Amp fart noise at turn on

**swift_gti** · 08-11-2006, 07:10 PM

Hi all,

I have just fitted a 4ch amplifier in my car to drive the speakers and when I turn on the HU the amp power light comes on and after about 5 seconds only what can be described as a farting noise comes from the speakers for about 1 second then the all sounds ok.

Details of the setup:-
Car - Vauxhall Astra 2004
Speakers - fronts are 17cm components with the woofer replaced with aftermarkets. rear door are standard - size unknown.
Amp - Pure Power 600w (cheapo - but just needed replacement amp for HU with no amp built in)
HU - Alpine CD/MP3

I have tried it with RCA's connected to my ipod instead of headunit to eliminate slow RCA powerup on the HU and it still made the same noise.
I've also moved the ground point for the amp and checked all connections.

Anyone have any idea what might cause this ?

Any help really appreciated!!

**blkwrx** · 08-11-2006, 08:19 PM

Is it like a pop?

**Will Albers** · 08-11-2006, 08:23 PM

Originally Posted by swift_gti

Amp - Pure Power 600w (cheapo - but just needed replacement amp for HU with no amp built in)

my guess is right here.

There is a reason why its cheap.

**swift_gti** · 08-11-2006, 08:23 PM

I wouldn't describe it as a pop, its varied it pitch - hard to describe, it sounds like 'ppwerrrp' starts low ends higher.
Probably doesn't make much sense but its really hard to describe it

**swift_gti** · 08-11-2006, 08:47 PM

Originally Posted by Will Albers

my guess is right here.

There is a reason why its cheap.

I hear what your saying - I'm not expecting this thing to be kicking out shedloads of power or anything, but surely it shouldn't do this even if it is lower end of the market!

**Will Albers** · 08-11-2006, 11:35 PM

Its the fact that it happens regardless of source that leads me to the idea. Are your gains too high?

**swift_gti** · 08-12-2006, 05:32 AM

No it seems to happen even with the gains turned right down (gain position doesn't make the noise any louder or quieter either)
I have tried it with my car CD player and notice its picking up noise from the cd player - if i skip track etc it whirrs while seeking.
Could the remote lead have any impact? I notice theres a small nick in the stereos remote output - Is it possible to test the amp by looping the +12 from the amp to the remote input also ?

Cheers

**Shadow** · 08-12-2006, 10:25 AM

Your ground is goofy on your amp. Where is it grounded? It sounds like your amp is trying to ground through the ground braid in your RCAs.

**swift_gti** · 08-12-2006, 11:31 AM

I've tried two different ground points one a bolt coming through from the body work and now its on a factory ground point that has two original items from the car connected to it.
Is there any way to test out the ground ?