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subwoofer

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ranatungawk

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Dear friends please give me a hint …

I need to build a subwoofer (only a subwoofer) for my desktop PC.

1. Please send me simple circuit which works with 12V (Low-pass + Power amp for woofer speaker 5’’). No need high quality one.
2. tell me to where should I connect this ? because I need to connect this with existing desktop speakers.

Regards
 
attached is a schematic that does what you need. It provides a low frequency boost. it was designed to be driven from an MP3 player and be battery powered. The 2 pots are for bass control and volume. You might also want to look at the LM380 as a general purpose audio amp
 

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Thanks brother, great job!

Please let me know followings

1. To where should I connect woofer speaker ?
2. what would be it’s type ( Ω / W / inches )
3. What did u mean by J1, PIN1,PIN2, ?
4. is this included both of low-pass and the amp ?

best regards!
Kushan



attached is a schematic that does what you need. It provides a low frequency boost. it was designed to be driven from an MP3 player and be battery powered. The 2 pots are for bass control and volume. You might also want to look at the LM380 as a general purpose audio amp
 
OK, a few words of explanation. Firstly, you need to change the op amp if you want to run the circuit from 12V. The MC33204 only runs up to 12V. Replace it with something like the TL071 from TI. When you state '5" speaker' above, is that the dimension of the actual speaker itself (the round bit that vibrates with the music) or is the size of the casing - the standard 5" tall white plastic speaker that most desktop PCs have, with a jack plug on them?

The circuit above is intended to drive into the 1k input impedance of the standard white plastic speakers that are about 5" high. Inside your this is a buffer amplifier chip that presents a high impedance to the PC, but still drives the 4 Ohm speaker inside. The MC33204 is not designed to drive the 4 Ohms speaker directly. For that you need to add an LM380 (just connect it up as an op amp buffer. You dont need any gain out of the LM380, you just need it for its drive capabilities). You need to connect this to the output of the second MC33204 and its output to the left hand side of C6

Ignore the battery and the diode and all the 'pin' references - these were part of the kit I designed - you just want the op amp and surrounding components.

You need to take the output from your PC into the left hand side of capacitor C2 and connect the PC speaker jack plug to the socket SKT1. You need 2 of the above circuit if you want stereo.

The first MC33204 acts as the low pass boost circuit. The second one acts as a gain/attenuator stage.

If you want to examine the circuit further, you can simulate it is LTSpice. Here is an LTSpice tutorial:
http://www.simonbramble.co.uk/lt_spice/ltspice_lt_spice.htm
 
An LM380 amp IC does not have enough power for a sub-woofer.
Most speakers are 8 ohms. With a 12V supply an LM380 produces only 1W into 8 ohms like a cheap clock radio.
You need a bridged car radio power amp IC but most are not made anymore.
 
Hi AG

You make a good point and I did consider that the LM380 might not be up to it. I could not work out if he needed just a little bass boost to make his external PC speakers sound less 'tinny' (in which case the LM380 would be good enough), or if he wanted a proper bass response that would shake the floorboards. He did not seem to be after good quality, but then talked of a 5" speaker which is quite large (and loud). You could always use 2 LM380 in a bridge tied load application to get a differential swing across the speaker. Also the TDA family of audio amplifiers (from ST and Philips) might be worth looking at for a single chip solution
 
I bought a brand-new little RCA "sub-woofer" for $3.00 at a thrift store. It has a 4" speaker in a bass-reflex ported enclosure that is 9.5" high x 8" deep x 5.75" wide. I use it for my little TV with the speaker not the port facing me. It is wide-range and is not actually a sub-woofer.

Years ago I had some 4" woofers that sounded pretty good. I still have and use the second speaker system that I ever made (about 43 years ago) with a 5" woofer and 1" dome tweeter in a sealed enclosure that sounds great. 80Hz is clearly produced and some lower frequencies are there but at reduced level.

My pc speakers have 3" drivers with huge magnets driven with 3.5W each. They sound pretty good.
 
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