noise-- audible tach!

[68sixspeed]

Hi- anyone have any trouble getting noise on their amp? I have an alpine amp for my rear speakers, and I get an audible tach from the MSD ignition- I am running the MSD capacitor on the ignition. Interestingly I do not get the noise out of the front speakers. I tried a noise filter on the RCA jacks, no difference. I was thinking of trying another MSD filter/cap just for the rear amps power, any thoughts?

It usually isn't a big deal, I prefer the sound of the motor, but on a long trip a little change is nice too.

[TonyL]

The last time I had that problem, I had to replace the head unit. No amount of shielding the wires, or regrounding the amp helped. Swapped the head unit, and it went away.

That said, make sure your RCAs are run on the opposite side of the car as the power wire and remote lead for the amp. make sure the stereo chassis is well grounded, not just with the "black wire" but the chassis itself.

Same for the amp. ensure the ground is as short as possible and is touching bare metal.

Make sure the engine has a good ground also.

[HzEmall]

Where is the battery in your car and what do you have for a grounding system ?

Noise like that is generally a ground issue.................

[dannyho]

definately sounds like a grounding problem. are the amps all grounded to the same place? move the grounding point around, that could cure it.

[68sixspeed]

Thanks for the suggestions. The battery is in the trunk. I only get the noise from the rear amp, nothing on the front, so it could be the amp, ground, or maybe the cables. I just picked up longer rca cables to run the amp around the drivers side away from the battery cable. I was also thinking of trying a MSD capacitor on the supply power to the amp? thanks- Dan

[dannyho]

I've always had a bad feeling about rear mounted batteries and their affect on ground loops. I've no proof, but you could check the engine ground. Maybe run a second one that connect much closer to the alternator. I haven't had a real chance to experiment with it yet though.
Ground loops are mysterious but I'm pretty sure the problem comes about because your amp is getting a ground connection in a much different place than the headunit, and when the ground on the RCA (I assume you are running RCAs) interracts with the ground on the amp there is a potential difference ( one that changes with alternator RPM). Because this difference is at the amplifier for your rear speakers it would not be heard in the fronts, as they are (assumably) powered by the head unit. perhaps grounding the headunit back at the amplifier might work, but that would include isolating the cage the headunit sits in as well. I'm just speculating there though.
One person mentioned changing the headunit might work. I suspect in his experience he changed to a headunit with higher voltage Pre-outs, that would definately help. (eclipse has some that go up to 8V, most higher ones are around 4-5).
You might be able to get rid of the problem by playing with the gain (sometimes called input sensitivity) on the amp. Adjust it down, then use the volume and fade cotrols on the headunit to get it where you want it. I'd recommend setting the headunit at 80% volume at the highest you would normally listen to it.

Also from a purely audiophile perspective, you really should be powering your front speakers with the amp, and the rear speakers with the headunit. It's just qualitatively better, IMHO.

hope I might've helped a little

[audioman]

Noise can come from a combination of places

12v,ground,rca's and antenna

Make sure the power and rca's are not running together,try different grouning places and put a noise filter on the rca's.

Do you have a class d amp on the rear? these amps can pick up noise from your antenna.
noise is a hard thing to find and can come from several places.
you could also run a ground wire from the head unit to the ground on the amp and see what it does. i could trouble shoot the system over the phone if you wanted. give me a call

[audioman]

Also
were do you live in CT? Jo Di's sound centers(i use to be the GM there can help you trouble shoot the problem.
Call Jodi at 860-953-5614 and she can direct you to the hearest store. Tell her I sent you.

[68sixspeed]

thanks- just an update- I routed a better quality RCA cable down the drivers side away from the battery cable and most of the noise went away. Thanks for the tips guys, and yes, a front amp and better front speakers are coming, but I needed the amp on the rear to overcome the exhaust!

JoDi's... no offense, but I won't let them touch my car... I bought the amp and speakers there originally and had an alarm put in a pickup in the mid 90's... the tech dented the c-pillar on the truck testing the shock sensor, and then I almost dented it again with the tech's head, so I don't think I'm welcome back or want to go back. They also screwed up the dash on my buddies new Jeep. Cut the hole too big, left 1/2 the screws out, not quality work.

[audioman]

thanks- just an update- I routed a better quality RCA cable down the drivers side away from the battery cable and most of the noise went away. Thanks for the tips guys, and yes, a front amp and better front speakers are coming, but I needed the amp on the rear to overcome the exhaust!

JoDi's... no offense, but I won't let them touch my car... I bought the amp and speakers there originally and had an alarm put in a pickup in the mid 90's... the tech dented the c-pillar on the truck testing the shock sensor, and then I almost dented it again with the tech's head, so I don't think I'm welcome back or want to go back. They also screwed up the dash on my buddies new Jeep. Cut the hole too big, left 1/2 the screws out, not quality work.

Sounds as if you had a bad time with Jo-Di's. As you may well know good help is hard to find. When I was the General Manager there I fired two store Managers on the same day. I ran the stores until I trained someone new. Joe Difazio is the owner and he would have fixed any damage that one of his employees created. He's got a good heart. If you need, call Joe and ask for his best guy, tell him I sent you and I'm sure you won't have any issues. You can also talk to his daughter Jodi and she would help as well.
You should not have those types of issues with a quality car stereo shop, Again good workers are hard to find.