DIY CD4069 state variable filter for modular synth 

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."

Your impromptu jam sounded great!

Amazing song at the end WOW!

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

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

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!

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

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!

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

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

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

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.

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

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.

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.😁

Sounds so good!!

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!

Great video! Thanks for sharing dude. I built 3 of then in a module to run in my diy modular. What oscillator are you using?

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

Really great video. Awesome song at the end.

Great stuff! I look forward to more of your videos

Great sounding filter!!

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

Aaaaawwwsome!! More modular plz plz plz !!!

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

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...

Really good video👏👏👏🙌

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

Similar to sh101 filter. The demo has tycho vibes

nice, need to check this dude

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

Nice track!

keep up the good work

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

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!!

Yesssss I love it

Inverters instead of op amps? Interesting!

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.

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

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

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!

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") ?

building this thanks buddeh

dang, how much was the knob $

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 ?

4096 or 40106?

uaaaaau!!!

Can I use 4069UBE?

Acid