Audio amp turn on by head unit not always working

GTamas · Jul 30, 2024

I have an aftermarket head unit (Blaupunkt Frankfurt RCM 82 DAB) and an aftermarket amp (Hiphonics Zeus Street ZXS 700/4). There is a power wire coming from the head unit for feeding an antenna motor with 12v, which can also be used for remote turning on the amp. I wired it to the remote input of the amp.
If I turn on the head unit with the engine NOT running (key off, or key on engine not running), it works flawlessly everytime.
If I turn on the head unit with the engine running it is sometimes turning on the amp, but mostly the amp shows red light (amp protect / error light) and won't turn on.
Why I think it has to do something with the remote turning on of the head unit because if I disconnect the remote wire and use the amp's audio signal sensing feature, it turns on everytime. (I don't like using this feature because it turns the amp off if there is a low or silent passage in the music and there is a delay for turning back on).

What do you think it could cause this? I'm wondering why it matters if the engine is running or not. What would you check / do?

ttocs · Jul 30, 2024

not sure what is going on there.

96blak54 · Jul 31, 2024

Id grab another known good amp from a buddy or something. Wire it in place of your amp to rule out queertronics of your amp.
I mean, if you still have 12v presence on the remote wire at the amp when the HU is on, engine on/off I think the amp should be operating just fine.

ttocs · Jul 31, 2024

worst case scenario, wire the amps remote turn on(blue normally) to the ignition to the radio(red on the power harness) and the amp will turn on/off with the key.

GTamas · Jul 31, 2024

ttocs said:
worst case scenario, wire the amps remote turn on(blue normally) to the ignition to the radio(red on the power harness) and the amp will turn on/off with the key.

I like this idea, will try it. I will also check if the voltage on the remote wire is different if the engine is running or not.

ttocs · Jul 31, 2024

is it the stock deck still?

GTamas · Jul 31, 2024

No

I was trying to save the stock one, but was having problems with the tape all the time.

ttocs · Jul 31, 2024

ok I was asking because the stock deck uses a 6v turn on, all aftermarket should be 12v. Now the power antenna wire only has power on it with the radio, not with the tape/bluetooth/anything else. Is is possible you were trying to play the tape, not the radio and that was the problem? There should be a power antenna wire and then a remote turn on wire(blue or blue/white). The remote turn on wire is the wire you want, not the power ant.

GTamas · Jul 31, 2024

ttocs said:
ok I was asking because the stock deck uses a 6v turn on, all aftermarket should be 12v. Now the power antenna wire only has power on it with the radio, not with the tape/bluetooth/anything else. Is is possible you were trying to play the tape, not the radio and that was the problem? There should be a power antenna wire and then a remote turn on wire(blue or blue/white). The remote turn on wire is the wire you want, not the power ant.

Thanks for the tip, but this head only has powerantenna wire, but it is live when the head unit is turned on, does not matter what source.

ttocs · Jul 31, 2024

ok then as long as you have confirmed it stays at 12v when not on the radio then it sounds like there is either an intermittent wiring problem that is sometimes making contact and sometimes is not. check the connections with the power on and see if dicking with the wiring causes any changes. IF not then just connect the amp to the red ignition and there will be no foul.

96blak54 · Jul 31, 2024

Do you have a direct remote line from the head unit to the amp? Thats 100% what i would do just for simplicity sake. Did you run the remote into the factory harness and then use the "suspected" remote from the factory amp harness in the trunk?

GTamas · Aug 1, 2024

96blak54 said:
Do you have a direct remote line from the head unit to the amp? Thats 100% what i would do just for simplicity sake. Did you run the remote into the factory harness and then use the "suspected" remote from the factory amp harness in the trunk?

I'm using direct lines for the whole system. The only factory wires I use are the ones feeding the head unit.

ttocs · Aug 1, 2024

then it is either a bad connection, or there are times the deck isn't supplying power, or a problem with the amp. Next time it does not have power, try disconnecting the remote turn on wire at the amp, then jump the connection between the +12v constant and the remote and see if the amp turns on. If the amp turns on then the amp is fine and there is no power on that wire for some reason. Ensure you have a good connection up front and if so then you might just want to connect it to the red ignition wire. The only thing that could cause is a slight turn on pop when you turn the deck on but nothing horrible

GTamas · Aug 3, 2024

The wiring is good. There will be something with the voltage.
I measured the voltage on the remote wire from the head unit. When engine is not running, it is 11.7v and the amp is turning on.
When engine is running, it is 13.7v and the amp is not turning on.

So I guess I need to put a resistor between the head unit and the amp to reduce the voltage to 12v. Can someone help me what value resistor I need?
I know this would reduce also the voltage when the engine is not running, but maybe 10v is also enough for the remote signal.

ttocs · Aug 3, 2024

that is not going to help you. If anything you need to raise the voltage maybe with a relay but there should be basically the same relay inside of each amp already. The deck should put out the same voltage as the battery so while we say 12v we mean anything between 11.5-13.5v ish. The only thing I can think of is that the 11.7v is low and right on the threshold voltage needed to turn the amp on so sometimes it kicks it on and sometimes it doesn't. Next time you can't get it to turn on, disconnect the remote turn on wire that goes to the deck and then take a small piece of wire and at the connection to the amp connect the remote to the 12v constant and see if it will turn on then.

GTamas · Aug 3, 2024

ttocs said:
that is not going to help you. If anything you need to raise the voltage maybe with a relay but there should be basically the same relay inside of each amp already. The deck should put out the same voltage as the battery so while we say 12v we mean anything between 11.5-13.5v ish. The only thing I can think of is that the 11.7v is low and right on the threshold voltage needed to turn the amp on so sometimes it kicks it on and sometimes it doesn't. Next time you can't get it to turn on, disconnect the remote turn on wire that goes to the deck and then take a small piece of wire and at the connection to the amp connect the remote to the 12v constant and see if it will turn on then.

I think you read my post the other way around. It does turn on with 11,7v fine. It does not turn on with 13,7v.
Well, it turns on with 13,7v but goes into error mode and stays silent.