[sdiy] Simple LPF Schematic ?

[John Mahoney]

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.
--
john