No, MFB filters are inherently inverting. If you're thinking of trying to input signal to non-inverting input of MFB filter, it won't work correctly. You must correct signal inversion elsewhere in the design. One way to accomplish that is to use another inverting circuit to "un-invert" final output, could be an inverting buffer or amp, or in the case of a 4th order lowpass for example, use two MFB filters in series, I've done that in some of my projects.
Mike
Mike
The multiple feedback filter comes after this inverting buffer, so my output would be positive.
I get the unity gain part with the negative feedback resistor. Now I just need the 28Hz roll off at the beginning from the .056uF cap and I believe the 100k resistor from the original non inverting buffer.
I get the unity gain part with the negative feedback resistor. Now I just need the 28Hz roll off at the beginning from the .056uF cap and I believe the 100k resistor from the original non inverting buffer.
Scaling resistor values will depend on desired goals and components used. Generally (very generally), it's considered wise to keep resistor values between 10k to 100k, however, some opamp chips have greater load driving capabalities, so lower values to keep noise levels as low as possible will be OK. Also, agian generally speaking, you can sometimes go with higher values, especially when using FET input opamps because of thier lower input bias currents. Bottom line here is you need to consider design goals, circuit topology and type of components used, there are no pat answers to proper circuit design.
Mike
Mike
No, the 100k ohm resistor to ground isn't actually part of the input circuit due to "virtual ground" at inverting input. The corner frequency in that circuit is determined by input cap and 10 ohm resistor, in this case would be 284205Hz, that's right 284kHz.
To get what you want from that circuit, change 10 ohm resistors to 100k resistors, and get rid of non-functional 100k resistor to ground.
Mike
To get what you want from that circuit, change 10 ohm resistors to 100k resistors, and get rid of non-functional 100k resistor to ground.
Mike
raygem,
The TLO74 is a fairly old chip, but can sound OK if utilized properly. First, it has JFET inputs, so higher circuit impedance (resistance) can work OK, but you need to be careful how you load its output, data sheet says above 2k ohms, but I would recommend nothing less than about 5k ohms minumum, otherwise you'll get increased distortion.
Mike
The TLO74 is a fairly old chip, but can sound OK if utilized properly. First, it has JFET inputs, so higher circuit impedance (resistance) can work OK, but you need to be careful how you load its output, data sheet says above 2k ohms, but I would recommend nothing less than about 5k ohms minumum, otherwise you'll get increased distortion.
Mike
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.