Does anyone knows how to configure a TDA2822 amp ic into a bridge-mode, subwoofer amp without any preamp just the ic itself (how to make the ic amplify only subwoofer frequencies). I would be thankful for your replies 🙂
Possibly you should not get your hopes too high.
The amplifiers in that chip only allows changing the feedback loop by changing the circuit from the negative input to ground.
Designing a low pass filter with this restriction will likely not allow a filter response sufficient for a subwoofer (like 6dB/octave, attenuation will not go below -40dB)
Doing so would also require that the amplifiers are unity-gain stable, which is not speficied.
You would be better off by just changing the input circuitry to act as a simple RC low pass filter.
In https://www.st.com/resource/en/datasheet/cd00000134.pdf there is a simple suggestion for bridging the two amplifiers on the chip.
The circuit suggested only specifies an input resistor (R1, 10K).
If you add a capacitor in parallel with this resistor and then add a resistor in series with the input, you can make a simple low pass filter.
In case you are not familiar with RC-filter design:
If you add a 330nF input capacitor in parallel with R1 and then add a 8.2K resistor in series with the input you will get a 100'ish Hz low pass filter.
This solution is not ideal by any means - the cut-over frequency will depend on the output impedance of the input source and total gain will be reduced.
Any steeper attenuation will require an extra opamp used as a dedicated filter.
You could of course use a LC filter on the input - but inductors for this usage is rather old style (except in speaker crossovers) and it may be hard to obtain the necessary values.
Cheers Martin
The amplifiers in that chip only allows changing the feedback loop by changing the circuit from the negative input to ground.
Designing a low pass filter with this restriction will likely not allow a filter response sufficient for a subwoofer (like 6dB/octave, attenuation will not go below -40dB)
Doing so would also require that the amplifiers are unity-gain stable, which is not speficied.
You would be better off by just changing the input circuitry to act as a simple RC low pass filter.
In https://www.st.com/resource/en/datasheet/cd00000134.pdf there is a simple suggestion for bridging the two amplifiers on the chip.
The circuit suggested only specifies an input resistor (R1, 10K).
If you add a capacitor in parallel with this resistor and then add a resistor in series with the input, you can make a simple low pass filter.
In case you are not familiar with RC-filter design:
If you add a 330nF input capacitor in parallel with R1 and then add a 8.2K resistor in series with the input you will get a 100'ish Hz low pass filter.
This solution is not ideal by any means - the cut-over frequency will depend on the output impedance of the input source and total gain will be reduced.
Any steeper attenuation will require an extra opamp used as a dedicated filter.
You could of course use a LC filter on the input - but inductors for this usage is rather old style (except in speaker crossovers) and it may be hard to obtain the necessary values.
Cheers Martin