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Hum depending on the power outlet!? 
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Author Hum depending on the power outlet!?
e-grad
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PostPosted: Sat Mar 15, 2014 1:50 pm    Post subject: Hum depending on the power outlet!? Reply with quote Add User to Ignore List

I just swapped a PSU on one of my racks. If I plug it into the same multiple socket outlet like (most) of my other racks there's a hum. A rather loud hum.

If I plug it into a different power outlet there's no hum. I used to think that it rather reduces any hum if one the same socket outlet would be used.

What might introduces such a servere humming?

I'm using a Power One psu and a Blacet PSCONN as distribution board
http://www.blacet.com/PS500PSCONN2manual.pdf

These boards have to 2 different rows of com which are not connected. However my modules do not support this. On board these 2 independend com rows meet. Thus I wired the PSU to the 15V; -15V and to one of the two rows of com only.

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analogmonster
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PostPosted: Sun Mar 16, 2014 4:47 am    Post subject: Reply with quote Add User to Ignore List

Ground loops can create severe humming. If the humming disappears when you change the power outlet this might be hint for a ground loop between your cabinets.

If I am right you can do the following:

1.) Keep it as it is now: use different outlets.

2.) If that is not practical check whether there are connections between module side ground (after the transformer) and ground of your wall outlets (before the tramsformer). Try to establish or cut that connection within both or on one of the PSUs. But be careful, always obey all security issues concerning 220V or 110V.
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Graham Hinton
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PostPosted: Sun Mar 16, 2014 6:08 am    Post subject: Reply with quote Add User to Ignore List

analogmonster wrote:
Try to establish or cut that connection within both or on one of the PSUs. But be careful, always obey all security issues concerning 220V or 110V.


NEVER cut ground connections! That advice is self contradictory.


e=grad wrote:
If I plug it into a different power outlet there's no hum. I used to think that it rather reduces any hum if one the same socket outlet would be used.

What might introduces such a servere humming?


Lack of proper grounding and an unbalanced monitor amp.

All 0Vs should be connected to mains Earth for safety. Check that by measuring continuity between the Earth connection on the mains lead and the screen of a jack lead plugged into a module. Do not have the rack patched to anything else.

Visually check that there is a mains Earth wire coming from the mains cord or inlet connected to the PSU 0V outputs. This should be green/yellow striped. Check that the mains lead is three wire and not two wire. All your equipment should be using the new CEE 7/7 plugs and not the older 7/4 "Schuko" plug or 2-pin 7/16 "Europlug".

Check that all mains outlets have a proper Earth. Either use an outlet tester or get a qualified electrician to look at it.

Why do questions like this always say that there is a humming without ever mentioning where the humming is coming from and then go straight in voodoo?

Obviously the humming is coming from loudspeakers so details on the monitor amplifier and how it is patched are essential for a correct diagnosis. Is the amplifier Earthed? Is the amplifier input balanced or unbalanced? What is the signal path to the amplifier? Is there a mains powered mixer? Is there a hum on its headphones outputs? What power leads are in use to your modules? Are they 3- or 4-wire?

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e-grad
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PostPosted: Sun Mar 16, 2014 7:48 am    Post subject: Reply with quote Add User to Ignore List

Thank you so much.

Graham Hinton wrote:
All 0Vs should be connected to mains Earth for safety. Check that by measuring continuity between the Earth connection on the mains lead and the screen of a jack lead plugged into a module. Do not have the rack patched to anything else.


That’s fine.

Graham Hinton wrote:
Visually check that there is a mains Earth wire coming from the mains cord or inlet connected to the PSU 0V outputs. This should be green/yellow striped. Check that the mains lead is three wire and not two wire. All your equipment should be using the new CEE 7/7 plugs and not the older 7/4 "Schuko" plug or 2-pin 7/16 "Europlug".

Check that all mains outlets have a proper Earth. Either use an outlet tester or get a qualified electrician to look at it.


For the particular rack in question anything as suggested.

I’m going to check this for my other racks later this month. Hopefully next weekend.

Graham Hinton wrote:

Why do questions like this always say that there is a humming without ever mentioning where the humming is coming from and then go straight in voodoo?


Since it was fine before I’ve changed the PSU I suspected the wiring and/or power distribution of the new PSU to be the culprit. However, this might be a naive approach.

Graham Hinton wrote:
Is the amplifier Earthed? Is the amplifier input balanced or unbalanced? What is the signal path to the amplifier? Is there a mains powered mixer? Is there a hum on its headphones outputs? What power leads are in use to your modules? Are they 3- or 4-wire?


Synth => unbalanced connectors to Interface (Hammerfall DSP Multiface) => Soundcard (Notebook) => back to Interface => unbalanced connectors to Adam Sub7 => balanced connectors to two Adam A3X.

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PrimateSynthesis
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PostPosted: Sun Mar 16, 2014 11:50 am    Post subject: Reply with quote Add User to Ignore List

I know I've posted this on the internet at least a hundred times in the last 20 years, but test the outlets.

Test the outlets before setting up a studio.

Test the outlets before setting up a PA.

Test the outlets before playing live.

Test the outlets before setting up a home stereo/theatre.

Even professional electricians make mistakes. Breaker boxes fail. Metals corrode. Rats chew wire.

So test the fucking outlets.

Dead Banana

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Graham Hinton
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PostPosted: Sun Mar 16, 2014 3:06 pm    Post subject: Reply with quote Add User to Ignore List

e-grad wrote:

Graham Hinton wrote:
Is the amplifier Earthed? Is the amplifier input balanced or unbalanced? What is the signal path to the amplifier? Is there a mains powered mixer? Is there a hum on its headphones outputs? What power leads are in use to your modules? Are they 3- or 4-wire?



That was meant to say: Are they 2-wire or 3-wire?

Quote:

Synth => unbalanced connectors to Interface (Hammerfall DSP Multiface) => Soundcard (Notebook) => back to Interface => unbalanced connectors to Adam Sub7 => balanced connectors to two Adam A3X.


Blimey! I'm surprised it ever didn't hum!

You are connecting a non-grounded interface and computer unbalanced to both monitor system and synth. Look at the PSU for the Multiface. Consumer grade figure of eight mains connector to external PSU with dc plug means no Earth. So the interface grounding is dependent on what it is connected to, which is completely wrong.

The Adam stuff has IEC inlets so should be grounded, but you should be connecting to them with TRS to XLR balanced cables cables. You should do that first even if the hum doesn't go away. Then make sure that the synth 0v is grounded like I said before and then make connections to the interface with TS to TRS balanced cables with the cold and screen connected inside the TS plug (not the TRS end). That will most likely fix your problem, but come back and say if it does or doesn't.

And do take the above advice and test your outlets. There are two issues here: safety and signal 0V common reference. Both should be done properly and neither are optional. At the moment you have neither.

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e-grad
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PostPosted: Mon Mar 17, 2014 10:51 am    Post subject: Reply with quote Add User to Ignore List

Thanks! That was food for thought.

Pls note my nick e-grad does not refer to a grad in EE - it's not even English. For the time being I've no idea how to test my outlets properly.

I will try to make good use of any advice given, however, this will be a long term project. Yet, I'll do my very best to upgrade my connectors and wiring.

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PrimateSynthesis
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PostPosted: Mon Mar 17, 2014 4:01 pm    Post subject: Reply with quote Add User to Ignore List

e-grad wrote:

Pls note my nick e-grad does not refer to a grad in EE - it's not even English. For the time being I've no idea how to test my outlets properly.


While I know little about European standards, I'm quite sure that there is a hardware store or electrical supplier that sells receptacle testers for your country.

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e-grad
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PostPosted: Tue Mar 18, 2014 5:51 am    Post subject: Reply with quote Add User to Ignore List

PrimateSynthesis wrote:
I'm quite sure that there is a hardware store or electrical supplier that sells receptacle testers for your country.


Sure, however I'm not so sure whether I'd use them appropriatley.

Mind you, I've even found an outlet tester for some 20Euro (28USD). However, a quick search on the net reveals that the electronic wizards think it an useless toy.


For sure there's a market for testing devices:


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