I want to have a low pass filter on the input of my gainclone amp. it is used to drive my subwoofer, and i thouht that it would be easier to have a LPF on the input, than to make on for the output. i am aiming for approx 80hz cutoff. im guessing this would be done with a capacitor and resistor?
try this
Its been posted before, search for pllxo, but I think this is one of the sites the thread refers to
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html
Thought about this for the car "sub" amp - they're 6" 4R 125watt nominal cheapies & a capacitor from the network point to phone converters in the office (PABX or secondary device selector) is polypropelene 185nF 250v which would give a F of 86Hz on 10k resistor & 172Hz on 5k
Cheers
Paul
Its been posted before, search for pllxo, but I think this is one of the sites the thread refers to
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html
Thought about this for the car "sub" amp - they're 6" 4R 125watt nominal cheapies & a capacitor from the network point to phone converters in the office (PABX or secondary device selector) is polypropelene 185nF 250v which would give a F of 86Hz on 10k resistor & 172Hz on 5k
Cheers
Paul
Check out this link
http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/filter/filter.html
It shows you how to make up to an 8th order filter with op amps. Might be overkill for you, but I thought it was interesting.
But yes, you can make a simple 2nd order filter just using a RC network.
Corner frequency = 1/2*pi*R*C
I think the resistor comes first in a low pass filter, but I won't swear to it, I was never very good at analog stuff.
Randy
http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/filter/filter.html
It shows you how to make up to an 8th order filter with op amps. Might be overkill for you, but I thought it was interesting.
But yes, you can make a simple 2nd order filter just using a RC network.
Corner frequency = 1/2*pi*R*C
I think the resistor comes first in a low pass filter, but I won't swear to it, I was never very good at analog stuff.
Randy
Hi Matt,
The link I posted is for putting in-front of the amp, it can just about be built into a matchbox size box with inputs for your rca leads & outputs that plug straight into your amp.
Component count is 1 cap & 1 resistor so its cheap as hell to try it & since the frequency point changes with the resistance you can even try a 10k resistor in parallel with a 10k & a 50k pot - that would give you a variable resistance from 5k to about 8.5k for experimentation. On my car setup idea that would result in a frequency cutoff of 172 to 100 Hz on a 185nF capacitor.
As always I haven't got round to trying this yet. I asked Santa for a few more hours a day for Christmas.
Cheers
Paul
The link I posted is for putting in-front of the amp, it can just about be built into a matchbox size box with inputs for your rca leads & outputs that plug straight into your amp.
Component count is 1 cap & 1 resistor so its cheap as hell to try it & since the frequency point changes with the resistance you can even try a 10k resistor in parallel with a 10k & a 50k pot - that would give you a variable resistance from 5k to about 8.5k for experimentation. On my car setup idea that would result in a frequency cutoff of 172 to 100 Hz on a 185nF capacitor.
As always I haven't got round to trying this yet. I asked Santa for a few more hours a day for Christmas.
Cheers
Paul
Paulr said:
a high-order filter usually is done on the feedback loop. get a National OPamp databook and it should have plenty of them.
millwood said:
Or you can go to the link I gave. It's an interactive page for opamp based filters, let's you define for 2-8 pole filter, define different filter types, gain, freqency, and maybe a few other things, then spits out a schematic, parts values etc.
randy
randy, that's a good suggestion.
Alternatively, you can get the opamp book everyone is talking about from National and it has plenty of examples for active filters.
Alternatively, you can get the opamp book everyone is talking about from National and it has plenty of examples for active filters.
Hi Millwood,
Yeah I saw that too. I downloaded it already, I plan to print it out later when most people have left work, since it's sooo long.
My analog knowledge is pretty weak, so I'm sure I'll learn alot from it.
Randy
Yeah I saw that too. I downloaded it already, I plan to print it out later when most people have left work, since it's sooo long.
My analog knowledge is pretty weak, so I'm sure I'll learn alot from it.
Randy
So has anyone actually built it and how does it sound?? Could perhaps include the component values...
Hi mattt,
If you put a 1st order low pass just before the input (one resistor and one cap) I read somewhere that you will drop the signal about 3db or so. If you use a pot with the right range, you could even have a variable cut-off frequency. I prefer dip switches and specific resistor values myself.
If you are willing to live with the extra device, make it active and use a line level opamp (like NE5532, TL0xx, OPA6xx, etc) with a gain of 2 or so to bring the level back to previous. With a 78xx volt reg, you could probably even power it off the GC supply without any significant losses to your GC. Of course, you'd have to open up your amp and add this stuff, but then you would have an "invisible" solution.
I know the GC purists will hate it, but depending on how good your sub driver is, you may not even notice the extra .00x% distortion placed by the extra components.
You also might to add a 5-10Hz high pass (yet 1 more RC) just to keep the DC out of it.
🙂ensen
If you put a 1st order low pass just before the input (one resistor and one cap) I read somewhere that you will drop the signal about 3db or so. If you use a pot with the right range, you could even have a variable cut-off frequency. I prefer dip switches and specific resistor values myself.
If you are willing to live with the extra device, make it active and use a line level opamp (like NE5532, TL0xx, OPA6xx, etc) with a gain of 2 or so to bring the level back to previous. With a 78xx volt reg, you could probably even power it off the GC supply without any significant losses to your GC. Of course, you'd have to open up your amp and add this stuff, but then you would have an "invisible" solution.
I know the GC purists will hate it, but depending on how good your sub driver is, you may not even notice the extra .00x% distortion placed by the extra components.
You also might to add a 5-10Hz high pass (yet 1 more RC) just to keep the DC out of it.
🙂ensen
Matttcattt said:
here is the link:
http://focus.ti.com/docs/apps/catalog/resources/appnoteabstract.jhtml?abstractName=slod006b
if it doesn't work, search for "op amps for everyone" at ti.com.
Member
Joined 2002
hm...wouyld a 185nF cap work with a 10k resistor for the fist order lowpass filter?? I might want to add a pot to control the frequency...comments?
what is the difference between a first and second order crossover? apart from the number of components?
I dunno...but I'm going with an Active filter on Elliot's webby...the ELF one...TI is a bit reluctant to send me samples of the Opamp though...anyone got other sources...or has anyone gotten them?? Thanks...the part No. I am referring to is TL071...
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