Change squarewaves into sinewaves with the help of a 3 pole filter (synth project) VLOG/schematic

Please read the textbox. About how to change square waves into sine waves. Related to the earlier project of the audio synthesizer. More video’s (links below) about that are on my YT Channel.

It is a VLOG + schematic related to the making of that simple synthesizer, made with a good hand full of transistors, as little as possible, but whatever to make the best audio effects. It is a project for the coming months in 2022.

I show how to change a square wave into a sine wave with the help of a 3 pole R-C filter.

In many cases no math is needed: everything can be made when using 3 or 4 sets of capacitors: 100 N or 50N or 10N or 4N7, combined with 3 sets of resistors: 1 K or 10 K or 30 K. More in the video.
Relations and how to make it:

a) High value capacitors (100 N-220 N= 0,1 uF-0,22 uF) suit low frequencies combined with 3 x a 10 K resistor in the 3 pole filter. That is a good setup. Please note: you sometimes need a 1 transistor audio amplifier afterwards, to compensate the loss in the (say any) 3 pole filter. Connect such a 1 transistor amplifier always via a blocking capacitor of (say) 220 N, going out of the last stage of the filter, to the base of the (in many cases) grounded emitter 1 transistor circuit. Link below.

b) Lower value capacitors (say 50 N= 0,05uF) suit the higher parts of the audio spectrum, say above 4 KC. Use say 3 x a 10 K resistor in the 3 pole audio filter combined with 3 x a 50 N capacitor on frequencies from 8 KC-12 KC.

c) Use (say) 3 X a capacitor in the 4N7 or 1N5 range, combined with 3 resistors of 10 K in the filter, to change the 10 KC-20 KC square wave freq. band into sine waves.

These are experimental and tested-out values, useful for (audio) experiments.

First relevant video 4 January 2022 about the synthesizer is here https://youtu.be/IOcN-yuc68s

Second relevant video 16 January 2022 about that circuit is here https://youtu.be/1EVJrrIqcXE

1 transistor amplifier schematic to amplify the output of the 3 pole filter is here https://youtu.be/7IHjYesM7UM

My You Tube channel trailer is here: https://youtu.be/xbgQ8T3oqh4 When you search, search always “NEWEST FIRST” to get the right overview. You can also search via the “looking glass” on my Channel trailer via keywords like ”audio”, “radio”, “amplifier”, “filter”, “Shortwave”, “transistor”, “FET”, “oscillator”, “generator”, “switch”, “schmitt trigger” etc; so the electronic subject you are interested in.

My books about electronics & analog radio technology are available via the website of "LULU”, search for author “Ko Tilman” there.
https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=Ko+Tilman

I keep all my YT videos constant actual, so the original video’s with the most recent information are always on YouTube. Search there, and avoid my circuits that are republished, re-arranged, re-edited on other websites, giving not probable re-wiring, etc. Some persons try to find gold via my circuits. I take distance from all these fake claims. I cannot help that these things happen. Upload 25 January 2022.