New 900BT - New Subwwofer POP on startup

[Bopper]

I had pro's install a Pioneer AVIC-900BT in my 2 day old 08 Expedition Limited. When i bring the ignition key to the ACC position, the HU receives power and seconds later the single factory Subwoofer in the back wall lets out a pop, then when I bring the key to the start position the HU loses power and then regains power, the subwoofer will then let out another pop. If I bring the key up quickly from off to start I will only get 1 pop out of the sub. The on/off powering of the Headunit during the ACC/start sequence is normal but the pop from the sub is not. The pro installers are acting like nothing can be done, this can't be the way it is supposed to work. They told me to search for a solution, find one, and they would fix it.

[minivek]

Hi there, I had the same problem on my 2003 limited explorer, it has something to do with the stock audiophile amp, It need a turn on voltage of 5v however the avic unit gives out 12v (assuming you connected the original sub amp to the head units sub turn on wire).

 

Prof. installers told me there was nothing to do, but I looked on and found out that if you put a 12v to 5v reducer (some places will tell you to put a cap on each side of it, I've done it both ways and it works, with of without, but apparently the caps ensure a more stable voltage source (at 5v) this voltage reducer has 3 legs, one has to be connected to the avics sub amp turn on wire, one is ground and the third one has 5v on it, and is therefore connected to you amp turn on wire.

 

anyways, check this link:

 

http://www.explorerforum.com/forums/sho ... ?p=1897412

 

it worked fine for me with the 2 caps, and I no longer have the pop.<

 

good luck

[joegr]

You can do that complicated way, or you can just put a 1K ohm resistor is series with the connection to the factory amplifier. It works just exactly the same (no more pop), it's cheaper, and more reliable.

[minivek]

It's true my way costs about 2,50$ and you have three wires to solder, but in no way is it less reliable. An inline resister will produce heat in order to get the voltage down. But my way is the exact same way computer are rigged up for example in order to supply reduced voltage to chips and stuff.

 

 

It's a bit more work, and I also know the resistor thing works, I just wanted something bullet proof and built for the exact purpose of reducing voltage to a set value.

 

Other people have also done a delay circuit in order to have the amp turn on after it recieve a signal from the head unit. I just prefered the voltage reducer.

[joegr]

It's true my way costs about 2,50$ and you have three wires to solder, but in no way is it less reliable. An inline resister will produce heat in order to get the voltage down. But my way is the exact same way computer are rigged up for example in order to supply reduced voltage to chips and stuff.

 

 

It's a bit more work, and I also know the resistor thing works, I just wanted something bullet proof and built for the exact purpose of reducing voltage to a set value.

 

Other people have also done a delay circuit in order to have the amp turn on after it recieve a signal from the head unit. I just prefered the voltage reducer.

Your way is a linear regulator. That means it varies its resistance to lower the voltage. So, it will produce just as much heat as the resistor. In fact, it will produce more heat, because of the current that goes to ground. It's a complicated active part with about 100 times more possibility for failure than a simple resistor. It has its place, and I have designed many of them in, but one of the rules of engineering is never use a complicated solution where a simple one will do. But, what do I know with just over 20 years of experience as an electrical engineer. It's not like I've designed alarms and accessory power controls for cars... Oh wait, I have.

[minivek]

Cool, I'm just a mechanical engineer so I'm more of a " make it work " kinda guy, the more complicated and high tech the better and I guess that because of my background I just assumed that a voltage regulator (theoretically built to reduce voltage) we be more adequate for this purpose.

 

I am however curious as to why they exist when resistors are more durable, reliable and everything. Both achieve a reduced voltage in the end, obviously both have to produce heat as no work is being produced (other than the 5 volts that are used)

 

Why build them if a simpler, cheaper more reliable solution exists?? It's not like they're novelty or luxury items...

 

I'd like to get your thoughts on this.

 

Thanks

[joegr]

That's simple. Voltage regulators and resistors do two different things. In fact, voltage regulators have several resistors built in. Resistors resist current flow, so they are generally used to limit current. Voltage regulators (linear ones) take a higher voltage in and provide a lower, fixed voltage output. When you pass current through a resistor, the voltage drop across the resistor will vary with the current. The linear voltage regulator works like a smart resistor. It changes its resistance to whatever value is required to cause the output voltage to be the desired amount. As such, it is much more complicated than just a resistor and therefore has more things that could fail and is more sensitive to voltage spikes and such.

 

So, a resistor and a voltage regulator do different things, that's why both are used. I'm sure you question then is why either one could be used and work in this one specific case? The answer is that what we are really trying to do is to limit the current flow into the factory amp on pin. This limited flow of current slows down its turn-on and avoids the pop. There are three ways that we have tried to drive the factory amp.

1. Directly from a 12V source. Too much current flows, the amp turns on too quickly, and we get a pop.

2. From a 5V regulator. Since a 5V potential is less than a 12V potential, less current flows, and things work out okay. Note however, that we really only limited the maximum possible current to about 1.5A, the max the regulator will pass. In practice, obviously much less current flows.

3. From a 12V source but through a 1000 ohm resistor, Current flow is now limited. In fact it is now limited to a maximum of 12 mA (that 12 thousandths of an amp). In practice, it will be less than that since the load resistance of the factory amp is much higher than zero ohms.

 

It's been proven from several installs, that both approaches 2 and 3 work. I prefer approach 3 because it (a) is simple, ( has less things to go wrong or fail, and © it is most directly doing what we want to do, limiting the current flow.

[Bopper]

You guys are rolling. I am learning a great deal. Keep it up.

 

Thank you

[Bopper]

I purchased a couple 12v/5v regulators at radio shack, 1 as a spare, brought them to the original installer (even though they didn't know the fix they had a happy to learn attitude) they installed one and everything is great so far.

 

Thanks for the help.