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facundonu 31st December 2006 07:24 AM

my little tiny low end active subwoofer
it all started when i got these harman/kardon speakers as a gift from a friend. well, not a gift. he got them for free and wasn't going to use them, so handed them to me because "i'm into that speaker ****".

i tried them and, of course, they were no good.
they have a 3,5mm jack named "subwoofer output", so i thought i could build a sub to match them and make them sound a little better.
as i opened the little speaker i was astonished when i discovered that 3,5mm jack wasn't connected to anything.
then i connected the jack to the speakers, through a couple of resistors to divide the amplitude.

this whole project was about not spending money.

so, what do i own?

-acrylic lacquer
-various electronic components (including some NE5532 and some TDA2040)
-pertinax board
-a HP printer PS (16V@650mA, 32V@950mA)
-some microphone connectors, with 3 pins, that could be used for the PS.
-a low frequency JVC driver i don't know the parameters of, but i know it belonged to a boombox and the size of the box it had.
-this piece of foam

so, the building of the box was something like copying the original size and port. no problem. just some shiny lacquer on it.
the plate amp...
TDA2040 with the single supply configuration showed in the datasheet. just changed the 2200uF output cap, for a 1000uF. and the 22uF at the feedback, for a 4,7uF. this was made in order to eliminate the low frequencies and protect the little driver.
before the TDA, a low pass filter with 3 stages. first, a summing blok. second, sallen key filter. third, first order low pass. the frequency of the filters was choosen just by listening to the speakers to be matched.

let's go to the last pictures,

it's guts, with homemade PCB's.

ready to work.

not having instruments to measure the freq response, i do it just listening to different tones sent by my computer. i guess the sub goes from 50Hz to 110Hz. not bad for this size.

another little thing on my desktop.
a home made gain clone. LM386 for headphones, TPA1517 for speakers.


facundonu 31st December 2006 08:01 AM

here are the schematics of it all.

facundonu 31st December 2006 04:28 PM

i don't know why, but i can't see the edit button.

these are the correct schematics.

suiraMB 31st December 2006 07:09 PM

Happy new year :)

It's quite nice to see a project like this every once in a while; truly it has the DIY nature :D

Not every DIY project needs to be about outdoing the high-end vendors on price or performance; incredible amounts of fun can be had with whatever one has in the parts bin, given the right inspiration.

My latest headphone amp experiment was such; I happened across some line level transformers for use in telephony equipment, and wired them up with a 2SK389V in the same configuration as Susan Parker uses in the Zeus amp. I expected it to be crap, given the dubious quality of the transformers, but to my surprise, it actually sounded fairly good, though the last couple of octaves of bass were missing and the top end was slightly rolled off. Well worth the time spent. :cool:

facundonu 1st January 2007 04:00 PM

if you don't waste a lot of money or get hurt, and even if the results suck, having fun with audio and electronics will always be well worth the time spent. :D

facundonu 3rd February 2007 03:39 PM

some more pics, now with a decent cammera.


beamnet 5th February 2007 08:39 PM

2 Attachment(s)
In the same spirit:

In my teens i owned an aiwa micro set with two sattelites and a "subwoofer" with an estimated volume of 4L.

when bored i learned about TL's, attacked an old cupboard with a a handsaw. One hour later i had a "TL-sub" using the original driver and amp.

Needless to say, the sound is significantly better than the old enclosure which was about 4times smaller.

beamnet 5th February 2007 08:40 PM

2 Attachment(s)
and amp

BTW, it holds two gloves and a woolen hat as damping ;)

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