Help with hum

[Claude D D]

Hey guys I have a problem when I hook my multi channel input from my Phillips DVD963SA to my Rotel RSP-1066(both have 2 prong IEC plugs).I get a nasty hum.It goes away when I unplug the video souce from my X1 front projo(3 prong IEC plug).
It really sucks because every time I want to listen to a SACD I have to connect all 6 cables to the multi input then unplug the video connection from my X1.Then unplug the multi input cables and reconnect the video connection to watch movies.
I have the DVD963SA connected with a coax digital cable to the Rotel and it is dead silent no hum at all.
Any suggestions??? :?

[ht_addict]

Claude you have a grounding issue similar to what I have with my Rotel RMB-1095. Try disconnecting the digital coax from the DVD to Rotel and see if it stops. If it does get an optical cable to connect the two. This solved my problem when I introduced the 3 prong 1095 into my setup. Then added a sub and it came back. Now I solve the problem by running so TV coax cable from the backk of my pre/pro(FM tunner) to my surge protector coax connection. I get the grounding I need and all is well.

ht_addict

[Claude D D]

Thanks for the input ht_addict but the coax digital input is not the problem.It's dead quite until I connect the multi-channel input then the hum begins.

[ht_addict]

Thanks for the input ht_addict but the coax digital input is not the problem.It's dead quite until I connect the multi-channel input then the hum begins.

But have you tried it? Even though the digital coax is quite maybe when the multi inputs are used the coax is carrying the noise.

ht_addict

[Claude D D]

Hey ht_addict,I see what you're getting at.I'll give it a try on Friday when I have some time.Thanks.

[Claude D D]

No luck still hums even when disconnecting the coax dig from the DVD.Any ideas???

[brucek]

Questions:

1. Are the Rotel and DVD plugged into the same receptacle/power bar?

2. Do you have the same problem when you temporarily use an AC extension cord to power the projector, run over to the same receptacle that the DVD and Rotel are powered from?

3. Do you have the same problem when you temporarily convert the projector to two prong AC with a cheater?

brucek

[Claude D D]

Hey brucek, I've tried running a extension cord to the HTS-5100 that the rest of my gear is plugged into.But it did not help.I don't want to lift the groung off the projo for safety reasons.But I might try it temporarily to see if the hum stops.
Thanks for your reply

[Brandon B]

Is your projector near any fluorescent or dimmmable light fixtures?

BB

[Claude D D]

Florecent No,dimmable Yes.

[Claude D D]

Can I safely lift the ground on my projo?Check link for more info.Thanks.

http://www.htguide.com/CFBoards/index.cfm?fuseaction=Threads.viewthread&Tid=96362&Forum=37&StartRow=1&CFB=1

[brucek]

I have a ground loop hum in my system when I hook up my multi channel outputs from my DVD player to my Rotel RSP-1066(also if I run a s-video cable from my projo to my 1066)
The projo has the 3 prong plug with the ground.When I temporarily plug the projo into an old surge protector with the ground pin broken off the system is silent again,no hum.
The question I have is how dangerous is this to do on a permanent basis? Or is there any safe way to ground the projo internally or other??

Hey Claude,

Yeah, I suspected that the cheater would work.... I'll try and answer your question. Let me clear a few things up first for you on this - try and not fall asleep....

The "third prong" is the electrical safety ground and is there to protect you and anyone who uses your equipment from electrocution. The safety ground is a cold conductor designed to provide a path to ground for safety protection against internal shorts inside your equipment when equipped with the three prong plug.

The third prong connects back to your service panel (where it is bonded to the neutral wire), and from there is connected either or both to your house plumbing or external ground rod.

On equipment with a third prong, the metal case and external metal parts are all connected to this safety ground when you plug the electrical cord into the wall. If a component fails inside a piece of equipment and the 120 volts shorts to the equipments case, then that case is now live and can electrocute you. If the safety ground was attached, then a breaker would trip to indicate you had a fault.

On equipment with two prong plugs, they are internally insulated from the external case to provide this protection without the third wire.

If a device has a two prong power cord, it is not connected to the safety ground in your house.
The two prong plug has a one of the two "blades" of its plug wider than the other. This is the neutral return - not a ground.

If a device, designed for a three prong plug, is modified by removing the safety prong of the plug or by using a cheater (which effectively removes the third prong), then you have created the unsafe condition I mentioned above.

If you have a hum from an amplifier caused by a ground loop, then removing the safety ground connection to amplifier (and perhaps other devices as well), can clear the resultant effect of the ground loop, but creates the safety issue. It's more advisable to try and clear the condition causing the ground loop than to mask its effect by applying unsafe practices.

In that regard though, ground loops are sometimes a difficult task to track down and remove because there are a million reasons for them to exist. The loop is caused by a difference in the ground potentials in your system. Breaking the safety ground almost as often clears the problem, and that is why it goes away with the use of two prong power cords or with the use of cheater plugs. This easy fix is obviously tempting, since it's so easy. I hesitate to say that sometimes it's the only thing in the end that works on some troublesome equipment, ensuring that cheated piece of equipment is hidden away from anyone touching it.

This is likely the situation in your case, where the projector is out of reach on the ceiling (I presume). You also have the (not recommended) secondary safety system that some people rely on and that is the fact that the shield of the interconnects (from the projector to rest of your system) will provide a safety ground effect as long as they remain connected and that the equipment they're hooked to have a third prong. This is generally considered bad practice, because once you remove your interconnects, the safety is broken - but there it is anyway.

Generally a ground loop can be tracked down to its source. Removing the problem can sometimes be a little more difficult.
You have to first ensure you have a ground loop situation and it would appear you've accomplished that.

One of the other major culprits in creating ground loops is the use of more than one circuit in an HT system. The larger systems demand more power, so several dedicated circuits are sometimes needed. But even using a single circuit with different receptacles can cause a ground loop.
Residential houses use 240 volt "single phase" three wire power. The two "hot" legs are 120 volts and are 180 degrees out of phase. The loads in your house are balanced between these two legs at the service panel. It is advisable, if you do have two circuits powering your HT system, to ensure you are using a common leg. It is fairly easy to establish this.

Let me explain a bit about ground loops.......Even though the safety ground is a cold conductor, it can, and usually does, develop a small potential, through mutual inductance, wire resistance and various other reasons that can be different at each receptacle in your house.

When I plug a power amp into one receptacle and a preamp into another receptacle, the metal cases of these two units can have a small potential difference in their safety grounds which means that this equipment's metal cases are at a slightly different potential. When I connect a single ended (RCA) cable between these two devices, a small AC current can flow in the shield because of the potential difference. This signal is in the signal loop circuit and can cause a hum. An interconnect circuit has a loop path (completed circuit) that flows through the centre conductor of the interconnect cable and back on the shield. If there is an AC signal on the shield flowing because of the ground difference potential, you'll hear a hum. Breaking the safety ground of one of the two devices removes the potential and the path for the unwanted signal flow...

Anyway, getting back to your problem. No you won't be harming your projector by using a cheater, but you have created an unsafe condition in the remote chance of an internal electrical fault that the case or external metal parts of the projector became live and the interconnects didn't provide a path to safety....... :roll:

brucek

[Claude D D]

Hey brucek,
Thank you for taking the time to write such a thorough explaination.I see I still have my work cut out for me to find the proper solution.
You should have seen the mess my HT rooms electrical was in when I started.( 2 recepticals had hot neutrals and my fridge was on the same circut,what a mess).Taking care of those two issuses and adding a Monster HTS5100 helped noticably lower the noise floor in my system.
I would have thought the problem would have dissappeared when I tried plugging my projo into the HTS5100 that the rest of my system is plugged into.But it didn't.
Oh well.What's a guy to do?Would a balanced power supply like the Monster HTS7000 help?

[brucek]

You should have seen the mess my HT rooms electrical was in when I started.( 2 recepticals had hot neutrals

Mmmm..that's bad. Are you sure you've got all that squared away now? and there is still nothing 'funny' in the wiring?

Is there any chance of installing a dedicated circuit to your HT area.....It can help a lot.

Yeah, the balanced power unit will likely clear all this up, but they're expensive...You might look at BPT for a better price.

I guess you've seen this thread?

http://www.htguide.com/CFBoards/index.cfm?fuseaction=Threads.viewthread&Tid=89974&Forum=6&StartRow=1&CFB=1

brucek

[Claude D D]

Yeah a dedicated circuit might be the answer.It wouldn't be that tough do do the way my basement is laid out.Then it would give me a reason to cut out my wall and recess my system.

[brucek]

it would give me a reason to cut out my wall

Yeah, woman usually love that sort of thing.... :roll:

Hopefully you'd be able to get a dedicated line up to where the projector plugs in....

[Claude D D]

Hopefully you'd be able to get a dedicated line up to where the projector plugs in....

Not a problem.I have a 22' 14/3 powercord on there right now and can make one longer if need be.