Looking for Simple LM741 Low-Pass Filter Schematic to work w/ regular+9V Supply

[Jasonmatthew911]

I'm looking to add a 741 Low Pass Filter to my 555 Octave Toy Organ circuit, without needing a (+) and (-) Supply rail....I tried the Sallen-Key with 741 using (2) 9V batteries for (+) & (-) supply, but I wasn't very happy with the results......I found this 741 LPF schematic, but I was hoping someone could help simplify this for me...(I really just wanted 1 Pot to control the "Q" of the filter, and was hoping I could do something like this, but maybe with a few less parts):




Has anyone here already made a successful  yet simple 741 Low-Pass Filter that works with a regular 9VDC Boss style adapter....Any help to simplify the above, so that I can run my Toy Organ circuit into a LPF and just control the filter with 1- Pot would be awesome....Or if anyone has a successful simple LPF schematic that you're willing to share would be cool too...Thanks.

[artifus]

http://www.geofex.com/article_folders/wahpedl/opampwah1.gif

http://www.fluxmonkey.com/electronoize/opampFilter.htm

http://www.diystompboxes.com/smfforum/index.php?topic=81602.0

[Jasonmatthew911]

http://www.geofex.com/article_folders/wahpedl/opampwah1.gif

http://www.fluxmonkey.com/electronoize/opampFilter.htm

http://www.diystompboxes.com/smfforum/index.php?topic=81602.0

Awesome, thanks....I assume the LM741 can be used in all of these, right?

[Jasonmatthew911]

http://www.geofex.com/article_folders/wahpedl/opampwah1.gif

http://www.fluxmonkey.com/electronoize/opampFilter.htm

http://www.diystompboxes.com/smfforum/index.php?topic=81602.0

Awesome, thanks....I assume the LM741 can be used in all of these, right?

The first very simple schematic seems to use a dual power supply....What can you tell me about the 3rd Schematic that has a transistor for the sound generator?...Does that one run on a single supply like the 2nd schematic you posted of the WSG Filter?...If so, that means that pin 4 (-V)  of LM741 becomes a GND connection, right?...I'm looking for any simple active Low-pass Filter that doesn't require a Bi-polar power supply, and that uses 1 Pot to control the filter....The first simple schematic you posted seems to look similar to the Sallen-Key LPF that didn't really work out for me.

[.Mike]

You can probably get some ideas if you check out TI's Single-Supply Op-Amp Circuit Collection [PDF].

It provides working examples of a bunch of single-supply filters.

Mike

[Jasonmatthew911]

Now that I've looked over the "WSG" LM741 Filter, I think I will try it out, but I had some questions about the Cut Off Frequency Pots....Can I just use the 1M "Coarse" pot to change my Freq. and get rid of the 100K "Fine" Pot, or should I at least replace it with a 100K fixed resistor?....This way I will only have 2 Pots, 1 for Freq. and the other for Resonance...

Alternatively, Can I just get rid of the 2 Cut off Freq. Pots completely, and just have the 1K resistor (R8) go directly into C3 and Lug 3 of Resonance Pot?...If I did this, will the Resonance pot still have a noticeable effect if it's being fed a range of frequencies between 262Hz - 988Hz from my Notes on my 555 Toy Organ, or do I need the Frequency Pot?

[Jasonmatthew911]

I just breadboarded the LM741 WSG Low pass filter, and it works, but with the frequencies I wanted to tune my 555 toy organ (262Hz - 988Hz), which are more like Mid frequencies, the low pass filter doesn't really do much, but when I tune down to the 50Hz - 150Hz range, that's where I can feel the Low Pass filter working and the "Q" factor is a lot more noticeable when moving my Freq. Pot

Can anyone give me an idea of which components/values I would need to change in the Weird Sound Generator's Filter section in order to tailor my Low Pass Filter to my 555 toy organs frequency range (262Hz - 988Hz)?

[Jasonmatthew911]

Just ignore my last messages....I already realized I have to feed frequencies below 200Hz to the 741 Low pass filter in order for the effect to work right...No point in the active filter with a freq. range of 262Hz - 988Hz....