Switched Cap Filter noise problem

[Longfuse]

Can anyone give me some tips on how to tame the noise in a MF10 switched cap filter? The background noise sounds like a TV/Radio that hasn’t been tuned into a station!


I’m using both halves as notch filters in a phaser circuit (modified Penfold circuit, though the original was just as noisy). The clock is a 4046 VCO operating above 20 kHz, which in turn is controlled by a LFO (1 - 12 Hz). It’s operating from a ultra quiet mains supply and I’ve even added additional RC filtering on the bias network/power connections in case the noise was feedback on the rails. There’s also a simple RC filter on the input AND output to cut high end noise but it doesn’t do much. If I disconnect the clock inputs it’s quiet, but with them connected there’s really loud background noise. Speeding the clock up doesn’t help either.

It's on a breadboard but I've paid attention to layout. I’m stumped, ideas anyone? Are they usually this noisy?!

 

[metal]

Hello

Have you tried to change the IC itself.

Another thing, try to change the values of decoupling capacitors. If it baecomes harder, try to separate the supplies of the oscillator, and the filter it self.

Regards

 

[metal]

Hello

If kkoko, take a look at the datasheet again olz, you will see that the cut-off frequency deoends on the clock mainly, so changing the clock frequency will change the cut-off frequency.

Regards[/img]