I'd like to incorporate a simple low pass filter in my chip amp to run a small subwoofer. One requirement is that it must have a variable cutoff frequency. I was surprisingly unable to find anything in my searches online that I wanted to use so I came up with this idea.
See the attached pic.
I think what I sketched is a 2nd order Sallen-Key Butterworth lowpass filter with unity gain.
Can someone tell me if I am on the right track with this design?
From my calculations with the 5k resistor and pot set to zero resistance the low pass will be at around 225hz -3dB.
With the 5k resistor and the pot set to 20k ohms for a total of 25k ohms the low pass will be around 45hz -3dB.
I used this formula: R = .707/(2*3.14*F*C)
Will this work? Is there a better way? I'm trying to keep it simple. I've never designed a crossover before.
Thanks,
Dave
See the attached pic.
I think what I sketched is a 2nd order Sallen-Key Butterworth lowpass filter with unity gain.
Can someone tell me if I am on the right track with this design?
From my calculations with the 5k resistor and pot set to zero resistance the low pass will be at around 225hz -3dB.
With the 5k resistor and the pot set to 20k ohms for a total of 25k ohms the low pass will be around 45hz -3dB.
I used this formula: R = .707/(2*3.14*F*C)
Will this work? Is there a better way? I'm trying to keep it simple. I've never designed a crossover before.
Thanks,
Dave
Attachments
Yes, it has been a long time and I have gotten bogged down with work and other projects. So I have not made much progress. I plan to incorporate this design into a six channel preamp that is on my list of things to do. I will be using OPA132 or OPA134 opamps for the filter, powered by +-15 volts.
I've used a circuit similar to the first one a few times and have had good results.
Basically this circuit:
Sub X-over
I think in the circuit I'm currently using I tweaked the caps a bit,for a lower range,and used a TL082 op-amp,with the second op-amp in the package used as an output buffer,with a bit of gain.
It's been working well for me.
Basically this circuit:
Sub X-over
I think in the circuit I'm currently using I tweaked the caps a bit,for a lower range,and used a TL082 op-amp,with the second op-amp in the package used as an output buffer,with a bit of gain.
It's been working well for me.
Variable X-over frequencies
Hey all:
I actually built a variation of the original X-over posted by DC Dave about 12 yrs ago, and it worked very well! My ckt was an adaptation of the two-taw x-over that first appeared in the July 1988 issue of Audio magazine. (At least, I think it was July 1988).
This was about the time that old-school car audio was the rage, and few brave souls were venturing into the DIY realm. This x-over was fixed at 120Hz, but I made it variable by replacing the two 100k resistors with a 2-ganged 100k linear pot, each section in series with a 11.3K 1% metal-film resistor. This yielded nearly the same 45-225Hz x-over frequency range.
Since it was a fouth-order Sallen-Key, it was in F and I could select between 12dB and 24dB per octave, simply by selecting where the output buffer was connected.
I also did its hi-pass counterpart for a complete two-way stereo x-over, slope-selectable, continuously variable independant left- and right-channel crossover.
Having the magazine article provide the formula for the cut-off frequency helped me choose the range I wanted, and the values of the tuning resistors to use.
If I find any information on this, I will post it here.
Cheers,
Steve
Hey all:
I actually built a variation of the original X-over posted by DC Dave about 12 yrs ago, and it worked very well! My ckt was an adaptation of the two-taw x-over that first appeared in the July 1988 issue of Audio magazine. (At least, I think it was July 1988).
This was about the time that old-school car audio was the rage, and few brave souls were venturing into the DIY realm. This x-over was fixed at 120Hz, but I made it variable by replacing the two 100k resistors with a 2-ganged 100k linear pot, each section in series with a 11.3K 1% metal-film resistor. This yielded nearly the same 45-225Hz x-over frequency range.
Since it was a fouth-order Sallen-Key, it was in F and I could select between 12dB and 24dB per octave, simply by selecting where the output buffer was connected.
I also did its hi-pass counterpart for a complete two-way stereo x-over, slope-selectable, continuously variable independant left- and right-channel crossover.
Having the magazine article provide the formula for the cut-off frequency helped me choose the range I wanted, and the values of the tuning resistors to use.
If I find any information on this, I will post it here.
Cheers,
Steve
Tested and proven.
RDV
An externally hosted image should be here but it was not working when we last tested it.
RDV
Ever thought of making both sections variable?
Actually, I did. But the problem was in pot. I couldn't find one that is 4-ganged, and didn't want to go in trouble trying to phisically connect two stereo pots so they turn together because I have no idea how to do that without destroying pots. If you know some easy solution, please let me know.
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