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osu1177 14th December 2006 11:17 PM

Tapping Car battery as voltage source for auxiliary amplifier
Hi everyone,
I am relatively young and naive in the field of electronics, and would appreciate any help.
I am trying to build an amplifier that would amplify my ipod's volume when connected to the auxillary input. This part is easy- I made a cmoy amp a few years back and dont see why I cant do it again. HOWEVER, this time I would like to replace the 9v battery as the primary voltage source and instead use the car's battery. I am aware that the car battery produces lots of noise, so I need some help designing a circuit to get around this.

The more details, the better...a schematic would be perfect. I am thinking some kind of rectifier or LC filters, what do you think? Thank you for your help.

MadMutt 15th December 2006 11:15 PM

The battery won't be the source of niose, it's all the other things in the car.
Ignition, spark plugs, switchs, alternator, and so on.

As for the power source I would think an mp3 player would not draw much power so why not just use a three pin voltage regulator chip.
Say a 7909.

As for filtering, try the above and see if ho wit goes first.

osu1177 16th December 2006 02:14 AM

a friend of mine recommends using whats called a "noise suppressor" to filter out this noise, and apparently it is made for this kind of thing, what do you think?>

osu1177 16th December 2006 02:21 AM

also, before i forget, i had a question about designing a particular switch.
How would I go about making a switch which powers a circuit when you insert a 3.5 mm male audio jack? I know the Ipod does this, and I would like a similar type mechanism for my circuit...any help would be appreciated.

v-bro 16th December 2006 02:28 AM

You would have to buy a switching type minijack chassispart or drill (if possible) and add a 'reed-contact'...

Amps and batteries?

Go for class D, 90% efficiency, no noise in the car (without extra filter!)

I like to use AMP32 from the link below....

osu1177 16th December 2006 02:37 AM

v-bro, can you elaborate on those? how would i add a reed to teh minijack?

what exactly are you referring to when you say

Go for class D, 90% efficiency, no noise in the car (without extra filter!)

v-bro 16th December 2006 02:56 AM

Class D amps, or frequently named class T (after the famed chips manufactured by 'Tripath') are very efficient with energy. You can't draw any car battery empty before falling asleep with this amp (AMP6 or AMP3....). Another advantage is the amp will hardly get warm.. And these amps are very uncritical to ripple or interference signals from your car. (I never had trouble with this and had them in many cars allready). They are easy to build (AMP6) and sound really great! (and I can see you start smiling when you look at the price...)

The minijack with reed add-on is not an easy mod, I did it successfully in the past, but you'd need to study the type of chassispart (minijack) very well to see if it is possible (don't take a reed with metal pushpin, unless you can detache it and use it without...). It's still best to buy one with a switch, but often they are of the 'open' type and collect more dust and dirt plus they don't seal off well...

v-bro 16th December 2006 02:59 AM

By the way, if you want to switch some higher current I would advise to add a relay on the reed first....

Jexx 17th December 2006 06:40 PM

The noise is usually induced from a bad ground if you're talking about car amplifiers. I've rarely seen noise induced from anything else.

Great project, I have the same problem with my Xm2Go and aux input on my Pioneer. When I switch sources from XM to the CD, I get blasted if I forget to turn it down (which happens more than I would care for). My previous head unit(Clarion) had an input sensitivity option, and it's a shame Pioneer ignored it. What head unit do you have, by the way?

osu1177 17th December 2006 08:26 PM

The head unit is JVC KD-AR860.

Unfortunatly, Ive found an easier solution to this problem. A part of me still wants to build it, but the alternative is just so easy....apparently there exists a cable which can be connected from the cd changer port to my ipod, which not only plays my music at a lower volume, but charges my ipod and shows song information on the screen. So I guess I wont be building this :(.

But thank you for your help everyone. I have plenty of projects in mind and will be here many more times.

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