samwood

Just installed a JVC ND-NX5000 nav unit the other day. I'm using the HU amp to drive the front and rear (panel behind seats) aftermarket speakers. I added bass shakers under each seat driven by a separate 35w Pyramid Amp sitting in the spare tire. I ran the RCA cables down the tranny tunnel to the amp. Used a cheap pair I had laying around. As soon as I powered up the amp, a ~2hz wamp wamp wamp comes thru the bass shakers. This occurs even with the ignition in acc and the HU off.

I did a simple test by driving the amp with a portable radio connected directly (via an other set of cheap RCAs) in the trunk (with the car ignition in acc and powering the amp) and the sound was clear.

I think a decent set of shielded RCA cables will solve this. Any thoughts? Any recommendations on a inexpensive set of shielded RCA cables? I don't want to spend $100 to drive a $40 amp.

BTW the JVC HU coupled with Modifry's DCI is an awesome upgrade!

Neutered Sputniks

Sounds like a ground loop of sorts. Definitely upgrade your RCAs to something with more shielding...but there's really nothing in the tunnel that would cause induction into the RCAs to cause the problem.

The reason you didn't hear it when you used an outside source is b/c the ground for the outside source is completely separate from that of the amplifier whereas the ground for the HU is not completely isolated from the amp ground - the difference in potential there acts as a capacitor and creates the noise...

samwood

Thanks for the ideas. With shielded RCAs going from $8 - $100, I'd like to hear some experiences with recommended brands. Streetwires seems to be a reasonably price solution. I've seen 10ft for $25 delivered.

Neutered Sputniks

I have Monster Cables 400XLN series...

But that's overkill. Check out these forums:

http://www.soundsolutionsaudio.com/forum/index.php?

Look around and you'll find all kinds of info on places to get high end stuff for less

samwood

Thanks. Your idea of the ground loop got me thinking. Since the amp only pulled 3 amps I pulled power and ground off the 12v accessory outlet on the console. Should I cut the ground and wire it directly to the chassis?

revhi

Definitely use a separate power and ground for the amp even if its not very powerful. The noise is only going to be present with the engine on. If the new power ground doesnt work first, than get RCA's and run down side of car, not with the power wire that you are getting from the battery directly. The tranny could cause engine noise.

samwood

Apparently it was a ground loop issue. A $13 isolator inline with the RCAs did the trick. Thanks for the help!

Neutered Sputniks

Good

Now, what you really need to do is eliminate the ground loop without the isolators. Make sure you have good amp and HU grounds and you won't have the loop. The isolators are a patch or a last resort, and they will affect sound quality (negatively, of course).

At least you're making progress though