12Vdc slowed power off circuit

[filterengineer]

Hi Guys,

So I installed a new head unit in my car the other day and now I get a pop out of the speakers when the head unit is powered off. I figure I can solve this by building a circuit that will let the voltage decay to zero of a second or two. There's is also a very slight pop when powering on so the circuit should work on power up as well. I apologize in advance for not being quite the wiz I'd like to be with circuit design. Thanks Guys!

 

[VEBill]

The usual approach is to 'mute' the system at power on, and (if possible) at power off. The mute can be a discrete signal (designed into the amplifier circuit), or relays on the speaker outputs. Does the amplifier offer a 'mute' discrete input?

Decaying the power supply voltage might help, or it might just delay the pops. You could experiment with a variable power supply, if you can put your hands on one with adequate current capability.

An old trick is a series resistor to 'slow' the current input, and use the rising voltage after the relay to close relay contacts across the resistor once the voltage has risen to the relay's pull-in voltage. This wouldn't help with power off.

Car stereo shops often have a selection of 'farad' class capacitors. They'd provide a fraction of a second 'decay' after the power supply was cut. They'd also potentially cause a large current spike on application of power.

These contradictory requirements are why the mute option is better.

 

[IRstuff]

There are processor "reset" chips specifically designed to prevent processors from operating until their power is stabilized:

http://www.st.com/content/st_com/en...M810|STM811|STM812|TS831|TS834|STM809|STM1001

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[filterengineer]

VE1Bll, the amplifier is a factory installed one kind of like the bose systems but my car has a Rockford Fosgate system. so I don't know very much at all about the amp or even where to find info. I'm debating whether or not to just update the entire system with a new speakers and an amp to go along with it. I have a strong feeling that this speaker pop is an easier fix if it still happens with an aftermarket amplifier. so... as near as I can tell there is no mute discrete input on it. how complex of a circuit would it be to make a separate "mute box"?

IRstuff, how would that work in the system, would that be able to act as a sound muting circuit like mentioned above?

Thanks for the response guys!

 

[IRstuff]

Sure, one could possibly use the reset signal to drive relays for the speakers, for example.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529