Digital Pot for Audio, any clicks heard?

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MrAl
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Digital Pot for Audio, any clicks heard?

Post by MrAl » Fri Apr 10, 2009 5:44 am

Hi,

Anyone here ever use a digital pot for low level audio (before amp) or medium level audio
(after maybe the first amp stage)?
What i was wondering is if you can hear any of the clocking signals going to the digital
pot in the final audio output. The pot will most likely be updated every 250ms or
maybe even faster, so the clock signals will always be present.
Output filter could be used, but it has to pass up to 20kHz so it might not do
much for the clock signals.
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haklesup
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Re: Digital Pot for Audio, any clicks heard?

Post by haklesup » Fri Apr 10, 2009 11:41 am

Properly designed and decoupled, the noise shouldn't go through the chip but it could couple in from PCB traces and cabling if you're not careful.

Rather than scaling the audio signal with the pot. Try a design where the pot divides a reference voltage used to set the gain of the output stage.

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MrAl
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Re: Digital Pot for Audio, any clicks heard?

Post by MrAl » Sat Apr 11, 2009 5:34 am

Hi hackle,


Well, i was hoping to use the digital pot as the gain control, which means i wouldnt need
a special gain controlled amplifier.
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languer
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Re: Digital Pot for Audio, any clicks heard?

Post by languer » Sat Apr 11, 2009 8:00 am

What you describe should work ok.

Make sure you have good filtering on the supply lines of the digital pot and the amplifier in use. Keeping the digital lines away from power supply lines and the analog lines should do the trick. This is not much different than using a DAC.

You do mention 250msec, this I would presume is the update rate (or frame sync); but the actual clock frequency should be much higher than this. Normally the clock frequency would be much higher. This is for a serial digital pot (i.e. SPI or I2C).

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MrAl
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Re: Digital Pot for Audio, any clicks heard?

Post by MrAl » Sun Apr 12, 2009 1:45 pm

Hello again,

Sounds good to me. My main intention was to build a decent audio compressor using a digital pot
for the gain control. The uC would sample the audio and set the pot accordingly.
The uC and pot would be two chips, plus maybe an amplifier chip later.
With TV commercials getting louder and louder something has to be done.


Think i should give it a go, or look for a more conventional compressor chip or something
even different than that?
LEDs vs Bulbs, LEDs are winning.

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