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help me with this computation


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Hi Nolram,
Welcome to our forum. ;D
We have two Digital Volume Control projects. Which one are you talking about?

The 1st one doesn't have a debounce circuit for the pushbuttons so the volume would switch thru many steps each time a button was pushed. It also seems to have the resistors in the wrong places. The volume steps are affected very much by the input impedance of what it drives.

The 2nd needs the audio to be DC-biased which isn't shown. It has linear steps which are crammed together and hardly noticed near max volume and huge steps in volume near minimum volume. In the middle of its 64 steps the volume is reduced only a little.

Maxim and I think Texas Instruments make modern volume control ICs that don't have the problems of these projects. Some of them are stereo.

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Hi Staigen,
People who post fuzzy Jpeg schematics should be shot! >:(
1) The output of the 555 is missing a wire at the left side of the schematic connecting it to the "up and down" buttons.
2) Yes, the ladder is backwards.
3) Maybe the author had a spare 74193 and wanted to heat his home with its massive power requirement. Sure a Cmos one would be fine but probably wasn't invented then.

I didn't look at the fuzzy pic anymore because it was making me blind. It seems to be a very old circuit, since digital pots ICs are common today, even stereo ones with memories. ;D

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