When ACC power turns off speakers “thump”

Togalock77 said:

Here’s the setup. Ford Transit 350 passenger van. Factory head unit to aftermarket amp. The amp powers speakers in factory locations. I also have a powered alpine sub. The amp and sub are powered from the van’s dedicated CCP2 Aux position which is ignition controlled and powers off 1/2 hour after you shutdown the van. At that 1/2 hour mark I get a loud thump from the speakers. I’m guessing it’s some kind of conflict from the line level input and ACC amp power supply. Any ideas?
Sequence of events for more detail.
Turn off ignition
Open door and stereo powers off
30 minutes after ignition off ACC (amp power) turns off
Speakers make a thump

Click to expand...

The thump you're experiencing likely results from a sudden drop in voltage or current when the amplifier and subwoofer are powering down. This thump can occur if the audio signal is present in the line-level inputs at the moment the power is cut, causing a pop or thump sound through the speakers.

Here are a few ideas on how to potentially mitigate the issue:

1. Delay Module: Install a delay relay module that keeps the power to the amp and sub on for a few seconds after the ignition is turned off. This can allow residual audio signals to dissipate before the power cuts off, which could prevent the thump.

2. Soft Shutdown: Some higher-end amplifiers have a soft shutdown feature, which gradually reduces the power to the amp instead of cutting it off abruptly. If your amp doesn't have this feature, you might consider upgrading.

3. Capacitor: Adding a capacitor in parallel with the power supply can help provide a buffer of power when the amp turns off, potentially reducing the impact of the sudden power loss.

4. Signal Conditioning: If feasible, you might consider using a high-quality line-level converter or incorporating a speaker-level to line-level adapter with built-in filtering to reduce the thump.

5. Ground Loop Isolation: Make sure that you are not experiencing ground loop issues, which can also contribute to noise in the audio system. Check your grounding points and ensure everything is secured.

6. Check for Loose Connections: Sometimes, loose connections can amplify issues. Check all your wiring and connections to make sure they are secure and well soldered.

Each vehicle audio setup can be unique, so you may need to try a combination of these approaches to resolve the thumping issue effectively.

Togalock77 said:

Here’s the setup. Ford Transit 350 passenger van. Factory head unit to aftermarket amp. The amp powers speakers in factory locations. I also have a powered alpine sub. The amp and sub are powered from the van’s dedicated CCP2 Aux position which is ignition controlled and powers off 1/2 hour after you shutdown the van. At that 1/2 hour mark I get a loud thump from the speakers. I’m guessing it’s some kind of conflict from the line level input and ACC amp power supply. Any ideas?
Sequence of events for more detail.
Turn off ignition
Open door and stereo powers off
30 minutes after ignition off ACC (amp power) turns off
Speakers make a thump

Click to expand...

The amp needs to turn off before the car does. Sounds silly I know. I would redo the power turn on wire to the subs amp such that when the key is fully off, there is no power to the amp. You can test to see if this will work by adding a switch to the turn on wire... turn it off while the car is on but not running... if there is no pop then yes, rewire the turn on lead to the amp. If there is a pop still you may have to re-do more than just that wire.

The capacitors in the amp store power and when the power is disconnected from the amp the caps are discharging (burst of power) that is audible through your speaker.