1 transistor 2 pole audio filter that can change squarewaves into kind of sinewaves demo & schematic



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Please read the textbox first before you comment. Demo/schematic of a 1 transistor 2 pole audio filter (mimicked a 3 pole filter when we take the 1 K volume potentiometer into account) circuit that can change square waves into kind of sine waves. Read: sometimes a kind of.

That waveform (pure or not) depends on the audio frequency & the potentiometer (1K) setting at the emitter of the BC 547B at the end of the filter. Oscilloscope views are showed for info.

Please read the textbox & watch the video, where I showed the effects of changing the value of the 1 K emitter potentiometer of the BC 547 B.

It was used (in this case: read in the audio band) in combination with a 10 uF capacitor from the wiper of the 1 K emitter BC 547 b resistor to ground (-).

Because it is a NPN transistor & for everyone understanding the basics of transistor audio & HF technology: that capacitor value sets in this case (GE=grounded emitter) the amplifier to work & amplify it into a certain frequency band, here with this 10 uF capacitor in the 100 Hz-8000 Hertz range. But surely in the 20 Hz-20 KC range with a 10 uF cap at the wiper-ground.

When you (say) use a 100 N or 47 N capacitor from wiper to ground in this case (pot 1 K at the emitter, the NPN transistor has a Hfe of 250) you can more easily amplify everything above 3000 Hertz, even to HF, say 500 or 800 KC.

This grounded emitter 1 NPN transistor amplifier works (thus) with a good quality Hfe NPN transistor, like the BC 547 B, current amplification is 250. Must be measured, it must be 250 x to make the circuit work.

Schematic & demo are in this video & thanks for watching.
Everything about that 1 transistor amplifier/2 pole filter, regarding the synth. project is told in this video now, 1 February 2022.

But many more video’s about that earlier synthesizer (first setups) project are, by the way, here. Please don’t get overflowed, it only shows the history of the project.
https://youtu.be/KisdQ0mednI

Elementary audio synthesizer: works & used, originally from 2014, schematics & more links in the description at this video. https://youtu.be/Zt0widtCGRU 4 January 2022.

Crazy sound(s) box, it shows the basics of making peculiar sounds, works & used. Is essential and will be essential in this synth. project. https://youtu.be/Ud2WjJGgaHE 5 January 2022.

Not used here in this project, but very usable. Works and was used but was in a certain way too sensitive. Easy Square wave oscillator/generator for audio and higher frequencies with the TL 071 FET Opamp and only a few components.

https://youtu.be/rxyXFnYJTVI 8 january 2022.

Not used here but very usable say as a measuring device or for whatever electronic use, a square wave and triangle wave oscillator made with a NE 555 Chip (20 Hz-20 KC). https://youtu.be/IOcN-yuc68s .

Works & was used and can also be integrated in the synth. project.
A very basic organ circuit via two 2 transistor A stabile multivibrators (read: square wave oscillators).

A good basic approach for many audio experiments, tests, etc. https://youtu.be/77L5scpjoQo

A one transistor sine wave oscillator that can be combined/integrated into this synth. project, works & was used. Useful everywhere where you want/need a proper sine wave for whatever purpose: test, measurements, etc. https://youtu.be/QwADz9-ozhM

About this video (upload 1 February 2022): how to change square waves into sine waves. A 2 pole audio filter that works, was used, and will be used in the future.
It shows the very basics/setup about how to do that, with a BC 547 B, say a normal NPN transistor in the grounded emitter mode, but it has to have a current amplification factor (Hfe) of 250 to make this filter work properly.

With a too low amplification the highest frequencies to be amplified (say above 1 or 4 KC) will drop too much.

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” etc. 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. I take distance from all kinds of fake claims, say people that try to find gold with my circuits, sorry that these things happen. 1 February 2022.
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