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Elementary audio sound synthesizer with 3 or 4 or more A stabile Muvibs schematic demo principles



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When you want to make/develop a primitive synthesizer with 3 or 4 or more A stabile multivibrators this video shows a good first setup.

Corrections: on 4.32 I say “resistors” but of course I mean “capacitors”. On 6.17 of course the signal comes out of the second transistor of the first Muvib.

Perhaps important to tell again: there is a THIRD squarewave generator (20 Hz-20 KHz) that sends its signal via a 100 N capacitor “somewhere” into the 2-multivibrator circuit, that gives specific effects.

With a FOURTH squarewave generator all these sound effects “multiply” and with higher value time dependent caps (1 uF-500 N) the circuit goes to a lower frequency band, with the same effects, by the way. So no longer in the “bird sound” frequency band that is showed here. Lower sounds are more impressive/ominous, in general.

As we all know: the frequency of such a multivibrator (in this case made with 2 x a BC 547 B, NPN Si, Hfe = 250) is set by:

A) the supply voltage
B) the 2 capacitors (their values) going from “collector to base” (from TS 1 to TS 2 and from TS 2 to TS 1, in this demo: 200 N/10N/or electrolytics). The (+) of electrolytics must be connected to the collectors of the transistors that are used in this Multivibrator (say the “most positive” point).
C) the base resistor(s) value, between (say) 10 K and 100 K

The earlier video (demo of sounds) of 22 November 2014 where this video is all about is here

https://youtu.be/DeEFlyEvfW8

The very first vid (electronic syren two tone horn) is here https://youtu.be/7ZaiqvRzKZQ
In that very first video you can surely see the direct schematic.

The whole circuit now (31 dec 2021) is very funny and easy to make and can be worked out into a serious synthesizer. Of course these sound synthesizers can be bought nowadays for a very low price, anyway, making it yourself gives more fun and satisfaction and surely you can get better results (in terms of specific audio effects) when you have understood the principles of the A stabile multivibrator and how to let them work together: 3 or more of them.
Some tips to work it all out:

1) Vary the voltage, gives other sound effects
2) Vary the value of the capacitors in the circuit (C to B)
3) Start with 100 N capacitors and the resistor values showed
4) Make the caps (that set the frequency) smaller in value or bigger in value
5) Thus: vary with the value of the cap going from the collector of transistor 1 to the base of transistor 2, and the cap going from the collector of TS 2 to the base of TS 1. Take different values, say 100 N and 10 N. Or 100 N and 47 N. Or 1 uF and 10 N. That all gives completely different sounds (duty cycle changes).
6) Always send in the squarewave signal/sound/AC voltage of an other external oscillator via a coupling capacitor; start with 100 N, then take 470 N, then 1 uF or even higher (more fierce drive, other sound effects). Driver caps 1 uF or higher: preferred bipolar (no electrolytics).
7) When you use electrolytics (10 uF-100 uF) the frequency of the 2 transistor A stabile Muvib. showed here goes down into the 100 Hertz-5 Hertz or lower range (more ominous sounds in this range and the 1 UF to 500 N range)
8) Make the level with which you “input/push” an AC signal into another multivibrator variable by using a potentiometer, say 1 K – 50 K. You can switch it in series with the coupling capacitor that sends the signal of generator (A) into generator (B), the injection of the external generator works best into the base of the used transistors
9) Use NPN transistors with a Hfe (current amplification) of approx. 250
10) Don’t directly connect (say by accident during these experiments) the base of the used (here NPN) transistors to the (+) lead, the transistor will die immediately without any sound due to a destructive base current. The oscillator does not work any longer; replace the transistor.

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 31 december 2021.
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