escalating hum on amp or speakers or receiver

[mike c]

one day, I paused during a movie ... went to pee

came back to hear a loud batatatatatatat sound. I turned off the receiver, turned it back on, everything ok.

that was about a month ago.

yesterday, I was watching the Matrix DVD, I can hear a slight hum coming from the front speakers, but it escalates in volume then disappears ... this happened 4-5 times during the movie.

of the 4-5 times, this is what I did each time to make the sound go away:
1st few times, paused, turned off receiver, turned back on
second to the last time, I let the hum disappear by itself
last time, I turned on and off JUST ONE of the front amps.

my setup:
Denon AVR2307 receiver
front LCR powered by 3 behringers A500 bridged.
LR surrounds powered by a single behringer.
LR rears powered by the receiver.

what's going on?!

 

[avaserfi]

Is there a specific type of scene in the movie that this is happening with? (i.e. loud scene with lots of base or quiet scene with just dialoge etc...)

 

[mike c]

the hum starts from inaudible then grows to sound like a 60hz hum, BUT escalates in volume then the volume of the hum goes back down ... that's with a short (a few seconds) of higher volume at the peak of the volume

 

[mike c]

it doesn't start during loud scenes, it starts during low volume sound effects, and if I'm not imagining things, it starts when there's background music that's the same tune as the hum.

 

[avaserfi]

Could it possibly be something with the matrix disc or have you noticed it with others? (sorry for all the questions, just trying to get every angle)

 

[mike c]

the loud blatatat thing happened on another time ...

but this is the 1st time the hum thing happened, and it just so happens to be the matrix dvd ... my next scheduled showing is friday for matrix reloaded.

had to divide the week with the wife. i get MWF, she gets TTHSS

 

[avaserfi]

The blatatatat almost sounds like there is a cut signal then it regains it and looses it repeatedly. This could be caused by a bad interconnect which also could be causing the hum.

The amp might be going too. Do you have a different coax you could hook up to see if that would get rid of the problem?

 

[mike c]

hmm, I'll open up all the interconnects to check.

i replaced the interconnect wires with 20+ foot length ones, because the first cables I had made was 46 feet ...

would power cords be doing this? I have some power cords running criss cross with the interconnects and speaker wires.

 

[avaserfi]

They might cause it but I doubt it as most cables should be shielded well enough to stop the interferance. I would check out the cables integrity as that would probably be the easiest fix.

 

[mike c]

im doubting the bad interconnect thing because the hum happens to the three LCR speakers.

and I haven't checked the surrounds if they're humming too ...

could it be the pre-outs?

 

[avaserfi]

im doubting the bad interconnect thing because the hum happens to the three LCR speakers.

I missed that they were all on separate amps...you are probably right about the interconnects. Have you made any recent changes before you noticed this problem?

 

[mike c]

no changes, but i'll check the cables if some are kicked lose or something

 

[avaserfi]

The only other thing I can think of and it might be a stretch is some sort of intermittent ground loop problem. Groundloop problems generally sound like they are in the 50-60hz range according to the AH article. Perhaps there is something odd going on with your wiring? Sorry I couldn't help more...couldn't find too much on google and I am out of ideas .

http://www.audioholics.com/tweaks/connecting-your-system/ground-loops-eliminating-system-hum-and-buzz/

 

[mike c]

that's ok, will check:

another movie
lose cables/interconnects
power cables

 

[Seth=L]

that's ok, will check:

another movie
lose cables/interconnects
power cables

Has anyone in your home gotten a new cell phone?

 

[mike c]

Has anyone in your home gotten a new cell phone?

in the house? how near or far should they be from the room?

hmm, i'll check with the wife if she normally brings her wireless and cellular phone to the HT, she had it that night, but I think she always does.

I always bring my phone.

 

[Seth=L]

in the house? how near or far should they be from the room?

hmm, i'll check with the wife if she normally brings her wireless and cellular phone to the HT, she had it that night, but I think she always does.

I always bring my phone.

Some phones mess with audio equipment when they are getting texts or calls. If you aren't getting a direct co-relation between the phones and the audio equipment, then the problem is elsewhere. I just thought I would add a potential disturbance to the list.

 

[Adam]

Some phones mess with audio equipment when they are getting texts or calls. If you aren't getting a direct co-relation between the phones and the audio equipment, then the problem is elsewhere. I just thought I would add a potential disturbance to the list.

Yeah, wireless is the first thing that entered my mind when I started reading this thread. When I first got an Airport Express, I started to hear a repetitive clicking sound in my PC speakers until I moved the two farther apart. Not to say that your system is as crappy as my PC speakers , but I'd agree with Seth=L that a wireless signal might be affecting something.

 

[mike c]

watched matrix reloaded last night ... no hum through the movie. but when I had a dinner break ... instead of leaving things on like before, I killed everything.

 

[mike c]

i'm beginning to regret buying cheap amps. but then again, with the price I paid for those amps, I can't think of any replacement.

maybe I should go back to a 180wpc bridged rotel amp ? it has auto sense too!