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Class D Switching Power Amplifiers and Power D/A conversion

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Old 17th January 2011, 10:38 PM   #21
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Yep ! That's right ! I remember I knew a guy on the street playing guitar with a mini amp-speaker ,and seeing the speaker in the box ,it had a huge magnet ,compared to the size . So it is better to invest on good drivers (as usual ) as they are the primary parts for good sound-sourcing.
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Old 18th January 2011, 03:35 AM   #22
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First off, thanks for all the response!

Quote:
Originally Posted by egberttheone View Post
What about using 2 hypex UcD180ST they are cheap, have good specs, ready to run auto of the box. they need +-50V.
one li-lion cell will give you 3.7v so you will need about 26 cells to build the battery. You will skip the part of making higher voltage from 12V.
This setup will be very efficient about 92% (datasheet hypex)!
those amps are a little out of my price range, especially if I have to use two of them! (unless I'm looking at the wrong amp here...)

also, i'll just restate my price range right now:
For ALL electronics and speakers, I'd like to limit the price to $250 or less...

On the discussion about the
Mark Audio CHR-70 's, if i need 8 of them, thats still going to be a pretty hefty price. Wouldn't it be just as good to get 2 good quality 8" or 6" woofer/mid range speakers, and two tweeter horns?

here's my idea for that: (yes, I added the LEDs for some neat detailing)
Click the image to open in full size.

for the woofers I'm looking at these two from eminence:
Eminence Alpha 6A speaker. The Eminence Alpha 6A is a 6" 8 ohm speaker. Alpha-6A is a 100 watt RMS 6" speaker.
Eminence Beta 8A speaker. The Eminence Beta 8A is a 8" 8 ohm speaker for all bass applications including bass guitar cabinets. Beta-8A is a 225 watt RMS 8" woofer.
I like the 6 inch, because it will give me more space at the bottom, to put the battery and amp.

and these tweeters seem pretty good:
Pyle Pro PSN1165 4.35" Piezo Horn Tweeter Pair | Parts-Express.com
but how good will they sound? opinions?

I don't know if that is the best way to do it, but it seems the most cost effective to me currently... this all with the lepai tripath, which is, in my mind, the best overall option.

Lastly, for the batery, I'd kinda figured on using gel-cells that i could pick up for free or cheap at a local recycling place of some sort. opinions on that, keeping in mind my price range?

thanks!
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Old 19th January 2011, 01:06 AM   #23
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I just started using Lithium polymer (LiPo) battery packs to power a DAC, but these offer a lot of advantages. Since they're used for R-C helicopters and other vehicles, they're all over eBay and pretty reasonable in cost. Search for 11.1v, as this is actually the bottom end of the voltage they'll supply. For mot of their discharge cycle, they'll actually be around 12 volts. Chargers are small and cheap, too, and you can get monitors that will either show the cell voltages and/or beep when you hit a certain discharge voltage, helpful for the life of the cells. A 5200 mah pack should give you several hours at a pretty good volume with a Tripath 2020 amp. Probably best to build it so packs can easily be swapped out for obvious reasons.

LiFePo cells are cool and do have the advantage of being long-lasting, but they're not widely available in 12v configurations, so they're much more expensive for now.

Lead/gel cells are heavy of course, but also need to be properly charged, and will poop out in a couple of years. Scavenged cells are likely to be problematic, seems to me. But IMO, the key to making this kind of project work is making it somewhat modular and easy to change. Start with gel cells if you want, but don't lock yourself into them. Oh, and also, make the electronics compartment really easy to open. You want to make it easy to make changes and also to show off your work.

--Buckapound
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Old 19th January 2011, 11:45 AM   #24
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hmmm... good ideas! yes, I like those LiPo packs, and they're well within my price range I suppose... there's several 2x 2800mah deals on ebay for 9.99 (the shipping kills though. 29.99)

anyways, would those two packs or similar ones be the way to go? or even more sets of smaller cells, for easy switch-out?
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Old 19th January 2011, 12:49 PM   #25
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Nothing wrong with using two packs, but swapping, charging and keeping track of the discharge level of more than that might get to be a pain. FYI, you'll have to solder on connectors for the power leads yourself. If you use the concentric type of connector that almost all "wall wart" type power supplies use, you can use one of those power supplies when you're close to an outlet. Tip: The power leads are heavy gauge, so you'll need to solder a short length of smaller gauge wire between the connector plug and the battery leads.

Poke around eBay, there are better deals, like 2 for $41.25, shipping included. You might also check your local hobby/RC shop. Base prices will be more expensive, but you won't have that expensive shipping.

--Buckapound
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Old 19th January 2011, 08:25 PM   #26
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I have to warn you about the quilty of some cells that are sold out on ebay, they do not meet the ratings that they are sold for. So beware, there are a lot of forums where the batterys are tested so you can buy the right ones
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Old 20th January 2011, 12:13 PM   #27
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alright, i'll take all of that into consideration. thanks!
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Old 20th January 2011, 01:44 PM   #28
v-bro is offline v-bro  Netherlands
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Quote:
Originally Posted by egberttheone View Post
I have to warn you about the quilty of some cells that are sold out on ebay, they do not meet the ratings that they are sold for. So beware, there are a lot of forums where the batterys are tested so you can buy the right ones
That goes for almost anything sold on Ebay...
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Old 20th January 2011, 07:52 PM   #29
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You know, I don't have any real issues about what battery you use, given the appropriate care and charging routine.

However, and I can't stress this enough, if you make a mistake with a LiPo battery, are careless in handling, testing or storage, or use a poor or failed charge monitoring and recharge regimen, or even make a slip with a VOM probe, you are in for some serious excitement, perhaps not of the "wow that was cool" kind and more along the "tragedy" kind.

This battery was (deliberately) overcharged:

http://video.google.com/videoplay?do...0570423705609#

Regardless of the cause, you can expect all LiPo fires to be similar to that example.

The RC model guys have a forum and this is a simple listing of the various forum posts there, regarding LiPo fires:

http://www.rcgroups.com/forums/showp...56&postcount=4

Mostly I just wanted to give a heads-up since this project has a very strict budget.

You will have to be very sure and take extreme care that you don't buy potentially defective or unreliable Lithium Polymer batteries (or Lithium Ion ... they are similar, use the same charge routines, but LiPo are lighter and uncased) or unreliable charge management circuitry in an attempt to save money.

Personally, since this is designed to be used on your person and in public, I would consider Lead-Acid myself. CTEK makes excellent chargers for these batteries. And remember: Wear eye protection when working with or charging batteries.
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Last edited by Johnny2Bad; 20th January 2011 at 08:13 PM.
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Old 20th January 2011, 09:08 PM   #30
v-bro is offline v-bro  Netherlands
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I would consider nimh AA cells, they give the best bang for the buck. They can be found already welded together in some shops and a charger doesn't have to cost too much.

If you are on a very tight budget and don't mind the weight then indeed SLA's are very good. If you ever consider solar power they are quite the ultimate actually...

Another down side of any lipo or liion battery I find the very limited cycle life. In relation to the cost they are not that good a deal at all!

Then the speaker drivers, I wouldn't recommend a pile of small drivers for this application, it's just too costly and likely to introduce a whole bunch of problems to get a good sound out of the system. Did you care to look at the link I posted earlier on? That is a combination of speakers with super high efficiency, reasonably light weight and it can sound very good.

It is often overlooked with backpack systems that the proximity of a large surface is very helpful to produce low frequencies. If this backpack is worn most of the times instead of put down on the floor it will have a real hard time to produce bass. This effect will happen equally with any speaker, so it is very important to start off with something really capable. PA speakers are designed for such situations and therefore I would look in that corner.

Actually what you are asking for, this whole system for a budget under $250 is rather extreme. The physical aspects of such a system all speak against feasibility, it's all contradictory. Actually you need some really high tech speaker drivers in there, the design itself has to be top notch. (you're super lucky if design number one pulls it off straight away) I don't want to discourage you, actually I guarantee you that you will probably look back upon it as a super valuable learning experience and it's often more important to just finish something instead of keep dreaming about it for years without doing anything. From what I have personally experienced it will take a couple of designs before the next one isn't 200% better....
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Last edited by v-bro; 20th January 2011 at 09:26 PM.
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