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Discussion Starter #1
Here's my situation. I use an Onkyo TX-NR809 as a pre/pro feeding an ATI-1505 for LCR+LR duty and an ATI 1502 to power a dual 15" IB. The signal feeding the 1505 seems to be fine with no real noise. However I get a substantial hum/noise coming from the sub-woofers if I increase the sub signal in the Onks level menu to anything near 0DB which I assume is just increasing the line voltage output. The hum does increase and decrease some with master volume adjustment but disappears completely when the unit is muted. If I am playing a CD near 0DB (volume setting) and pause the track the hum is VERY loud but while playing at that volume it is of course not audible.

The hum is not present when the interconnects are disconnected. Based on what I've tried so far I have assume it's a signal issue and not a ground loop although I've gone through every usual exercise in isolating the problem as just that (trust me :) ).

The problem gets worse because I now plan to use a pro QSC DCA amp to drive not only the IB sub but also a sealed Tempest that will be located within feet of the listening position. I am probably like several here, quite OCD when it comes to noise issues and this is really driving me nuts :coocoo:. I spent some time today speaking with a tech at QSC and he thinks it's an issue with the Onkyo. I also spoke to a local repair tech that said it sounded like a ground issue inside the Onk. I tested the grounds on the Sub outputs and they tested ohmed out just like all the others.

Has anyone else experienced anything like this? I'm at a loss. Could it be that the LFE signal from the Onk is just noisy as hell or might it be that there truly is something amiss in the circuitry?

When I have the level set to say -9db and powering the subs with the ATI there's very little hum although still there. When I use the QSC amp I need more voltage to drive it to the same level as the ATI. Yes, I can turn the gains up on the QSC but it just increases the hum.

ARRGH! :help:

Front stage before flooring..

 

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I have an Onkyo TX-NR809 and suffer an oddity in relation to the sub out but not quite the same as yours.

I noticed that when playing the Onkyo's subwoofer level tone or the Audyssey set up tone there seems to be noise introduced into the signal. This is with the frequency contour on the sub set to bypass. If I back off the frequency control until it clicks, so now it is at 120dB the noise goes away. Another symptom with the frequency contour on bypass is that on a very few films the sub misbehaves, the driver making a whack whack noise but with the contour at 120dB this does not happen.

At this point I have no idea whether the frequency control on the sub is to blame or the line output on the Onkyo. Making an assumption that maybe the line output on the Onkyo is too high I did the following. (Not sure about this but the 809 being THX certified the line out has to be a certain level which can be higher than some subs like. My sub is not THX)

Setting the subs output to 75dB using Audyssey the level setting in the Onkyo is about 0dB. Setting the level with Audyssey to 82dB the setting in the Onkyo is about -6dB so the line out signal is 6dB lower. This improves things considerably. The final thing I did was to set the subs frequency contour to 80dB. the rationale for this is that THX subs have as an option a fixed THX 80dB crossover. This has stopped any films misbehaving even the dreaded 'Edge of Tomorrow' which I can play at all levels up to reference level without the subwoofer driver throwing a wobbly.

My sub is a BK Monolith Plus. 'BK Subwoofers Direct' is a UK internet direct company.
http://www.bkelec.com/HiFi/Sub_Woofers/monolith-FF_Plus.htm

I have no idea if any of this will be any help to you.
 

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Discussion Starter #3
Well I feel dumb. But I am a very happy camper at the same time.

I traced it down to a ground loop after all. I had the tv plugged into a different circuit in a recessed wall box behind the tv. The hum went away when I unplugged the tv from that outlet and the HDMI cord. I ran an extension cord for the tv over to the monster power line conditioner/surge protector and no more hum, DOH! Waht a dope. I though I had tried this already without success.

No the question is how to remedy this? Since the power strip is not right behind the tv how does one go about tying the two together to eliminate the loop?
 

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Well I feel dumb. But I am a very happy camper at the same time.

I traced it down to a ground loop after all. I had the tv plugged into a different circuit in a recessed wall box behind the tv. The hum went away when I unplugged the tv from that outlet and the HDMI cord. I ran an extension cord for the tv over to the monster power line conditioner/surge protector and no more hum, DOH! Waht a dope. I though I had tried this already without success.

No the question is how to remedy this? Since the power strip is not right behind the tv how does one go about tying the two together to eliminate the loop?
I wish you posted that a few minutes earlier. >:)
 

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Discussion Starter #6
Picked up a "Hum X" this afternoon. I will update thread as soon as I get a chance to test it out whether it fixes the problem.
 

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Discussion Starter #7
Just got home and plugged in the Hum X between the plasma and wall. It appears to have done the trick isolating the ground loop from the TV. I still have some very slight noise if I put my ear close to the sub and I boost the level output and volume control but it's not a 60hz hum. More like digital noise I think that is unavoidable. I can certainly live with it as there's no way I will ever hear it under normal listening situations.

Overall I am tickled pink that this has been solved. I hope that my experience can save someone else the turmoil I just went through for the last few days trying to figure this out.
 

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Just got home and plugged in the Hum X between the plasma and wall. It appears to have done the trick isolating the ground loop from the TV. I still have some very slight noise if I put my ear close to the sub and I boost the level output and volume control but it's not a 60hz hum. More like digital noise I think that is unavoidable. I can certainly live with it as there's no way I will ever hear it under normal listening situations.

Overall I am tickled pink that this has been solved. I hope that my experience can save someone else the turmoil I just went through for the last few days trying to figure this out.
I am glad you have it sorted. I wonder if the noise you hear is the same as I hear with the subs frequency control set at bypass. Maybe it is something to do with 809.
 
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