Frustrating electrical car audio issue

Automotive
#1

Hi everyone, I have a problem getting my mind wrapped around why my pre amp (ap4-ch31) remote wire does not send 12v to my amp. Iv tested the voltage coming out from the wire AND from the pin inside the module. It will say 11.8v when the car is off. But as soon as I turn on the car, it will jump to 13-14v and then drop and stay at 2.8v. Iv checked the fuses and wiring. I can’t find any reason why this would happen. It feels like it goes into “protection mode” but I called customer support and the technician said that it does not have protection mode. The ap4-ch31 seems to be on. It will flash its lights and when I turn the volume knob, it will flicker like it should (the technician agreed that it is behaving like it’s on).

The only thing that I can think of, is I did update module to its latest software updates using a laptop as the manual said to. Could the update somehow be my problem? I reset the module but I dont believe that does anything to the software.

There are dip switches but only two have any functionality. One changes the rca(the rca’s don’t produce any signal at all, I used an oscilloscope to test this) voltage and the other turning one to two channels.

And to add the last bit of information that might help to know is, the ap4-ch31 needs to go through two sleep cycles to “marry” into the system since it is plugged into the head unit harness. The key fob has to be far away from my car to accomplish this.

I believe iv given all the information possible. This has been an insanely frustrating issue. The whole point of buying the $300 ap4-ch31 was its plug and play claim for my specific car. Istead I’m reduced to installing a $20 hi to low converter box instead. Which lead me to a whole nother question. If my car came with a premium sound system that included a subwoofer(I removed both subwoofers) in the trunk and rear deck, do I need a high to low converter if I just tap into those wires?

I have a 2014 Dodge Charger SXT with Beats by Dre sound system.

If you got this far, thank you!

#2

11.8V resting sounds normal. 13.8-14.4 engine running sounds normal.

Sounds like the 2.8V may be the “Amplifier on”, as in the line is pulled to a lower voltage to activate the amp. Check the docs on your amps to verify this. If the amp expects 12V on the remote lead to power on, then a relay may be the solution. Or there may be something in the software to configure whether the remote starts high and goes low or starts low and goes high.

#3

It mentioned a relay. But I don’t understand how that would change the voltage (my relay knowledge is limited). Also where does the relay go? Do I wire it with the remote wire or with the power wire of the module?

Thank you for the help

#4

The coil of the relay would connect between the remote lead from the preamp and +12V. ( use an automotive relay - easy to get. ) The you use the normally open contacts ( NO ) on the relay and the common terminals. Connect NO to 12V, and common to your amp. It’s best practice to install a diode across the relay’s coil contacts as well.

When off, the remote line from your pre-amp is at 12V. So is the other side of the relay coil. So no current flows. When the pre-amp comes on, the relay coil would then see 12V on one side and 2.5V on the other. That should energize the relay. At which time the Normally Open contact will connect to the common contact, thus applying 12V to to amp’s remote input.

The diode may not be needed. It’s there so that when the coil de-energizes, the charge generated by the collapsing magnetic field has a place to go. ( It’s called “Back EMF” if you want to read up. )

Sketch attached.

amp relay schematic.pdf (197.6 KB)

2 Likes
#5

Wow that makes incredible sense… I tried watching a few videos but you explained it way better. Haha I feel kinda dumb because that would have saved me days of troubleshooting. Thank you for taking the time to help out!

1 Like
#6

Not a problem. Pretty simple after 50 years of BTDT. ( Yes, I built my first HeathKit at age 7… )
You’d have found it eventually, but shortcuts are good.

Hope it works out for you.