easy DIY passive filter

[Karloff70]

And after another few years.....lol....another man seeking help.

I am after putting a passive filter before my nearfield amp at 80Hz/-6dB rolloff, to save the speakers having to deal with the bottom that the sub has in check. From what I read here it seems a pair of matched 6.9uF's, no resistor would get me 100Hz/-6dB, so as I don't see the calculator, I guess around a little more, say 8uF or so would get me in the area?

If anyone can point me towards how to calculate it to be 80Hz or give me a value I would be most grateful indeed.......

[tINY]

Depends on the input impedance of the active speakers...

Freq = 1/(2*pi*R*C)



-tINY

[Karloff70]

No active speakers. Line output from Coleman LS-3 into filter and then straight to amp for passive monitors.

[tINY]

Originally Posted by Karloff70

No active speakers. Line output from Coleman LS-3 into filter and then straight to amp for passive monitors.

As long as you aren't putting the filter directly in front of the passive speakers...




-tINY

[LeeYoo]

Hi Karloff70.
Not possible to calculate if you don't know the input impedance of your amp.
A 1uF film cap with a 2kohm resistance to ground (amp+resistor, amp side), will give you a corner frequency of 80 herz.
Depending on the amp, your resistor could be from 2.2k to 5k or so.

[Karloff70]

Originally Posted by LeeYoo

Hi Karloff70.
Not possible to calculate if you don't know the input impedance of your amp.
A 1uF film cap with a 2kohm resistance to ground (amp+resistor, amp side), will give you a corner frequency of 80 herz.
Depending on the amp, your resistor could be from 2.2k to 5k or so.

Now you have me confused. I thought I would just add identical caps into leg 2 and 3 and need no resistor. And that these caps would need be bigger than 6.9uF as that value would give a corner of 100Hz.

You're saying a 1 uF cap where, and resistor to pin 1? From where?

The amp is going to be Hypex UcD180HG modules, not sure of their impedance.

Tiny, no not in front of speakers, between the Coleman splitter (line splitter!) and the Hypex amp.

[LeeYoo]

Hi Karloff70.
Now I'm confused as well. For some strange reason, I did not read the previous posts, and assumed unballanced amp inputs.
I have gathered that you want to make a high-pass filter with 80herz corner frequency for a Hypex amp module.
These amps have ballanced inputs, but the spec sheet does not state any impedance.
Just a recommendation, to stay under 7kohm, to keep the noise level down.
I presume, you want to drive them ballanced.
And I don't know what the output impedance is of whatever is driving the switch.
You have to pick a resistor value to put between the two ballanced inputs of the amp.
And put two caps in series with each hot line.
IMHO, a 2.2kohm resistor is a good trade-off. Then the two caps have to be 1.8uF each, for 80herz corner freq.
A lower resistance will need bigger caps.
I don't see any advantage in that.
Leo..

[Karloff70]

Originally Posted by LeeYoo

Hi Karloff70.
Now I'm confused as well. For some strange reason, I did not read the previous page, and assumed unballanced inputs.
I have gathered that you want to make a high-pass filter with 80herz corner frequency for a Hypex amp module.
These amps have ballanced inputs, but the spec sheet does not state any impedance.
Just a recommendation, to stay under 7kohm, to keep the noise level down.
I presume, you want to drive them ballanced.
You have to pick a resistor value to put between the two ballanced inputs of the amp.
And two caps in series with each hot line.
IMHO, a 2.2kohm resistor is a good trade-off. Then the two caps have to be 1.8uF (film) each for 80herz corner freq.
A lower resistance will need bigger cap values.
I don't see any advantage in that.
Leo..

Yep, driving the Hypex will be balanced.

So if I understand you right I insert matching 1.8uF caps into pin 2 and 3 respectively and then connect 2 and 3 with the 2.2kohm resistor after, like in the diagram on Ethan's page? And then I get a corner frequency of 80Hz with 6dB slope? If so, thank you very much!

[tINY]

That should get you pretty close. Do a quick check with a swept sine wave and a (1kHz capable) meter to check.

If the corner is too low, use a slightly larger resistor...




-tINY

[Karloff70]

Cool, thanks for the help, chaps!!