Possible ground problem, but not sure

[RaveDigger]

So I spent the past two nights after work removing the interior panels in my 2000 Sport (no easy task) and installing a set of 6x9's that I had lying around. 6x9's don't really fit, but I convinced them to fit with a sawzall and a dremel.

So basically the setup that I have is:

The existing rear speaker wires are running directly to my aftermarket amp from the stock headunit as speaker level inputs.

The amp is connected to the two 6X9's.

The remote amp power on wire runs from the 12v yellow lead at the back of the stock headunit to the amp.

The positive 8 gauge wire comes from the positive terminal of the battery all the way back to the positive connection on my amp.

The ground goes from the amp to a hole that I've drilled into the body near the rear taillight.

The problem that I have is this:

When I turn the car on, everything turns on as it should including the amp, though I get no sound from anything INCLUDING the stock speakers in the front door that have not even been rewired (They're still connected to the headunit as they have been).

If I disconnect my ground and reconnect it with the car already on, everything starts working correctly. I've tried a few different spots for the ground, all dremeled down to bare metal, and the result is the same.

I've installed quite a few car stereos before including an entirely new stereo in my Z and though I don't consider myself an expert, I'm certainly not a noob.

I'm completely stumped on this one and any help would be greatly appreciated.

 

[PandorasCustoms]

The remote amp power on wire runs from the 12v yellow lead at the back of the stock headunit to the amp.

I have not performed many installs using this method, but there may be a high voltage surge when the radio is initially turned on, so it could be causing the amplifer remote to go into a protection mode.
Do any lights from the amplifier come on (Protection is the main one I am thinking of)?
It certainly sounds like a voltage issue since it seems to be isolated to when the radio is turned on and off.

If you remote is still long enough (And if you still have the dash apart), I would suggest running the remote temporarily directly to the battery. While the car is off, the amplifier would be on, and then, if you turn the car on, the radio should come on and play.

If so, then you can start by looking into this, or consider setting up a mounted switch for the amplifier remote instead of running it off of the Acc wire for the head unit.

If not, then it could be something with the tie in for the high-level of the amplifier.
As an alternative to using a high level input, there is an alternative that can be used by getting a Hi to Lo Level line converter.

This is one that does all four channels, but you would only need one with two channels on it. You would just need to make sure that the input power can be greater than 15~20 watts each channel, as that is average what the factroy head unit can produce.


I love troubleshooting, but this is a tough one not being at the site.

 

[RaveDigger]

Thanks for the info and your suggestion to use a different source for the 12v remote power on is along the same lines as what I was thinking too. Once I get out of work, I'll try using a different 12v source for it instead of the 12v lead that powers the head unit. I'll report back here with the results.

Thanks again!

 

[PandorasCustoms]

You know, I was thinking, and it may not be a voltage surge but a limit in voltage instead.
By tapping into a wire the only provides limited power/amperage, it may not have enough power to power on both units at exactly the same time. So, it will be turning on the radio controls, but it won't have enough power to activate the internal amplifier or your aftermarket amplifier. Because, both are trying to get enough power to activate at the same time.

But, once the current draw is gone, (You removing the ground wire for a second), the internal amplifier has time to get up to the right amount of power, and then reattaching it allows the aftermarket to get up to the recommended power range.

What amplifier are you using? If you can figure out what the voltage range for the Remote connection is, then you can use a volt meter to test it when you turn it on and see if it is too low. This may help with confirmation there.

Honestly, right now, I have 100 theories running in my head...
Lets try and find the right one.

 

[RaveDigger]

It's an MTX amp. Small and old. It's left over from an install that I had set up in my Volvo in high school quite a few years ago. Unfortunately I don't have any of the documentation, though I'm sure I could find it online.

If your theory is correct, switching to a different 12v remote power on source should do the trick, though I doubt that the MTX amp isn't receiving enough of a signal from the 12v remote power on because the amp DOES turn on.

 

[RaveDigger]

OK, so here's my solution. Unfortunately all of what we had figured was incorrect. I disconnected the 12v remote power wire, and was confused when the amp still turned on. BIG WTF! I used my Google-fu and determined that some MTX amps are designed to work without that wire when used with speaker level inputs. Apparently my problem has nothing to do with where the 12v remote power wire is connected, because the amp still turned on without it, and the problem was identical.

Still, even with the remote power wire disconnected, I didn't get any sound from ANY of the speakers until I disconnected and reconnected the ground. Also, when I started the car, there was a terrible ground loop somewhere causing an unbearable alternator whine.

My resolution: I happened to have an old Pac Audio sni 8 speaker level to RCA converter. It basically accomplishes the same thing that my MTX amp SHOULD do. I connected my speaker wire inputs, connected my RCA cables, reconnected my 12v remote power on wire, and I was golden. The Kenwood 6x9's are something like 450w each, so they CRANK. I'm very pleased with the results.

Next on the list is subwoofers. Again I have a pair of 12 inch MTX's left over from a previous vehicle that I'm going to recycle into this project. When I had all the interior panels ripped apart for my 6x9's, I used some forward thinking and ran extra cabling for the woofers so I wouldn't have to deal with the interior panels on the sport ever again (once is more than enough for me). Once I take the time to pick out a mid-level quality class D mono-block amp, I'll connect everything and call it complete.

PandorasCustoms, we were both wrong. I'm still not sure exactly what the problem was. That amp did sit in the garage during a Massachusetts winter, so it's a bit corroded. Either way, my theory is that the speaker level inputs failed causing the initially reported problem. Thanks again for your input. You're part of the reason why the internet is such a powerful tool.

I'm left with what I believe is an aftermarket sub box that fits inside the passenger side trim in the hatch of a sport. I have no need for it, so if anyone is interested, it can be picked up in MA for $50.

If anyone has any questions that I might be able to answer, please let me know.

 

[PandorasCustoms]

Well, too bad we troubleshot wrong, but at least it is working correctly now.

I have only done one other install with using the High Level speaker input for the amplifier. I have always tried to steer clear of it just because I have never heard good things about them.

Glad to hear the alternative, Line Converter, solved the problem thus far.
Good luck on the AMP hunt. Looking to stay with MTX equipment?

 

[RaveDigger]

Generally the speaker level inputs are to be avoided, but I'm looking to do this mostly with leftover parts which do not include a new headunit. Also, I plan on leaving the truck parked in Philly, so I don't want an aftermarket deck on display saying "Hey steal me!"