Humm caused by external QSC sub AMP

[Rippyman]

My buddy brought over his James EMB 15" subwoofer with external QSC AMP to try out on my system.

When we tried hooking it up it instantly caused a hum throughout all my speakers.

The AMP wasn't even turned on, just power to it. And the moment you turned the reciever on a hum would come out of all the speakers.

Any ideas what would cause this?

 

[jcl]

Sounds like a ground loop to me. Here's some advice from audioholics - Ground Loops - Eliminating System Hum and Buzz — Reviews and News from Audioholics

You can use a radio shack transformer to eliminate ground loops for higher frequencies (Ground Loop Isolator - RadioShack.com), but I think better quality ones are suggested for subs.

 

[TLS Guy]

My buddy brought over his James EMB 15" subwoofer with external QSC AMP to try out on my system.

When we tried hooking it up it instantly caused a hum throughout all my speakers.

The AMP wasn't even turned on, just power to it. And the moment you turned the reciever on a hum would come out of all the speakers.

Any ideas what would cause this?

This is a ground loop caused by you having more than one ground.

 

[Rippyman]

This is a ground loop caused by you having more than one ground.

What grounds are we talking about?

 

[TLS Guy]

What grounds are we talking about?

Any grounds. All grounding pins, telephone grounds, cable and satellite grounds.

Your problem is always caused by voltages between grounds: - no exceptions.

 

[Rippyman]

Doesn't my Monster Cable Power conditioner do that?

What kind of Isolation transformer do I get?

 

[TLS Guy]

Doesn't my Monster Cable Power conditioner do that?

What kind of Isolation transformer do I get?

No.

We don't know if you need a transformer yet.

You need to post your system in great detail and tell us every ground, especially Internet, cable satellite grounds etc.

You need to study ground loops, so that you understand them.

 

[Rippyman]

Checking grounds because one is bad?

The house is brand new, should I be bringing in the electricians to check their work?

 

[TLS Guy]

Checking grounds because one is bad?

The house is brand new, should I be bringing in the electricians to check their work?

No the electricians will be no use.

Don't post any further nonsense until you describe exactly all your connections, and all grounds, and especially including telephone, cable, satellite grounds etc.

I can be of no help without detailed information.

All this comes about because the chassis of your equipment are at different potentials, or a ground such as a cable ground is at a different potential to your house ground. So in addition to details of all interconnections, knowing which units have grounded plugs and which units are double insulated with two pin plugs is important.

You have provided no further useful information than included in your first post so far.

Have you read the thread about ground loops yet?

 

[Rippyman]

So you need to know everything in the house, or just whats in the HT room?

My list of components.

Marantz SR7005 receiver
Sony PS3
LG Plasma TV
Monster Power supply.

The three main wall jacks are all on separate breakers. The Monster power conditioner is plugged into one of them and the Marantz receiver and PS3 is plugged into that.

The LG TV is plugged into its own power supply behind the TV.

My Klipsch sub is plugged into its own power supply as well.

All the video connections are plugged into my Marantz receiver.

All the speaker connections are run through the wall using Monster 14/4 THX certified shielded wire.

There is two CAT6 lines and two Cable lines behind the components. My PS3 is plugged into one line and my Shaw portal is plugged into one of the cable lines.

No issues with my stuff.

It was only when we tried hooking up the James sub and QSC amp that we had issues with feedback through the speakers.

We hooked that up directly to the Marantz receiver and the power was through a wall jack that had its own breaker. Without even turning the AMP or sub on we were getting feedback through the rest of the speakers. The hum only appeared when we hooked up the OSC amp to the receiver via an RCA line.

 

[lsiberian]

All of your devices should be on the same ground. It's pretty obvious they are not. First lets get the sub and receiver on the same power supply or at least on the same breaker. That should solve a lot of issues. Never put the sub and receiver on different strips. It is asking for trouble. If you need a more rugged supply then get one.

 

[Rippyman]

All of your devices should be on the same ground. It's pretty obvious they are not. First lets get the sub and receiver on the same power supply or at least on the same breaker. That should solve a lot of issues. Never put the sub and receiver on different strips. It is asking for trouble. If you need a more rugged supply then get one.

We tried powering the QSC amp through my Monster power conditioner and no difference.

A friend of mine thinks it may be that the QSC amp is a different impedance then the my receiver.

 

[Rippyman]

Honestly I have a feeling it has something to do with the QSC amp, whether its something wrong with the AMP itself or his RCA line. Because all of my equipment works flawlessly, no hum, no issues.

 

[TLS Guy]

Honestly I have a feeling it has something to do with the QSC amp, whether its something wrong with the AMP itself or his RCA line. Because all of my equipment works flawlessly, no hum, no issues.

Only indirectly. This is absolutely nothing to do with impedance, only potentials between grounds.

We still have incomplete information, as we don't know which units are three pin and which two.

Disconnect the TV, Cat and cable lines.

If the hum is gone, then reconnect one by one to see which is rogue.

If the hum is not gone, and if the QSC amp is three pin, use a cheater plug and convert it to two pin. In general it is a bad plan to ground power amps, it almost always causes a problem.

You really need to tie your grounds together.

Getting CAT and cable grounds sorted is a real art. Basically phone and cable should enter the house within twenty feet of your house ground and those grounds should be tied to the house ground with No 4 copper.

 

[Rippyman]

We discovered the cause of the hummm.

My cable company didn't ground the main line coming into my home. The moment we grounded the cable, the hum went away.

Problems solved, thanks to my buddy who happens to be an electrician..

 

[TLS Guy]

We discovered the cause of the hummm.

My cable company didn't ground the main line coming into my home. The moment we grounded the cable, the hum went away.

Problems solved, thanks to my buddy who happens to be an electrician..

As well as being very lazy on the part of the installer, the installation was dangerous and against code.

I would make a formal compliant and make the cable company aware of this.

You can tell them you will be informing neighbors. I would tell you neighbors who use the same cable service and make the cable company fix under threat of code violations and fines.

This sort of thing is very common. It is just not good enough and inexcusable.

I'm glad you have the problem solved.

 

[Rippyman]

As well as being very lazy on the part of the installer, the installation was dangerous and against code.

I would make a formal compliant and make the cable company aware of this.

You can tell them you will be informing neighbors. I would tell you neighbors who use the same cable service and make the cable company fix under threat of code violations and fines.

This sort of thing is very common. It is just not good enough and inexcusable.

I'm glad you have the problem solved.

How is it against code? It's low voltage wiring.

 

[TLS Guy]

How is it against code? It's low voltage wiring.

Its against code, as it can lead stray voltages right into your home, including lightning strikes that otherwise would be inconsequential.

The same applies to all outdoor antennas and and satellite dishes, that are required to have grounding block and strict codes about grounding.

What that installer did is a serious code violation in all jurisdictions and with good reasons.