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remla

Lowpass filter for subwoofer

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:-\ hi,

does this circuit need a pre-amp or it can drive power amp directly? I can't find potentiometers stated in the diagram here in our place we have here 50k and 25k pots we don't have 47k and 22k. Can I use them? Is there any effect in the cut-off frequency of the circuit? Does the input of this circuit need a low output from crossover? Pls. advise.

thanks,
almer

Project Link: http://www.electronics-lab.com/projects/audio/008/index.html

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The designer of the circuit writes that the filter must be driven by a preaplifier, but i think that it can be also driven by an amplifier directly.

Don't worry about the pontesiometers. They will do the jod.

I haven't tested it, so i don't know about any effect in the cut-off frequency.

No there is no need of a crossover. The circuit will cut off all frequences out from the 20-100Hz ragne.

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"[D]oes this circuit need a pre-amp or it can drive power amp directly?"

The source Z of an op-amp's output is essentially 0. Note that there's a 220 ohm resistor on the last amp's output. So ithe output Z of the filter is 220 ohms. The input Z of a typical power amp is something like 5-10K, so the filter will have no problem driving an amp directly.

"I can't find potentiometers stated in the diagram here in our place we have here 50k and 25k pots..."

You'll note from the schematic that the pots are connected as rheostats. 25 and 50K will be fine. You could even use 100K pots, though adjusting them might be touchy.

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Hi
I didn't make the filter yet. But i have some questions ::)
-caps 4.7/35V in the schematic don't appear, why? i don't understand ;
and they are two
-might they replace the 0.4uF cap?
-what does the led ?

Please help me!
Thanks!

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Hi Roby,
Aren't you talking about this circuit that doesn't have any 4.7/35V caps?
Where's the LED?
Here's the project's link again:
http://www.electronics-lab.com/projects/audio/008/index.html

The TL062 is lousy and the TL082 is noisy. I would use a low noise TL072. 

I would like to know where the author gets caps with values of 0.2uF and 0.4uF. I can get 0.22uF and 0.47uF. But they aren't exactly times 2 so would be wrong.

The translation is a joke, isn't it?  ;D

post-1706-14279142167567_thumb.gif

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Hi Roby,
I see, the pcb has more parts than the schematic:
1) Two 4.7uF/35V bypass caps in parallel with C2 and C6.
2) An LED (isn't it backwards?) and 1.5K current-limiting resistor at the positive supply.
3) Two 100nF caps paralleled to make the 0.2uF cap and a 180nF and 220nF caps paralleled to make the 0.4uF cap.
4) A 100 ohm output resistor instead of 220 ohms.
Did I miss anything else? I am glad that the pcb uses a low-noise TL072 opamp instead of the lousy TL062 on the schematic.
It will work fine (check the polarity of the LED).

Man, this "high tendency of catering and high honor of rhythm" low-pass filter project is just as confusing as its translation!

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Hi,
So you don't advice me to procede with this project?
I liked it because it is rather simple and small (I am low on money and space in my ampl case).
I have made a amplifier after the schematic in the picture attached and I need a filter for it...
What is your advice? Should I make the filter or should I look for a better one? I am o bass lover  :)
Thanks a lot!

post-7877-14279142167854_thumb.gif

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Hi Roby,
That's a nice, powerful looking amp you have there.
This sub-woofer low-pass filter project uses a Butterworth filter with a gradual slope of 12dB/octave. Many speakers need a sharper slope. You will also need its opposite, a high-pass filter for your main speakers.
If you combine a Butterworth 12dB/octave low-pass filter with the opposite, you end up with a notch filter, where the sound cancels at the crossover frequency.
Therefore I recommend using a Linkwitz-Riley set of filters that don't cancel, one is 12dB/octave and the other is 24dB/octave like these:
http://www.sound.westhost.com/project81.htm
http://www.sound.westhost.com/project09.htm

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Roby,
Why don't you make your own? Texas Instruments has a free program that you can download named "FilterPro". You can design low pass and high pass filters with different slopes and up to 10 poles. The program is free and there are lots of features including graphs to show you the response and phase change.

MP

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Hi guys, I'm new to the site so my question may seem stupid for some , so sorry in advance :)

I have a 20W stereo power amp with a built in pre-amp for treble and base control,but with VERY POOR BASE RESPONSE ! ! ! I'd just like to know where this bass boost will go in, between the source and the amp ( ie the pre amp and the power amp ) or between the power amp and the speaker.

Thanks , You people RocK !

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Hi Dakshitha,
Welcome to our forum. ;D
This project won't boost the bass of your sound system. It is designed to cut high frequencies at a frequency determined by its pot setting, and pass very low frequencies to a separate additional amp that drives a subwoofer speaker. The volume control on the subwoofer's amp controls the amount of bass that is heard.

Since your sound system has poor bass response, maybe its speakers are defective or just too cheap and small.
Maybe you have the speakers connected with opposite polarities which cancels the bass.
Maybe your amp is defective or produces 20 Whats instead of 20 real Watts. 20 phoney Whats could be as low as only 2 real Watts like a cheap clock radio.
Maybe you need a subwoofer speaker and a high-power amp to drive it.

Even 20 real Watts is very low for good bass. The amp posted earlier in this thread produces 570 real Watts to its subwoofer speaker. ;D

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frt, what help do you need? In looking at the thread linked to the project, it seems to work ok for those who posted. There is also an email link that will connect you directly with the author of the project if you need specific help.

MP

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In the project, there is a link to a discussion about this confusing project.
Last year, I wrote this about it:
"I see, the pcb has more parts than the schematic:
1) Two 4.7uF/35V bypass caps in parallel with C2 and C6.
2) An LED (isn't it backwards?) and 1.5K current-limiting resistor at the positive supply.
3) Two 100nF caps paralleled to make the 0.2uF cap and a 180nF and 220nF caps paralleled to make the 0.4uF cap.
4) A 100 ohm output resistor instead of 220 ohms.
Did I miss anything else? I am glad that the pcb uses a low-noise TL072 opamp instead of the lousy TL062 on the schematic.
It will work fine (check the polarity of the LED)."

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i want to now if the parts indicated in pcb realy works?and what kind of preamp should i use i was very confused on that project because the schematic are very far from the parts indicated in pcb if 


p.s
if the parts inthe pcb are rong just make a correct list of parts for me plsssssss :'(

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