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#382091 - 08/25/12 06:56 PM Amplifier hum
grantlyt1 Offline
regular

Registered: 08/25/12
Posts: 8
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


Edited by grantlyt1 (08/25/12 06:57 PM)

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#382092 - 08/25/12 07:08 PM Re: Amplifier hum [Re: grantlyt1]
MarkSJohnson Online   happy
shareholder in the making

Registered: 09/27/04
Posts: 10832
Loc: Central NH
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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#382095 - 08/25/12 07:23 PM Re: Amplifier hum [Re: grantlyt1]
grantlyt1 Offline
regular

Registered: 08/25/12
Posts: 8
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?

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#382097 - 08/25/12 07:24 PM Re: Amplifier hum [Re: grantlyt1]
SirQuack Offline
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Registered: 01/29/04
Posts: 13318
Loc: Iowa
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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#382099 - 08/25/12 07:25 PM Re: Amplifier hum [Re: grantlyt1]
MarkSJohnson Online   happy
shareholder in the making

Registered: 09/27/04
Posts: 10832
Loc: Central NH
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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#382101 - 08/25/12 07:35 PM Re: Amplifier hum [Re: SirQuack]
grantlyt1 Offline
regular

Registered: 08/25/12
Posts: 8
Yes the outlets are on the same circuit breaker. Disconnecting the pre-amp out to the sub has no effect on the hum.

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#382102 - 08/25/12 07:37 PM Re: Amplifier hum [Re: grantlyt1]
dakkon Offline
connoisseur

Registered: 02/08/04
Posts: 1844
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.....

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#382103 - 08/25/12 07:39 PM Re: Amplifier hum [Re: MarkSJohnson]
grantlyt1 Offline
regular

Registered: 08/25/12
Posts: 8
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.

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#382105 - 08/25/12 07:40 PM Re: Amplifier hum [Re: grantlyt1]
dakkon Offline
connoisseur

Registered: 02/08/04
Posts: 1844
you may not have a good earth ground.... that is one other possibility.

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#382107 - 08/25/12 08:20 PM Re: Amplifier hum [Re: grantlyt1]
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17741
Loc: NoVA
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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