BUZZING-- sound through speakers after amp... - AVS Forum
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post #1 of 21 Old 05-28-2010, 05:31 PM - Thread Starter
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so i just hooked up my amps (gli pro pvx 9000) to my harman kardon avr 354...
the speakers are cerwin vega vs150's...
now after going through the amplifier there is a buzzing/humming sound that is coming through the cerwins, and it is driving me nuts...
i tried an adapter for the plug to take away the ground... still buzzing/humming....
i cant really tell if it is a hum or a buzz... sounds like both..
we are using 14gauge to go from the amp to the speakers, and RCA to XLR(male) to go to the amp... the wire between the RCA to XLR is 12gauge speaker wire(one 12gauge for "hot" one 12 gauge wire for the shield)

what can this be?

thanks alot
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post #2 of 21 Old 05-28-2010, 08:06 PM
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Try turning the amp's volume controls all the way off. If the hum goes away, it is coming in thru the inputs. In that case, make sure the audio wires are not near power cords or running in parallel with them. Also watch out for wall warts or other inline power converters--they can throw off a hum field.

If the hum remains, then while leaving the volume controls off, disconnect the audio inputs. If the hum goes away, it is some grounding disagreement between the amp and the audio source.

Since the AVR 354 has no XLR outputs, how are you converting from phono to XLR? That may be an issue.

The amp is a bit of an odd bird. How do they claim to output 2,000 W per channel and 10,000 W total when the wall outlet only supplies 2,400 W total?
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post #3 of 21 Old 05-28-2010, 08:29 PM - Thread Starter
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If the receivers volume is turned off than the hum stops

are you saying if the power cords are tangled with the wires for the amp and speaker it can create interference (humming)????



this is exactly what i have for (amp pre outs(rca) to amp input(xlr))

http://www.creativevideo.co.uk/publi...rca-stereo.jpg
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post #4 of 21 Old 05-28-2010, 08:36 PM
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Quote:
Originally Posted by dom08 View Post

If the receivers volume is turned off than the hum stops

The receiver? Or the amp? If the hum is controlled by the receiver's master volume control, then there's no problem with the amp or the interconnects. The hum is coming from an input source.

Quote:


are you saying if the power cords are tangled with the wires for the amp and speaker it can create interference (humming)????

Not the speaker wires, but if there are power wires close to the low-level audio interconnects, it is possible.

Let's first figure out where in the chain the hum is coming in. Right now I am confused by your reply.
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post #5 of 21 Old 05-29-2010, 02:08 AM - Thread Starter
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alright what happens is.. ill turn the amps on; the hum only starts when there is sound playing.. the master volume no matter how much it is turned up or down will not make the hum go louder or softer. Once i turn the master volume (all on the receiver) to 0.. it kills all sound, once i turn it up a notch, the hum starts...
i hope that clears it up??? let me know and i can try to explain it better
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post #6 of 21 Old 05-29-2010, 08:12 AM
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It seems to be coming from the receiver or pre amp in the receiver. This is usually not the case. Most pro amps do have a noise floor but is usually not that loud. Some pro amps may have a louder noise floor than others. It will make the noise with just the pro amp on and the receiver off. I have a similar set up like yours but my receiver does not induce any noise. I just have the usual slight tweeter hiss with no music playing. You have to almost put your ear right next to the speaker to hear it. I have a pair of Cerwin Vega CLS-215's powered by a CV2800 pro amp and pre amped by an Onkyo 805 with a DBX1231 EQ in the chain. Check the cable from the receiver to the pro amp and try to keep it away from any other cables or power cords as others have suggested. Possibly try another cable if possible. I have never had any issues with cables being ran close together but it is always something to consider.
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post #7 of 21 Old 05-29-2010, 11:56 AM
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Quote:
Originally Posted by dom08 View Post

alright what happens is.. ill turn the amps on; the hum only starts when there is sound playing.. the master volume no matter how much it is turned up or down will not make the hum go louder or softer. Once i turn the master volume (all on the receiver) to 0.. it kills all sound, once i turn it up a notch, the hum starts...
i hope that clears it up??? let me know and i can try to explain it better

Still some conflicting evidence. a) >>the master volume no matter how much it is turned up or down will not make the hum go louder or softer<< vs. b) >>Once i turn the master volume (all on the receiver) to 0.. it kills all sound, once i turn it up a notch, the hum starts...<<

1) Can you confirm that the hum is present when you select, say, a CD or DVD input, while the player is stopped? Does it matter if you change sources? Can you also confirm that the hum in this case behaves as in a), or does it in fact vary in loudness as the volume changes?

2) It looks like the power amp has its own volume controls. If you turn them all the way down, does the hum go away?

3) Assuming Yes to 2), do you hear the same hum if you drive a speaker directly from the AVR? Leave the amp connected and humming--just move the speaker connection, and since the other speakers are making hum, you will need to either check the AVR's speaker very closely, or temporarily reduce the amp's volume (and hum) so you can hear if it is coming from the AVR or not.

If the hum is coming from the AVR, try disconnecting the inputs to see if one of them is causing it. Often, a cable/sat box brings in another ground from the antenna, and this can cause hum.

If the AVR can be shown to be totally hum free when standing alone (no other inputs/outputs, and speakers directly connected), then the issue is to find which of those external connections, or the combination, is introducing the hum problem.

If the AVR has a hum even when running bare bones, and it is not being induced by some unusual electrical field nearby, it would appear to have an internal power supply problem.

Hence, all this effort to try to figure out where it originates.
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post #8 of 21 Old 05-29-2010, 02:28 PM - Thread Starter
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Quote:
Originally Posted by Roger Dressler View Post

Still some conflicting evidence. a) >>the master volume no matter how much it is turned up or down will not make the hum go louder or softer<< vs. b) >>Once i turn the master volume (all on the receiver) to 0.. it kills all sound, once i turn it up a notch, the hum starts...<<

1) Can you confirm that the hum is present when you select, say, a CD or DVD input, while the player is stopped? Does it matter if you change sources? Can you also confirm that the hum in this case behaves as in a), or does it in fact vary in loudness as the volume changes?
when dvd is selected it hums, when game is selected it hums, i havent tried it with tv.. it only hums when the avr's volume control is not turned to 0 (off)


2) It looks like the power amp has its own volume controls. If you turn them all the way down, does the hum go away?
when the amps volume controls are off(turned to 0) it stops... you just get a static noise

3) Assuming Yes to 2), do you hear the same hum if you drive a speaker directly from the AVR? Leave the amp connected and humming--just move the speaker connection, and since the other speakers are making hum, you will need to either check the AVR's speaker very closely, or temporarily reduce the amp's volume (and hum) so you can hear if it is coming from the AVR or not.
from the AVR we get no hum,

If the hum is coming from the AVR, try disconnecting the inputs to see if one of them is causing it. Often, a cable/sat box brings in another ground from the antenna, and this can cause hum.

If the AVR can be shown to be totally hum free when standing alone (no other inputs/outputs, and speakers directly connected), then the issue is to find which of those external connections, or the combination, is introducing the hum problem.

If the AVR has a hum even when running bare bones, and it is not being induced by some unusual electrical field nearby, it would appear to have an internal power supply problem.

Hence, all this effort to try to figure out where it originates.



when i take the rca's off of the AVR the little silver with the color inside comes off...
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post #9 of 21 Old 05-29-2010, 05:11 PM
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Do you mean the female inside of the rca on your receiver starts coming apart? Or the male pin in the center of the rca cable is coming apart? Neither of those situations sounds good. Both may cause the hum you are talking about.
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post #10 of 21 Old 05-29-2010, 06:47 PM - Thread Starter
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its the female part on the receiver....
when it comes off, the female part is just plastic... it looks like the silver is just a slip that goes over and makes it not look plastic'y
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post #11 of 21 Old 05-29-2010, 11:38 PM
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Quote:
Originally Posted by dom08 View Post

when the amp's volume controls are off (turned to 0) it stops.

from the AVR we get no hum

Ok, so my deduction is that the AVR and it's sources are all fine, and the power amp is fine, but they do not like to be connected together.

[Wait a minute] I re-read your first post and see that I missed something: >>we are using 14 gauge to go from the amp to the speakers, and RCA to XLR(male) to go to the amp... the wire between the RCA to XLR is 12 gauge speaker wire (one 12gauge for "hot" one 12 gauge wire for the shield)<< Are you saying that you are using a 2-conductor speaker wire to drive the power amp audio? If so, replace them with proper shielded RCA cables. If the amp has RCA inputs, try them, it's cheaper. If you need to use RCA-XLR, try BlueJeansCable (sponsor button at the top for your convenience) and order the desired length.
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post #12 of 21 Old 05-30-2010, 12:12 AM
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OT,
I have a hum in the left side surround speaker when the pre/pro is turned off....When I turn the pre/pro on, the hum disappears. I've swoped out rca's and the same thing happens. Could be a ground issue or some other anomaly. Any comments on that? I live close to an AM tower just 1/8th of a mile away. Sometimes when the ground/dirt is wet, I can hear AM thru my speakers....I will try to see if it's my amp (NAD 925THX) by switching the outputs....In any case it doesn't matter; this only happens when the pre/pro is turned off...............

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post #13 of 21 Old 05-30-2010, 12:30 AM
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Quote:
Originally Posted by KBMAN View Post

OT,
I have a hum in the left side surround speaker when the pre/pro is turned off....When I turn the pre/pro on, the hum disappears. I've swoped out rca's and the same thing happens. Could be a ground issue or some other anomaly. Any comments on that? I live close to an AM tower just 1/8th of a mile away. Sometimes when the ground/dirt is wet, I can hear AM thru my speakers....I will try to see if it's my amp (NAD 925THX) by switching the outputs....In any case it doesn't matter; this only happens when the pre/pro is turned off...............

The output impedance of a preamp (or even a power amp) is low when powered on, as only then do the output devices exhibit a low impedance due to being turned on and having bias current running through. Add to that the negative feedback typically used further reduces the output impedance, but that is also gone when powered off.

When the output stage is turned off and in a high impedance state, the audio interconnect is able to pick up the hum fields driving the high impedance of the amp's input.
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post #14 of 21 Old 05-30-2010, 03:04 AM - Thread Starter
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i think i solved the problem, i believe its the ACRs pre-outs

i cut off the rca and hooked the positive and negative to the banana plugs for the speaker out put. the hum goes away.
there is still a slight buzzing when the amps volume is turned up all the way.


also the speakers kick alot more when the amps are hooked up to the speaker out outs.


also this amp does not need to be hooked up to a pre-amp slot
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post #15 of 21 Old 05-30-2010, 08:26 AM
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Whatever is causing the hum is likely aggravated by the unusually high sensitivity of Cerwin Vega speakers (FWIW). Using a pro amp with consumer electronics can be sometimes result in connection mismatches, which I think is at the root of your problem. If I were you I would replace the pro power amp with something more consumer friendly such as a Sherwood Newcastle A-965, or a similar amp from ATI, Outlaw, Emotiva, NAD, Parasound, or Sherbourn. If you decide to stick with the pro amp you might consider this device, which cures hums and also adapts single ended to balanced connections:

http://www.sweetwater.com/store/detail/DTI/

This is a 2 ch version, I think they may also make a multichannel version - contact Sweetwater and ask. They are a great vendor.

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post #16 of 21 Old 05-30-2010, 08:52 AM
 
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Quote:


i cut off the rca and hooked the positive and negative to the banana plugs for the speaker out put. the hum goes away.

OMG, don't do this.

How are your RCA to XLR cables wired anyway? Are pins 1 and 3 shorted?
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post #17 of 21 Old 05-30-2010, 09:07 AM
 
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Quote:
Originally Posted by dom08 View Post

so i just hooked up my amps (gli pro pvx 9000) to my harman kardon avr 354...
the speakers are cerwin vega vs150's...
now after going through the amplifier there is a buzzing/humming sound that is coming through the cerwins, and it is driving me nuts...
i tried an adapter for the plug to take away the ground... still buzzing/humming....
i cant really tell if it is a hum or a buzz... sounds like both..
we are using 14gauge to go from the amp to the speakers, and RCA to XLR(male) to go to the amp... the wire between the RCA to XLR is 12gauge speaker wire(one 12gauge for "hot" one 12 gauge wire for the shield)

what can this be?

thanks alot

You are connecting a unbalanced output (avr 354) to balanced (gli pro pvx 9000)?. There is a way to do this, passively, that simulates a balance signal, and suppresses hum/noise. The cables you mention may or may not be wired to do this. I do not know how they are wired internally. If you google Behringer, Yorkville, Mackie websites you will see a wiring document to provide this passive hum/noise defeating set up. Here is another reference:
http://srforums.prosoundweb.com/inde...222#msg_540562

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post #18 of 21 Old 05-30-2010, 10:10 AM
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If your pro amp accepts 1/4 in I would use a pre made RCA to 1/4TRS cord. I think it does from the pictures I was able to find of your amp. About $4.99 a piece at Radio Shack. This is how I have my consumer pre amp and pro amp connected. Why are you using rigged cables? Your just asking for trouble. Just hook speaker wire to the binding posts on the pro amp and hook the wire to your speakers. XLR is a nice option but is a P.I.T.A. for the reason that not all of the pins are wired the same from device to device. That is why almost all pro gear comes with a diagram to show how the pins are wired for that particular unit. You can only reap the true balanced benefits if you go with XLR at both ends, which you really can't do when putting most home gear and pro gear together. XLR is used on stages over long runs and when there is a lot of interference being fought. So unless you have a huge stage in your room with hundreds of feet of other wires and equipment grouped together forget about XLR from the receiver to the pro amp. Sorry if this seems bold. Not trying to be rude.
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post #19 of 21 Old 05-30-2010, 11:48 AM - Thread Starter
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the problem with the amp is it only accepts XLR for inputs..
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post #20 of 21 Old 05-31-2010, 12:34 PM
 
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How are your cables wired?
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post #21 of 21 Old 06-01-2010, 10:23 PM - Thread Starter
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they are wired with a rca at one end and a XLR male connector at the other end. rca goes to acr xlr male goes to amp.
the wire is 14gauge.
xlr- 2 is hot; 1and3 are spliced together
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