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HELP!!! Anthem MRX -300 connect Power amp humming

post #1 of 13
6/6/12 at 9:34pm
Thread Starter 
I use MRX-300 as a Pre/Pro. There is hum sound from all speakers in my 7.1 setup including subwoofer when ANTHEM MRX-300 is connected to power amp (simaudio Titan 5channels),

Following are tests being taken and still hum：
1. Turn off MRX-300
2. Disconnect power cord from MRX-300
3. Take out the GROUND from MRX-300
4. disconnect all HDMI and ANTENNA from MRX-300

7 channels main speakers, NO MORE HUM only if:
Disconnect RCA connectors at power amp from MRX-300!

subwoofer, NO MORE HUM only if:
Disconnect subwoofer RCA cable from MRX-300!

Does anyone has this issue or it is a design defect for using a receiver as a pre? I wonder if this is a defective unit, I don't want to send it back to dealer immediately since all my sources depend on it currently and it has to wait for at least a week to be back, so I want to know more before I decide to take it for service.
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post #2 of 13
6/7/12 at 6:12am
You have a ground loop problem. How do you have the amp and MRX connected to the AC? Is it on the same circuit, and/or same/different outlet? And what about the sub, where is it connected to the AC?
Have you tried the MRX w/o the amp?
I one time I had a ground loop problem and moving one of the subs connection to the last outlet on the circuit got rid of the hum.
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post #3 of 13
6/7/12 at 7:05am
I had the same problem, isolated it to my cable box and a dimmer switch. The only way I could fix it was to use a cheater plug on the amp. Isolating the cable input with an input on a surge suppressor got rid of 90% of the hum.
Cable is the most likely culprit. There are isolators you can buy as well.
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post #4 of 13
6/7/12 at 7:16am
Thread Starter 
Quote:
Originally Posted by 4DHD View Post

You have a ground loop problem. How do you have the amp and MRX connected to the AC? Is it on the same circuit, and/or same/different outlet? And what about the sub, where is it connected to the AC?
Have you tried the MRX w/o the amp?
I one time I had a ground loop problem and moving one of the subs connection to the last outlet on the circuit got rid of the hum.

AMP and subwoofer are on a dedicated 20A line, MRX is on another 20A.

What do you mean try w/o amp? Without amp of course there will be no hum because no power to speakers.

Will ground loop loops to everything including SUBWOOFER? There are hum on Sub even MRX off.
My surround back speakers x 2 are connected by ATI 2505 5 CHANNEL AMP, it also hum if amp on. Same as my Simaudio titan. for other main speakers.
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post #5 of 13
6/7/12 at 7:17am
Thread Starter 
Quote:
Originally Posted by saeyedoc View Post

I had the same problem, isolated it to my cable box and a dimmer switch. The only way I could fix it was to use a cheater plug on the amp. Isolating the cable input with an input on a surge suppressor got rid of 90% of the hum.
Cable is the most likely culprit. There are isolators you can buy as well.

What is cheater plug? surge suppressor? isolators?
What are these things.....
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post #6 of 13
6/7/12 at 7:41am
By cheater plug I'm referring to one that takes a 3-prong plug and eliminates the ground plug, thus "cheating". You can buy one just about anywhere. It does comes with some risk that if you have a problem with your amp you could get electrocuted if you touch the chassis.
The isolator can be found on Amazon and other places, just search cable isolator.
Ground loops are tricky, they can occur even if the equipment is not on, it travels through the connecting wires.
What 4DHD was referring to was using the amps in the MRX instead of your amp to help isolate the problem.
Are you using a cable box? If so, while you're hearing the hum, simply disconnect the cable input to the cable box, when I did that the hum went away. I was getting the hum even when I wasn't using the cable box.
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post #7 of 13
6/7/12 at 12:30pm
Thread Starter 
Quote:
Originally Posted by saeyedoc View Post

By cheater plug I'm referring to one that takes a 3-prong plug and eliminates the ground plug, thus "cheating". You can buy one just about anywhere. It does comes with some risk that if you have a problem with your amp you could get electrocuted if you touch the chassis.
The isolator can be found on Amazon and other places, just search cable isolator.
Ground loops are tricky, they can occur even if the equipment is not on, it travels through the connecting wires.
What 4DHD was referring to was using the amps in the MRX instead of your amp to help isolate the problem.
Are you using a cable box? If so, while you're hearing the hum, simply disconnect the cable input to the cable box, when I did that the hum went away. I was getting the hum even when I wasn't using the cable box.

I tried take away the cable input with no luck as well, does anyone here may think I have a defective unit by any chance?
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post #8 of 13
6/7/12 at 2:47pm
Like a previous poster suggested, try taking your amp out of the equation, hook up at least one of your speakers directly to the Anthem and disconnect the Amp from the Anthem and the wall.
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post #9 of 13
6/7/12 at 5:07pm
Also try plugging all the equipment into the same circut. It doesn seem like you tried that and thats the 1st thing Id do since I read you had the units in different plugs......Usually casues ground loops almost as frequently as the damn cable boxes.
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post #10 of 13
6/7/12 at 8:32pm
Thread Starter 
Quote:
Originally Posted by saeyedoc View Post

Like a previous poster suggested, try taking your amp out of the equation, hook up at least one of your speakers directly to the Anthem and disconnect the Amp from the Anthem and the wall.

Can you tell me what will it conclude if either still hum and no more hum when direct connect to Anthem with speakers?

p.s. Since I have to move the anthem out of a tight space while it has many cables tightly fit with it, it will took quite some efforts to do so.
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post #11 of 13
6/7/12 at 8:34pm
Thread Starter 
Quote:
Originally Posted by Vic C View Post

Also try plugging all the equipment into the same circut. It doesn seem like you tried that and thats the 1st thing Id do since I read you had the units in different plugs......Usually casues ground loops almost as frequently as the damn cable boxes.


try plugging all the equipment into the same circut.
-- i can't do that.

I did disconnect all cable box antenna and power plugs, no luck.
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post #12 of 13
6/8/12 at 6:45am
Get a power strip so you can plug everything into one outlet.
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post #13 of 13
2/20/13 at 9:30am
Was there a resolution to this?
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AVS › AVS Forum › Audio › Receivers, Amps, and Processors › HELP!!! Anthem MRX -300 connect Power amp humming