You have swapped the input pins of the S&K filters.
It's the output to -IN pin that get connected to set to unity gain.
The signal is fed to the +IN pin.
https://en.wikipedia.org/wiki/Sallen–Key_topology
Are you using the top two opamps to invert the signals and set the filter gain/attenuation?
Then using the inverting summing stage to sum the two channels to a common channel? And bring the phase back to match original?
The upper and lower summing channels both have a low impedance at the Pin 7 OUT node of the last opamp. After you have wired it correctly. The extra pin14 OUT is not required.
If you want a low output impedance of 100ohms you need to ADD a 100r resistor for your output.
It's the output to -IN pin that get connected to set to unity gain.
The signal is fed to the +IN pin.
https://en.wikipedia.org/wiki/Sallen–Key_topology
Are you using the top two opamps to invert the signals and set the filter gain/attenuation?
Then using the inverting summing stage to sum the two channels to a common channel? And bring the phase back to match original?
The upper and lower summing channels both have a low impedance at the Pin 7 OUT node of the last opamp. After you have wired it correctly. The extra pin14 OUT is not required.
If you want a low output impedance of 100ohms you need to ADD a 100r resistor for your output.
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I know enough to be dangerous but seeking understanding. I have a 4.0 tuner/amp and wish to add a subwoofer. Does your filter act as a crossover? Thank you.
A crossover is two filters.
A high pass filter that passes the high frequencies to the high frequency amplifier+speaker.
A low pass filter that passes the low frequencies to the low frequency amplifier+speaker.
If you want the crossover to be smooth you need the two filters to cross at the same frequency and one of them will need a little bit of attenuation adjustment to equalise the levels coming from the speakers.
You also need some EQ to get the correct roll off at the crossover.
Back to your bass only.
The filter can be a 2pole (12dB/Octave = 40dB/decade), or a 3pole, or a 4pole. Very few go steeper than that, but some do go to 6pole and even 8pole.
You can choose Butterworth or Linkwitz Riley, or Bessel for the roll-off shape.
The final shape of roll-off is at the speaker output. The electrical filters need to be massaged with the required EQ to achieve the correct speaker output through the crossover range.
But I'll offer a bit of advice.
Try a simple 4pole Linkwitz Riley (LR4) using a cascaded pair of Butterworth 2poles (B2 + B2) for each filter. And no EQ.
Listen to how that sounds with your satelites rolled off at around 100Hz to 160Hz and the bass only rolled off at the same frequency.
A high pass filter that passes the high frequencies to the high frequency amplifier+speaker.
A low pass filter that passes the low frequencies to the low frequency amplifier+speaker.
If you want the crossover to be smooth you need the two filters to cross at the same frequency and one of them will need a little bit of attenuation adjustment to equalise the levels coming from the speakers.
You also need some EQ to get the correct roll off at the crossover.
Back to your bass only.
The filter can be a 2pole (12dB/Octave = 40dB/decade), or a 3pole, or a 4pole. Very few go steeper than that, but some do go to 6pole and even 8pole.
You can choose Butterworth or Linkwitz Riley, or Bessel for the roll-off shape.
The final shape of roll-off is at the speaker output. The electrical filters need to be massaged with the required EQ to achieve the correct speaker output through the crossover range.
But I'll offer a bit of advice.
Try a simple 4pole Linkwitz Riley (LR4) using a cascaded pair of Butterworth 2poles (B2 + B2) for each filter. And no EQ.
Listen to how that sounds with your satelites rolled off at around 100Hz to 160Hz and the bass only rolled off at the same frequency.
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> i want output impdance to be low nearly 100 ohms
The impedance right off the LM837 _is_ far under 100 Ohms. (Probably under 10r at 50KHz and much less in lower frequencies.)
Adding the emitter follower does no good, and will force a DC-block coupling cap at the output.
And I don't like those filters, but others have covered this point.
The impedance right off the LM837 _is_ far under 100 Ohms. (Probably under 10r at 50KHz and much less in lower frequencies.)
Adding the emitter follower does no good, and will force a DC-block coupling cap at the output.
And I don't like those filters, but others have covered this point.
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