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Old 10th March 2015, 10:08 PM   #1
zoltlegacy is offline zoltlegacy
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Default Can any one help me?

Hello i have currently under taken a project to build a portable bluetooth speaker and i an puting a small sub in it, it is 6 ohm 8 W and i need to make a simple low pass filter can any one help, thanks.
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Old 11th March 2015, 03:08 AM   #2
dannyjmf is offline dannyjmf  Saudi Arabia
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Here u go ... there is one ... Low pass filter at 80Hz

Using a simple basic opamp (TL072) does the job ...

Resistor 20Kohm and capacitor 0.1uf (104)
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Old 11th March 2015, 03:16 AM   #3
zoltlegacy is offline zoltlegacy
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What about one that goes after the amp?
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Old 11th March 2015, 03:50 AM   #4
dannyjmf is offline dannyjmf  Saudi Arabia
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The circuit i drawn is the stage (filter) before the amplifier ... therefore ... the input signal should enter the filter as shown and the filter output goes into your amplifier ... do u have the full photos of your parts that u r going to use for ur project ... ? is kinda hard to figure out if i dunno what u had in mind
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Old 11th March 2015, 03:52 AM   #5
dannyjmf is offline dannyjmf  Saudi Arabia
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Quote:
Originally Posted by zoltlegacy View Post
What about one that goes after the amp?
u mean the passive low pass filter?
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Old 11th March 2015, 11:34 AM   #6
chris661 is offline chris661  United Kingdom
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A passive low-pass would be physically very large and expensive.

It would be cheaper, and produce better sound quality, to use an active crossover and another amplifier channel. By using an active crossover, you can also take bass duties away from the midrange speakers, leaving them with more headroom.

Chris
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Old 11th March 2015, 03:24 PM   #7
bjorno is offline bjorno  Sweden
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Hi All,

Post#2 scrutinized:

b
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Old 11th March 2015, 04:44 PM   #8
zoltlegacy is offline zoltlegacy
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I am using this amp. http://www.amazon.com/Gikfun-Channel...ier+class+d+3w
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Old 11th March 2015, 09:28 PM   #9
Shadydave is offline Shadydave  United States
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I used to use a Ratshack 3 way active (before amp) automotive crossover that I bought for $19.95 (in the late '80's).
It did require 12 volts but so did the 300W automotive amp on my subs.
You might look at EBAY under "crossover car audio".
There are a few for $10 to $30.

Optimus Electronic Subwoofer Crossover | eBay

Before that I used a right out of the big linear design handbook, State Variable Filter circuit that was on a plastic protoboard for years.
It worked quite nicely.

Or, the circuit shown above would work well.

If you wanted to use a passive XO and those amps for both subs and main speakers, a passive XO might use up 1/2 of your power depending on it's topology.

Best of luck,
Dave

Last edited by Shadydave; 11th March 2015 at 09:34 PM. Reason: fix error
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Old 12th March 2015, 12:05 AM   #10
zoltlegacy is offline zoltlegacy
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I have attached the speakers i am using and the amp that i am using (i am using several amps). the speaker in the middle (silver) is the sub. Also can i run the 2 channel amp off of one channel? The BT module i am using is Mono.
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