A whole lotta feedback from CV-5000 - AVS Forum
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post #1 of 28 Old 09-18-2013, 07:09 PM - Thread Starter
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Hey guys, just hooked up the cv-5000 to its own dedicated 20 amp breaker. Now I am getting a whole lotta feedback. More feedback then bass it seems.

How the heck do I fix this?
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post #2 of 28 Old 09-18-2013, 07:15 PM
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Quote:
Originally Posted by 04rex View Post

Hey guys, just hooked up the cv-5000 to its own dedicated 20 amp breaker. Now I am getting a whole lotta feedback. More feedback then bass it seems.

How the heck do I fix this?

I'll bet money you don't mean feedback, you mean hum. Two very different things!

You are probably getting a ground potential difference, due to the amp being on a different circuit.

Is the audio line to the amp balanced or unbalanced?

One quick solution is a ground isolator - you can find them at Radio Shack and other electronics stores.
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post #3 of 28 Old 09-18-2013, 07:32 PM - Thread Starter
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Yeah I guess it could be that. The louder I out the volume the louder the noise. Like I said it is louder than the bass pretty much.

The audio line is a RCA cable as my receiver only supports that.

So is the ground loop isolator the best option?
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post #4 of 28 Old 09-18-2013, 08:39 PM
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with the amp completely disconnected from the signal inputs, does it make any noise or dead quiet?

also, is there anything else on the circuit with the amp such as a light with a dimmer switch?

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post #5 of 28 Old 09-18-2013, 08:41 PM
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i'm thinking this is your solution:

http://www.amazon.com/Stinger-SGN20-Ground-Loop-Isolator/dp/B002ZRQ3PW

or

http://www.amazon.com/Behringer-HD400-2-Channel-Hum-Destroyer/dp/B000KUD2G4

:-)

but just want to make sure that you don't have a bad amp first.

tough to know what the rolloff is though.

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post #6 of 28 Old 09-18-2013, 08:43 PM
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Try running a ground wire from the chassis of the amp to the chassis of your receiver.
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post #7 of 28 Old 09-18-2013, 08:55 PM
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see, this is the problem: http://www.k6jrf.com/FT_HUM.html

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post #8 of 28 Old 09-19-2013, 05:22 AM - Thread Starter
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There is nothing else on the circuit for sure.

I will try to remove the signal inputs and see if it makes noise.
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post #9 of 28 Old 09-19-2013, 05:27 AM - Thread Starter
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Ok, when I remove the signal connection, there is zero noise. Dead silent. As soon as I plug in the signal cable, the hum comes back.
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post #10 of 28 Old 09-19-2013, 05:42 AM
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That is a good thing. Now you know it is a grounding issue. Do what the posts above say and you will be fine.

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post #11 of 28 Old 09-19-2013, 06:01 AM
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Quote:
Originally Posted by LTD02 View Post

see, this is the problem: http://www.k6jrf.com/FT_HUM.html

Something like it.

Here's another reference:

http://www.epanorama.net/documents/groundloop/basics.html

This is IMO the key illustration from that document:



The safety ground shown above as one wire above may actually be a network of wiries in an actual home. It is formed of the (usually green insulated or uninsulated) safety ground wiring related to the grounding pin on modern electrical outputs. Typically, there is a continuous (but spliced and tapped) piece of copper from the outlet back to the distribution panel, and the safety ground on the distribution panel is connected to a ground rod driven into the earth or something like it.

The amount of current flowing in this wire should be zero or just leakage current, but sometimes it is actually quite a bit. The gauge of this wire is usually the gauge of your house wiring, in the US either 12 or 14 gauge. The advice to connect the two chassis with a piece of wire basically puts that wire in parallel with a 12 or 14 gauge wire, and given the good conductivity of 12 or 14 gauge wire you aren't going to improve on it very much! You can improve on it if it is defective.

I've measured as much as several volts difference between safety grounds in different parts of the same building. This will make unbalanced lines hum like a thousand bees! Most modern balanced inputs are active circuits which lack the ability to reject high ground potential differences. Transformers and optical fiber are nearly perfect at rejecting hum from this source.

The source you cited shows a lot of frequency response losses due to transformers that are not cheap. I'm surprised! I'm most familiar with the RS transformer which actually has better response than the high priced ones. My own measurements show even better performance. But the author has tapped into one undeniable truth and that is the fact that the RS transformer picks up hum fields very strongly. I have one in the signal path to my subwoofer, and it didn't stop humming until I placed it inside a small tomato paste can, with the top replaced with a jar lid that just happened to slip in nice and tight.
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post #12 of 28 Old 09-19-2013, 06:02 AM
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Quote:
Originally Posted by 04rex View Post

Ok, when I remove the signal connection, there is zero noise. Dead silent. As soon as I plug in the signal cable, the hum comes back.

The noise is hum and the problem is called a ground loop or ground potential difference.
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post #13 of 28 Old 09-19-2013, 08:05 AM - Thread Starter
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Ok. Thanks guys. I will get a ground loop isolator and let you guys know how it works.
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post #14 of 28 Old 09-19-2013, 08:20 AM
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Quote:
Originally Posted by 04rex View Post

Ok. Thanks guys. I will get a ground loop isolator and let you guys know how it works.

Make sure it is a ground loop isolate for the "low voltage" signal (as linked above) and not the power cable . While clipping the ground pin can work...it puts you in harms way if there is a fault in the amplifier.



Note: Edited to clean up confusion.

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post #15 of 28 Old 09-19-2013, 09:28 AM
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"Ok, when I remove the signal connection, there is zero noise. Dead silent."

great! there is an outside chance that the ground loop is coming through something like your television cable or something like that into your avr and isolating that may be better than in between your avr and amp, but isolation in between your avr and amp should clean it up.

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post #16 of 28 Old 09-19-2013, 12:29 PM - Thread Starter
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It worked!!!! Thanks guys. At first it greatly reduced it. There was still a bit of noise that I could hear when it was quiet. A whole lot less than before. It was an amount that was very annoying and bothered me, but I could live with. I could hear it while playing a scene but I am sure a regular person wouldn't notice. But I sure did.

After that I swapped out my cheap RCA cable and connected an Acoustic Research Master Series cable and the noise is now completely gone. I guess there really is a difference between cables. Has a lot better shielding or what have you.

Thanks for all the help and advice.
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post #17 of 28 Old 09-19-2013, 12:36 PM
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A WIN!

out of curiousity, which device did you go with?

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post #18 of 28 Old 09-19-2013, 12:51 PM - Thread Starter
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I live in Canada. There is a store called The Source which is like radio shack.

Here's the link: http://www.thesource.ca/estore/product.aspx?language=en-ca&catalog=online&category=Stereo%20Cables&product=2700054
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post #19 of 28 Old 09-19-2013, 12:55 PM
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roger.

so where was this change made?

"After that I swapped out my cheap RCA cable and connected an Acoustic Research Master Series cable and the noise is now completely gone."

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post #20 of 28 Old 09-19-2013, 12:58 PM - Thread Starter
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The huge change was by putting the ground loop isolator. But there was still a small hum. Not really noticeable with a movie but I could still slightly hear it. Then on a hunch, since I bought the AR cables, I switched out the regular RCA and put in the AR cables. Now it is completely silent.
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post #21 of 28 Old 09-19-2013, 01:02 PM
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I understood that much. :-) where in the setup did you switch out the rca cable, i.e. the switch was made to the better cable in between which two devices?

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post #22 of 28 Old 09-19-2013, 02:07 PM - Thread Starter
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Lol. Sorry. So it was from my receiver to the isolator hat I switched. The isolator is connected to the CV.
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post #23 of 28 Old 09-19-2013, 02:26 PM
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So you extended to isolators rca cable using the Audio Research RCA?

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post #24 of 28 Old 09-19-2013, 03:36 PM
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"Lol. Sorry. So it was from my receiver to the isolator hat I switched. The isolator is connected to the CV."

ok, got it. thanks. that is an interesting one to keep in mind.

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post #25 of 28 Old 09-19-2013, 06:21 PM - Thread Starter
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Another question more towards the subs. I noticed that after I built the boxes and put the subs in, if I pushed the sub in there was a tiny amount of an air leak on one of the screw areas for 3 of the subs (I have 4 total). I tried to tighten the screw but it doesn't go anymore. How will this affect sound quality and is there an easy fix to it?

I'll start a new thread for this.
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post #26 of 28 Old 09-19-2013, 08:24 PM
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Quote:
Originally Posted by 04rex View Post

Another question more towards the subs. I noticed that after I built the boxes and put the subs in, if I pushed the sub in there was a tiny amount of an air leak on one of the screw areas for 3 of the subs (I have 4 total). I tried to tighten the screw but it doesn't go anymore. How will this affect sound quality and is there an easy fix to it?

I'll start a new thread for this.

Take the sub out, use some gasket tape and re-install. Also check for a bent basket while the sub is out.

Blasting brown notes for 10 years and counting!

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post #27 of 28 Old 09-20-2013, 05:32 AM
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Do what N8DOGG said because the sound quality will be very bad with an air leak. Kinda like a car with an exhaust leak, sounds so bad!

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post #28 of 28 Old 09-20-2013, 07:26 AM - Thread Starter
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Yeah. I am hearing a fluttering sound. The leak isn't that big at all. But I have already ordered the gasket tape.
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