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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Square wave to sine wave without attenuation
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nullpainter



Joined: Nov 07, 2011
Posts: 18
Location: Wellington, New Zealand

PostPosted: Sat Oct 12, 2013 4:24 pm    Post subject: Square wave to sine wave without attenuation
Subject description: Is it possible to convert a basic frequency-independent square wave to sine wave?
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Hi,

I've recently made the infamous Melody Generator, with a few little tweaks for fun. A recording is here. It currently sports a basic, fixed passive low-pass filter to round out the sound slightly, but I'm keen to convert the square wave output to a sine wave so I can have more fun with it (such as making a quick LFO and summing it with the output).

I hooked up this opamp-based circuit in LTSpice and it works well, however the resistor values need to be tweaked according to input frequency otherwise attenuation occurs. I suspect that a frequency-independent solution would be fairly complex? Is the 'solution' to make the values optimal for, say, 440Hz and just put up with it being good enough frequencies around this?

M
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nullpainter



Joined: Nov 07, 2011
Posts: 18
Location: Wellington, New Zealand

PostPosted: Sun Oct 13, 2013 10:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah, looking at section A.4.8 and A.4.9 of the Single-Supply Circuit Collection, the solution could be to use a JFET instead of a resistor across the cap.
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