Erich_870

I'm having some seriously strange problems with my current install of my system. I'm trying to hook up my MXT Thunder 250x amp with a 10" Pioneer 350 watt sub.

I was doing a dry run to look at final wire lengths, testing different wire routing, and then finally hearing how this set up sounds. Let me explain that I've had both the sub and the amp for a long time, but they haven't been used in over 3 years. They worked last time they were hooked up in my buddies car, so they "should" still be in working order.

Now to the strangest things... I have the power coming from the battery, in a 4 gauge wire, then to a splitter box and to the amp in an 8 gauge wire. The ground is also 8 gauge to one of my jumper cables so I could test it back to the neg battery post.

I have a Sony CDX-M850MP head unit and it is equipped with a RCA mono Sub output as well as a remote wire. I have all of that connected. When I turn on the head unit nothing happens on the subs end, all the stock speakers still work.

Attention: This sounds crazy, but its true. When I disconnect the ground from the negative terminal, the power light on the amp turns on!! I measure the voltage across the (+) and (-) terminals on the amp and it reads 7 volts!!

Also, when I connect the remote wire to the amp, the stock speakers get quite - slowly, and come back the same speed when I disengage.

What the heck is going on?? I feel like I'm in the twilight zone!
I've attached 3 pics to illistrate.

This is showing that the power light is NOT on when the ground is connected to the (-) terminal at the battery.





This is showing that the power light IS on when the ground is disconnected from the (-) terminal at the battery.





This is showing the voltage between the (+) and (-) posts on the amp when the ground is not connected at the battery.




Erich

Bumpin' Yota

are you pulling the ground from the amp when the HU is on? If so the amp is trying to find a ground and is doing so through the RCA sheilds...

Is the subwoofer out on your deck actually turned on? What about the amps settings? Im quite familiar with that generation of MTX amps and they are TANKS. (proud ownder of 2 mtx 2300x's)

Erich_870

I was hoping you'd respond Bumpin'

Yes, the head unit was on when I disconnect the ground.

I'm still trying to identify the actual settings within the head unit for the use of a sub. I "thought" it was turned on, but I don't know how to tell for sure. I tried adjusting the sub volume, but after reading through the user manual http://www.docs.sony.com/release/CDXM850MP.pdf I still couldn't find anything definitive about turning it on.

I had the settings in the middle.

I'll go get a pic of the controls so we can look at them in more depth.

I'm glad to hear they are tanks

Erich

Erich_870

Here's a pic of the controls on the MTX Thunder 250x.



I've never had a sub before so I'm not familiar with where the settings should be. I started with them all down or off and hoped I could figure it out by turning them up slowly until everything worked properly. That didn't get me anywhere.

Some real know-how would be much appreciated

Erich

Bumpin' Yota

ok turn the crossover button to "on" by depressing it. Set it to "LP" by allowing the second button to stick out farther.

Set the "EQ" to the far left.

Turn up both gains to approximately 1/2.
Turn on HU and set it at a moderate, just shy of loud setting.

You should hear some kind of output from the sub. You may have to slowly turn up the "EQ" a little, but not much.

If you still get no output try turning the crossover to "OFF" (using that first button on the left) and change where the RCAs are plugged into the deck to the front RCA jacks. This way you know the amp is getting signal.

obviously those are just setting to see if it works not the final listening settings.

Erich_870

Awesome, thanks Bumpin'

I'm really glad you cleared up the ground issue too. I didn't know the amp could still ground through the RCA's so I was pretty confused

Erich

Bumpin' Yota

be careful doing that, you are lucky you didnt toast the HU.

Erich_870

eeeek, yeah, I started to worry when I thought about the RCA's handling that ground. I didn't notice any changes, so hopefully the Mono Sub Pre-amp is still working

Erich

Erich_870

Thank god, I figured out what was wrong....

You ready for this?

I didn't have the remote power wire connected to the amp as I previously thought. I accidentally hooked up the "ATT" wire, which then explains why the head unit would go quite when ever I made contact to the remote wire terminal on the amp


In my defense, the "ATT" wire was blue and the remote power wire was blue with a white stripe. It was my mistake reading the schematics.


Anyway, everything works great, I didn't fry my head unit or amp and I have bass for the first time. Modest bass, but I'm jazzed


I am kind of proud of my custom enclosure, so I plan to make a new thread, but first I need to wire it up for real. No more Bumpin' Yota wire forest for me

Thanks again for your help Bumpin'.

Erich

Erich_870

Well, I finally had a free Saturday to finish routing my wiring and now I'm running into another problem. I haven't run the sub in over a month, and it's been in my garage.

Nothing has changed except my power antenna died yesterday and I'm running the wires under the carpet and finalizing my custom sub box.

Here's the current problem.

The sub works when I have the radio on, but as soon as I switch to the CD source the bass cuts out and is only intermittent. Like I said, my power antenna just died yesterday, and it seems to cause the power led on the amp to dim as it tries to extend.

What could be causing the sub to be sporadic?

Thanks,

Erich

Bumpin' Yota

you say that it's sporadic in its ouput on the CD source or does it shut off completely?

If the power ant died in the radio, im inclined to think the fault is the decks so long as your connections all check out.

Oh and be sure the check your subwoofer settings on that sony. Each source should have independant subwoofer, bass, treble, and mid controls.

Erich_870

It's sporadic on the CD source, but I can switch to Radio and it comes right on.

The power antenna died at the motor/gears. It tires to extend or retract and just keeps grinding until it finally gives up. But I do notice that the power LED on the amp fluctuates when the antenna is trying to do it's thing on CD source.

I'll double check the settings on the HU.

Thanks Bumpin,

Erich

Bumpin' Yota

hmmm

Try hooking the amp's remote turn on (REM) to the radio's accessory (ACC) wire (should be red on the HU side.) This way the amp's REM will have a full 12v whenever your ignition is on. Dont forget to fuse the REM to 5 amps or less if you do this. That way if the REM line ever gets grounded you merely pop the 5 amp fuse rather than your kickpanel fuse or worse yet, toast the wiring.

Then test out the different sources. Ill betcha that will solve the issue.

btw - did you hook up the illumination or dimmer wire (orange or orange/white on the HU side)?

Erich_870

Sounds good, I'll give them all a check. IIRC I think the dimmer wire is connected.

I have another head unit I might swap in to see if anything changes. I can't tell if it's the HU or the amp. I hope it's something fixable, but I don't know why this would be a problem all of a sudden.

Is it best to always fuse the (REM) wire or is it just for the testing?

Erich

Greg_Canada

If you have that dimmer connected, Disconnect it! I did it and it blew the fuse for my instrument panel (thank god it was nothing wors)....

Bumpin' Yota

Sorry was out of the country for 7 days there.

Anyhoo, yes disconnect the dimmer/illumination wire. That thing causes more problems than anything. That may be the whole culprit....