Weird Stereo Problem- Help Please

[Hosehumper]

I had a system (amp, sub, door speakers, head unit) installed a couple of months ago. Since the weather has cooled down, I noticed when I start my truck in the morning, the bass from the sub pulses loudly (like a rapid heartbeat) no matter what mode the stereo is on.

-the pulsing can't be controlled by the volume knob
-it stops once my truck is warmed up after driving for about 10 minutes
-this only happens when it's cold outside and/or when the trucks been sitting a few hours

Any help is appreciated.

 

[Long Duck Dong]

It could be a few things.....

1. Remote Turn on to your amp is hooked up to an accessory wire. When you turn on the key the amp is on, with no signal input sometimes the amp will pulse the sub like that. Boils down to inproper installation if you were not told about this when it was installed or a faulty head unit but not likely.

2. Bad ground....I have never experienced a bad ground pulsing a sub, but I dont know what amp, deck, or sub your running so it's a possibility.

3. The installer used cheap RCA cables and ran them next to the power wire. This is happens all too often. Cheap RCA will pick up a signal from the power cable. The audioable noise you hear usually goes with the rpm's of the engine but then again I dont know what equipment your running so I cant say for certain.

4. My first guess is this one......The installer might have run the RCA's under the carpet and somewhere in the RCA line there is a short that is grounding out. For instance: if you run RCA cables in a vehicle and barely knick the RCA cable with a screw that holds down a panel, once the screw is grounded over time the RCA cable can develop an exposed wire where the screw is partially through it and become grounded out causing noise in the sub.

5. I would also check is the battery, it's not likely but as a car audio store owner I have seen odder things go wrong. Again not knowing the equipment you might have too much draw from the battery causing the amp to "clip" or "Low Volt". Low volting an amp often time causes bizzare and unusual noises.

6. Lastly, you might have a blown sub or a sub on the way out. I have seen this before....A sub that is near the end of it's life will act bizzare and do funny things when the unburnt portions of the voice coil make a good contact and the sub comes back to life.

Just a few things to look into on your own, I would think the place who installed it would warranty their labor and look at it free of charge. I know I would if we installed it ay my shop. Try taking it back to who installed it and see what they some up with. If the noise is driving you crazy unplug the sub.

Good Luck,
Steve

 

[Hosehumper]

Steve-
Thanks for the quick and detailed response. I was wondering if I was grounding out somewhere, why does the pulsing stop and the stereo returns to normal after it warms up? Wouldn't the pulsing be continuous? Thanks. Rob

 

[Erratic]

I once had a customer who had an oldschool Pheonix gold amp that made a whine for the first few minutes of operation. It was not alternator whine, and did not matter if the car was running or not. It was internal to the amp and the guy didn't mind that much cuz he really loved the amp. So you issue could be internal to the amp. Some info could help us help you.

1. What brand of amp?
2. What brand of head unit?
3. How many subwoofers?
4. If you turn the head unit off, does it disappear?
5. Is it rythimic thumping, or erratic?

 

[Long Duck Dong]

Steve-
Thanks for the quick and detailed response. I was wondering if I was grounding out somewhere, why does the pulsing stop and the stereo returns to normal after it warms up? Wouldn't the pulsing be continuous? Thanks. Rob

Well Erratic made a good point that I forgot to make on my first post....follow along...

Diamond Audio makes a phenominal product but recently I have seen a few Diamond Audio amps come back and we had to warranty swap them out for new ones, which brings me to Erratic's point.

Diamond had a batch of amps that were bad from the manufacture. If you mounted these defective amps on the sub box the vibration from the enclosure would cause the internals of the amp to jar loose. One customer complained of something similar to your situation, but the sub make a loud growel when the amp turned on.

This maybe a sign of your amp going bad if it was mounted on the box or near the subwoofer. Again not knowing your equipment anything is possible and we are all really guessing at this point.

As for why it stops when the truck is warm....Assuming it's something internal in the amp I would guess that once the amp itself is warm the internal bad conncetion expands enough to make a decent connection. Same thing if it was a bad or a loose ground. The problem is definetly a weird one thats for sure.....

 

[tech_dog]

One way to find out for sure is to put some shorted out RCA connectors on the subamp's inputs. If that doesn't fix it, then you know it's a problem with the amp.

It's possible that the amp is oscilating at very cold temperatures.

 

[Hosehumper]

I once had a customer who had an oldschool Pheonix gold amp that made a whine for the first few minutes of operation. It was not alternator whine, and did not matter if the car was running or not. It was internal to the amp and the guy didn't mind that much cuz he really loved the amp. So you issue could be internal to the amp. Some info could help us help you.

1. What brand of amp?
2. What brand of head unit?
3. How many subwoofers?
4. If you turn the head unit off, does it disappear?
5. Is it rythimic thumping, or erratic?

Oops, I guess that info would help.

1.Memphis Audio
2.Kenwood head unit
3.One 12" Memphis Audio sub
4.The pulsing stops when the head unit's off (on "standby"
5.The thumping is rhythmic. the volume level is constant and does not vary

All the goods were bought new.

 

[619TOY]

One way to find out for sure is to put some shorted out RCA connectors on the subamp's inputs. If that doesn't fix it, then you know it's a problem with the amp.

What are you asking him to do? An RCA connector with the center conductor connected to the shield can be used for noise troubleshooting purposes. However, this procedure doesn't have the ability to fix anything, just narrow your search.

To me, it sounds like a grounded output, perhaps intermittent. Without hearing it and being there, difficult to troubleshoot. I'd wait 'til its cold and having the problem then disconnect the outputs and measure the resistance of the wire to ground as well as from pos. to neg. to verify that the speaker and wire are not the cause. It could be the amp itself, cold temps causing contraction and shorting pins of the circuit board to the chassis.

In conclusion, the sound as you've described it sounds like a grounded output

 

[Erratic]

It could definetly be a grounded output causing the amp to come in and out of protection. The temperature thing really leads to an internal issue with a component or solder I would think. That's pretty decent equipment, but even the best have issues from time to time. I'm sure if you go back to where you bought it all they will be able to fix it pretty easily. If it was new as you say, it is definetly covered under warranty. It's really tricky to see what the issue is over the net. We cant tell if you have a good install or not. It's definetly not a common thing with a quick easy fix.