[ $4 ] DIY eurorack modular synth VCF - Diode ladder low pass filter

My 39th original eurorack modular synth DIY projects.
4-pole diode ladder low pass filter. It has the characteristics of a thick and warm sound.
The concept is to make it with low cost, few parts, and easily available parts.
working documents ( schematics )
note.com/solder_state/n/n598f...
Please support me to continue projects.
/ hagiwo
DIY $6 SSM2044 type VCF
• [ $6 ] DIY modular syn...
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/ hagiwo_1
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[@benjiaomodular]

The resonance on this sounds so clean! Another one on my to-do list. Really loving your analog stuff lately.

[@flourfree2K]

I LOVE ANALOGUE MODULES!

[@MalbekTV]

wonderful

[@K.D.Fischer_HEPHY]

Pretty impressive DIY Setup what you have going there. 👍

[@robman80808]

Wish I was clever enough to turn this into a stripboard!!

[@paterfiets]

Amazing sounding filter ! If you would put your modules out for sale i would def buy them !!

[@flourfree2K]

But I'd like ALUMINUM panels! Sorry, but I'm much Doepfer-ish

[@circuitben]

Are the capacitors tantalums?

[@ProjetHomeStudio]

Hi, Thanks a lot for that :) I will most likely build it. Technical question : you mention that the CV input expects a 0-5 volts signal. Could you explain why, and why it wouldn't work if I was sending a bipolar -5 to 5V signal ? My question is both : 1/ would it damage something ? 2/ I'm trying to understand how the schematic works, so how can I know from the schematic ? :)

[@hughman8597]

WOW! This is a really, really cool sounding VCF. But I don't have to tell you that, EVERYTHING that you build sounds great :)! Is there an alternative to the 2SC1815? As always, greetings from Germany

[@AnalogDude_]

2n3904 / 2n3906, BC847 / BC857, 2sc945 / 2SA733 ... they all work.

[@krishna34674]

any small signal NPN type transistor

[@finonomastropiero4261]

@@AnalogDude_ thankkkkks analog dudeeee:}!

[@balcony_birds]

This filter sounds really good in your video! I took a look at the schematic on your blog and I've been wondering if the red caps are 0.068µF (the same as 68nf) or 0.068nf? I just want to be sure before ordering parts. Thank you in advance!

[@HAGIWO]

it is uF. Thank you!

[@burakyavuz5093]

hello, I use google translate because my english is not good. I hope I can express myself this way. :) First of all, thank you for sharing. I have a lot of respect for what you're trying to do. We can implement any module we choose by following the right path. I don't know how to read schematics. I'm trying to learn as I have a new interest yet. While doing my experiments, I can visually follow what and where to solder on the board. Is there a visual diagram you can share besides the diagram?

[@ff-qf1th]

learn to read schematics it's a very useful skill

[@IG-88r]

Are the caps of between the resonance and output non polarized 4.7 Uf or ceramic 4.7 nf?

[@HAGIWO]

It is 4.7uF.

[@lordlollops1]

So a low pass filter cuts the frequency to give it a tighter punchier sound where opening it extends the sound? Sorry im a synth newb

[@erlannderrantem6972]

In it’s basic form the Lowpass filters out all high frequencies above the cutoff point and let‘s through all the low frequencies below the cutoff point. Every filter stage or pole attenuates all freq. above cutoff with 6db/octave. this filter is a 4 pole design so it has an attenuation of 24db/oct, meaning the cutoff is steeper and lets through less freq above cut off than a 1,2 or 3 pole design, making it darker, but with increased initial resonance. To get even more resonance (the typical synthesizer sounds) the output of the last filter stage is fed back into an earlier stage and thereby amplifying the area around the cutoff. I hope this helps.

[@guiguizizouniet]

Hello, how to increase the resonance peak? I already reduced the 100KOhms resistor of the resonance stage but the peak amplitude depends on the cut off frequency. Do you know how to make it stable? Thanks in advance

[@HAGIWO]

I have tried several circuits, but could not increase the resonance. Many other DIYers have published diode ladder filter designs.

[@guiguizizouniet]

@@HAGIWO actually it's not a big deal, I will replace the 100KOhm resistor of the resonance stage by a 33KOhm resistor and I will get a higher resonance peak. I think it's not a problem if the amplitude of the peak increases with the cut off frequency, i.e. it's the case in the TB-303 ladder filter. Sounds more acid 😁

[@_DRMR_]

Fantastic! Definitely has its own characteristics. How does the number of stages in the diode ladder affect the output?

[@HAGIWO]

The number of diode stages affects the attenuation factor of the filter. There are many documents on the web, so you can deepen your understanding by looking at their explanations.