Advice on Ground power supply?

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Advice on Ground power supply?

Post by Pitchfork »

I have the Macbook issue with noise coming from my output, when I have a 2nd DVI monitor plugged in (lots of online problems about this apparently!) as Apple haven't fixed this..

Anyway i have been reading that this noise/hum 'vanishes' if you plug the monitor into a grounded power supply?

I have no real clue as to what this is? I am running from a 4-plug extension with other studio bits plugged in, do they mean plugging directly into the wall?

How do i know if I have a grounded power supply to stop any hum?

Where my setup is now, im running off 4-plug extensions, but at my studio I did have lots of individual plugs fitted, does this make a difference?

Sorry for the ignorance, but I know this is a safety issue, and know this can be dangerous! :?
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Re: Advice on Ground power supply?

Post by TrickyDicky »

Bump anyone?
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Re: Advice on Ground power supply?

Post by ef37a »

Morning P'

Firstly, would this not get more attention in the Mac Music section?

Ok, power strips. Are they all fed from ONE 13A outlet? If not do that.
I know jack of macs. Do the monitors have mains in IEC connectors or are they fed from separate "line lump" power supplies? If the latter and they have a 3 pole mains in (often a clover leaf style, not IEC)you might be able to get an earth free, two pin version.

Things will only become dangerous if you lift earths in mains plugs so DON'T DO THAT!

Dave.
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Re: Advice on Ground power supply?

Post by chris... »

Are you using the Apple powerbrick with:

(A) the stubby plug the plugs directly into a mains socket

or

(B) the 1-2 metre long AC lead connecting powerbrick to mains plug.

Which ever you're currently doing, try the other, and let us know if that helps.

With my MBP, (B) results in the powerbrick having a ground connection, but (A) does not. This does not matter for safety reasons, as it's double-insultated. But perhaps there might be an affect on audio things.

More info in this thread:

http://soundonsound.com/forum/showflat.php?Cat=&Number=782582

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Re: Advice on Ground power supply?

Post by Pitchfork »

I'm using the standard power brick from Apple but with a (B) the 1-2 metre long AC lead connecting powerbrick to mains plug.

Can I disconnect this and plug the actual 'brick' into the power socket?
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Re: Advice on Ground power supply?

Post by chris... »

Yes - if you can find the stubby plug thing that clips onto the powerbrick in place of the mains lead. If it's like mine and others, this will result in the power brick NOT having an earth connection, but I've no idea if this'll help or not.

Its quite tidy, if nothing else...
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Re: Advice on Ground power supply?

Post by Pitchfork »

chris... wrote:Are you using the Apple powerbrick with:

(A) the stubby plug the plugs directly into a mains socket

or

(B) the 1-2 metre long AC lead connecting powerbrick to mains plug.

Which ever you're currently doing, try the other, and let us know if that helps.

Tried the both above and still the same - noise bleeding through when DVI connected to monitor :headbang:
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Re: Advice on Ground power supply?

Post by Pitchfork »

Having moved this around and tried various plugs/leads/grounded etc

I have now noticed that when I unplug my PC Laptop power supply (its a Mac with DVI Monitor going into a PC as a recorder) that the noise vanishes?!

So im really scratching my head, as this noise/Laptop power doesn't happen when there is no DVI connected, now it vanishes when the PC laptop power is removed?

Is there anyway around this? I am running off other plugs, and this thread now being moved to the Mac forum, may need to be moved to the PC forum?! :headbang:
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Re: Advice on Ground power supply?

Post by . . . Delete This User . . . »

ahhhh you have a loop between the PC laptop and the Mac, via the Mac external screen.

A) don't use the PC on PSU

B) if you're connecting over analogue audio, lift the ground off the audio cables on the PC end.

C) if you're connecting over SPDIF, use optical, not coaxial.... OR, get 2 optical/coaxial converters anda really short optical cable, , and out them between the PC and Mac audio devices coaxial SPDIF I/O , so you have no electrical connection....

basically, lift the signal (NOT power) ground between the PC and Mac, and it should be sorted.
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Re: Advice on Ground power supply?

Post by Pitchfork »

Off duty BBQ lighter AKA Idris wrote:ahhhh you have a loop between the PC laptop and the Mac, via the Mac external screen.

A) don't use the PC on PSU

B) if you're connecting over analogue audio, lift the ground off the audio cables on the PC end.

C) if you're connecting over SPDIF, use optical, not coaxial.... OR, get 2 optical/coaxial converters anda really short optical cable, , and out them between the PC and Mac audio devices coaxial SPDIF I/O , so you have no electrical connection....

basically, lift the signal (NOT power) ground between the PC and Mac, and it should be sorted.

Hi, sorry for being thick but not sure on how to "lift the ground off the audio cables"?

So in response to your q's

A. I have to use the PSU on the PC laptop as battery is dead, so it needs to run on power im afraid, so thats a necessity.

B. Not sure on how i do this or what that means?! Sorry for being dense but does it mean lifting the cables up in the air? lol

C. Not connecting via SPDIF

Its an analog out Mac to Analog into USB Soundcard on PC, and I get this noise, so any help on "lifting the ground" would be a big help - i'm already with my spade if that helps? :headbang:
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Re: Advice on Ground power supply?

Post by ef37a »

Pitchfork wrote:Having moved this around and tried various plugs/leads/grounded etc

I have now noticed that when I unplug my PC Laptop power supply (its a Mac with DVI Monitor going into a PC as a recorder) that the noise vanishes?!

So im really scratching my head, as this noise/Laptop power doesn't happen when there is no DVI connected, now it vanishes when the PC laptop power is removed?

Is there anyway around this? I am running off other plugs, and this thread now being moved to the Mac forum, may need to be moved to the PC forum?! :headbang:

Aha! So, the Mighty Mac suffers the same problems as windows laps? You need a power supply that does not have a mains earth connection.

I get the same problem if I run my HP lap' and a fast rack pro then jack the analogue outs into the main pc (my solution cannot be shown here.)

Dave.
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Re: Advice on Ground power supply?

Post by Pitchfork »

ef37a wrote:
Aha! So, the Mighty Mac suffers the same problems as windows laps? You need a power supply that does not have a mains earth connection.

No i do think this is down to the PC Laptops PSU, as removing the Mac power, does nothing, but removing the PC AC power kills the noise

I think its the PC's power supply, and as its an old laptop brick adaptor between standard UK plug and small ac adaptor with cord on other end, im not sure how i remove the ground on this?

Or going by BBQ lighter's post, I need to do this to the "audio" but after much trawling on google, am still no clearer on how exactly to do this with my USB soundcard (Edirol UA25 older version)? :roll:
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