[sdiy] Square to Sine

[Andrew Simper]

On 5 April 2017 at 13:46, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>
> The backside of that would be that the 2 pole gives only 12 dB/oct compared to the 3 pole giving 18 dB/oct, thus giving less suppression of the square overtones. Their roll off would be 18 dB/Oct vs 24 dB/Oct from the filters. You would have to add a passive RC-link to achieve the same performance.
>
> The simplicity of the RC link setup is good starting point from a learning perspective.
>
> Cheers,
> Magnus
>

The original passive 3 pole filter was drooping a bit much for Elaine,
I was just proposing a very simple way of swapping in a BJT sallen key
section cascaded with a passive low pass to keep the signal level a
bit higher while still delivering the same 3 poles of filtering. I'm
not following what you're talking about with the 12 dB/oct vs 18
dB/oct vs 24 dB/oct, can you please let me know where the fewer / more
poles are coming from?

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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