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digital pot rather than analog pot

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Hi,

I would like to use a digital pot in place of the analog pot in this circuit. However, it does not work properly. There are some very tiny sound fluctuations but that is all. I wonder what needs to be done, or why its not working as expected, or how I can work out what the problem is.

thanks
 

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Hi,

we can´t see the digital pot in your circuit.

--> show your exact circuit with all electrical connections - especially of the EPOT.

Klaus
 

Not sure what you mean with "tiny sound fluctuations"? An effectively useless description.

You missed however to tell the used digipot type and how it's connected in the circuit.

Just in case, notice that the analog potentiometer is exposed to an AC voltage, to avoid distortions, a digipot in this place would need a dual power supply. Or be connected slightly different, with DC bias and capacitor at the pot ground node.

Or does "fluctuations" refer to crosstalk of the digital control signal? This can easily happen.
 

FvM said:
Not sure what you mean with "tiny sound fluctuations"? An effectively useless description.

You missed however to tell the used digipot type and how it's connected in the circuit.

Just in case, notice that the analog potentiometer is exposed to an AC voltage, to avoid distortions, a digipot in this place would need a dual power supply. Or be connected slightly different, with DC bias and capacitor at the pot ground node.

Or does "fluctuations" refer to crosstalk of the digital control signal? This can easily happen.
Click to expand...

Tiny fluctuations refers to tiny bandwidth filter changes, just as you would expect with a wah wah circuit, but very tiny. The digital pot replaces the 100k analog pot in the circuit.

The digital pot simply has a two potentiometer ends and a wiper.

can you explain how it would be connected differently. thanks
 

Hi,

The digital pot simply has a two potentiometer ends and a wiper.
Click to expand...
This means your digital pot has no power supply connections and no control pins. --> I´ve never seen such a thing.

Klaus
 

the micro and dig pot are running on 5 volts. a separate supply, but with the same ground as the analog circuit.
 

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Your problem is that the audio signal fed to the digipot is not biased at Vdd/2 to allow the positive and negative excursions that an audio signal has.

Download the datasheet, and look for Figure 2-64.
 

Connect P0A to a virtual ground node, a sufficient large capacitor to ground (e.g. 1 µF) and a voltage divider generating Vdd/2.

It's not obvious to me, if clipping of AC voltage can produce "tiny bandwidth filter changes", but may be it does. You'll know after testing a correct digipot bias.
 

thanks. what is a "virtual ground node". I have googled it, but don't understand what is required. How is that done?
 

A virtual ground circuit is completely described in the previous post.
 

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