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Need amp advice.

post #1 of 4
Thread Starter 
I need some help figurout out how I'd make this:

http://www.parts-express.com/pe/show...number=300-773

portable for say, boom box purposes. I plan on using two 5 inch kevlar woofers, a 10 inch shallow mount sub which goes down to 29Hz and taking out the transformer and making a big ass battery system in it. My plan would basically making a 2.1 system with a shallow mount sub which is both nearly Hifi and portable. It will use ribbon tweeters if I can make it reliable enough, so most likely cheap silk domes in the first model, seeing that ribbon's are basically $50+ fuses.

Anyway, I have no idea how make this portable, but I have a 14.6V battery@ 2.4 amps, and a laptop battery if that helps at all.

Can anyone tell me how I would make a 150 watt trickle charge ready plug and play battery system work with this and how I'd make that charge an iphone off the power leads? I have no idea how to regulate voltage to around 3.7 volts for the ipod.
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Pimprig
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post #2 of 4
My advice would be to skip the costly DC-AC conversion, since all this plate amp is going to do is convert back to DC anyways. It'll just cost you efficiency and weight.
Look to car/marine applications for a 12v amplifier.

As for getting your iPod some juice... The easiest way would be to buy and harvest parts from a car 12v socket -> USB adapter. If you want to learn a little bit and save a little bit on money, I'll point you in the direction of a very nice voltage regulator chip that only needs a few other parts to make a reliable voltage regulation circuit to your output spec.

http://www.national.com/mpf/LM/LM317.html#Overview

The LM3117 is incredibly common, and a little Google-fu could probably turn up folks who have done exactly what you're trying to do here. I need to run, I can't join the hunt now.

EDIT:

Oh, I forgot about a really cool company called 41hz that makes a wide variety of nice little chipamps and kits. Again, a little more work to be done here, but a lot more reward in my opinion. They've got a selection of stuff that runs off 12v, too. http://shop.41hz.com/shop/category.asp?catid=42

You'd need to build crossovers, in that case, but a simple second-order network won't be complicated to build and would probably cost under $20 for the kinds of power you're dealing with here. Yet more cool stuff to learn!
http://www.apicsllc.com/apics/Misc/filter2.html
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post #3 of 4
Thread Starter 
Quote:
Originally Posted by Chipp View Post
My advice would be to skip the costly DC-AC conversion, since all this plate amp is going to do is convert back to DC anyways. It'll just cost you efficiency and weight.
Look to car/marine applications for a 12v amplifier.

As for getting your iPod some juice... The easiest way would be to buy and harvest parts from a car 12v socket -> USB adapter. If you want to learn a little bit and save a little bit on money, I'll point you in the direction of a very nice voltage regulator chip that only needs a few other parts to make a reliable voltage regulation circuit to your output spec.

http://www.national.com/mpf/LM/LM317.html#Overview

The LM3117 is incredibly common, and a little Google-fu could probably turn up folks who have done exactly what you're trying to do here. I need to run, I can't join the hunt now.

EDIT:

Oh, I forgot about a really cool company called 41hz that makes a wide variety of nice little chipamps and kits. Again, a little more work to be done here, but a lot more reward in my opinion. They've got a selection of stuff that runs off 12v, too. http://shop.41hz.com/shop/category.asp?catid=42

You'd need to build crossovers, in that case, but a simple second-order network won't be complicated to build and would probably cost under $20 for the kinds of power you're dealing with here. Yet more cool stuff to learn!
http://www.apicsllc.com/apics/Misc/filter2.html
Thanks for the reply, Chipp, before I go ahead and try to build my own amp, the ipod car charger option seems very appealing to me.

http://www.parts-express.com/pe/show...number=320-300

Using this with a 12v battery source with about 25 watts a channel seems like a good idea to me. I could build some birch enclosure for the 5 inch kevlar woofers I got lying around, get some cheap very efficient ribbon tweeters and make really small, effective ipod speakers. If I do that, would it be a better idea to run off of rechargeable D batteries with cheap battery holder i have lying around and intermittently use it only when charged or is there a better option to use it play and charge style with a more solid battery?

2.1 in my mind is out of the question at this point kind of.
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Pimprig
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post #4 of 4
Quote:
Originally Posted by coreyL View Post
Thanks for the reply, Chipp, before I go ahead and try to build my own amp, the ipod car charger option seems very appealing to me.

http://www.parts-express.com/pe/show...number=320-300

Using this with a 12v battery source with about 25 watts a channel seems like a good idea to me. I could build some birch enclosure for the 5 inch kevlar woofers I got lying around, get some cheap very efficient ribbon tweeters and make really small, effective ipod speakers. If I do that, would it be a better idea to run off of rechargeable D batteries with cheap battery holder i have lying around and intermittently use it only when charged or is there a better option to use it play and charge style with a more solid battery?

2.1 in my mind is out of the question at this point kind of.
That looks like a pretty nifty little amplifier to me. Hard to go wrong with Tripath based stuff for cheap-n-cheerful projects like this. They're pretty darned good chips if you don't try to over-drive them.

If you're mounting the amplifier in a box, I'd plan on rigging up some kind of external-facing heatsink (or create a 'vent' of sorts separate from the audio chamber to get airflow to the fan).

10 rechargable D cells will get you 12v reliably enough. As for runtime... We can estimate the current draw with Ohm's law. I = sqrt(P/R), or current - sqrt(power/resistance). The specs tell us the amp is good for 35w into an 8ohm load, so the approximate current output for those conditions is a hair over 2amps. If we average the efficiency ratings to something around 85%, we can guess total draw is around 2.4 amps. A little looking around shows that decent D-cell rechargeable are good for around 7 amp-hours, and you'd have 10 of those. Compensate a little bit to reflect that you'll not be running at your peak output all the time (we can multiply the peak output value by .707 to get the RMS value, which is a good average for audio) and we find that:

70 total amp hours / ~1.4a RMS current draw = 50 hours

Now, there was a metric crapton of guestimation involved there, and no battery will give you its full capacity over and over, and no battery is ever 100% fully charged - but, that at least tells us we can expect more than just a few hours of runtime.
Morpheus Mini
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Morpheus Mini
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