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Amplifier hum
#382091 08/25/12 10:56 PM
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I have just recently purchased a crown XLS1500 amplifier to be used with my Onkyo 875 receiver to power my front M80s. I didn't realize that the amp could only work with a 120 volt power supply. I only have 240 volt where I live. I then decided to try a cheap step down transformer to step 240v down to 120v. Suprising that this crown XLS1500 amp only draws max 250 watts yet claims to put out over 500 watts/channel into 4 ohms. Anyway that is a separate story.
With everything connected up I am getting a low frequency hum from the fronts. When I disconnect the rca input to the crown the hum disappears. It is only present when the onkyo receiver is on and the pre-amp out is connected to the crown amp.
Is there any way I can eliminate this hum or reduce it.
Should I use the XLR inputs on the Crown. To do this I would need to get an RCA to XLR adaptor. Is it possible this hum is caused by the step down transformer? I doubt it since the hum is not always present. Any ideas? confused

Last edited by grantlyt1; 08/25/12 10:57 PM.
Re: Amplifier hum
grantlyt1 #382092 08/25/12 11:08 PM
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Is everything plugged into one outlet? It sounds like a ground hum which often pops up when interconnected devices are plugged into different outlets.

Try a cheater plug (no ground prong) to see if that makes the hum go away.


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Re: Amplifier hum
grantlyt1 #382095 08/25/12 11:23 PM
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Yes everything is plugged into the one outlet. I even disconnected all devices and left only the receiver and amplifier connected but still the same problem.
Is the use of this cheater plug dangerous?

Re: Amplifier hum
grantlyt1 #382097 08/25/12 11:24 PM
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Are all your outlets on the same circuit to the breaker? Might be a ground loop hum. If you have a sub, what happens if you unplug the interconnect?


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Re: Amplifier hum
grantlyt1 #382099 08/25/12 11:25 PM
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No, though it's better used as a diagnostic tool than a permanent solution.

Do you have a coax cable (TV, Cable) going into a device that's plugged into the receiver? If so, try disconnecting the coax cable.


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Re: Amplifier hum
SirQuack #382101 08/25/12 11:35 PM
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Yes the outlets are on the same circuit breaker. Disconnecting the pre-amp out to the sub has no effect on the hum.

Re: Amplifier hum
grantlyt1 #382102 08/25/12 11:37 PM
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Originally Posted By: grantlyt1

Should I use the XLR inputs on the Crown. To do this I would need to get an RCA to XLR adaptor. Is it possible this hum is caused by the step down transformer? I doubt it since the hum is not always present. Any ideas? confused


To get the true benefit of XLR connectors you're receiver/processor would have to have XLR outs... XLR's are a 3 wire system, RCA is a 2 wire system... To get rid of the hum, you need a true 3 wire system.

I had the same problem, i think it's the wiring in my house.. I am using all XLR connectors. However, my processor has XLR outputs....

By using a step down transformer, are isolating that outlet.
My money is on a ground loop problem. My house also have a ground loop... So, i have to deal with multiple electrical issues.....

Re: Amplifier hum
MarkSJohnson #382103 08/25/12 11:39 PM
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I disconnected all inputs to the receiver but no difference however I just disconnected the hdmi out from the receiver and the hum is significantly reduced. Still annoying but much better. But I need to use this HDMI output.

Re: Amplifier hum
grantlyt1 #382105 08/25/12 11:40 PM
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you may not have a good earth ground.... that is one other possibility.

Re: Amplifier hum
grantlyt1 #382107 08/26/12 12:20 AM
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Where do you live? I would wager that this has something to do with the step down transformer.

Guys, if he's got 240V, I doubt they even have cheater plugs...


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