Hello,
I'm working on learning about filter design and have seen this guide (http://alpha.science.unitn.it/~bassi/Signal/TInotes/sloa049.pdf) to active low pass filters recommended in the forums a few times. I captured and simulated the "original" filter on page 15 (see attached image) and found that changing the value of R1 changes the frequency response. So I built it on a breadboard and put a variable resistor there, but no sound comes out. I am just starting out and would be grateful for some help figuring out why and understanding the circuit.
For the audio source and output, I have stripped the cover from a jack cable plugged into a keyboard, connected the ground wire directly to a small speaker and the other wire to the left side terminal on my circuit. The right side terminal connects to the other speaker input. Connecting the two jack cable wires directly to the speaker plays a sound, so I'm inferring that these connections are fine and the problem is with the circuit.
I changed C1's connection to the negative battery terminal rather than ground used in the pdf because I'm working with batteries and don't have a true ground. I'm surprised that this made no difference to the output of the simulator, but then the op amp works without power in simulation so perhaps it's not modelling this correctly. Will this make a difference?
I'm using the maligned 741 as it's the only op amp I have to hand. From what I've read about it here, I understand that it might not work so well at higher frequencies, but I don't know at what frequencies it could cause problems. From my simulations, I find that the filter's peak is at 2.5kHz when R1 is 200k, and 100kHz when R1 is 200k. Given this range, I'm assuming that it may not be ideal but I should at least hear something, is this right?
Also I'm only supplying the 741 with 9 volts. I see that it should have 15V, but I'm guessing that it would still do something with 9? Will it work on 9V, or do I have to go to 15? Will the performance and amplifying range degrade with lower voltages, or is there a minimum voltage requirement for it to do anything? My suspicion is that this is why there is no sound, am I right or is there more to it?
Any help appreciated, thanks.
Ogg
I'm working on learning about filter design and have seen this guide (http://alpha.science.unitn.it/~bassi/Signal/TInotes/sloa049.pdf) to active low pass filters recommended in the forums a few times. I captured and simulated the "original" filter on page 15 (see attached image) and found that changing the value of R1 changes the frequency response. So I built it on a breadboard and put a variable resistor there, but no sound comes out. I am just starting out and would be grateful for some help figuring out why and understanding the circuit.
For the audio source and output, I have stripped the cover from a jack cable plugged into a keyboard, connected the ground wire directly to a small speaker and the other wire to the left side terminal on my circuit. The right side terminal connects to the other speaker input. Connecting the two jack cable wires directly to the speaker plays a sound, so I'm inferring that these connections are fine and the problem is with the circuit.
I changed C1's connection to the negative battery terminal rather than ground used in the pdf because I'm working with batteries and don't have a true ground. I'm surprised that this made no difference to the output of the simulator, but then the op amp works without power in simulation so perhaps it's not modelling this correctly. Will this make a difference?
I'm using the maligned 741 as it's the only op amp I have to hand. From what I've read about it here, I understand that it might not work so well at higher frequencies, but I don't know at what frequencies it could cause problems. From my simulations, I find that the filter's peak is at 2.5kHz when R1 is 200k, and 100kHz when R1 is 200k. Given this range, I'm assuming that it may not be ideal but I should at least hear something, is this right?
Also I'm only supplying the 741 with 9 volts. I see that it should have 15V, but I'm guessing that it would still do something with 9? Will it work on 9V, or do I have to go to 15? Will the performance and amplifying range degrade with lower voltages, or is there a minimum voltage requirement for it to do anything? My suspicion is that this is why there is no sound, am I right or is there more to it?
Any help appreciated, thanks.
Ogg