Vancouver Reefer: First off that is only a first order filter, if you are using an op amp you can implement a second order filter. The way you tell is that a second order filter has frequency dependent components (capacitors) in the feedback loop.

The filter rolls of at 3dB per octave, per order, so a second order filter rolls off twice as fast as a first order one. You can get a second order with each op amp, so with three op amps you can have a 6th order filter. That rolls off at 18dB per octave. An octave by the way is a doubling of frequency.

Second that 8K in the feedback loop isn't doing anything it might as well not be there (replace by a short).

darudude:- Thanks for the complement flattery will get you everywhere.

I have considered the PWM tutorial although I have some real projects on at the moment. (Latest in the Exhibition area today)

I would set the 3dB frequency at the maximum frequency you want to change the DC output. Then the PWM will be attenuated the maximum it can afford to be with the attenuation dependent on the filter order.

Filter gain and attenuation are essentially separate quantities. If you are designing an active filter ou can have what ever gain you design into it.