Amp thuds when turned on and off fast

[audiobahnkid592]

If my amp is on then you cycle the key off then right back on it puts out a very large thud into my subs. Would this be caused by capacitors being bad in the amp? And its only my subwoofer amp doing this not any of my speaker amps.

[Perry Babin]

If the remote turn-on for the amp is switched with the key (as it should be), there's something wrong with the muting circuit in the amplifier.

[audiobahnkid592]

Thanks Perry, but if i wait about 3 seconds before re cycling the key it does not make any noise. The amp is the audiobahn A18001DT amp that I fixed and has done this ever since I have owned it. If it is the muting circuit were do I look?

[Perry Babin]

The muting circuit has a delay that's determined by a capacitor and a resistor. When the voltage on the capacitor reaches a certain point (2.5v?), the muting is defeated and the driver board switches on.

To engage the muting quickly when the amp is switched off, the the capacitor is discharged through a diode.

For some reason, yours doesn't seem to be discharging quickly enough. There could be several reasons.

Since these amps typically have a long turn on delay, I'm guessing that this only happens when you're listening to it with the engine off and then quickly go from acc to start while the amp is on. If that's the case, I'd suggest leaving as it is. There's a chance to do much more damage if you make a mistake while working on the amp.

[audiobahnkid592]

If you say leave it I will but is it bad for my subs and or amp to have that happen?

[Perry Babin]

It depends on how bad the thump is.

If it only does it after you've been listening to it with the engine off, turn the key from acc to off and wait 3 seconds before starting the engine.