loops (other than opening up the amp and/or wallwart and really locating the problem, which is beyond the scope of a quick posting) is to break the loop by inserting a transformer in the line. This positively fixes the problem by preventing the loop currents from circulating in the first place. In addition to carrying several 3-2 pin adaptors in my gig toolbox, I never leave home without at least one of these: http://www.ebtechaudio.com/hedes.html . These are the Swiss army knife of killing hum loops at gigs: they work brilliantly, and are worth every dime. This lets everything keep its safety ground connection, and is why I advocate it most strongly. Buy one of these once, and you'll probably use it to clean up the PA at every gig you do for the rest of your career...

I have an HE2 permanently installed in the feed from my TD20/DM5/Alesis mixer back to the main board in my studio: There is an intractable problem inside the wallwart for the DM5 that I have never been able to correct. Similarly, a keyboard player I often play with has to use one between his Nord keyboard and his Peavey combo amp: somewhere there is power supply leakage that causes a hum, no matter what he has tried. Very annoying, but very fixable....

The quickie 3-2 power plug adaptor is cheap and easy, but it simply masks a deeper problem. Worth a try, though.
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  #4  
Old 08-28-2012, 02:14 AM
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BacteriumFendYoke BacteriumFendYoke is offline
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Default Re: Hum from sound module!

Personally my first point of call is always to switch the plugs around. It can sometimes eliminate grounding issues but it doesn't always work. Quite often, making sure that you use a 'star' distribution (i.e. everything running from one extension from one plug) can solve the problem because the potential and ground resistance are more likely to be the same if only one source is used. Having the module operating from a separate wall supply can often cause grounding issues.

Transformers are a good solution but cost money. They're not expensive but do usually work very well. I've got two and I use them on both of my systems. They eliminate the problem effectively with minimal setup. They just go in-line in the audio chain; usually on an RCA connector.
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Old 08-28-2012, 04:13 AM
Soupy Soupy is offline
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Default Re: Hum from sound module!

Quote:
Originally Posted by BacteriumFendYoke View Post
Personally my first point of call is always to switch the plugs around. It can sometimes eliminate grounding issues but it doesn't always work. Quite often, making sure that you use a 'star' distribution (i.e. everything running from one extension from one plug) can solve the problem because the potential and ground resistance are more likely to be the same if only one source is used. Having the module operating from a separate wall supply can often cause grounding issues.
I second this. Easy to try as well.

Disconnecting the grounding wire on the amp is bad mojo. The ground is there to prevent you from being electrocuted.
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  #6  
Old 08-31-2012, 08:44 AM
New Tricks New Tricks is offline
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Default Re: Hum from sound module!

My module hummed like a mofo because of a ground loop isue.

I don't comprehend what it means but I know it's real.

You can spend like 80 bucks on a device that will take away the hum or you can spend 99 cents and do what I did.



I've been an electrician for decades and, although the ground wire is there for your safety, I am not a bit concerned. I'd have to be standing barefoot on damp concrete AND there would have to be a fault inside the module for me to get hurt. That chain of events is not going to happen but, if it does, it's my fault and I'll accept responsibility.
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