SparkFun Forums

[chrisrice93]

Hi all, I recently built the audio amp kit from sparkfun and am using it in my car. I have the power line connected directly to the 12V vehicle rail and everything works fine except that whenever it is on it picks up noise from the 12V rail and amplifies it through my speaker. I replaced the included 1000 uF cap with a 10000 uF cap but that did not reduce the noise. Any ideas on how to clean the power coming to my amp? Thanks!

[MichaelN]

Which kit are you referring to? If it’s KIT-09612, then you also have to worry about the board being damaged (it doesn’t have any protection against overvoltage / spikes). A car is a very harsh place for electronics.

Adding a capacitor as you did will have some benefit, but for an effective input filter you really want to use one or more inductors as well. Or you could use a ready-made power supply filter (which will normally have a couple of filter stages to reduce the noise further). You should add some spike protection (e.g. 16V rated transzorbs) to the amplifier side of the filter to clamp any spikes.

[Ross Robotics]

In my experience with car audio, the engine noise is due to bad grounds. If the you are hooking up the ground of the amp to the ground at the battery, you will get noise. You can leave that connection but take another wire and hook it to a ground close to the amp. The best way is to ground it on some kind of metal, NOT a ground wire. If the amp is under the dash, find the nearest metal brace or mount and make your own ground connection.

If you still get noise, take the ground wire off the battery.

[chrisrice93]

Which kit are you referring to? If it’s KIT-09612, then you also have to worry about the board being damaged (it doesn’t have any protection against overvoltage / spikes). A car is a very harsh place for electronics.

Adding a capacitor as you did will have some benefit, but for an effective input filter you really want to use one or more inductors as well. Or you could use a ready-made power supply filter (which will normally have a couple of filter stages to reduce the noise further). You should add some spike protection (e.g. 16V rated transzorbs) to the amplifier side of the filter to clamp any spikes.

Thanks for the reply Michael. Would you recommend using a pi filter right before the power into the board? If so what would be a good inductance value to use (assuming I am using two 10000 uF caps)? This is all new to me so any help is appreciated, thanks!

[Dave Mueller]

I'm guessing about 20 mH for the inductor. Make sure it's sized for the current you need.

[MichaelN]

I'm guessing about 20 mH for the inductor. Make sure it's sized for the current you need.

That's probably fine, although larger values wouldn't hurt. The inductor value in this application isn't critical.

[chrisrice93]

Alright, I got a 20mH inductor from mouser but it looks like it's actually two 10mH inductors in one part so, would it be a better filter if I used the two 10mH inductors in series to make one 20mH inductor and only one pi filter, make two pi filters with both of the 10mH inductors and 3 10000 uF caps, or would it not matter? Thanks for all the help!

[MichaelN]

Alright, I got a 20mH inductor from mouser but it looks like it's actually two 10mH inductors in one part so, would it be a better filter if I used the two 10mH inductors in series to make one 20mH inductor and only one pi filter, make two pi filters with both of the 10mH inductors and 3 10000 uF caps, or would it not matter? Thanks for all the help!

What's the part number? The manner in which the inductors are coupled together will determine how they should be used.

[chrisrice93]

http://www.mouser.com/ProductDetail/Sch ... hmIg%3d%3d That is the link to the mouser page. It is part number EV35-2.0-02-20M.

[MichaelN]

http://www.mouser.com/ProductDetail/Sch ... hmIg%3d%3d That is the link to the mouser page. It is part number EV35-2.0-02-20M.

OK, that’s a common-mode filter, and the inductors are coupled together. You would connect the +12V supply to pin 1, GND to pin 4, then connect pins 2 and 3 to the equipment power input. Put capacitors between pins 1 & 4 and between pins 2 & 3. It’s a good idea to put a ceramic or plastic-film capacitors (say 100nF to 1uF) in parallel with the electrolytic capacitors, to improve the high-frequency performance.

EDIT: watch that you don't exceed the 2A rated current of the filter, or it could overheat.

[chrisrice93]

Awesome it works great now! No audible whine even when it's idling. Thanks so much for your help!