# Issues with simple RC Filter **URL:** \ **Category:** DIY STUFF\ **Created:** [February 7, 2021, 2:13pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895 "2021-02-07T14:13:25Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Lars](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lars](https://lookmumnocomputer.discourse.group/u/Lars)\ **Post date:** [February 7, 2021, 2:13pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/1 "2021-02-07T14:13:26Z")
Hey guys, I am pretty new to these DIY electronics things so maybe someone has an idea how to fix my issue. I started out by building the super simple oscillator. This works fine and is putting out a nice stable sawtooth. Now I wanted to build a simple filter for it. I wired everything together like in Sam’s video: [![](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/6/6e01fa93ef7124a00de352732f205bebd1c70960.jpeg "FILTERS? Build a simple DIY passive electronic low pass filter. #Electronics #Synth") ](https://www.youtube.com/watch?v=Ch9w5JtbZSc) The filtering itself seems to work. My problem is, that when I turn the “tone” pot, the oscillators pitch changes with it. I tried some different ones on breadboard and different pots create a different change in pitch. Im using a Frequency Central Minibus power supply, if that is of any help. Thanks in advance Cheers ---
**Author:** ![Caustic](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/caustic/32/15588_2.png) [@Caustic](https://lookmumnocomputer.discourse.group/u/Caustic)\ **Post date:** [February 7, 2021, 5:35pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/2 "2021-02-07T17:35:37Z")
Any change i could hear a recording? Even a poo poo phone recording would suffice. ---
**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\ **Post date:** [February 8, 2021, 8:45am UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/3 "2021-02-08T08:45:35Z")
You probably need to put a buffer stage between the output of the super simple oscillator and the filter. This prevents the filter from influencing the workings of the circuitry that make up the super simple oscillator. The buffer could be an op-amp which is configured as a voltage follower, as described [here](https://www.allaboutcircuits.com/video-tutorials/op-amp-applications-voltage-follower/). So from left to right you would then have: super simple oscillator → buffering opamp → filter → amplifier → loudspeaker ---
**Author:** ![Lars](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lars](https://lookmumnocomputer.discourse.group/u/Lars)\ **Post date:** [February 8, 2021, 11:27am UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/4 "2021-02-08T11:27:01Z")
Here, maybe this helps: > **[Filter troubles.m4a](https://drive.google.com/file/d/1-fY4OjCLAicOlv4Bav2i-Qtt4ICIwSu9/view?usp=sharing)** > > Google Drive file. I tried it with different capacitors. The second one is bigger and there the effect is more audible ---
**Author:** ![Lars](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lars](https://lookmumnocomputer.discourse.group/u/Lars)\ **Post date:** [February 8, 2021, 11:27am UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/5 "2021-02-08T11:27:54Z")
Thank you so much. I´ll try this today and tell you if I made it. ---
**Author:** ![Lars](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lars](https://lookmumnocomputer.discourse.group/u/Lars)\ **Post date:** [February 8, 2021, 1:16pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/6 "2021-02-08T13:16:31Z")
Actually none of the op amps I have here seem to be working. I’ve tried a TL074CN and a TL072IP. Maybe these are the wrong ones? Whenever I plug in the voltage leads to them, my whole circuit drops out. Maybe I am missing something. Is there maybe a schematic I could look up or a breadboard layout? ---
**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\ **Post date:** [February 8, 2021, 2:20pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/7 "2021-02-08T14:20:26Z")
Opamp buffer schematic ![opAmpBuffer](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/6/6584f24971808c6917db989537fc8a8751d9ff22.jpeg) plus +12V & -12V power (pin 7 & 4 for TL071 / pin 8 & 4 for TL072 / pin 4 & 11 for TL074) TL071 have 1 opamp TL072 have 2 opamp TL074 have 4 opamp and bypass cap 100nf for all power pin to GND (the more near as possible of the opamp pin) ---
**Author:** ![eric](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@eric](https://lookmumnocomputer.discourse.group/u/eric)\ **Post date:** [February 8, 2021, 2:37pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/8 "2021-02-08T14:37:16Z")
Look here for some example uses of OpAmps : https://www.youtube.com/embed/gHHTN3Vav3o?feature=oembed&wmode=opaque&list=UUp6OK4J97aPWccFpUgKj_Mg and the pdf for the presentation : [http://musicfromouterspace.com/PDF/Ray%20Wilson%20Presents%20the%20TL07X%20Op%20Amp%20Nov%2013%202013.pdf](http://musicfromouterspace.com/PDF/Ray%20Wilson%20Presents%20the%20TL07X%20Op%20Amp%20Nov%2013%202013.pdf) You need a voltage follower. ---
**Author:** ![Lars](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lars](https://lookmumnocomputer.discourse.group/u/Lars)\ **Post date:** [February 8, 2021, 4:21pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/9 "2021-02-08T16:21:22Z")
Thanks, that´s very helpful! But I don’t even get that far. Once I hook up the op-amp to my +12v and -12v the whole circuit stops working. The LED on the oscillator turns off and it doesn’t oscillate. Also the op-amp gets piping hot really quickly. Could it be that I have a faulty amp? ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [February 8, 2021, 4:28pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/10 "2021-02-08T16:28:35Z")
Those are all symptoms of connecting the IC incorrectly. Check that it’s oriented the right way and that the ±12 V are each connected to the correct pin as @Dud explained above. In particular make sure they aren’t reversed. If the chip got hot it’s possible it was damaged and you’ll have to use another one. Definitely if it looks like this one (I put it in backwards): ![IMG_6475](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/c/cf6af15a8a7d51b6ee59388fc04b75ce6e518913.jpeg) ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [February 8, 2021, 4:39pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/11 "2021-02-08T16:39:39Z")
With TL072 it should look like this: ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/8/8746ca92f98c4de7e4e6f50df7970d99fa1e2767.png) (Bypass capacitors omitted, you can work on those once this much is working.) ---
**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\ **Post date:** [February 8, 2021, 4:53pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/12 "2021-02-08T16:53:21Z")
Either use the schematic suggested by @Dud, or draw us a schematic by hand and upload a image e.g. taken with your phone thereof so that we can see how you are trying to connect the circuit parts. The + input of the op-amp has an almost infinite impedance and therefore should not influence its signal source i.e. your simple oscillator (when connected correctly, of course). ---
**Author:** ![Lars](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lars](https://lookmumnocomputer.discourse.group/u/Lars)\ **Post date:** [February 8, 2021, 5:38pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/13 "2021-02-08T17:38:56Z")
I´ve hooked it up like this now. If I put the oscillator straight through the filter it works (but changes the pitch). Now it does not give any output. I used the TL074 because my TL072 always got to hot. Now even the TL074 is overheating witch it didn’t do earlier. ![20210208_183435](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/0/0d49853864240acfa2a280470c7d56ac2d2eeda5.jpeg) ---
**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\ **Post date:** [February 8, 2021, 5:42pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/14 "2021-02-08T17:42:31Z")
> [@Lars](#): > > Now even the TL074 is overheating witch it didn’t do earlier. This should never happen. The signals processing consumes hardly any power. The current of the opamp will be a matter of milli-amps. If you have reversed the plus and minus, then the opamp will draw much more current and will get hot and eventually die. For a TL074 pin 4 should be positive and pin 11 should be negative. The colors of your leads suggest they are reversed. Red is normally positive, blue or black is normally negative. You better check that using a multi meter. Note, for a TL072 this is different. There pin 4 should be negative and pin 7 positive. You should tap the output signal from the middle lead of the potmeter and connect one of the outside ones to the output of the op-amp and the other to GND. So use all 3 leads of the potentiometer. In your setup, if you turn the potmeter you will short out the op-amp (it will not break from this, it has a short circuit protection) and will get a lower signal, but that is not the way to do that properly. A potmeter of a few tens of kilo ohms or 100k should be oke. ---
**Author:** ![Lars](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lars](https://lookmumnocomputer.discourse.group/u/Lars)\ **Post date:** [February 9, 2021, 11:18am UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/15 "2021-02-09T11:18:30Z")
Alright, thanks. I tried both the breadboard schematic and switching the +/- but it seems I might have fried my op-amps. I´ll continue this once the amps I ordered arrive. Thank you guys! ---
**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\ **Post date:** [February 9, 2021, 12:08pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/16 "2021-02-09T12:08:26Z")
There are 4 op-amps in a TL074, so while you may have fried one, one of the others might still be OK. To quote a well known maker: “Don’t be afraid to try it!” ---
**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\ **Post date:** [February 9, 2021, 12:18pm UTC](https://lookmumnocomputer.discourse.group/t/issues-with-simple-rc-filter/2895/17 "2021-02-09T12:18:18Z")
![tl074 pin](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/8/8d88edf5992462773e091a02bebdd0c75946f0a7.jpeg)