DIY CD4069 state variable filter for modular synth

Here's my simple DIY state variable filter based around the cd4069ube hex inverter CMOS chip. I'm working on other synth modules and projects, so sub to the channel if you wanna see more!
Oh yeah and i forgot to mention this on the video, but the filter is also eurorack compatible! My modular is basically eurorack but with banana jacks and bigger modules. Just remember you have to wire all your input and output jacks sleeve connections to ground!
I checked the tone switch caps and they are 20nF in my setup! (203)
I also made a slight correction to the way the input and cv input potentiometers are wired. The updated schematic is in the dropbox link below. The schematic works fine the way it is in the video but its not good to ground the cv source when the pot is turned all the way down.
The original forum thread: electro-music.com/forum/topic...
Schematics: www.dropbox.com/sh/9v1usdmlsw...
Also follow me on instagram: / lauri_diy

[@josbouten]

Suggestion: "When using an AC signal the diode will distort it. It will in fact leave all of the negative signal outside the filter. Instead of a diode to protect the chip from negative voltages it is possible to use a bias voltage to lift the input signal to half the supply voltage. You connect two 47k resistors in series from +V to GND. The center point you connect to the input of the 1st inverter. The outside signal you connect from the attenuator pot via an elco (will pass AC but not DC) to the center point of the resistors. In that way the AC signal is lifted up to 1/2 power supply voltage. The filter will then work on the whole AC range of the input signal. The outputs of the filter will carry the filtered AC signal superimposed on half of the power supply voltage, so you need to use elco's at the outputs as well. Connect all elco's with their negative side to the "outside world". The filter will then works like a true SVF without distorting the signal."

[@LAURISDIYCHANNELTV]

Awesome, thanks a lot for this! I was wondering whats a smart way to do just this! 👍

[@klassisch9093]

Amazing song at the end WOW!

[@klassisch9093]

Literally i cant stop listening to the end song, do make more music like this?

[@klassisch3039]

Yeah this is sick!!

[@Sarahbuildsstepsequencers]

Your impromptu jam sounded great!

[@tonton1303]

sound is amazing ! thank you for this nice work !!

[@CircularMirror7]

Great video. LOVE the panels that you painted white and inked with marker. Good work. 👍

[@darkmax2007]

Awesome work man! That demo song gave me chills, so great

[@LAURISDIYCHANNELTV]

Thanks! 🙏😊

[@jean-philippefalcon3238]

So cool, thanks so much for sharing. The way you drew your schematic is very nice, I'll build it today :)

[@LAURISDIYCHANNELTV]

Thanks! 😊 I hope the schematics are clear enough for people, because i dont know how to use any software for that and cant bother learning haha

[@tinfoilcat]

Very nice! I found you today via Reddit, instant subscription! Your video made me pick up my ICD1820 module and fiddle with electronics for the first time in months! Working on making it CV controllable, it looks promising!

[@LAURISDIYCHANNELTV]

Thanks, thats so cool! Be shure to check the link to bastl instruments’ website in the sampler video’s description! Its packed with good info on the isd chip!

[@tinfoilcat]

@@LAURISDIYCHANNELTV Thank you! I had missed that method, so I just replaced the resistor with a NPN transistor. A bit more work with biasing it. I'll try the Bastl method soon. It can be really haunting when you loop something and change it's pitch with a sequencer.

[@ArrayzableMusic]

That filter sounds awesome! Not a problem that it doesn't close fully - I mean - I want sound to come out of it 😊 Anyway - killer track at the end. I really love your hihat playing!

[@LAURISDIYCHANNELTV]

Thanks a bunch! 👏

[@channelite]

Really great video. Awesome song at the end.

[@arenotdiy7280]

Great stuff! I look forward to more of your videos

[@SOULDIY]

Great video. Built it with cd4049 ( !!!! pinlayout is different !!!! ) instead of cd4069. Works great !!! Thanks for this great scematic....

[@jimivandebeek]

Great sounding filter!!

[@canterburyaudio5836]

Sounds so good!!

[@shaiant5316]

Really good video👏👏👏🙌

[@Soundbrigade]

Love the design of your modules! I understand the concept of the euromodules with nice shiny alupanels, but if it is DIY, it must carry the personality of the creator (I am doing the same too). A small minus for the lack of voltage control, but this would find its way into a lot of fun stuff like drones or in various noise-makers, which makes it very versatile.

[@LAURISDIYCHANNELTV]

Thanks! 🥰 Yeah it was a conscious choise not to include cv, so the machine would force itself to be used for drones and things of that nature. But it would be easy to add the cv and gate control and you can find schematics for that in the bast article i linked in the description!

[@Soundbrigade]

@@LAURISDIYCHANNELTV I inherited (was given) a box with MFOS Weirds Sound Generator and will add a PT2399 echo and a simple VCA (4069 oscillator + MFC6040). There's a filter in the WSG, else this one had been a good choice. And this is what I mean that the filter can go into fun stuff.

[@LAURISDIYCHANNELTV]

WSGs are awesome and the filter is awesome, especially for how simple the circuit is!

[@LAURISDIYCHANNELTV]

Hey i just realized i thought this comment was on a different video i posted at that time! So i was actually talking about my sampler, not the filter haha. ’Cause the filter does have voltage control, although its done with vactrols, so its not very fast and the response time depends a lot on the vactrols you use. I dont really talk about it that much in the video, but its there!

[@StephenMcLeod]

Dead smart. I had no idea that those alu panels were theoretically that straightforward to 'cut'. I didn't even know you could get sheets like that. HmmmmmmmmmMMMMMM

[@LAURISDIYCHANNELTV]

Yeah its surprisingly easy to cut them this way! I scratch a couple of times with a knife (im guessing the tip of the knife feels happy about this lol) so that it makes a clear line in the panel and then as you bend it back and forth, the sheet brakes neatly at the cut! I cant remember for shure, but i think the sheet is 1,5mm or 2mm thick. Of course the thicker the sheet the harder it is to cut like this

[@JackNiles]

Thanks man thanks bro thanks for sharing your thoughts on how to make your own life happiness and your thoughts on how to make your own life better

[@sachagirard561]

Aaaaawwwsome!! More modular plz plz plz !!!

[@The_Overconfident_Incompetent]

The song you do at the end is sick man! You are surely a talented fellow! You should check out the UAF42 chips man, that is if you ever want to make another state variable filter again. It is literally a state variable filter IC. I have some coming from ebay soon. going to make a q-tron clone/mod type thing and use them in it.😁

[@LAURISDIYCHANNELTV]

Oh cool! I havent seen this chip before, seems cool! I’ll look into it 🔥 Thanks for the tip

[@a-z-n-b-a-i]

keep up the good work

[@royjacqvanstraeten668]

Good music for such equipment , i would like to see you making music on expensive instruments ..good job

[@dannyroessler]

nice, need to check this dude

[@jimivandebeek]

Nice track!

[@jimgoodinmusic]

Enjoying your. creativity and series particularly this one and your closing piece, really nice. I'm just starting to build after doing some formal kits so dangerously wide eyed eyeing the DIY path but why not! One question where are you going for parts? I have been using Digikey as they are friendly to buying small quanities. Keep up the good work and power to your muse!

[@LAURISDIYCHANNELTV]

Thanks! I’ve been ordering most parts from ebay and sometimes from a small local electronics store

[@Swainer19]

Yesssss I love it

[@LAURISDIYCHANNELTV]

Thanks! 🎉🎉🎉

[@floretionguru2977]

This sounds wonderful- thanks for the detailed video. I see I have all the parts except instead of 100k stereo pots mine are 10k- I'm guessing I can make both the 103 twice as large for similar result...

[@LAURISDIYCHANNELTV]

Thanks! Yeah i would assume the caps should give a similar result, but cant say for shure. If you’re using a 10k pot i think the cutoff range might not be as wide!

[@floretionguru2977]

@@LAURISDIYCHANNELTV Thanks again and great work on your song. I meant to say 10 times as large on the caps not twice- I think will just have to breadboard it up first to know for sure :) .

[@LAURISDIYCHANNELTV]

Okay! Yeah the filter should still work but the difference might be bigger! I tried out some different values of caps when making this but i dont remember if i tried 100nF caps at any point!

[@Chris-vr8cd]

building this thanks buddeh

[@josbouten]

I built this filter and added a small change: a 1 k resistor between the resonance pot and pin 8 of IC1. This prevents the pot from shorting pin 8 to pin 9 of the 4th inverter section in IC1 when rotated to its extreme position. What value did you set the 100K trimpot to (text near trim pot says: "affects the resonance") ?

[@LAURISDIYCHANNELTV]

Nice! Sorry i haven’t measured the trim pot and i have even changed the position at some point, because i wanted the filter to be more resonant! At the other extreme the filter self oscillates in a nasty way and sounds kinda thin even at lower resonance settings, and at the other end the filter sounds nice, but doesnt sound that resonant even when turned all the way up! So i think its best to try it out and see what you like! BUT i remember building this on a breadboard at some point and i think i used a 91k resistor instead of the trim pot and it sounded nice to my ear!

[@chronozphere]

Hey, really cool video! I have just breadboarded this filter and it works well. I also have the CD4049 but I cannot find any information about it accepting negative voltages. Do you have any idea how to build this filter using the CD4049 so it can work with negative voltages too? The datasheet says the chip can only handle 20V max so if I connect the Vcc to +12V and Vss to -12V I'm pretty sure I'll blow it up. Thanks a lot!!

[@LAURISDIYCHANNELTV]

Thanks! Oh yeah don’t try powering it with negative voltages! I ment that the audio inputs can handle i think 10V positive and negative. So you wont brake it with bipolar oscillator waves for example. But i still havent tested this with the 4049!

[@nathanschagen2790]

@@LAURISDIYCHANNELTV I've tried to build it as well, but I was not succesful yet but I want to make it work since it sounds so good. I have another question. Do your oscillators create signals that are completely positive? As far as I know, pretty much all audio signals in modular go into the negative range. That means that the diode at the beginning will clip and distort the input signal. Doesn't that happen often in your system?

[@LAURISDIYCHANNELTV]

@@nathanschagen2790 my oscillators are cem3340 VCOs so they are all positive voltages! But if i patch for example a resonant high pass filter in front of it, the diode does mess up the sound! It would have been way smarter to come up with some sort of a clamping circuit for the input, but i dont know that much about this stuff and just wanted to get the filter working fast haha

[@karimazeli2653]

Nice filter, powerful!! What vactrol model did you use?

[@LAURISDIYCHANNELTV]

Thanks! 🤘 The vactrols are VTL5C

[@josbouten]

Are you sure the schematic shows the potentiometers connected to the IN and CV in the right way? I would expect the input and CV signal to be connected to the 'top' of their respective potentiometers and the signal to the vactrols and the signal to the diode to come from the 'middle'-pin of their respective potentiometers. In the schematic shown the CV input will be shorted when you turn the potentiometer all the way to one side. That could be bad for the source of the CV signal.

[@LAURISDIYCHANNELTV]

Oh shit, youre absolutely right! I might fix the schematic for the dropbox link. Thanks for pointing that out! ✌️

[@Sarahbuildsstepsequencers]

If you socketed the inverter chip, you can just swap it out for the CD4049.

[@LAURISDIYCHANNELTV]

the 2 ic chips actually have different pinouts and even different number of pins! 4049 has a weird pinout compared to other 4000-series ic chips

[@KiR_3d]

Thanks for sharing! It's my case probably - I'm proto-ing a side kick for my Volca Modular. I want to be on 0-9v or 0-12v rails for it. Do you know some good VCO CMOS (preferably) design to work off 0-9v rails? 40106 (or 4069 - basically the same Rene Schmitz design) oscillator works good from a single power supply... But I've didn't managed how to add an expo-converter to it. I've seen some single rail designs (there is a little bunch) but didn't tried. If you know some best design... Would be cool to know :) P.S. Your synthwave composition sounds nice! I've didn't heard anything made with live drums in this style yet.

[@LAURISDIYCHANNELTV]

I havent built any single supply VCOs like that but i think Moritz Kleins oscillator videos are really good! Go look him up if you haven’t already!

[@LAURISDIYCHANNELTV]

And for CMOS systems i think 40106 designs are the best!!

[@KiR_3d]

@@LAURISDIYCHANNELTV Kleins goes from bipolar supply in all his designs (which I've seen).

[@joeneoj]

Thanks alot for your videos, i love them. And your studio/workshop. I have a question. Can i simply replace the stereo pot for a mono pot and just route the third stage to it in series with the second step? I figured all that it would do is make it mono. Am i correct or am i missing anything? Does that also mean that i can remove the third stage all togheter? Thank you, from sweden with hugs

[@LAURISDIYCHANNELTV]

Thanks! 🥰 You do need the stereo pot, if you want to make the filter a 2 pole filter, and thats a big part of the sound. If you remove the last stage, the filter becomes a 6db/oct filter. And im not sure if the resonance works like this with a one pole filter. So the the pot isn’t ”stereo” as in 2 channels of audio, but controlling two different stages of this mono filter at the same time! Im not sure if thats what you ment or if my explanations make sense, but oh well!

[@LAURISDIYCHANNELTV]

Oh yeah and there are only 2 filter stages in the circuit, they are the inverters with the 103 caps in them

[@joeneoj]

@@LAURISDIYCHANNELTV Okay, i think i understand it a bit better now. But that leaves me with having to order more parts. Again. It's fun though. Thanks a bunch

[@LAURISDIYCHANNELTV]

Hahah yeah i feel you! You always need that one part more! But you can use the dual potentiometers also in other cool filters and for example twin t drums, like the one in my other video!

[@joeneoj]

@@LAURISDIYCHANNELTV Thats fun! I plan on doing a lot more of your tutorials. But first i need me a powersupply for my briefcase-case

[@bydeattic8319]

Cool build! Those sheet metal hi-hats "sound dead but delicious". What thickness/diameter should I cut my own set?

[@LAURISDIYCHANNELTV]

Thanks! They are 0,5mm smooth steel sheet metal, but i havent measured the diameter yet, i just eyeballed it. But i’m making a video on the hihats and cymbals in the near future as well!

[@LAURISDIYCHANNELTV]

Its most likely my next video or the one after that!

[@bydeattic8319]

@@LAURISDIYCHANNELTV Thanks! To mee they look between a 13" - 12" set. I am going to try it out.

[@LAURISDIYCHANNELTV]

@@bydeattic8319 hey i measured them for you and they are actually really small, about 8”. I tried making bigger ones but they sounded way worse, probably because its such a thin metal and its actually flat unlike real hats! And i hammered small bells to the hats by just placing the sheet on a metal coffee cup to get a round shape and hammering it pretty gently with a ball-peen hammer. I think its preatty easy to brake the sheet as i have no idea what im doing when working with metal lol

[@bydeattic8319]

@@LAURISDIYCHANNELTV WOW! Camera makes them look a lot bigger. I will try 8" first. I dig the odd sound from yours. Sounds almost like a synth snare.

[@maikmario71]

Hi there, I just built the filter on a stripboard, everything works! Unfortunately, it doesn't sound quite as "fruity" as in your video, there are sometimes sound dropouts, I'm still trying to find errors. I think it could also be due to the Chinese TC4069UBP that I used. Question: Can you say which LDR or Vactrol you used, there are also differences here!

[@LAURISDIYCHANNELTV]

They were VTL5C vactrols i ordered from china!

[@maikmario71]

@@LAURISDIYCHANNELTV Hi there, sorry I have to ask something again! The 1K resistors for the potentiometers are not symmetrical. One Vactrol has a series resistor (1K), the other Vactrol doesn't, is that how it should be? Greetings and thanks again in advance

[@LAURISDIYCHANNELTV]

@@maikmario71 oh hey i think thats a mistake in the schematic! I think the vactrol should not go through the 1k resistor at all! Thanks for pointing that out, i’ll fix it to the schematic in the dropbox link

[@nemeik]

If i build the simple schematic, with only 1 output, is it then an adjustable high pass filter of low pass filter? If low pass filter, how do i make it a high pass filter, which adjustments? cause i wan't to build a adjustable hpf not lpf

[@LAURISDIYCHANNELTV]

It's a low pass output, but you can get a high pass output from the output of the first inverter, so pin 2. You dont have to make any other changes to the circuit

[@nemeik]

hello lauri, do you think it's possible to put this filter on a audio signal like from a turntable? I would love to build this and use it in my DJ setup for live audio performance! regards

[@LAURISDIYCHANNELTV]

Hey! I havent tried the filter with line level audio or anything other than modular synth oscillators / noise. I think the filter might not be the best for a dj setup, because its not a very clean circuit and i think you would have to amplify the input signal some more with audio levels going into the filter! That being said, it might also work just fine, depending on your setup and style you’re going for 🤷‍♀️

[@nemeik]

@@LAURISDIYCHANNELTV Okay, thanks! on 3:09 you say if not using for modular, but if i use it for live mixing and audio performance, i still need this right? Or for what reason should i let this out of the schematic? i have same question for the CV .... 😅

[@LAURISDIYCHANNELTV]

Modular synth levels are higher than line level signals, thats why you need to amplify the output. I'm not sure if it would work with line levels without the output amplifier, but i would still build it myself so you can use the trim pot to set a good level for the output. You can take the CV input out if you dont need it! So if youre not using an envelope, LFO etc.

[@RafaelMareco]

uaaaaau!!!

[@nekelly123]

Inverters instead of op amps? Interesting!

[@sachagirard561]

Why don't you start a video series of your diy modules I can see a lot of them in your modular

[@marcocarvalho9866]

Great Job , just if i want to change stereo cutoff by Mono cutoff how do i do ? I don't know where i can place my cutoff potentiometer because it's writed "Stereo POT 100K" but you use a simple potentiometer ... Or your Trim Pot is the cutoff ?

[@LAURISDIYCHANNELTV]

Thanks! You need a ”stereo pot” or ”dual potentiometer” for this circuit. The filter is mono, but the cutoff potentiometer needs to change resistance in two parts of the circuit at the same time. So basically its two potentiometers built into one! Thats why it looks like a regular pot

[@LAURISDIYCHANNELTV]

But they are quite regular electronic components, so you can probably find them wherever you buy your normal potentiometers from! Hope this helps!

[@marcocarvalho9866]

@@LAURISDIYCHANNELTV Ooh ok ok , and it's possible to make a module (like synth pedal just with input and output ? ) because i want to add a Switch 2 postion to activate or desactivate this module . Can you sends me a link for your dual potentiometer ? and trimmer pot it's a personnal setting's ?

[@marcocarvalho9866]

Or it's Possible adapt this circuit for a mono potentiometer ?

[@LAURISDIYCHANNELTV]

This is what you should look for: www.ebay.com/itm/221787933467?hash=item33a3974b1b:g:HkYAAOSwl8NVapzN or does youtube allow me to link stuff in the comments idk. I’m not shure if this is the best price, or where you would like to buy them, but you can get these anywhere you’d like to!

[@Alkatross]

Similar to sh101 filter. The demo has tycho vibes

[@72ndHUMAN]

dang, how much was the knob $

[@LAURISDIYCHANNELTV]

I think i bought a 5 pack for about 15 euros. You can search ”MF-A05 45mm” for example on ebay and look for the best deal

[@soejrd24978]

Can I use 4069UBE?

[@LAURISDIYCHANNELTV]

Yeah, thats the same one i used! I’ll add that info to the description, thanks! ✌️

[@soejrd24978]

@@LAURISDIYCHANNELTV nice! I designed a wasp clone using this chip and it doesn't work, so troubleshooting time yaaaay. Gotta say it looks like you feel more comfortable showing yourself here, lean into that :)

[@LAURISDIYCHANNELTV]

@@soejrd24978 yay thaks! Yeah ive also been looking at some 4069 wasp schematics but havent built one yet. Hope you find the problem! Troubleshooting is the worst haha

[@kuro758]

4096 or 40106?

[@LAURISDIYCHANNELTV]

4069

[@kuro758]

@@LAURISDIYCHANNELTV 🙌🏽

[@andrak5946]

Acid