Axiom Home Page Forums General Discussion Technical Questions Who can solve this problem?

First of all, I want to thank Wid for helping me resolve 1 of the three problems I have, thanks Rick!

As most of you know I received my Emotiva mps-1 amp chassis recently plus two of their epm-300 monoblock modules for starters to drive my m80's. The amp is very cool and top quality.

Anyway, I have some issues as I'm hearing some static in the m80 tweeters occasionally. In addition, I've been hearing a slight "hum" from the woofers, and what sounds like pink noise emitting from the tweeters at a very very low level (have to put my ear right up against the tweeters) when I don't hear the static mentioned above.

Anyway, below is a post on my thread I started on AV123, as their are many Emotiva owners on that website. Was hoping for some ideas from my Axiom buddies.

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With the help of one of my Axiom buddies, "Wid", I made some progress. It appears the static sound and hum situation are two different animals. I'll talk about the static in a bit.

First of all, I took the screws out of the epm300's that secure it to the chassis and that seemed to make no difference for any of my issues, so I put them back in...

In troubleshooting the "hum" I noticed I was getting some hum out of my center speaker which was not hooked to my mps-1. I thought this was odd. My monster Axiom ep600 sub is placed right below my center speaker about 1 ft. The center speaker is mounted on the wall below my screen. I noticed when I unplugged the sub, the hum went away. Also, the hum that I was hearing in my m80 mains reduced somewhat.

The Axiom subs have a ground screw you can remove if you hear the 60hz hum in the sub. So I removed the screw and plugged the sub back in, and shazaam, the hum from the center disappeared and the hum from the mains was greatly reduced. So my guess is something was feeding back through the "Blue Jeans" coax to my receiver and creating a hum in the speakers.

I still have the hum in the mps-1 amps I can hear from 5-6" away, and there is still a very small hum in my main speakers which appear to be originating from the amp. Not sure if this is normal? I'm thinking if I was using speakers that were not as efficient, I would not hear anything from them?

Another thing I didn't mention before, and not sure if this is a problem, is that I didn't place the two epm-300 mono's right next to each other. I placed one in the first slot and placed the second one in the third slot over. I figured this would give a little more air flow. I plan to purchase one more to drive my center, and then 2 of the 2-channel epm-2150's for the surrounds. So I'll have plenty of room.

In regards to the static sound I hear. This is a weird problem. AT first I thought it was cable related, but after using the better cables I purchased tonight at Radio Shack, the static noise was still in the tweeters of my mains. It was not consistant, sometimes it was there, and other times it was not. I was freaking out.

Then I noticed that it had to do with the light switch in my AV closet. When I had the close light ON, there was no static. When I turned the light OFF, the static could be heard in the tweeters. That to me is very strange, you would think it would be the opposite.

It gets better, the light switch for my closet light is on a totally different circuit. I have a dedicated 20amp circuit for my AV stuff. The closet light switch is on a different 15amp breaker for other lights in the basement.

So then I went and turned off the 15amp breaker for the closet light, and the static was still present. It is only when the light is turned on, that the static goes away, and the only thing is the hum from the amp.

Sorry for being so long, I'm just totally lost on this one....

What kind of bulb is it? Flourescent, incandescent? If you switch the type of bulb, does it change the static?

Randy, other than turning the closet light on when you listen, no solution comes to mind immediately, but I'll continue to ponder the situation.

Thanks Ken and John,

The bulbs are just your normal white colored 60-75 watt bulbs you buy at walmart, I think they are GE, nothing expensive.

I'm puzzled because this static sound shows up in the tweeters when the switch is OFF, not ON. Also, being on a different circuit puzzles me. Now in the breaker box, these two breakers are next to each other, not sure if that would play a role. When I turned off the 15 amp breaker for the lights in the rec room, which includes the close light, I still hear the static. It is only when the circuit is active and the lights are ON.

Weird.

Randy is there any fluorescent fixtures or anything with a motor i.e. refrigerator or freezer running on the same circuit as the bulb in the equipment closet?

Sounds like the perfect situation to see if one of those monster power filters would do as they claim...You could always return it if it doesn't do as claimed.

Randy,

You said you have the HT on an independent circuit. Do you know if it shares a neutral with that lighting circuit, or was the wiring home ran to the panel for the HT circuit? If they are sharing a neutral, the circuit path will still be routed through the lighting fixture (neutral to ground) regardless of whether the light switch is open or closed. If any of the fixtures on that circuit are not properly grounded to the ground wire, you could be getting feedback on the neutral. I’m not saying this is your culprit, but it ‘could’ be.

Let me know and I’ll run this scenario by one of the EE’s at work to see if they have any ideas.

I just talked to a guy at work who is pretty good with electrical stuff. He said to first check to obvious stuff like the ground wire, etc.

I think I'm getting some type of interference on the secondary ground (bare wire). He said often it will act like an antenna. I also don't think it is coming from the 15amp circuit the light switch is on, because I turned that breaker off and still hear the static. He said it is possible that when I turn the light ON, it is "absorbing", if you will, the static, that is why I don't hear it when the light is on.

It sounds like since I have the Primary Ground (larger lug) I can remove the "secondary ground" from the Green screw on the outlet and see if that eliminates the static from the amp/speakers. Unless of course the static is coming from the primary ground.

fun fun fun

I agree with Mike in that with the breaker for the light switched off, the Neutral (White) wire is still connected and may be shared with your dedicated theater circuit.

I think you are on track in checking the ground (bare wire) to the light fixture and the light switch, and even the theater outlets. They should all be connected, and the source of the problem is probably a missing ground, and/or a device introducing noise into the ground or Neutral. You could go around unplugging everything on the other circuit to see if the hum quits.

If that doesn't work, you could try removing the circuits from your breaker box one at a time to find out which one may be introducing the hum into the system. To do this you may need to do more than just turning off the breakers one at a time. You probably need to locate the White Neutral wire as well and disconnect it from the panel. When you find the one that removes the hum (maybe the one with the light or not, but start there first), you know it is something on that circuit.

*** DISCLAIMER *** I am not an electrician, but I have dealt with these kinds of issues before. Hopefully others may chime in on if this would make any sense or be worthwhile. It was just an idea I had. Please be careful in what you do in the box (just want to be sure you are safe). Get someone who knows what they are doing if you need help, and turn off the power to the box before working in it.

Dear Randy,

Two problems I notice immediately...

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you buy at walmart

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Now, really, you'd have been disappointed in me if I'd not bitten on that, right? Buy better bulbs.

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have to put my ear right up against the tweeters

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Have you considered moving your listening position back just a bit?

Could you leave the light on but unscrew the bulb?

Perhaps your bulb is unscrewed already?

How many Home Theatre guys DOES it take to change a light bulb, anyway?