single opamp low pass filter

[littlewing]

does anyone have a schematic for a single opamp LP filter?

thanks
vito

[salocin]

This if from Para's site:


"everyone keeps asking me for this so here it is, but i'm not going to give you the values of the components so DON'T ASK. i had to find them myself, so do you, that is the fun part!!! this was one of thee most rewarding projects i ever worked on, once you really figure out how a sullen key low pass works it will open you up to so much more. stop bitching…. teach a man to fish and all that………

power is set up for bipolar, first cap is just for AC coupling and can be around 100n  doesn’t really matter too much, first pull down res is the impedance and should be around 100k in most cases, any op amp should work fine, different values for the rest will give you different ranges and flavors, experimentation is king "
http://http://thesquarewaveparade.com/brdlayot.html

[para]

this isn't dickish is it? i really mean that shit


s

[danoisefactory]

...stop bitching…. teach a man to fish and all that………

No man, that's cool.

And very true as well. You put effort into it and came out a genius (althought there's probably some genetic going on as well) so we all should put effort into it.

The things i've learned so far, with the help of this place, helped me figure out the how and the why stuff works, which makes it possible to dream up new stuff.
You can't get that with just copying.

[expanoncolin]

this isn't dickish is it? i really mean that shit


s

People will learn more if others don't do all the learning for them.

-Colin

[littlewing]

this isn't dickish is it? i really mean that shit


s

totally legitimate - thanks for providing the schematic on your site. is the dual-gang pot necessary to control the frequency?

thanks to salocin for the reply.

[para]

how many possibilities can there be really, there are only 5 values to guess. replace all the resistors with pots until you start to get something and get the cap values right then start to tailor it out to what you like, not what i like

there are so many elements that you’ll learn if you pay attention, i could spend the rest of the day just going over what i learned from spending time with this and figuring out the res setup knowing nothing about how opamps or biasing worked at the time

i walked away able to design my own pres, line amps, mixers, dist, res filters, etc…… from fucking scratch

“is the dual-gang pot necessary to control the frequency?”

well its necessary to get a "sullen key" setup but you might find some other options after you get it going. for the very first tests i just used two of the same value and tried to turn them the same amount each time while waiting for the pot shipment to arrive


steven

[fNNR]

Simple first order (-6 dB per octave) LP filter, taken from Wikipedia:



Cutoff frequency: fc = 1/(2*pi*R2*C)

Gain in the passband: Ap = -R2/R1 (the minus sign denotes a 180 degree phase change)

[crochambeau]

Interesting, I stumbled over eBay auctions for these a short while back:

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0390804869

And absolutely believe I have one underfoot, hiding in the lab somewhere. When I dig it up I'll have to have a go at building this.