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Old 15th September 2014, 11:58 AM   #1
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Default buzz when connecting projector/laptop/amp

Hi all,
I've just moved into a new house, and to my surprise, my partner suggested a projector for the lounge instead of a TV. Moving swiftly to take advantage of this moment I found myself with a new projector installed in the lounge.

Firing it up using a laptop as a source I encountered an issue.

laptop -> amp = nobuzz
projector <- laptop -> amp = buzz!
Connection to the projector is via HDMI, and the buzz persisted with two separate amps.

Neither amp has a ground breaker installed, so I assume that what I've got is a ground loop of some kind. I ran an extension cable from the projector to the power board that the amp is on and that appears to have reduced the buzz a smidge.

Whats bugging me is that it's quite the different buzz to the usual ground loop humm. A difference that I am for now putting down to the PSU in the projector putting some noise into the ground, but I'm starting to wonder about long term solutions to the issue and the quality of the wiring in the house...

Any thoughts on why the buzz and how to solve it?
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Old 15th September 2014, 12:46 PM   #2
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Your projector is plugged into a (real) grounded outlet? Other components, all grounded?
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Old 15th September 2014, 01:01 PM   #3
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Yep, thats mandatory for all wall outlets were in oz, and the projector has a 3 pin IEC, so I can only assume that it's earthed correctly.

The laptop has been tried both on mains power and on battery to no difference in buzz. Amps are all made by myself and grounded correctly.

What're you thinking?
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Old 15th September 2014, 01:04 PM   #4
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In my brother's system I've encountered the same problem, everything was fine, until he connected a DVD player to the system, then this strange buzz (no ground loop type) came in..... The problem is (I think), that the filtering system on many switced-mode PSU-s (including almost all PC-s) connect the half of the AC line voltage to the metal case (altough with minimal current) through the Y connected filter part. In this case - if your entire system is NOT connected to a real minimal resistance grounding path- the distorted AC residue shows up in your systems common ground line and gets amplified by the rest of your playback chain.
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Old 15th September 2014, 11:53 PM   #5
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Default Thanks!

Thanks!

I do recall reading about that sort of 'grounding' scheme somewhere before (Rod Elliotts site perhaps?), and that would seem to match the symptoms... however more testing might well be in order. I suppose I could 'scope the ground in the amp and see if that's where the noise is entering the amp.

Dragonweed, thanks for the input; I'll have a play and see if that's the reason.

If it is though, what is the solution?
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Old 16th September 2014, 12:30 AM   #6
Budgie is offline Budgie  United States
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Sounds like a "ground loop" issue. Jensen transformer has an excellent per on avoiding and curing that problem.

Last edited by Budgie; 16th September 2014 at 12:34 AM.
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Old 16th September 2014, 12:41 AM   #7
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When you say your home-made amps are 'grounded correctly' what do you mean? I suspect you do have a ground loop between the projector and your amps. The noise source is primarily going to be the projector which is why your extension cable modification only made the noise slightly better.
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Old 16th September 2014, 09:21 AM   #8
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Quote:
Thanks!

I do recall reading about that sort of 'grounding' scheme somewhere before (Rod Elliotts site perhaps?), and that would seem to match the symptoms... however more testing might well be in order. I suppose I could 'scope the ground in the amp and see if that's where the noise is entering the amp.
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques in the conclusion is the situation dragonweed suggested in a bit more detail...

@abraxalito When I say "correctly grounded" I mean chassis and amp star ground connected to the earth provided by the outlet, and with the speaker posts and rca sockets isolated from the chassis (ie connected appropriately, not the return to the chassis)

@Budgie thanks for the lead on more reading - I'll chase that down when I can.

The solution would appear (for now) to use the optical connection from the set top box or HTPC to the DAC I built a while back. That would indeed break the loop!
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