Why Does My DIY Theremin Sound Gravelly?

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SUMMARY

The discussion centers on the gravelly sound produced by a DIY Theremin built using a protoboard circuit from Popular Science. The user suspects issues related to the 555 timer, specifically the possibility of using a low-voltage version, and queries about the tolerance of photocells. The output distortion is attributed to the square wave nature of the 555 timer, which can be mitigated by adjusting capacitor values, such as increasing the bottom capacitor to 0.1uF or 0.47uF. Resources for further understanding of the 555 timer are also provided, including links to Wikipedia and other educational sites.

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  • Understanding of 555 timer functionality and applications
  • Basic knowledge of electronic components like capacitors and photocells
  • Familiarity with protoboard circuit assembly
  • Experience with sound waveforms, particularly square waves vs. sine waves
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  • Research the 555 timer IC and its various configurations
  • Learn about sound waveforms and their impact on audio quality
  • Explore capacitor selection and its effect on circuit performance
  • Investigate the role of photocell resistance in audio circuits
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Electronics enthusiasts, DIY hobbyists, and anyone interested in building or troubleshooting audio circuits, particularly those involving the 555 timer.

k_squared
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I protoboarded this circuit:
http://www.popsci.com/diy/article/2008-04/build-pocket-theremin-cheap

alas, it seems to make an extremely gravelly noise - the term "hoarse cat" came to mind. Anyways, what could be causing this? I think I have developed a general idea of how the circuit works, however, it does not explain this given that I simply used a proto board to hook up that exact circuit. I mean, could I have accidentally used a low-voltage 555 (if that does anything?) or, you know, whatever. I'm thinking my part tolerances are close enough (well, radioshack). Thanks!

Oh yea... are my photocells supposed to be of very similar values? I can get a slightly better sound out of it by using a bigger capacitor on chip '2'.

Speaking of which, does anyone know any good (fairly) detailed explanations of the 555 timer? That little thing is ubiquitous. Oh, and uh, thanks a lot for any help.
 
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The output of a 555 is a square wave which is going to sound distorted if you are used to sinewave or musical sound.

The MP3 on that website disguises this a bit by using a high frequency. This means you can't hear the harmonics so the sound seems acceptable.
If the frequency is lower, you can hear the harmonics and they may sound unpleasant.
You can lower the frequency by making the bottom 0.01uF capacitor larger. Maybe 0.1 uF or even 0.47 uF.


There are lots of 555 sites but the one on Wikipedia would be a good start.
http://en.wikipedia.org/wiki/555_timer_IC
Here is another one:
http://www.kpsec.freeuk.com/555timer.htm
Try Google for others




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