Hey all
This problem has been plaguing me for a few months now. I have my Zapco AG1000 bridged, wired to 3 parallel Dynaudio MW190's and ONLY when the ignition is off do I get a motorboating noise coming from the subs. Output is -16Dbm max but it comes and goes randomly it seems. Temperature doesn't affect it either.

Using my scope/software it shows to be 52Hz regardless of if the deck is playing or muted. When the car is running there is no indication of it either sonically or electrically.

I have tried using only 1 sub at a time, but there is no difference. If anyone has a suggestion I'd love to hear it.
Thanks, J

 

Sounds like you're under powering the amp...or the battery is going low...check the voltage at the amp, between the 12 volt terminal and a good chassis ground....not the amp's ground, with a good loud bass tone playing.

 

Hey
When I measure the B+ voltage at the power terminal on the amp I get 12.2V off and 13.9V running, using a seatbelt bolt as the reference. Even looking at it on a scope the voltage is steady with no dropping out. It does this even when I use shorting plugs on the amps input.

This problem has occured with 2 different amps installed differently using the same subs. I know this sounds odd, but I think they are cursed [img]smile.gif[/img] .

I just measured the power wire resistance to the battery and to chassis, 16.5 mohm and 7.2 mohm respectively.
Thanks, J

 

What kind of car?
If you've changed amps, and eliminated the deck, and RCA's, and it only occurrs with the alt off....it's gotta be the power/gnd, or a voltage thing.
Ummm try grounding the rca's....

Was the voltage test stable when the amp is drawing lots of current? You should see a drop of some kind.

I hope you're not using the seatbelt bolt as your ground for the amp! Need to go to clean, bare metal, preferably not a welded on bracket.

Also check the voltage from batt neg post to ground wth engine off, and running, with the amp at idle, and under load...you might have a weak batt gnd.

 

Hey Car Trek
I'm not using the seat belt bolt as the ground, it was just the closest clean metal I could get my probe clamped on. My ground is about 12" long and bolted to cleaned metal under the hat shelf (also used dielectric grease).
At most there was 0.25V drop at the amp with a loud note played continuously. I didn't check the battery ground.....I'll have to check that tomorrow.
Thanks, John

 

Hey
I checked the battery ground and it was a solid electrical connection. After changing some wiring around and the noise still being there I decided to remove power from all devices including my power cap. I started by powering just the Zapco and voila no more noise!!! I then reconnected all of my other amps and the noise was still gone. I tried with the cap again and the noise returned????? I don't know why removing the cap would do this? Anyways, it sounds much better key-off now.
Thanks, J

 

I believe the problem was related to fluctuating voltage, as current demand varied with musical peaks, the cap, simply magnified the demand of charge/discharge.
Keeping in mind the original motorboating was with ignition OFF, the battery would have a harder time maintaining voltage with such high demand.
By re-connecting the amplifiers, you may have provided better contact to the amp that draws the most, and aleviated your problem. Try looking at the ground return system, I presume that a deep cycle battery is used.
Also, since multiple units are being trigered by the HU, I presume(I do a lot of that) you are using a relayed remote-on system.
Is it a lead-acid type battery? (with caps?) If so, check fluid levels in the cells.