Sure amp in car, thump/noise on power up - diyAudio
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Old 10th July 2011, 11:13 PM   #1
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Default Sure amp in car, thump/noise on power up

i finally got my amp in my car and i have it powering up with a relay, only problem is there is a noise when i first turn it on and when i start the car.
is there some way to stop that?? ive google the crap out of chip amp thump, but all results are not car related
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Old 12th July 2011, 04:28 AM   #2
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Well after not getting any responses, i figured out the problem. It was cause the amp turned on before the head unit. But i now have another problem, a whine with the rpm. As i can tell its not from the audio signal, but from the power/ground. I haven't had time to rewire the whole thing, but could the relay have an effect on that? I will try and connect it without a relay and see. Just was hoping for SOME kind of insight on this.
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Old 12th July 2011, 06:12 PM   #3
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Use a big capacitor to filter the Car's 12V line. The whine comes from the alternator and is normal. The capacitor will store and filter the power and clean it up.

On the Head Unit, use a noise filter (coil inductor and capacitor)

Problem Solved
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Old 12th July 2011, 06:25 PM   #4
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thank you for the reply.
sorry to seem totally noobish(i am at this stuff), but what size roughly?
also, it is the oem head unit, do i still need the indutor and capacitor, or only if there is still whine/noise??3
thank you again. i normally can use the internet to find just about anything, but this was different. i read about using a capacitor, but no sold details on sizes/types or where in the line to put it.
i have built simple crossovers before, but figured this out made me feel pretty stupid
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Old 12th July 2011, 07:48 PM   #5
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OK, no problem. I'll help you with that.

Even though it's OEM, they may not have good filtering in the headunit.

Run the +12V line through the inductor first, then parallel the capacitor across positive and negative for the head unit. You can get the inductor from an old computer PSU toroid output inductor, and use the coil that has the most turns.

Any 2200, 3300, 4700, or 10000 microfarad capacitor will be fine, but the more the better.

With the main electrical system, in parallel with your amplifier, use any where from 100,000uf to 1,000,000uf (1FARAD) and same rule here, the more the better.

Also this will improve your bass response as well.

Also one more question.........Being this is OEM, Are you using RCA outs from the headunit, or are you converting power from the speakers? How is your music getting from the head to your amp?
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Old 12th July 2011, 08:15 PM   #6
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whoops, i thought i put that in there..
i used 2 line out converters, the cheap PE ones. i ran new wire from the outputs of the head unit to under the seat, there i soldered the hi-lo converters and connected them to the amp. ive read that with a vag-com cable i can code the head unit to output line level, but then it becomes direct-balanced or somthing. i think the neg leads would then be the same?? which may work, because the amp has a input jack that with just the 2 pos, and a shared neg. i dont know.
well, time to search PE for some big caps. any type in general better than the others?? there seem to be quite a few diff types/brands?
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Old 14th July 2011, 02:03 PM   #7
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i have an old computer psu, that i think is fine. can i just use the output caps too??
it is only rated at 90w tho, not sure if that would matter?? thanks
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