Help...Weird Loud Bass Noise when deck is "OFF"!

[b_knockwood]

A friend of mine has a 2001 Neon with a single Bandpass Swiss Audio 10 inch sub (300w max) powered by a Kenwood KAC-5201 (250w max).

We switched his box with 2 sealed GNX 124 subs and he loved the sound. We noticed that the amp was turned down all the way, so we bumped it the gain up to half way.

Now here is where it gets really wierd.

He turned his deck "off" by mistake, and a really loud bass noise came from the subs. We turned the amp back down to where it was, and the noice dissappears. What is more wierd is when we have the deck "off" and the amp up, if we walk away from the car, the noise stops, but if we get close, it comes back...and if we actually touch the subs with our fingers, it stops. All this happens when the deck is "off" and the amp turned up just a little over 20%. When it is "on", it sounds great and works perfectly fine.

He only has a factory deck, so he is using a highlevel input from his back speakers.

Does anybody have any idea what is going on?

Thanks

B

[Jstas]

Are you sure it stops when you walk away or is it just that you can't hear it?

What kind of alram system does he have? Does he have proximity alarms?

Also, when you walk near the car, do you have electronic devices like a cellphone, pager or even a hand held CB/HAM radio or walkie talkie?

[b_knockwood]

he doesn't have an alarm, and we left our cells in the house...lol. it seems to get louder from our bodies getting close to it, if we actually stand closer together, it gets more loud. I'm talking about, near 140db loud.

[RuSsMaN]

Agreed, the walking away and it stopping seems very odd.

I'm no car stereo buff, but I know home audio amps (usually sub amps), can start to 'motorboat' and make a consistant farting / warbling noise.

Not sure if that's what you are experiencing, but here is an explanation an EE told me that might be helpful, if you are getting some noise on the inputs, with the system off:

"Motor boating is the amplifier going into an unstable low-frequency oscillation mode. You're getting positive feedback into the input. It stops when the amp is shut down, doesn't start at power up, but starts when the amp is fed a signal - the amp tries to amplify, and goes into the unstable oscillation. That is why once it starts the input signal is no longer relevant, and why the noise is rhythmic.

Slight chance it is connections or a bad connector. I'd pull everything apart, clean it and reconnect. Couldn't hurt. You could do this in the internal wiring for the amp and driver as well.

Could be the isolation capacitors... they are no longer... capacitating.

The amplifier itself *may be* fine.. this is fundamentally an isolation problem, i.e. lack of isolation gets the oscillation going. The amplifier is still amplifying.. just not the proper signal."

Cheers, and good luck.

Russ

[PoweredByDodge]

follow the above given advice, but also... make sure you have a nice solid good ground for the amp - with the spot where you ground to shaved down to metal.

be sure you're using at least 10 gauge power wire for that amp.

if all else fails, put a 30A relay on the power wire for the amp -- because its only a 250 watt amp, 30A is sufficient power delivery, and so you can solder a relay onto the power line and have the trigger for the relay up by teh dash -- that way, when you get out of the car -- turn the relay off -- and the amp will have zero power delivered to it.

[chris48198]

I've seen this problem before, its feedback. The amp turn on is wired to ignition or swithched power for the amp turn on so when the car is on the amp is on even with the radio off. When the radio is off the rear speakers act like michrophones for the high lever to RCA converter, they pick up a vibration that plays through the sub then the sound from the sub causes the speaker to vibrate more making the sub play the sound louder in an endless loop. The best solution would be to get rid of that factory radio and run RCA's straight to a new radio.

[chris48198]

Or a more cost effective solution would be to run the high level signal off the front channels instead of the rear.

[PoweredByDodge]

if it is the rear speakers acting as mic's then the best solution would not be to replace teh deck but rather to properly wire the remote turn on line -- put a toggle switch on the remote turn on line which is obviously jumped to acc switched power. toggle off when the radio goes off.

[b_knockwood]

Thanks for all the input. Happens to be feedback, jus like you said. We are going to put in a Toggle for the the amp remote. His deck has a factory 4 disc changer, so he don't want to replace the deck and loose that feature. Thank again.

[Josh]

That radio has a power antenna output even if you don't have a power antenna. The wire is in the last pin on the black plug. If you don't have a power antenna, it will be blank. You have a couple of options: 1. Go to the junkyard and find a Chrysler that you can remove one of the pins from the radio plug and cut off the wire and use a pick to remove the pin. 2. Buy a harness from Metra (71-1817) and use one of the pins from that. The latter is easier, but the first is probably cheaper or free.
Metra 71-1817 Chrysler Plug

[PoweredByDodge]

Originally posted by Josh
The wire is in the last pin on the black plug. If you don't have a power antenna, it will be blank. You have a couple of options: ...

... option 3 as well -- since the pin is supposedly on the end of hte harness... take a razor and/or jacknife and trim off the last pin's section and then solder right on to the back of the deck.

[Nelsonfortmyers]

I haven't read all these super long blogs, cuz I already know and it's quite simple. Maybe It's already been answered for you but your problem is your "remote" wire. I've had this problem in older cars that don't have all the wiring necessary to swap the wiring harness. Esp If you have a higher quality amp that may or may not have some kind of small "capacitor" built into it. If your still having the problem Have someone stand in the back, look at the power light on the amp, kill the motor after playing some music to get some juice. Either the pop (from the sub) will come right away or the light on the amp will slowly fade rather than disappear and once it goes out then the pop will come. This problem also comes if you just hard wire your deck to the battery. I can't tell you the best fix, but if this sounds like your problem, then the easiest way (not sayin it's the best) is rather than hook up your Decks "remote" wire to the internal one (or however you have it hooked up) simply run a wire from the remote on the back of the deck and stuff it into a 15 or 20 amp fuse underneath your steering column. Btw when this works, be sure to spread the word. Oh, And If your remote wire doesn't have a tiny fuse already just splice and throw one of those tiny cylindrical ones on it.

[evilgenius68]

Do you have the amp remotely powered by an ignition source, or from the fuse box where it comes on when the key is on , you may be experiencing magnetic field disturbance caused by the cars ground. or.Ill ask is the high level converter also powered. on/off..some cheaper level converters that are powered, share the same ground circuit and can cause what you have going on....unplug the conv. from the amp. does it go away?.could also be you ned to I know it will sound stupid but check your main ground from the battery to the body of the car.. residual grounding can uccur in a bad connection and start playing tricks on all of your electronics.

[JimAckley]

Dude... this thread was from '03... I think he's figured it out in the last 7 1/2 years.

[AsSiMiLaTeD]

WTF is wrong with people on here lately...?

[evilgenius68]

I wasn't even paying attention to be honest..thanks for the date check.