Is the amp at fault?

Tim Lake · 06-24-2006, 02:18 PM

I have had no end of trouble with alternator whine feedback on my audio.
I have checked the grounding and redone them all at least twice. I have ground loop isolators on everything and those little magnetic clip jobbies that go round the wires.
I have NEVER been able to shift the feedback completely. Now I have fitted my new computer touchscreen and everything it's back with a vengeance!

I have a lot of earthed stuff (two amps, active crossover, computer startup controller, screen) and they are all solid earths!

If I remove the fuse from the 2-way amp (which goes to the components) then it stops. Is it possible/likely that the amp is at fault and is there a way to find out without replacing the amp?

Tim Lake · 06-25-2006, 06:27 AM

bump

Will Albers · 06-25-2006, 08:15 AM

Did you isolate and follow the steps i posted in the stickies at the top? You need to start pulling out components.

Shadow · 06-25-2006, 10:47 AM

Did you by any chance upgrade your battery and engine grounds?

Tim Lake · 06-25-2006, 01:59 PM

@Will : I have disconnected things in turn and it does seem to be the amp. If I pull the fuse from that amp then run the car there is no feedback at all.

@Shadow: No I didn't do either of those.

Will Albers · 06-25-2006, 02:58 PM

if you pull the fuse from the amp, there is no sound at all, therefore no feedback.

If you plug a pair of headphones into the compuetr sound card, do you hear the noise?

What happens if you go directly from the carouter to the amp?

Shadow · 06-25-2006, 04:16 PM

In a PC case the power supply and motherboard share a common ground. If you're using a non-standard PC case then you should check into this.

Tim Lake · 06-25-2006, 04:20 PM

I have two amps and the other one is still on but doesn't cause the feedback.

I already go direct from the carputer to the amp (thanks to your prior advice).

I haven't tried the headphone thing yet but I will do and let you know.

Will Albers · 06-25-2006, 06:34 PM

ahhh, ok, so one causes feedback and the other does not? VERY interesting. Are both amps grounded to the same spot? Have you tried using a test speaker? same thing?

Tim Lake · 06-26-2006, 03:40 AM

They aren't grounded to the same spot cos the mono amps grounding spot is now VERY difficult to get to. The component amp does have a good solid ground.
How do you mean, use a test speaker?

Will Albers · 06-26-2006, 06:13 AM

Well thats your first issue. You have a ground differential between the PC and one of the amps. They need to be grounded to the same point.

A test speaker allows you to cut out the possibility that the noise is picked up through the spekaer wires/crossovers, etc. A test speaker is any old speaker witha little bit of wire attached that you plug into the amp output. If you hear noise with your normal speakers, but not when you disconnect them and plug in your test speaker, then the noise is not the amplifier.

I think your first issue is you need to ground the amps to the same point

Tim Lake · 06-26-2006, 07:23 AM

Ok, I guess I'll have to tear the car apart this weekend

Does everything (carnetix unit, head unit, crossover and amps) need to be grounded to the same place?
Do I need to ground the PC chassis in some way?

Will Albers · 06-26-2006, 08:44 AM

did you read my sticky!?

Yes, you want everything grounded to the same spot if possible. It cuts down on ground loops.

Yes, it cant hurt to ground the PC chassis as well

parksgm · 06-26-2006, 08:52 AM

Quote: Originally Posted by Will Albers

Yes, you want everything grounded to the same spot if possible. It cuts down on ground loops.

Yes, it cant hurt to ground the PC chassis as well

...and another thing...it's nice to use the same size and length of wire from each component to the ground to minimize differences in resistance from wires. But grounding to the same point is the first, best, step.

Also, there's a great FAQ in the ...wait for it... FAQ section on this, IIRC.

Tim Lake · 06-26-2006, 09:50 AM

Ok, I just re-read it!
So I'll rip the trim out, get some good thick wire and earth EVERYTHING to the same (good) ground point?
Is the battery the best idea or would it be better to go to the car chassis?
Are these the things I should be earthing:
Head unit/screen
Computer chassis
Startup/shutdown controller
Active crossover
Component amp
Mono amp

One more thing. Does it matter if I have to run quite a long length of wire in order to earth things to the same place or will using good wire avoid any problems?

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