Active Band Pass Filter with +/- Gain

[JoshwaBurke]

Could someone point me in the direction of where I can find some good information on a simple band pass filter that will allow me to have positive and negative gain.

I've been using this website
Op-amp Filter - The Active Band Pass Filter


For example say I'd like a band pass filter of 1000 Hz with a gain of +/-15 dB.

Can I use a combination of an inverting and non-inverting band pass filter to get and positive and negative gain?

 

[JoshwaBurke]

This is my circuit at the moment which only creates positive gain. All of the band pass filters are connected to a inverted summing amplifier. Any help or recommendations to create at least -15dB would be helpful

 

[DF96]

Vary the output resistor from each channel. Or use a volume control.

 

[JoshwaBurke]

Thank you for the help. I'll play around with calculations of the output resistor. I could use volume control but I need to have a controllable gain of +/-15 dB on each band. That means I'd have to have a volume knob for each band.

 

[JoshwaBurke]

Input/Output Voltage levels

Hey everyone, I have the circuit above connected on my breadboard. Except that voltage output is 1/10 the value of what it should be.

I thought it may have been the probes I was using on the oscilloscope but they checked out. I even setup just one band pass filter and my values were still off by 1/10. Anyone have any trouble shooting suggestions or tips? Circuit is currently working multisim.

 

[DF96]

You probably have a resistor which is 10 times or 0.1 times the value it should be. Easy to confuse orange (3) and yellow (4) as a multiplier.

 

[JoshwaBurke]

Just checked them again with the multimeter out of paranoia. All the pin outs of the op-amps and values of the electrical components seem correct.Thanks for the suggestion. Could it have anything thing to do with the dual power supply and my ground on the breadboard? Any other suggestions are welcome.

 

[DF96]

How have you wired the channel gain controls? The circuit in post 2 looks wrong, as it allows you to remove all feedback from the final channel opamp thus getting very high gain at one end of the pot.

At the other end of the pot you will get gain about 0.25: 0.5 from the filter and 0.5 from the final opamp. Is this what you intend?

 

[JoshwaBurke]

Not sure exactly what you mean. Maybe you could look at this single band-pass filter setup which is still giving me 1/10 the gain I calculated. Am I connecting the gain of R2 and R1 wrong?

I simply have a 10kohm resistor and a 100kohm pot to give me a potential gain of 11 (1+(R2/R1)). I need to get a gain of at least 5.6 for my specifications of +15dB.