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Class D Switching Power Amplifiers and Power D/A conversion

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Old 20th September 2007, 04:22 AM   #21
NED 209 is offline NED 209  Ireland
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good God. that is a serious thing. hi there, ive been working on a technically inferior version of the same idea for a long time now. inferior because basically i dont have a clue what im doing, i just wanted a really loud ghettoblaster. heres mine

Click the image to open in full size.

Click the image to open in full size.

its got an amp32 from a very king guy at 41hz, 2 p-audio sn8mb woofers, and morel tweeters. i dunno much about building a crossover but i bought a few off ebay and found the sansui two ways that im using sound real sweet. i was aiming for a weight of 8kg, i can carry that all day, but it ended up being 10kg, still pretty portable over medium distances.

id love your know how! aggh, really i would. id say yours would eat mine for breakfast. those fuel cells sound interesting, do they come in a reasonablly sized 12v or 24v form?

cheers,
ned .
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Old 18th October 2007, 12:48 AM   #22
coit is offline coit  Australia
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I would like to make something similar if you don't mind.
Two questions:
Did you wire 2 woofers and 2 tweeters in series-parallel on each channel to keep impedance up?
Aren't you worried that amp clipping will wreck the speakers?
thanks
Paul
PS What's happened to the 41HZ shop?
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Old 18th November 2007, 07:44 PM   #23
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Sorry for the long silence.

NED209, excellent work! reminds me of the first boombox build I did which also was refurbishing an old 80s style boombox with new drivers and a new amp. Currently, I'm mostly inclined to ditch the fuel cell idea. Simply to much hassle but if you're interested, visit www.ird.dk

coit, aboslutely no problem. You should note that I plan to sell these at some point in the future but for your own use there's absolutely no problem in building your own. You should note that this is the final prototype version and that the real full version will have slightly different dimensions as I'm putting in a 14 watts a-Si solar panel to cover the entire top. I'm also using another tweeter now instead of the peizo type in the prototype.

This one: http://www.partsexpress.com/pe/showd...number=270-049

That also means that I'm using a proper filter now. It's just a simple 6/12db octave type so it shouldn't be too difficult sorting out component values. I'm not finished tweaking the filter yet.

As for your questions. No, I wire the driver pairs in parallel to lower the impedance to roughly 4 Ohms to draw maximum power from the amps. And I'm not at all worried about wrecking the drivers, they are professinal types that are rated at 20 times the maximum power the currently recieve.

The www.41hz.com shop and forum should be up and running now.

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Old 19th November 2007, 05:42 PM   #24
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I forgot to mention that the solar panel I'm going to use in the full version is a custom version without frame and backplate but otherwise identical to this:

http://www.freeenergyeurope.com/htm/...olar_panel.htm
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Old 21st November 2007, 05:13 PM   #25
v-bro is offline v-bro  Netherlands
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Hey Saturnus, cool posts!

I wondered about the piezo drivers before, because I never find they sound very nice and the limiting factor is mostly the bass/mid driver regarding efficiency. So it must have been the sturdyness and simple filter technique that drove you to use them. I think the soundquality will be much better with your new choice.

Quote:
Originally posted by Saturnus
And I'm not at all worried about wrecking the drivers, they are professinal types that are rated at 20 times the maximum power the currently recieve.

Be carfull with clipping behavior of the amp though, some noobs (that read you post) don't know about this danger. Clipping is much like DC and DC keeps the speaker cone in a fixed position for too long. This stands in the way for the coil to cool because there's no/hardly movement/no airflow.

Please show some pics as soon as you have built something and have the time, thanks!

Keep up the good work!
__________________
Max. cone displacement can be several foot on any speaker!Too bad it can be done only once......
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Old 4th December 2007, 03:38 AM   #26
NED 209 is offline NED 209  Ireland
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hey thanks Saturnus, id love to see both your new one and the first refurb you did of the 80s boombox. im addicted to them, have been for years.

following V-bros advice im going to build one from scratch, though im essentially building a wooden replica of an existing model, this one

the big one -

Click the image to open in full size.

weight is critical to me. cant stress that enough. the whole thing has to be as close to 8kg as i can get it. (i dont have a car!) so the amp32 and 41hz series are a real blessing for me. i bought the killer drivers for this project, 1.5kg and 99db, im in love. - http://www.musicgear4u.com/bass-guit...10150-neo.html

so id like advice, on what type of wood to go for? probably plywood ill go for, im tempted to go as thin as possible, quarter inch, and brace it. but im open to advice or suggestions. the bbx is huge, id say about 36lt.

heres a pic of the previous radio at night, i got all car hi-fi on it, and sanded down the fins on the p-audios for a more dramatic effect http://i8.tinypic.com/6z6ckfr.jpg

Saturnus i hope i havnt hi-jacked this thread, i was a bit nervous of starting a new one!
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Old 4th December 2007, 03:57 AM   #27
pekar is offline pekar  United States
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Definitely plywood, but I wouldn't consider less than 3/8".
here's a fun one-
http://www.flickr.com/photos/kanoa/2...ol-318192@N24/
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Old 4th December 2007, 04:29 AM   #28
NED 209 is offline NED 209  Ireland
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mmm, the more i read the more im thinkin that. but 3/4 inch would be insanely heavy at that size, not portable at all. i like the Benosonic mine will be more realistic. im going to strip the adornments from the original blaster (chrome, stickers ect.) and affix them to the new box. should look exactly like the original with enough coats of black gloss.
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Old 4th December 2007, 04:46 AM   #29
Variac is offline Variac  United States
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Seems that some sort of high tech sandwich material would be best.
Like epoxy and carbon fiber/glass skin with foam or hexagonal cell or balsa core. Not cheap but I'll bet you can get sheets of stuff like that somewhere.. maybe 1/2" thick. Boats and airplanes use it.. Celestion used the stuff with metal skin for the SL6 speakers I believe..

Like here,

http://www.acp-composites.com/acp-lp.htm

or here,

http://www.cstsales.com/fiberglass_sandwich_panel.html


ooooh too pricey
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Old 4th December 2007, 05:06 PM   #30
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I use 12mm 7 ply birch plywood. It's lighter and more rigid than any other kind of wood you can get. I the mark II version I've also experimented with cutting some weight while maintain the properties of the plywood, mainly because as I want to start selling them online the weight has to be under 25kg or the price for international shipping goes through the roof. So with a heavier tweeter and much larger (and heavier) solarpanel I had to find a way to cut some weight.

I achieved that by routing 4mm deep 16mm wide grooves with a spacing between the grooves of at least 12mm into the 12mm board. Note that the mark II version still only exist as a 3D model but the modelling program (CATIA) is usually pretty accurate.

I'm not at bothered by the hi-jack. So few people are interested in portable audio here that the 2 main threads about it needs to be bumped from time to time.
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