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low pass filter active adjustable
low pass filter active adjustable
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Old 27th July 2015, 01:51 PM   #1
9justinas9 is offline 9justinas9  Lithuania
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Question low pass filter active adjustable

hey guys i have been doing a research and stuff i have found some low pass filters but nothing that would fit my needs. my needs are that the low pass filter cut off frequency would be at about 200hz and it would be adjustable with a decent quality setup i have is.
sound from pc/phone to an amp to speakers

it would be the best that it would go before an amp all i need is 2 knobs(pots) one for bass volume and one for cut off frequency adjust or it could be fixed 200

please if somebody have or know pcb layout with components please post it here
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Old 27th July 2015, 05:23 PM   #2
9justinas9 is offline 9justinas9  Lithuania
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can anybody please reply?
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Old 27th July 2015, 05:35 PM   #3
Mooly is offline Mooly  United Kingdom
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low pass filter active adjustable
Quote:
Originally Posted by 9justinas9 View Post
can anybody please reply?

How about we move it to Line Level forum....... done !

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Old 27th July 2015, 06:12 PM   #4
tom31415926 is offline tom31415926  United States
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Default Maybe a lilttle help

9justinas9,

I don't know if I will be able to get back to this thread, but maybe I can help.

It sounds like your terminology may need to be more precise. If you want to hear audio (like intelligible speech) from this amplifier, you might want a 200Hz _high-pass_ filter. The effect of this filter would be to remove bass (like low-frequency noise below the frequency range needed to understand voice). Is that what you need to do? The rest of this paragraph assumes that you want a high-pass filter. You probably want at least a second-order filter. The higher the filter order, the steeper the slope of the frequency response as it transitions from the pass band (above 200 Hz) to the stop band (below 200 Hz.) For analog filters, adjusting the corner frequency of a second-order filter requires that two components be adjusted simultaneously (three for a third-order, and so on).

Perhaps you can implement the filter you want in the digital domain? Like software or an app for your phone?

If you use a 200Hz _low-pass_ filter then what you will get out is only the low-frequency part of the program. The program material below 200 Hz will not be understandable speech by itself. If the subsequent amplifier and speaker are intended to reproduce just the low frequencies, then the associated speaker would be called a woofer or subwoofer, and another system (one that uses a high-pass filter) would be responsible for the higher frequencies. Together, the two systems would cover the audio range. Ideally, the design of the low-pass filter and the high-pass filter would be done together, and ideally taking into account the capabilities of all the speakers used. If you do this, the volume control of the amplifier for the low frequency system's amplifier would act like a bass control, but not a very good one.

I don't know if I can get back to this thread, but I hope this information helps you formulate your problem.

Tom
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Old 27th July 2015, 06:21 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

Its a standard circuit for subwoofers and not hard to find at all.

rgds, sreten.
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Old 27th July 2015, 10:02 PM   #6
AndrewT is offline AndrewT  Scotland
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look up Sallen and Key (S&K) filter.
This one opamp filter is 2pole with a slope of 12dB/octave (=40dB/decade)
You could also use an MFB filter (Multiple FeedBack). It too is a 2pole filter but has an extra degree of freedom in that gain is independent of Q

In both types you can change either the frequency setting resistors, or change the frequency setting capacitors.
If you want continuous variability then use a VR (pot wired as a variable resistor) as your control. Switchable using a multi-pole dip switch is probably better, particularly if you want 3pole, or more, of slope.
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Old 28th July 2015, 10:04 AM   #7
9justinas9 is offline 9justinas9  Lithuania
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I need something like 4pole low pass filter for two 40w 8ohm woofers connected in paralel idk if its good idea but I can't find an appropriate amp for my setup but basicly I will use 2x20w for anything above 200hz with tda 1554q and for subs I will use lm3886t with a low pass filter coz there is times when I don't like sub and there is times when I can't live with out it
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Old 28th July 2015, 10:11 AM   #8
9justinas9 is offline 9justinas9  Lithuania
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I'm not sure about the poles but I have heard that more poles equal more quality so I'm not sure what I want talking about the poles but even in this forum I could not find a decent low pass filter. With things I specified. I would like to adjust the cut off frequency but as AndrewT suggested VR (variable pot) would be enough so basicly I need one pot witch would adjust volume of bass with out messing with the main audio so if has to be done with filter of some sort. But now that i cone to think of it I need high pass filter too with variable cut off frequency. I will get back to this forum as soon as I'm not on my phone
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Old 28th July 2015, 11:44 AM   #9
Conrad Hoffman is offline Conrad Hoffman  United States
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In a research setting you'd just grab your Krohn-Hite filter off the shelf and plug it in. They had/have a bunch of different models, usually available on eBay. The 3202 is a good choice.
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Old 28th July 2015, 12:55 PM   #10
9justinas9 is offline 9justinas9  Lithuania
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Quote:
Originally Posted by Conrad Hoffman View Post
In a research setting you'd just grab your Krohn-Hite filter off the shelf and plug it in. They had/have a bunch of different models, usually available on eBay. The 3202 is a good choice.
i dont have that much to spend my budged would be 10$ at most and i want a DIY project for various reasons
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