[sdiy] Square to Sine

[Tom Wiltshire]

On 4 Apr 2017, at 11:32, Elaine Klopke <functionofform at gmail.com> wrote:

> Does this actually work? 
> http://www.learningaboutelectronics.com/Articles/Square-to-sine-wave-converter-circuit.php
> 
> I would assume that being 3 RC networks in series means quite the drop in volume.

Yes, it works, and yes, it'll kill the volume. It's a three-pole passive filter. The recommendation (which they've ignored in this example) is for each resistor to be ten times the previous one to help avoid one stage loading the next. So it could be improved. There's an example in my LoopEnv datasheet, pg.6:

http://www.electricdruid.net/datasheets/LOOPENV1Datasheet.pdf

It'll only work properly at one particular frequency, as you've realised. Changing the input frequency will change both the level and the harmonic content of the output (although perhaps not enough to matter for small changes in input frequency - e.g. vibrato?)

> Also, in a related article they show two networks in series converting the square wave to a triangle.

Probably running the square into an integrator. That gives you a nice triangle, but the same volume problem - the volume halves for each octave you go up. Have a look at the stuff online about DCOs for more about this, since this is the problem they had to overcome.

> All of the converters being dependent on the frequency of the input wave being roughly the same as what the RC networks are tuned to. 

Exactly.

Tom


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