I am attempting to build a bandpass filter using the 741 (I have also tried the LM324) and I am having some difficulties. When using the 324 I get no bandpass response at all, more like a linear high-pass through 120 kHz.
I am looking for a center frequency of 33kHz, and have used this calculator to get me in the ballpark:
Active Filter Calculator - Bandpass with OpAmp Designer in Javascript
I am using typical E12 resistor values for R1 and R2, which I know will skew my center frequency and BW a bit, and a variable 1k pot for R3
**broken link removed**
The values I've used are as follows:
fc= 33000 Hz
BW=1500 Hz
A=10
C=1 nF
And theses are the initial results
Q=20
R1=10610 Ω
R2=212207 Ω
R3=111 Ω
I then used the second tool and used these standard values
R1=10k
R2=220k
R3=100Ω
which yielded,
fc=34101.2 Hz
BW=1447 Hz
Q=23.5
When I use these resistors (within the best tolerance possible) my peak output occurs at 20kHz. The caps I am using are 102J polyester film. I have access to drawers full of electrolytics but the lowest I've seen is .47uF which yields resistor values that are all under 100Ω and 1 being 0Ω using the calculator.
Am I trying to get too much out of this amp?
Too much Q?
Unreliable capacitor size?
I don't want to pay more for shipping than the cost of replacing the caps with 10nF caps unless this is the likely culprit.
I would prefer to use an amp that is quad with gnd to V+ instead of rail to rail as there are size constraints on the project.
I would be grateful for any suggestions or help.
I am looking for a center frequency of 33kHz, and have used this calculator to get me in the ballpark:
Active Filter Calculator - Bandpass with OpAmp Designer in Javascript
I am using typical E12 resistor values for R1 and R2, which I know will skew my center frequency and BW a bit, and a variable 1k pot for R3
**broken link removed**
The values I've used are as follows:
fc= 33000 Hz
BW=1500 Hz
A=10
C=1 nF
And theses are the initial results
Q=20
R1=10610 Ω
R2=212207 Ω
R3=111 Ω
I then used the second tool and used these standard values
R1=10k
R2=220k
R3=100Ω
which yielded,
fc=34101.2 Hz
BW=1447 Hz
Q=23.5
When I use these resistors (within the best tolerance possible) my peak output occurs at 20kHz. The caps I am using are 102J polyester film. I have access to drawers full of electrolytics but the lowest I've seen is .47uF which yields resistor values that are all under 100Ω and 1 being 0Ω using the calculator.
Am I trying to get too much out of this amp?
Too much Q?
Unreliable capacitor size?
I don't want to pay more for shipping than the cost of replacing the caps with 10nF caps unless this is the likely culprit.
I would prefer to use an amp that is quad with gnd to V+ instead of rail to rail as there are size constraints on the project.
I would be grateful for any suggestions or help.