Noise problem in system

soth · Post by **soth** » Thu Jun 26, 2008 6:01 pm

Yet here is another problem with some noise. I will start off by describing where everything is located first.

HU
EQ-215x
AX-406A
Multiple amplifiers

01. RCA's are ran from the Eclipse cd5000 HU to the input of the eq-215x.
02. Aux output from the EQ is going to the input of the crossover.
03. Gains have been set to where the crossover is getting around 7 volts from the aux output of the eq.
04. I have looked at all the how to faqs here for amplifier noise and system noise in general.
05. Power cables are ran on the left side of the vehicle.
06. RCA and speaker wires are ran on the right side of the vehicle.
07. Crossover, eq, amplifiers are all grounded to the chassis of the vehicle in a common point.
08. Upgraded the negative battery terminals and the cable from the battery to the chassis.
09. Not upgraded the other "2" of the big 3 yet.

I have narrowed it down to my noise is coming from the crossover. If I take the crossover out of the picture I have 0 noise. If I add the crossover back in the picture then I get a humming/whining noise when the engine starts. I've tried multiple rca cables and everything else I can think of.

All crossovers, amplifiers, etc are mounted directly to wood by amplifier racks or other racks. The eq is mounted to wood that is carpeted, but the crossover is mounted to an amplifier rack with the mps2240 in front of it. It is painted flat black (rustoleum). That wouldn't have anything to do with it would it?

Any ideas why I get noise when I hook the crossover up and no noise whenever I take it out of the design?

I'm up for any suggestions

Thanks!!!!

PS: Need more info, ask and i'll provide

Post by **Jacampb2** » Thu Jun 26, 2008 6:38 pm

My guess would be a ground loop problem with the xover. Typically caused by a signal path sharing an un-isolated ground with the power supply. It won't be that way by design in a mid to high end product, but there could be an internal failure.

The other possibility is that one of your signal cables connected to the crossover has a bad shield connection, or the shield is connected to power supply ground somewhere. If any of the signal shields are touching ground anywhere, even unused outputs behind the HU, you can introduce problems to the entire system. All of the signal grounds are common in the source unit, and typically at vehicle ground, and this should be the ONLY place they are at vehicle ground potential. Any other vehicle ground connection to the shield, even a few inches away can screw the pooch.

Good Luck,
Jason

soth · Post by **soth** » Thu Jun 26, 2008 6:54 pm

I'll definately go check and make sure of that. The only thing I don't think i've checked is with the crossover hooked up with only the inputs connected and no outputs. I've used the same rca going from the HU to the eqs input to hook it to the inputs of the crossover. Noise with the crossover but no noise with the eq.

Thanks for the suggestions Jason,

Kevin

Post by **Jacampb2** » Thu Jun 26, 2008 7:42 pm

I edited the above a little bit. After re-reading it, the explanation of signal grounds at the source wasn't very well explained.

Regarding the same signal cable having no noise w/ one processor, and not the next: That is not a 100% valid test as to whether the signal path is the problem. The reason is that different preamp input stages have varying levels of noise rejection. It is entirely possible for one processor, or piece of audio equipment to reject the noise that picked up on the cable and another processor will not be able to. The circuit works by processing only the difference in information found on the signal and shield. Any radiated noise should be common to both the signal and shield, and therefore gets rejected. The problem comes if one piece of equipment toward the front of the chain does not do a good job of rejecting the noise. After it has processed it, it passes it along on the signal conductor, and it is no longer the same as the noise on the shield. The next piece of equipment in line, then cannot reject it, because the processed noise is no longer the same as the noise on the shield. Make sense?

The above does not really apply to a ground loop situation, but rather to a radiated noise source of some form. All current flow induces EMF in nearby conductors, so it is a perfectly applicable scenario to have radiated noise in a vehicle.

Check the xover with a DMM for continuity between the RCA shield connections and the power - input. Do this with nothing connected to the xover. No RCAs or power/ground/remote connections. If you have continuity, there is almost certainly a problem with the xover. Check that none of the RCA shield connections on the crossover are making contact with it's case.

Good Luck,
Jason

shaheen · Post by **shaheen** » Fri Jun 27, 2008 2:08 am

A406 problem,

I posted about this a few weeks ago , check the switches inside the unit , they tend to gum up and cause noise issues. I have verified this with 2 people who have them as well, some silicone based cleaner on the switches should clean them out.

soth · Post by **soth** » Fri Jun 27, 2008 3:03 am

Jacampb2 wrote:I edited the above a little bit. After re-reading it, the explanation of signal grounds at the source wasn't very well explained.

Regarding the same signal cable having no noise w/ one processor, and not the next: That is not a 100% valid test as to whether the signal path is the problem. The reason is that different preamp input stages have varying levels of noise rejection. It is entirely possible for one processor, or piece of audio equipment to reject the noise that picked up on the cable and another processor will not be able to. The circuit works by processing only the difference in information found on the signal and shield. Any radiated noise should be common to both the signal and shield, and therefore gets rejected. The problem comes if one piece of equipment toward the front of the chain does not do a good job of rejecting the noise. After it has processed it, it passes it along on the signal conductor, and it is no longer the same as the noise on the shield. The next piece of equipment in line, then cannot reject it, because the processed noise is no longer the same as the noise on the shield. Make sense?

The above does not really apply to a ground loop situation, but rather to a radiated noise source of some form. All current flow induces EMF in nearby conductors, so it is a perfectly applicable scenario to have radiated noise in a vehicle.

Check the xover with a DMM for continuity between the RCA shield connections and the power - input. Do this with nothing connected to the xover. No RCAs or power/ground/remote connections. If you have continuity, there is almost certainly a problem with the xover. Check that none of the RCA shield connections on the crossover are making contact with it's case.

Good Luck,
Jason

Ok, makes more sense now

. I will check those tests later this morning and post back with results. Come to think of it I had noise in my prior vehicle, but I had a different HU, didn't have the eq at that time either. I had just ruled it with having to upgrade the big 3 at that time though and never got around to fixing it though.

Thanks,
Kevin

soth · Post by **soth** » Fri Jun 27, 2008 3:04 am

shaheen wrote:A406 problem,

I posted about this a few weeks ago , check the switches inside the unit , they tend to gum up and cause noise issues. I have verified this with 2 people who have them as well, some silicone based cleaner on the switches should clean them out.

From what I can tell everything inside looks clean, but i'll give it a cleaning out anyway

Thanks,

Kevin

soth · Post by **soth** » Fri Jun 27, 2008 5:49 pm

Ok, update. I placed the ground probe on the rca shield connectors on the x-over with nothing connected to it at all. Placed the red probe in the b+ connector on the x-over. The DMM doesn't do anything. However when I touch the red probe to the black probe it counts down to 0.00 or just 0. Am I testing this correctly Jason?

Also cleaned the switches inside also, but that didn't help though.

Thanks,

Kevin

Post by **Jacampb2** » Fri Jun 27, 2008 8:16 pm

You want to check between the shield and the b- (ground) connection on the crossover. If it goes to 0 or any other resistance then you have a problem. The reading you see on your meter with neither lead touching anything, is what you want to see when you touch the leads to the shield and ground. The meter reading when the two leads are directly in contact will be 0 ohms, or a direct short.

Check all of the shield connections, not just one, or even one pair. The inputs are sometimes isolated from the outputs and, a problem on one side may not be seen by testing the other.

Hope that helps,
Jason

soth · Post by **soth** » Sat Jun 28, 2008 6:12 am

Sure does Jason. I will go check that in a bit, but first I have to fix my water leak outside, been at that for a day almost now, but finally found the leak

Thanks again

Kevin

soth · Post by **soth** » Sat Jun 28, 2008 3:50 pm

Well looks like everything checks out ok so i'm back to square 1

Just doesn't make sense.

soth · Post by **soth** » Tue Jul 08, 2008 10:21 am

After re-doing the ground and upgrading 2 of the big 3 i've still got noise. Checking my resistance on the ground returned 0.2 so i'm thinking it's not a ground issue at this point.

After following steps from some other car audio sites it really appears there is a problem with the x-over. If I pull it out of the signal path absolutely 0 noise, but whenever it gets placed in the path HU->X-Over->Amp for example there is noise.

Anything else I should try that you guys can think of before starting to look for another x-over? I don't think the EQ-215x will serve my purpose for the bandpass range as i'm thinking it goes from 600-2000hz or something like that, not sure.

I'd like to just take the 406a out of the equation at this point, but the ms/mps series doesn't have a built in x-over in them, grrrrrr

Thanks.

soth · Post by **soth** » Wed Jul 09, 2008 4:35 pm

Ok, update on the problem. Seems as though my right rca jack on the bandpass is what is causing the noise. With rcas plugged into the lowpass or highpass there is no noise. With the right rca out of the bandpass there is no noise, but once the rca is plugged back into the right side of the bandpass section I get noise.

Now to try and figure out what is causing that

soth · Post by **soth** » Sat Jul 12, 2008 2:42 pm

Problem fixed