4th order Active bandpass

[Juglenaut]

I am using general purpose op amps LM741 to filter a 2 channel audio signal from the RCA output, for a total of 8 op amps. I know there is better, and thought about about a dual channel op amp.

My question is how do I set the voltage for a single supply. The circuit works very well when using a dual power supply, but when using a single supply it clips negative and I know why because of the negitive is tied to ground.

Do I use off-set null option, I just can't remember or don't know how to swing the signal in the center of a positive voltage DC 0-14.4 typical. Is there a way to make a single power supply split the potencial so I have 1/2 positive and 1/2 negitive??

Will a op amp in inverting mode flip the offset to negitive when positive is applied to the inverting input??

curents and voltages of this circuit are low and doesn't need alot to drive.

 

[Nigel Goodwin]

I am using general purpose op amps LM741 to filter a 2 channel audio signal from the RCA output, for a total of 8 op amps. I know there is better, and thought about about a dual channel op amp.

My question is how do I set the voltage for a single supply. The circuit works very well when using a dual power supply, but when using a single supply it clips negative and I know why because of the negitive is tied to ground.

Do I use off-set null option, I just can't remember or don't know how to swing the signal in the center of a positive voltage DC 0-14.4 typical. Is there a way to make a single power supply split the potencial so I have 1/2 positive and 1/2 negitive??

Will a op amp in inverting mode flip the offset to negitive when positive is applied to the inverting input??

curents and voltages of this circuit are low and doesn't need alot to drive.

You simply generate a crude split-supply, you can do this as easily as two resistors in series across the supply rails (the centre of them becomes the 0V line). A 'less crude' way is to use a buffer after the two resistors, another opamp is usually used to do this.

I would also suggest you use a better opamp than a 741, vastly better ones are freely available at very modest cost - the 741 is an antique, and has very poor performance.

 

[Russlk]

This 4th order bandpass uses 2 op amps. The LT1631 is a quad op amp, I used 3 of them. I don't recommend that you actually use the LT1631 because it has 30 mHz bandwidth and will be prone to oscillation, plus it probably is expensive. The TS272 that I would use was not in the database.

This filter is centered on 1kHz with 100 Hz bandwidth and 20 dB gain overall.

 

[Juglenaut]

I am choosing the LM741 for reason that it is availible at school cheap.

My target is 40Hz to 150Hz with a 90Hz bandwidth.

 

[jnegowski]

Hi
lm741 has a high off set voltage when useing a single end supply
A split supply will solve this ..nulling requires a negative or postive
supply to offset. Have never seen a easy way to do this...adding parts
cost more money and space.. maybe a lm324 which has 4 lm741 in
it has one of the lowest offsets when used with a single ended
supply Their are others if you look at the spec sheets it will tell you
how much the offset is with different supply types and voltage
levels.
joe

 

[Russlk]

40Hz to 150 Hz is 110 Hz bandwidth? What do you mean 90 Hz bandwidth?

 

[Juglenaut]

Knee 90 Hz between Knees. Yes 110Hz total with -3dB, I am not looking to gain alot as this is going to be used in-line with the RCA input. My target is Unity to +3dB gain.

 

[Russlk]

This circuit should be what you want.