[sdiy] Simple LPF Schematic ?

[Tom Wiltshire]

On 19 Jan 2007, at 23:44, John Mahoney wrote:

> At 06:01 PM 1/19/2007, sven deejay wrote:
>> Hallo
>>
>> Im buiding a whitenoise generator and need a simple
>> filter to roll off some high frequencies ,
>> just one knob and no cv control is needed, any
>> suggestions ?
>>
>> DJS
>
> See "Simple lowpass" here, it's the old RC passive filter:
> http://www.doepfer.de/DIY/a100_diy.htm
> You can do more than one (in series) if you need greater slope, but 
> that is impractical beyond 2-in-a-row using a dual ganged pot.
>
> Google for "low pass active filter" (without quotes) and you'll find 
> plenty, such as here:
> http://www.discovercircuits.com/PDF-FILES/LowPassFilt1.pdf
> There are one or 2 op amps in these circuits, you can use just about 
> anything; TL071 and TL072 are typical SDIY op amps.
>
> Change all the filter cap values to change the cutoff frequency; 
> doubling the values lowers the cutoff by an octave.


I'd just like to add:

http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm

The 2nd Order Op-amp filters would be good. Replace Rs with a dual-gang 
pot, as John suggested.

T.