7 replies to this topic

[peter65]

hi there. i have an intermittent hum (white noise i think) from one speaker only (left). I also get a "thump" when the ignition or HU power are switched off. i have disconnected the head and the hum is still there - unchanged. When i swap L & R outputs from the amp the hum moves.

i did not short cct the amp inputs yet as suggested by another thread - as it sounds perilous to the amp (?).

Any suggestions please? i am pretty capable so all suggestions considered. cheers and thanks in advance. Data below.

Equipment:
HU: Eclipse 8061;
Amp: Precision 4 * 100w digital, amp screwed to metal panel behind rear seat in the boot;
Speakers - front only: Sony 100mm's in the car standard mounts (in the dash board)
Car: VP commodore;

Cabling:
Power cable to amp: 8 GA, in drivers side kick panel, fused in engine bay;
Amp earth: 8 GA from the amp to the car body (to a rear seat mounting bolt).
Head earth: standard thru car wiring. Is this good enough?
Speaker cables: std with speakers down drivers side of the car, joints into the vehicle loom are soldered;
Signal cables & turn-on wire: Jaycar shielded (blue) down passengers side kick panel. Relocated here post original installation due to ignition whine.

All equipment and cables are new.

[SirNemesis]

peter65, on Jan 2 2007, 11:18 AM, said:

Amp: Precision 4 * 100w digital, amp screwed to metal panel behind rear seat in the boot;

Is this metal panel isolated? Or is it part of the car chassis?

[peter65]

SirNemesis, on Jan 2 2007, 12:14 PM, said:

Is this metal panel isolated? Or is it part of the car chassis?

Hi - thanks for your response. The metal panel that the amp is screwed onto is welded to the car body, and forms part of the structure of the car (it is the rear seat back support panel). The bolt that i have the Amp earth connected to (via a semi-circular connector & 8 GA wire) is a bolt into the floor of the car. Cheers, Peter.

[peter65]

hi all. an update.
The thump:
1. Ran a separate blue "turn on" wire (previously used the "turn on" wire that was integrated with one of the signal RCA's) - still there but less. Reduced amp gain and a lot less thump therefore will keep gain low.
The white noise in one channel (left front) only:
1. Swapped L & R speaker output wires on the amp - noise moves to other speaker: eliminates possibly faulty speaker/speaker wire.
2. Disconnected signal outputs from the head unit. still noisy: eliminated head as noise source.
3. The head unit is screwed into a metal cradle into metal dash support thus should have good earth: eliminate head unit earth loop.
3. Unscrewed amp from car, still noisy: eliminates amp earth loop.
4. Separated amp main power wire from other car wiring as much as possible - still noisy: minimises induction from other electrics.

Conclusions. 1 reduce gain to reduce impact. 2. have to look for a good noise suppression device i think.

[Poisoner]

to test amp use shorting plugs
simply get an old rca cable any will do cut the cable and join the pos and neg together of the wire. this is not power and not on the out put side of the amp. or go down to jaycar/diick smith and buy a few plastic rca plugs about 50c each and simply silder the 2 terminal s insdie together.

id also suggest not bolting amp direct to metal, get a piece of mdf and screw it to metal and then amp to wood, with the screws not extending thru to the metal.

also if its only 1 channel that suggests faulty amp. as normally u will get noise thru all channels or a set of channels i.e. 1 and 2 or 3and 4.

try swapping L & R rcas too and see if that makes the noise change side.

[peter65]

hey poisoner - thank for the tips and will try them on the w/end. i had heard about using shorted RCA's on the i/p but was worried about damaging the amp. cheers & thanks, pete.

[Poisoner]

just make all changes with amps off(i.e. acc off)

disconnect rcas and connect shorting plugs. then switch back on.

[peter65]

ok poisoner - will do. bought the plugs and have now lost the little devils. have to look some more.....