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Old 7th November 2005, 05:23 PM   #1
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Default Loe Pass filter

I need an op-amp based low pass filter for a subwoofer. I have 5 tda7264's laying around and a 7265 as well and want to make a 6.1 system for my computer. I want to use the 7265 in bridge for my subwoofer.

Any ideas on where I can get a schematic for a low pass filter that cuts off at 100hz, and is variable down to 50 hz?
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Old 7th November 2005, 05:31 PM   #2
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If you are having proper surround output from the computer the LFE channel should already be filtered appropriately.

Otherwise look on the ESP site.
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
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Old 7th November 2005, 10:43 PM   #3
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oh my gosh, how did I do that! I misspelled low. sorry


well I would like to be able to use it as just a 2.1 system as well, so I can use my cd player with it etc.

I saw the sub filter on esp, but I don't have a tlo72. I only have some lm324's, a 272, two 351's and 3 741's to use. Can I maybe substitute one of these? I am not sure, because I'm not very familiar with op-amp substitutions as there are so many different ones.
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Old 8th November 2005, 12:21 AM   #4
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Considering that the '072 costs about 75 cents at Radio Shack, you won't have to break the bank to buy a couple. On the other hand, there are lots of cheap opamps out there that will do as well.
On the other hand, you can do quite well with a single transistor in follower mode. I had a thread on this a while back.
If you intend to sum the low end to mono (i.e. ".1" instead of having stereo subs), that will require a little more attention, but it's not hard to do.


EDIT: I probably didn't make it clear enough that you can pretty much substitute opamps at will. There are a few oddball types, but you're not likely to mistake them for ordinary opamps. The most desirable characteristic for your purpose is an FET input. This will give you high impedance and make the performance of the filter more predictable.
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Old 8th November 2005, 02:53 AM   #5
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oh ok, I didn't know radio shack carried the TLO72, so I'll just get that. Thanks for the help guys!
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