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Topic: Need help building an amp (Read 609 times) previous topic - next topic


May 02, 2014, 01:06 pm Last Edit: May 02, 2014, 01:11 pm by pmck91 Reason: 1
I'm currently building a car computer,  it's going to use an odroid u3 for the main head unit to give it all that androidy goodness and an arduino to handle things like fm radio, and steering wheel controls integration. The only part I'm truly stuck on at the moment is the audio part. I've never worked with audio before.

My plan was to use an fm IC like the Si4703 to handle the radio by using the cars (bmw e46 if that helps) OEM antenna, which I'm not even sure is possible, but thats for another forum post. And then to output the sound from that and from the odroid to an arduino powered amp which would play radio by default unless the odroid was outputting sound. and then the amp would split the audio up into 5 channels FR FL BR BL sub. I've no idea how I would go about doing this I was going to use two LM3886 ics per channel, but 67w wont be enough for the sub and I also dont really know how to create an amp that will sound like a professionally built one.

I'd love any advice or help with the design of this amp, or if anyone knows of similar projects I could draw inspiration from.

I forgot to mention I was looking at the PT2322 IC for splitting the audio into channels, is that any good for it?


Look at boxes at crutchfield.com, otherwise you're gonna end up with lots of audio hum from alternator/generator noise and other car system noise, and never be happy with your system.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.


LM3886 ics per channel, but 67w
That requires a +/-28V power supply.   With a +14.4V power supply the theoretical maximum maximum power you can get from a bridge amplifier into 4 ohms is about 26 Watts (twice that into 2 Ohms).   With a real-world amplifier, you'll be lucky to get 20W (less if your voltage drops to 12V).  (With a standard non-bridged design, you can only get 1/4th the power.)

Car stereo manufacturers use voltage-boosting switching power supplies[/b] to get higher voltage.   These power supplies re not easy to build.  So, so I agree with CrossRoads...   Buy a car amplifier from someone who has the design nailed and builds them in bulk (at least the subwoofer amp).

...and then the amp would split the audio up into 5 channels FR FL BR BL sub.
That's complicated shtuff!!!   If you have a DVD, Blu-Ray, or some other true-discrete 5.1 channel source, then you have 6 channels of audio to begin with.   And of course, you need the appropriate Dolby AC3 or and/or DTS decoders. Usually, those decoders come with DVD/Blu-Ray player software such as PowerDVD or WinDVD, or the decoders are built into your home theater receiver.   (I have no idea what's available for the ODROID.)    You can get a 5.1 channel (or 7.1 channel) soundcard, but you need the software decoders to drive it.

There is also the old "analog" Dolby Surround (i.e. Pro Logic), but you'll only find that on VHS tapes and some DVDs.  It doesn't  work properly with FM radio, CDs or MP3s., etc.    For that you also need a Dolby Decoder (or decoder software).   

For regular 2-channel stereo sources CDs, MP3s, etc., there are Dolby Pro Logic II "soundfield" options for sending reverb to the rear channels, etc.  Some soundcards come with similar (non-Dolby) surround-sound effects for "spreading around" 2-channel stereo.

Typically, a home theater receiver has "bass management" to filter the bass out of the 5 surround speakers and send it to the subwoofer.   With a DVD or Blu-Ray, the "point one" channel is called the LFE channel (low channel effects channel) and it ONLY contains "booms and explosions", with the other 5 channels containing the normal bass.   (Bass management is used to re-route all of the bass to the sub when you have 5 small surround speakers that can't put-out bass.)

I forgot to mention I was looking at the PT2322 IC for splitting the audio into channels, is that any good for it?
No.   That's NOT a surround-sound decoder.   It's a dual active crossover chip for tri-amplified systems with separate amplifiers for bass, mids, and highs.      A traditional speaker (passive) system has a passive 2 or 3-way crossover to send the lows to the woofer, (mids to the midrange if you have a 3-speaker), and highs to the tweeter.    Active crossover filters the line level signal before it's amplified.   Many car amplifiers have a crossover built-in so the amp can be used as a subwoofer amp, or tweeter amp, etc., so you don't need a separate crossover.   

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