100khz square wave generator

The musical signal`s form does never resemble a square wave. The frequency range perceived by an average adult hardly goes above 17KHz. Hence I do not give a dime to those heated discussions whether it`s appropriate to test audio amplifiers using a 100KHz meander signal. But being an electronic engineer in my heart as well as by education and pass
100khz square wave generator - schematic

ion - I can assure you that giving an audio amplifier a try with 100KHz square wave test signal can reveal quite some technical qualities (or lack of those) in the design. Overshots caused by negative feedback loops or signal slopes formed by input/Miller capacitances are amongst things that are easier to observe with meander than when using sound-frequency test signal. Before turning to the true and tried CMOS 555 I tested several oscillators based on old soviet 561 › 7, 561 › 2, as well as 74HC04 and 74HCT04; the last unsuccessful attempt was made using LM555. All the attempts listed above have failed due to the horrible ringing the chips were generating at its outputs. The current spikes in the power line were also quite hard to tolerate. Therefore I came up with only two budget solutions: People who love micro-controllers may start laughing at me here. Honestly I was also tempted to build a universal square wave generator based on ATmega-8 that I had at hands. But somehow I am too lazy to program when the same result can be achieved by a comparable amount of soldering without turning on that annoying thing (computer. And to tell you the truth I strived to have as minimal of those high bandwidth current spikes as possible - in order to test quality audio equipment I wanted to have a quality test signal as well. Regardless the fact that the generator`s bill of materials amounted for just a few bucks. Obviously testing...

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