Amp turn on wire whine

[WhiteYota]

Quick question - Do you know if anyone has had issues with Knu's Karma SS RCA cables - I used both the 4 channel and 2 channel 6 meter ones

 

[m4ick 10+ year member]

Can you eliminate the noise by disconnecting a particular pair of RCAs?

 

[WhiteYota]

@m4ick
I did try disconnecting the rca's off of the 3800 (amp side) last night and the noise does go away. I also tried just plugging them in one at a time and it still produced the whine.

I also will mention that when I had the HU apart to check the pico fuses - I did find two but with an ohm's meter only one was open and I did solder a jumper on it.

 

[wew lad 5,000+ posts]

You have two amps correct? Be sure to check that one amp isn't backfeeding bad noise back into the other. It happens more often than you think, I experienced it. I assume it occurs due to a ground loop causing there to be a difference in voltage between the two amps which cause DC voltage to be sent back up the RCAs to the HU and back out to your other amps.

Next thing id try would be a completely different source unit... it sounds like you're pretty technically experienced and know how to solder and whatnot, but there could be things you don't see.

 

[WhiteYota]

You have two amps correct? Be sure to check that one amp isn't backfeeding bad noise back into the other. It happens more often than you think, I experienced it. I assume it occurs due to a ground loop causing there to be a difference in voltage between the two amps which cause DC voltage to be sent back up the RCAs to the HU and back out to your other amps.
Next thing id try would be a completely different source unit... it sounds like you're pretty technically experienced and know how to solder and whatnot, but there could be things you don't see.

Ya - two amps, a 4 channel and a monoblock. If they are backfeeding, it could be either through the REM wire, power and/or ground where the rca's are all seperate.

I don't exactly have another HU to try and the closest place to get one for me is about an hour and half drive or buy one off the net. One of the joys of living way out in the sticks lol.

I went through a crash course in electronics (so to speak) about 10 years or so ago

 

[wew lad 5,000+ posts]

Let me be a little more specific, are all your amps connected to the same HU via RCAs? The RCAs may be routed seperate, that's not the point. If they're connected to the source and one amp is bad and muddying up the reference signal it will sometimes cause the reference in the HU to also be disturbed on the outputs for your other amplifiers.

I would tell you to use an aux 3.5mm to RCA but the issue is it's not the same as a HU with all your RCAs connected (aux is a lower pre out voltage than most hu's). You can't rule the headunit in or out until you either use an oscilloscope on it, or try a different headunit.

 

[WhiteYota]

Let me be a little more specific, are all your amps connected to the same HU via RCAs? The RCAs may be routed seperate, that's not the point. If they're connected to the source and one amp is bad and muddying up the reference signal it will sometimes cause the reference in the HU to also be disturbed on the outputs for your other amplifiers.
I would tell you to use an aux 3.5mm to RCA but the issue is it's not the same as a HU with all your RCAs connected (aux is a lower pre out voltage than most hu's). You can't rule the headunit in or out until you either use an oscilloscope on it, or try a different headunit.

Ah ok gotcha - I just figured it was something I did wrong with the mono amp because the only time the whine/hiss is there is when it is either turned on or with the rca's connected to it. Thats also why I didnt think the HU was creating it.

I think I am going to try to find some RCA Y splitters and go from one of the 4 channel outputs and see if it is just the sub out on the HU.

 

[wew lad 5,000+ posts]

the only time the whine/hiss is there is when it is either turned on or with the rca's connected to it. Thats also why I didnt think the HU was creating it.

This should be a big red flag that the mono amp is causing the problem. If you only get noise when the sub amp is plugged in to the same hu as the other 4 channel amp then you have a problem with your mono amp being bad(possible open ground to reference) or it's grounding relative to your other grounded components (headunit, 4 channel amp, etc). the previous is true IF you've already rules out the RCAs and routing with alternates.

I have the exact same issue, however it's not that bad, I can barely hear it. If it's as bad as you say then it's a definite problem.

 

[fly_marlin]

This is one of those problems that would drive me crazy as figuring out the noise problem can be maddening. I'll start off by saying I use exclusively Knu RCAs and exclusively krystal kables, never had an issue. Barring that your sub amp is causing the issue and needs to be sent back for repair/exchange, did you try to find a new ground for the sub amp? Also, perhaps new ground wire? Also, RCAs could be the issue - maybe you have a spare to swap and check. Hope this works out for you, I know how insane these noises are.

 

[WhiteYota]

This should be a big red flag that the mono amp is causing the problem. If you only get noise when the sub amp is plugged in to the same hu as the other 4 channel amp then you have a problem with your mono amp being bad(possible open ground to reference) or it's grounding relative to your other grounded components (headunit, 4 channel amp, etc). the previous is true IF you've already rules out the RCAs and routing with alternates.
I have the exact same issue, however it's not that bad, I can barely hear it. If it's as bad as you say then it's a definite problem.

My wife didn't notice the whine until I mentioned it, so it really might not be that bad lol. You think it would be worth warranting the amp for or should I try filters or do my own checking on it?

 

[WhiteYota]

This is one of those problems that would drive me crazy as figuring out the noise problem can be maddening. I'll start off by saying I use exclusively Knu RCAs and exclusively krystal kables, never had an issue. Barring that your sub amp is causing the issue and needs to be sent back for repair/exchange, did you try to find a new ground for the sub amp? Also, perhaps new ground wire? Also, RCAs could be the issue - maybe you have a spare to swap and check. Hope this works out for you, I know how insane these noises are.

That is good to know - I think I remember reading a post on here about one of knu's rca cables but I didnt have much luck finding the one I read.

On the grounds - I will take pics of how I did them, kinda forgot that part when I was doing my build log.

 

[fly_marlin]

Ok, sounds good. Not sure if your grounds are shared between the amps, but it's advisable that they be separate.

 

[los33 10+ year member]

Ok, sounds good. Not sure if your grounds are shared between the amps, but it's advisable that they be separate.

Why is that?

Sent from my Z970 using Tapatalk

 

[fly_marlin]

Don't recall the reasoning behind it exactly, but I can look into it. Have read it many times before and my installer has also advised that.

 

[WhiteYota]

Yes they do share a common ground point - it is however a 3/8" bolt.

Here is with them disconnected

Here they are connected - the bottom is the 4 guage for the 4 channel and the top is 1/0 Knu klossus flex OFC using a Knu lug. The other purple wire is 4 guage power for the 4 channel.

Here is the ground from the battery - using the same wire and method as the back ground in the above pics