Stereo Woes

legion · 07-19-2005, 04:55 AM

So...I moved one of the amps for my car to the trunk under the mat in the spare tire well (the other amp was already there). I changed none of the settings (or so I thought). As soon as I turn on the system to test it, I get something around a 220 Hz sine wave coming out of the two 12" speakers. After some experimenting, I figure out that if I disconnect the two 6" speakers (which sit between the two twelves), the sound goes away. I figure it must be a bad ground as I have both amps, a capacitor, and the car's tail lights all grounding to the same place. I created three new grounds, so I each amp and the capacitor has its own ground separate from the tail lights. Test...still the 220 Hz tone.

I decide to disconnect the sixes one at a time to see if there is a short in one of the speakers. Disconnect the right 6"...still get the 220 Hz tone. This seems to indicate a short in the right 6". Just to be certain, I reconnected the right 6" and disconnected the left 6"...guess what! I still get a 220 Hz tone!

What are the chances both speakers have a short? I figure none.

Now there was one minor thing that I changed when I moved the amp. I switched the signals going to the two 6" speakers to see if I got better imaging. The right speaker was getting a left signal and the left speaker was getting a right signal. No big deal, right?

So I switch the signals to the 6" speakers, and guess what? The tone goes away. I can't figure out why this happened in the first place, and how switching the signal to two speakers would fix it. I called my friend who works for Blaupunkt, and he is equally confused.

gorfllub · 07-19-2005, 06:52 AM

That sound is usually caused by a burnt ground trace somewhere. The easiest way to find out is the process of elimination.

(Are the 6" and the subs in the same enclosure? Thats a big no-no if thats the case)

Not knowing how your system is set up, i will try and help....

First, unplug the RCA's going to the sub amp. Is the sound still there? If so, the amp is picking up noise itself, or may be damaged.

If the noise goes away, you know the problem is coming from the cables. Plug them back into the amp, but unplug them from the deck. If the sound is still there, you know its the cables for sure. Check your routing, make sure you didnt pinch them, or worse yet, drill a screw through them.

If the problem is gone, then it is originating from the deck. Odds are a burnt ground trace in the head unit. Not too expensive to get fixed. Try a ground loop isolator on the RCA's. If it is a burnt ground or bad ground mis-match it should clear it up. Another thing to check is the ground on the deck. I know it may "look" good, but to make sure all your grounds are equally referenced, run a wire from the ground on the deck to the place where you grounded the amps. Now of course just for testing, you need not be pretty about this process. Dont bother hiding wires till you get it figured out.

Give me more details on the system. What kind of gear do you have, what is connected to where, and what are the settings set at on all the equipment.

Gratuitous pics of the sound system in my wifes mustang here:
http://saskjunction.com/stang2/5.htm

(I had to throw that in!)

legion · 07-19-2005, 07:01 AM

It is fixed right now...I was just perplexed by the solution.

The speaker box I am using has three enclosures. There is one for each 12", and one for both of the 6"s.

I have a Kenwood head unit that was installed by the PO. It appears to me that it is designed to work with the 5-channel amp that is in the spare-tire well.

I'm using the 5-channel amp as a 4-channel, so the door and rear speakers are powered from that amp.

The RCA cable for the subs originally went into the 5th channel on that amp, but now goes to a separate 2-channel amp for the subs. The 6" speakers are also wired from the sub amp, but come from special outputs designed for mid-to-high speakers, not the sub outputs.