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Aux_ADC and Single Slew Ext Vol introduces noise.

Question asked by alex12345 on Jul 28, 2017
Latest reply on Jul 29, 2017 by KJBob

I've been getting noise (hiss) in my project when (and only when) a test signal is applied. I've tracked the problem down to the single slew external volume control, more specifically when it is controled by an aux_ADC.

 

If it is controlled by a DC source, it is fine. If I change the slew rate from (the preferred) 3 up to 10, the noise is gone, but leaves a laggy feeling control which I'd like to avoid if possible.

 

I assume the problem is noise? With that in mind, if I low pass filter (2nd order, 10hz) the aux_ADC before it reaches the volume control the noise is gone, however this introduces a stuttering effect if the pot is moved quickly. Raising the filter reduces the stuttering but also reduces its effectiveness at stopping the noise. The ADC filter modes in DSP register modes 2 seem to make no difference at all.

 

I guess a cap at the ADC input is the ideal solution but that's easier said than done, I'm ideally looking for a software solution that doesn't cause the control to slow down, if possible.

 

Thanking you,

 

Alex.

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