Hi All,
Yes, I am again having problems while trying to build filters for my synthesizers. I swear I should just... eh, nevermind, here's my problem:
http://img692.imageshack.us/img692/3426/555intolp.png
This schematic shows exactly what is on my breadboard, save the batteries being my external PSU and the OpAmp is a 741. The rheostat is a 1M pot set at 500k.
In trying to create a filter (in this case just a simple 12dB butterworth lowpass), I'm finding that there are numerous problems with the physical circuit (LTSpice doesn't seem to like simulating it). Firstly, for whatever reason my 555's output is a pulse similar to that with what would come out of a highpass filter.
Then, going into the filter, the first part (the RC setup) works flawlessly: I can adjust the cutoff and the signal is lowpassed, no problem. After the rest of the filter (the OpAmp, etc.), if I get any output it's a muffled pulse; adjusting the filter cutoff does nothing.
What's interesting is that I've used this exact circuit before for a filter and it works great! I can't figure out what the issue is. You'd think that maybe my IC's are shot, but they work fine for everything else I've used them for. Any idea as to what might be wrong?
Secondly (slightly different topic), I was talking with a friend of Nyle Steiner (creator of the famous Steiner Filter) and he showed me original schematics for Nyle's filter. One thing that I noticed was interesting was that, to make the filter resonant, Nyle simply used a potentiometer to increase the gain of the OpAmp. Given that my filter is currently non-functional and can't test, I must ask: does this really work? I'd assume so, but it seems too simple to work.
Thank you for any help you can provide.
PS: I'm using this filter circuit because it's the only one that worked when I was first trying filter designs. Standard Sallen-Key designs don't seem to work for me for varying reasons.
Yes, I am again having problems while trying to build filters for my synthesizers. I swear I should just... eh, nevermind, here's my problem:
http://img692.imageshack.us/img692/3426/555intolp.png
This schematic shows exactly what is on my breadboard, save the batteries being my external PSU and the OpAmp is a 741. The rheostat is a 1M pot set at 500k.
In trying to create a filter (in this case just a simple 12dB butterworth lowpass), I'm finding that there are numerous problems with the physical circuit (LTSpice doesn't seem to like simulating it). Firstly, for whatever reason my 555's output is a pulse similar to that with what would come out of a highpass filter.
Then, going into the filter, the first part (the RC setup) works flawlessly: I can adjust the cutoff and the signal is lowpassed, no problem. After the rest of the filter (the OpAmp, etc.), if I get any output it's a muffled pulse; adjusting the filter cutoff does nothing.
What's interesting is that I've used this exact circuit before for a filter and it works great! I can't figure out what the issue is. You'd think that maybe my IC's are shot, but they work fine for everything else I've used them for. Any idea as to what might be wrong?
Secondly (slightly different topic), I was talking with a friend of Nyle Steiner (creator of the famous Steiner Filter) and he showed me original schematics for Nyle's filter. One thing that I noticed was interesting was that, to make the filter resonant, Nyle simply used a potentiometer to increase the gain of the OpAmp. Given that my filter is currently non-functional and can't test, I must ask: does this really work? I'd assume so, but it seems too simple to work.
Thank you for any help you can provide.
PS: I'm using this filter circuit because it's the only one that worked when I was first trying filter designs. Standard Sallen-Key designs don't seem to work for me for varying reasons.
