Strange Amp Noise

eulogious · Post by **eulogious** » Fri May 14, 2010 12:50 pm

I asked this in my install thread, but figured I would get more help if I posted it over here…

Here's where I am at…

eulogious wrote:Ok, so I am now trying to isolate my amp noise, and I am really confused now. So the first thing I did was unplug the RCA's, one at a time from the amp. I unplugged the top one (left) and the noise went away. Unplugged the bottom one (right) and still no noise. So I then plugged the left RCA into the right input to see if the RCA was at fault. No noise. I then took the right RCA, which never had any noise on it, and plugged it into the amps left input, and I got noise. The noise is coming from the front left amp input I then proceeded to take my HU out and move RCA around to see what that did, it was always the same result. The left amp input makes noise, no matter the RCA

What does this mean? I replaced the 4 input caps, could I have gotten a ground wrong, or my solder didn't make a good connection? I really don't want to open the amp up again, but if I must… HELP! Thanks

stipud wrote:Hmmm maybe the RCA shield is broken on the left amp input? Not really sure man...

eulogious wrote:What do I look for? This is were my inexperience with amps kicks in

stipud wrote:You would have to check conductivity between the RCA shield and the circuit board where it mounts to.

eulogious wrote:Damn, it's got to come out and apart *sigh* Oh well. Thanks for the starting point, I will start there and see what I find. Can I test this in the car to see? I tried ground the RCA end to something else, and nothing changed, but that might not be the same thing...

Could it be the ribbon cable by chance? Any other ideas??

Thanks for the quick replies!!

So I am not going to take the amp out just yet, because I ran out of time today, and I have to drive to bellingham in the morning, and then back home on sunday, so I want to have tunes for the long drive

So I will pull the amp on Sunday and see what's up.

Any other suggestions on what it might be?? Thanks all!

eulogious · Post by **eulogious** » Sun May 16, 2010 10:21 pm

Alrighty, so I decided that I wanted to fix this damn alt whine, so I took the amp out to take a looksy at it. Once I pulled it apart, I started testing the resistance between the two ground trying to figure out what was different, if anything. Between the front 2 inputs, I was getting around 100 ohms

I then tested the rear input (I was assuming they were ok off my previous tests) and they were getting like .200k ohms. So there was a difference going on, so that must have something to do with it. So I started looking around the daughter board and notice some surface mount resistors that look like they got really hot. Well these all tied into the RCA's one way or another. There were 4 total that looked like they got really hot. So I tested them. All but 1 tested at 100 ohm, curious, and the one that didn't test looked real black, so I just took my iron, heated up the solder pads to see if that would help, and retested. This time I got a 100 ohms, just like the others. Weird. So I tested the ground between the rca on the front input, and I got .200k ohms, just like the rear. Ok, so I put it all back together and went out and installed it in my car, started the car, and no whine!!

It's fixed!!

So when I was thinking back, I have always had an alt whine from day one in the 2 cars that this amp has been used in, but I always ruled it on me not doing the big three

and just never cared to research it any farther. But now I think that it was a factory defect

The only thing that I touched with my iron was that resistor, and now it works just fine, and is super quite!!! Makes me way happier! I am still going to do the big three, but at least now I know it wasn't my wiring or anything, but a actual problem with the amp! Thanks for pointing me in the right direction stipud!

dBincognito · Post by **dBincognito** » Mon May 17, 2010 2:04 am

Read this

http://phoenixphorum.com/amplifier-dist ... t3428.html

eulogious · Post by **eulogious** » Mon May 17, 2010 9:14 am

dBincognito wrote:Read this

http://phoenixphorum.com/amplifier-dist ... t3428.html

That's good info, but doesn't apply to me, I don't think, unless I missed something... My music never sounded bad, I just had the whine in the background. Simply heating up that one resistor was all I needed.

Post by **stipud** » Mon May 17, 2010 10:00 am

Phew... glad I didn't send you on a wild goose chase!

eulogious · Post by **eulogious** » Mon May 17, 2010 10:37 am

stipud wrote:Phew... glad I didn't send you on a wild goose chase!

Your telling me! I was super afraid that it was going to be something complicated, and it ended up being something so simple, I love it! If only everything were that easy… Thanks again man!

eulogious · Post by **eulogious** » Mon May 17, 2010 4:58 pm

Well, I took the amp out of the car to put it all back together from my testing, and after putting it all back together, I put it back into the car, and I had the alt whine, but this time in both channels!! So I pulled it back out, took it all back apart and looked at everything again. Everything looked good and tested ok. When I put it back together the one thing I did not do, that I did before was I "clipped" the daughter board to the bottom of the case like it's suppose to from the factory. The last time I put it together I didn't manage to get both sides firmly pressed into place, and this time I did. Well when I took it apart and back together for the last time, I did not clip it in at all, just like in my testing, and I have no noise again. What does that mean. I am just going to leave it disconnected like it is sense it works, but is this something I should be concerned about? I don't think it will be, but I really don't know… Thanks!

Post by **stipud** » Mon May 17, 2010 5:13 pm

Make sure the screws that mount the amp down aren't touching the body at all. Some amps don't like being grounded to the vehicle.

eulogious · Post by **eulogious** » Mon May 17, 2010 5:16 pm

stipud wrote:Make sure the screws that mount the amp down aren't touching the body at all. Some amps don't like being grounded to the vehicle.

All the screws are in and it's working fine. I have a piece of wood that they are mounted to, and my screws aren't super long.

The "clip" that I am talking about is you just press down on the circuit board and it snaps into place. I just didn't snap it, it's just resting on the pins, if that makes sense...