[sdiy] Square to Sine

[Elaine Klopke]

> You where talking about a 2 pole filter, which is different from the original 3-pole filter, or at least that is what I saw from your contribution.

I think I can clear this one up... I did a search on google for the thing and there's a guitar delay pedal that uses basically the same filter layout, but it ends up being a third passive pole tacked onto the front end of a two pole Sallen-Key bjt filter. 

> Now, a smarter approach is to use a resonant lowpass filter setup, as the resonance located on the fundamental will provide an additional fundamental gain offset for all overtones, and then the roll-off takes care of the rest. This is fairly feasable to do for a fixed frequency thing like the organ/tone-wheel thing.
> 

Can you describe this a little more? Is it as simple and space-effective as the transistor one?





> Cheers,
> Magnus
> 
>> Cheers,
>> 
>> Andy
>> 
>> 
>>> 
>>> 
>>>> On 04/05/2017 04:41 AM, Andrew Simper wrote:
>>>> 
>>>> One way to avoid some of the volume drop is to use a 2 pole sallen key
>>>> BJT filter with a cascaded passive stage. This is a common circuit
>>>> used around BBD chips, eg:
>>>> 
>>>> http://www.hobby-hour.com/electronics/s/schematics/boss-ce2-chorus-schematic.gif
>>>> 
>>>> Andy
>>>> 
>>>>> On 4 April 2017 at 19:50, Elaine Klopke <functionofform at gmail.com> wrote:
>>>>> 
>>>>> Thanks for the info Tom!
>>>>> 
>>>>> Magnus, the sources are fixed square waves coming from a set of PIC chips. So the fixed filtering doesn't bother me a bit. One filter for one frequency. What worries me is the volume drop.
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