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Old 2nd January 2004, 10:17 PM   #1
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Default amp case grounding

I think I remember that amps cases should not be grounded, right? That's why they include those little plastic inserts for the holes.

What if you installed three amps (front, rear, sub) directly bolted to an aluminum plate but not ground the plate. Will the fact that the amps are joined electrically cause prolems?

The reason I ask is because I want to install some amps in a tight space and mount them directly metal-to-metal on an aluminum heatsink to help get rid of heat.
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Old 6th January 2004, 01:02 PM   #2
Immo_G is offline Immo_G  Australia
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All car amps i've seen have the casing grounded, but it isn't actually used as a conductor for anything.

Most people mount amplifiers to an MDF sheet or to the back of a wood subbox, so i guess the problem of interfering grounds doesn't come up.

Since the car amp grounds are linked together usually at either a ground distro block, or bolted separately to the car body, i guess if they touch and are casing grounded, it shouldn't be an issue.

However, if the internal ground connection was weak, but the alu plate was more conductive than the ground wire, you could stress that connection on a high power amp.
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Old 6th January 2004, 02:12 PM   #3
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i dont know anything specifically about car amps, but i would power up the amps, and measure the voltage on the case (using a multimeter). if it is at ground, i think it should be OK, and i would ground the plate/heatsink.
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Old 6th January 2004, 06:15 PM   #4
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Thanks guys, I especially like the idea about testing the voltage from case to ground.

I was told (by the owners manual) not to ground the cases. All of the amps I've ever owned came with little plastic clips that fit in the mounting holes so the screw wouldn't contact the case. The manual said that it will make a ground noise loop and cause a whine or excess noise.

I think I could successfully not ground the aluminum plate. Its a little hard to describe without pictures and and easel, but it would be sitting passively on a ring of dynamat around the spare tire opening. I'm just worried that if there is voltage present, it would be a different signal for each amp and it might make some weird noises.
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Old 6th January 2004, 06:41 PM   #5
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never ground a car amp chassis as you could blow the amp because the chassis is at signal ground and not power ground potential



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Old 6th January 2004, 08:08 PM   #6
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Hey, JoeDirt, not sure if you saw my original post, but one more question while you're here. What about attaching more than one amp to a common piece of metal, but not grounding that metal. The cases wouldn't be grounded to the car, but it would be like they were touching each other with continuity. Any problems with that? I'm putting three amps in a tight spot and want to mount them metal-to-metal on an aluminum heatsink, but not mount the metal to the chassis of the car. Thoughts? If you need to know, amps might be of different manufacturers, sizes, and or frequencies. (i.e. one is going to be a sub amp)
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Old 8th January 2004, 04:53 PM   #7
ddog is offline ddog  Finland
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There souldn't be any problems, signal ground is same from the headunit to amp, and with many amps there is still just one signal ground as long as all signals come from same source with common ground. But then, it can cause problems somewhere for some odd reason (most likely only ground loop noise, not amps blowing) i think.
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Old 8th January 2004, 05:51 PM   #8
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OK, thanks for all the help. Knowing that it won't destroy anything in a fiery ball of hades I will try it and let you know if I get any noise.

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Old 9th January 2004, 12:49 PM   #9
Immo_G is offline Immo_G  Australia
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Having a look at an amp i've pulled apart for a friend (blown output, usual), theres a medium thickness (maybe 20 amp) wire from power ground to casing.

The signal ground seems to be very well isolated from this, over 20k resistance from it to power ground.
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