Lonnie
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Post by Lonnie on Mar 15, 2010 20:48:19 GMT -5
Has everyone here ruled out the preamp? And if not is the preamp using analog inputs/outputs? I know a bunch of guys said they disconnected everything but for the others that are having this issue & don't think its a gorund loop issue, I'd second checking the pre as well. I had what I thought sounded like a ground loop when my HK receiver was feeding my amp but I ruled that issue out & still had the hum. Swapped to a proper pro & the speakers are silent. Guess some cheeper pro's or receivers don't have good isolation on the power supply transformer & it gets transferred on out to the power amp. The best way to find out what is causing the noise is simply to start at the end of hte chain and move your way up, one unit at a time. Unplug all the inputs to the amp and turn it on. If noise is there with no input cables connected, then the amp is noisy. If no noise then turn the amp off. Plug in the cables from the Pre to the amp but unplug all cables going into the pre. So that only the pre and hte amp are connected. it is very important to unplug everything else including the output cable to the TV so it is only the Pre and the amp. Then turn on the pre and the amp and turn the volume all the way down and see if the noise is there. If it is then the amp is just amplifying the noise being sent into it from the pre and we need to determine how loud the noise is and if ths is normal. If no noise, then connect one source unit at a time and retest. When you plug in a source and test it and the noise returns, then that is source of the issue. Hope this helps.
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Post by Nemesis.ie on Mar 16, 2010 5:35:51 GMT -5
As mentioned earlier, all other gear should be physically unplugged too (power cable) for 100% verification. Check each component on its own, one by one.
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Post by ufokillerz on Mar 20, 2010 8:33:45 GMT -5
Hmm i get a tiny bit of hiss on my mps-1 and xpa-5, the hiss comes from the tweeters of my speakers, and i do have to put my ear up to it to hear it. i am running xlr to xlr interconnects. Could my 98db sensitive speakers be causing the slight hiss?
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Mister L'fe
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Post by Mister L'fe on Mar 21, 2010 16:56:18 GMT -5
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Mister L'fe
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Post by Mister L'fe on Mar 21, 2010 17:17:22 GMT -5
I know a bunch of guys said they disconnected everything but for the others that are having this issue & don't think its a gorund loop issue, I'd second checking the pre as well. I had what I thought sounded like a ground loop when my HK receiver was feeding my amp but I ruled that issue out & still had the hum. Swapped to a proper pro & the speakers are silent. Guess some cheeper pro's or receivers don't have good isolation on the power supply transformer & it gets transferred on out to the power amp. The best way to find out what is causing the noise is simply to start at the end of hte chain and move your way up, one unit at a time. Unplug all the inputs to the amp and turn it on. If noise is there with no input cables connected, then the amp is noisy. If no noise then turn the amp off. Plug in the cables from the Pre to the amp but unplug all cables going into the pre. So that only the pre and hte amp are connected. it is very important to unplug everything else including the output cable to the TV so it is only the Pre and the amp. Then turn on the pre and the amp and turn the volume all the way down and see if the noise is there. If it is then the amp is just amplifying the noise being sent into it from the pre and we need to determine how loud the noise is and if ths is normal. If no noise, then connect one source unit at a time and retest. When you plug in a source and test it and the noise returns, then that is source of the issue. Hope this helps. So, Lonnie I've done all of this and have spent literally hours trying to find the cause of the hum/buzz in my speakers. Finally as a last resort I got out the DMM. I measure 26 VAC between the chassises of the XPA-3 and XPA-5 with all the RCA cables disconnected. Measuring between the pre-pro and the XPA-5 (chassis or RCA grounds) I get 0 VAC, but between the XPA-3 I again get 26 VAC. Whats going on? Is there a grounding problem in the XPA-3? The hum/buzz problem is with the speakers connected to the XPA-5. The XPA-3 is dead quiet. I'm puzzled. Is there anything else I can do short of sending things back? Possibly something is miss-wired in the XPA-3? Can I pull the cover off and look without voiding the warranty? BTW: I've changed my cables from the RCAs to balanced and the hum (lack of) seems to be much better at this point. But, I'm still concerned about the 26 volts I see.
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DYohn
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Post by DYohn on Mar 21, 2010 17:47:40 GMT -5
The best way to find out what is causing the noise is simply to start at the end of hte chain and move your way up, one unit at a time. Unplug all the inputs to the amp and turn it on. If noise is there with no input cables connected, then the amp is noisy. If no noise then turn the amp off. Plug in the cables from the Pre to the amp but unplug all cables going into the pre. So that only the pre and hte amp are connected. it is very important to unplug everything else including the output cable to the TV so it is only the Pre and the amp. Then turn on the pre and the amp and turn the volume all the way down and see if the noise is there. If it is then the amp is just amplifying the noise being sent into it from the pre and we need to determine how loud the noise is and if ths is normal. If no noise, then connect one source unit at a time and retest. When you plug in a source and test it and the noise returns, then that is source of the issue. Hope this helps. So, Lonnie I've done all of this and have spent literally hours trying to find the cause of the hum/buzz in my speakers. Finally as a last resort I got out the DMM. I measure 26 VAC between the chassises of the XPA-3 and XPA-5 with all the RCA cables disconnected. Measuring between the pre-pro and the XPA-5 (chassis or RCA grounds) I get 0 VAC, but between the XPA-3 I again get 26 VAC. Whats going on? Is there a grounding problem in the XPA-3? The hum/buzz problem is with the speakers connected to the XPA-5. The XPA-3 is dead quiet. I'm puzzled. Is there anything else I can do short of sending things back? Possibly something is miss-wired in the XPA-3? Can I pull the cover off and look without voiding the warranty? BTW: I've changed my cables from the RCAs to balanced and the hum (lack of) seems to be much better at this point. But, I'm still concerned about the 26 volts I see. 26 volts between chassis is not good and is almost certain to create a ground-loop hum. Try this: use a piece of wire, any wire, and with the power off on both amps connect the two chassis together. Then turn everything back on and see if the hum goes away.
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Mister L'fe
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Post by Mister L'fe on Mar 21, 2010 20:23:51 GMT -5
So, Lonnie I've done all of this and have spent literally hours trying to find the cause of the hum/buzz in my speakers. Finally as a last resort I got out the DMM. I measure 26 VAC between the chassises of the XPA-3 and XPA-5 with all the RCA cables disconnected. Measuring between the pre-pro and the XPA-5 (chassis or RCA grounds) I get 0 VAC, but between the XPA-3 I again get 26 VAC. Whats going on? Is there a grounding problem in the XPA-3? The hum/buzz problem is with the speakers connected to the XPA-5. The XPA-3 is dead quiet. I'm puzzled. Is there anything else I can do short of sending things back? Possibly something is miss-wired in the XPA-3? Can I pull the cover off and look without voiding the warranty? BTW: I've changed my cables from the RCAs to balanced and the hum (lack of) seems to be much better at this point. But, I'm still concerned about the 26 volts I see. 26 volts between chassis is not good and is almost certain to create a ground-loop hum. Try this: use a piece of wire, any wire, and with the power off on both amps connect the two chassis together. Then turn everything back on and see if the hum goes away. I had thought about doing that. But isn't everything already tied together by the grounds (shield side of the RCAs) anyway? Their common point being the pre-pro. My question still is why the 26 volts on one amp and not the other? Another question, why not tie both amps and the pre-pro together with the same ground wire? Maybe Mr Vaughn can give us (me) an answer? Edit: Thinking about this a bit more. This doesn't sound like a very good idea. I've got one amp with a "hot" chassis. Now I put a piece of wire between them and I've got 2 amps with 'hot" chassises. I really don't think this is a good solution!!!
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Mister L'fe
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Post by Mister L'fe on Mar 21, 2010 21:24:02 GMT -5
Did one more thing. I measured between the chassis on the XPA-3 and the ground pin of the wall outlet. Amplifier plugged in and rear power switch on, amp off (front button) I measure 45 VAC. With the amp on I measure 23 VAC. Doing the same thing with the XPA-5 I measure 0 volts.
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Lonnie
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Post by Lonnie on Mar 21, 2010 21:43:54 GMT -5
Hmm i get a tiny bit of hiss on my mps-1 and xpa-5, the hiss comes from the tweeters of my speakers, and i do have to put my ear up to it to hear it. i am running xlr to xlr interconnects. Could my 98db sensitive speakers be causing the slight hiss? Since all stand a lone amplifiers have a fixed gain ratio, it is normal to hear a hiss within a foot or less.
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Lonnie
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Post by Lonnie on Mar 21, 2010 21:49:38 GMT -5
The best way to find out what is causing the noise is simply to start at the end of hte chain and move your way up, one unit at a time. Unplug all the inputs to the amp and turn it on. If noise is there with no input cables connected, then the amp is noisy. If no noise then turn the amp off. Plug in the cables from the Pre to the amp but unplug all cables going into the pre. So that only the pre and hte amp are connected. it is very important to unplug everything else including the output cable to the TV so it is only the Pre and the amp. Then turn on the pre and the amp and turn the volume all the way down and see if the noise is there. If it is then the amp is just amplifying the noise being sent into it from the pre and we need to determine how loud the noise is and if ths is normal. If no noise, then connect one source unit at a time and retest. When you plug in a source and test it and the noise returns, then that is source of the issue. Hope this helps. So, Lonnie I've done all of this and have spent literally hours trying to find the cause of the hum/buzz in my speakers. Finally as a last resort I got out the DMM. I measure 26 VAC between the chassises of the XPA-3 and XPA-5 with all the RCA cables disconnected. Measuring between the pre-pro and the XPA-5 (chassis or RCA grounds) I get 0 VAC, but between the XPA-3 I again get 26 VAC. Whats going on? Is there a grounding problem in the XPA-3? The hum/buzz problem is with the speakers connected to the XPA-5. The XPA-3 is dead quiet. I'm puzzled. Is there anything else I can do short of sending things back? Possibly something is miss-wired in the XPA-3? Can I pull the cover off and look without voiding the warranty? BTW: I've changed my cables from the RCAs to balanced and the hum (lack of) seems to be much better at this point. But, I'm still concerned about the 26 volts I see. The voltage differential is not an issue here. If the amps were actually grounded and you could read a voltage differential, then we would have an issue, but the amps are double shielded and are not grounded so this is not a problem. I guess the one thing we never really established is how loud is this slight hiss? With all fixed gain amplifiers (not just ours) it is normal to have a small amount of hiss in the speakers. Basically the amp is amplifying whatever comes into it a fixed number of times and being a dedicated unit, has no way of determining what is background noise and what is actually signal. If the hiss can be heard from around a foot or less, then this is normal. Also, you didn't actually say what the outcome of the various test were.
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Mister L'fe
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Post by Mister L'fe on Mar 21, 2010 21:58:50 GMT -5
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Lonnie
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Post by Lonnie on Mar 21, 2010 22:35:34 GMT -5
I was just reading through post 26 and didn't see what you are referring too. What I was asking is when you unplugged everything from the amp and turned it on what did you hear? When you went up the chain and connected only one piece of gear at a time and tested what did you get? this woudl be helpful.
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Mister L'fe
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There is nothing in the dark that isn't there when the lights are on.
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Post by Mister L'fe on Mar 22, 2010 8:56:19 GMT -5
Either amp no inputs, no noise. XPA-3 and pre-pro, no noise. XPA-5 and pre-pro noise in the two outer channels. I had exactly the same results when I us using the Onkyo 707 pre-amp outs before switching to the 5507. Now with the balanced cables there is just a very faint noise (ear right at the drivers) from the same two outer channels on the XPA-5. All other channels (both amps) are dead silent.
Edit: Thinking back, if I plug one channel at a time into the XPA-5, starting from left to right, the first channel is quiet. As I add channel inputs the first channel then becomes noisy.
Edit 2: From your above post about how loud the hum was. At the beginning of this exercise I could hear the hum from the listening position, 11 feet from the speakers.
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