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 Post subject: Amp hum
PostPosted: Sat Feb 04, 2017 8:58 am 
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Joined: Sat Jul 20, 2013 6:01 am
Posts: 37
Location: ste-marthe-sur-le-lac, QC, CA
Hello,
I`m looking for help in eliminating an amp hum that I suspect is due to the mess of cables in back of my system.I have disconnected all sources from my amp and the hum can still be heard. If I move my amp away from it`s usual place and plug it in ,the hum disappears.
Is there anything I can do to eliminate cable interference? Can a hum be caused by a source or power unit if it is not plugged in?
Thanks for your help


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 9:08 am 
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Joined: Sun Jun 16, 2013 11:17 am
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Location: St. John's, NL, CA
Hums can be caused by so many things it's sometimes difficult to isolate them. When you move the amp to the spot that's quiet, are you plugging it into a different socket? And if it is a different socket, is that socket on a completely different circuit from the noisy socket (and thus on a different breaker in the electrical panel)?


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 9:11 am 
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Joined: Sun Oct 14, 2007 2:32 pm
Posts: 582
Location: winnipeg, MB, CA
If everything else is disconnected and unplugged the problem might be the wall outlet itself. Is this a new problem, a new amp, or have you recently moved it to a new location?


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 9:20 am 
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Location: ste-marthe-sur-le-lac, QC, CA
If I move the amp away from it's usual place and plug it in the same outlet, the hum will go away.I have plugged it in another outlet in the same room but on a different circuit and the hum is gone.That is why I am suspecting the cables in back of my system causing interference.


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 9:26 am 
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Location: winnipeg, MB, CA
I had a similar problem. Turned out to be the preamp ( power supply for the preamp) was too close to another device. Pretty much trial and error moving things around and hoping it goes away. Try rerouting cables, keeping components spaced apart, etc...


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 9:30 am 
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Location: St. John's, NL, CA
If you leave the amp in its regular place, and unplug the other devices (tt, cdp etc) is the hum there or not? (not just disconnect the interconnects, but unplugged from the wall)


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 10:27 am 
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Location: ste-marthe-sur-le-lac, QC, CA
Yes, I have unplugged all sources from the amp and power and left the amp in it's usual place...hum still there.


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 10:49 am 
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Location: Toronto, ON, CA
Is this a hum in the speakers or from the amp itself?

I will bet if from the amp itself that you have dc offset in your ac power line. Get an Emotiva CMX-2. Your amp will barely be running anywhere close to where it is supposed to if the transformer is humming.

DC offset is a major problem these days. Between the USB chargers, LED lights and Tesla charging stations if you are close to an urban area the ac power is polluted...


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 10:52 am 
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Location: St. John's, NL, CA
Is the hum still there even if you remove the other devices from the area? If you remove everything from the area and the amp goes quiet, that means it is some sort of weird interaction between the amp and one of the other device. So then the thing to do is hold the other devices next to the amp, one at a time, in order to discover which one causes the hum.


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 12:02 pm 
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Location: Montreal, QC, CA
andym wrote:
Yes, I have unplugged all sources from the amp and power and left the amp in it's usual place...hum still there.


The hum is being induced by the power supply of an adjacent component. Turn amp on and then start unplugging the power (not just turning them off) to nearby components, one by one.


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 2:28 pm 
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Location: ste-marthe-sur-le-lac, QC, CA
Michael F---I did mention previously that I disconnected all sources from the amp and the power from all sources and that the hum was still there..BTW I forgot to mention that the hum can only be heard up close to the amp and not through the speakers.

EL34--If I move the amp away from all other devices the hum disappears...I will follow your suggestion and move one device at a time close to the amp and hopefully find the culprit. I don`t understand how a source with no power through it can affect the amp.Can someone explain?


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 2:45 pm 
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Location: Montreal, QC, CA
andym wrote:
Michael F---I did mention previously that I disconnected all sources from the amp and the power from all sources and that the hum was still there..BTW I forgot to mention that the hum can only be heard up close to the amp and not through the speakers.

EL34--If I move the amp away from all other devices the hum disappears...I will follow your suggestion and move one device at a time close to the amp and hopefully find the culprit. I don`t understand how a source with no power through it can affect the amp.Can someone explain?


That is why you should physically unplug the power cable. Some components might be in a standby state when the power button is in off position or perhaps only the power supply secondaries are switched, both scenarios would see the transformer energized.
I encountered a similar issue once on a powered subwoofer that had me scratching my head. It turned out my cable TV provider was performing some maintenance in my building and that somehow induced a hum into the sub because of it`s close proximity to the wall coax/F connector.
Strangest thing that I saw in a while and I`ve seen alot of strange things :)


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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 2:49 pm 
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Location: Dodge City, NB, CA
andym wrote:
Michael F---I did mention previously that I disconnected all sources from the amp and the power from all sources and that the hum was still there..BTW I forgot to mention that the hum can only be heard up close to the amp and not through the speakers.

EL34--If I move the amp away from all other devices the hum disappears...I will follow your suggestion and move one device at a time close to the amp and hopefully find the culprit. I don`t understand how a source with no power through it can affect the amp.Can someone explain?

It sounds to me that there is a component ( transformer perhaps? ) inside your amp that is loose and vibrating. It is creating a sympathetic hum in the case or the stand and when you move it you change the conditions so it stops.

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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 3:19 pm 
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Location: CAMBRIDGE, ON, CA
something on the circuit is introducing dc offset
which causes transformer hum esp toroidal transformers.
Find the source of the issue ie/plasma tv, Florence/led lights... and eliminate
or a few companys make dc offset blockers. Blue Circle, PS Audio, and emotiva.
Emotiva makes one which is available at summit hifi for $149 (no affiliation)...
I've have this issue through my whole house caused near by industry.

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 Post subject: Re: Amp hum
PostPosted: Sat Feb 04, 2017 4:20 pm 
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Joined: Sat Jul 20, 2013 6:01 am
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Location: ste-marthe-sur-le-lac, QC, CA
Hi Guys,
I just found the culprit.It the cathode ray tube TV that I have seating in the cabinet over the amp.(Please don't laugh :wink: ..I don't watch TV but for the odd video, this old TV does the trick).
The easiest fix would be to move those two apart but not my favorite option right now.Can I use an "insulator" between the TV and the amp? Does this hum, although annoying but not audible from were I seat, affect SQ?
Thanks


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