help me with this computation

[nolram]

Good day! I am having a hard time computing the gain of the resistor-switch network of a digital volume control published in electronics-lab.com. The author is unknown. Can anyone shed light on this?

 

[Alun]

Plkease provide more information, like a link to the area of our site, finally it's highly unlikely that anyone will email you with your request.

 

[audioguru2]

Hi Nolram,
Welcome to our forum. ;D
We have two Digital Volume Control projects. Which one are you talking about?
http://www.electronics-lab.com/projects/audio/010/index.html
http://www.electronics-lab.com/projects/audio/033/index.html

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.

 

[nolram]

Good day! Ok. The one that employs cd4066. God bless! ;D

 

[Staigen1]

Hey Audioguru, take a look at the first one you linked to, what is the 555 doing there? Also look at the resistor divider, isnt that one backwards? And, why 74193? A 40193 is the same, and cmos! There are many moore errors there!

/Staigen

 

[audioguru2]

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

 

[nolram]

can anyone provide me with a schematic diagram of an automatic gain control circuit. thanks... ;D

 

[audioguru2]

Hi Nolram,
I'm glad you abandoned the obsolete project that is wired wrong.

A very good Fast Audio Peak Limiter project is here: http://www.sound.westhost.com/project67.htm

View attachment 37913

 

[V8meathead]

haha audioguru your second to last post cracked me up!

 

[nolram]

thank you audioguru, u r such a great help. ;D

 

[nolram]

thanks for all of you guys who posted ur opinions concerning my problem. Can i ask another favor? Please provide me some links to pages where i can get mcu-based automatic gain control. This will be a very great help on my project. Thanks. God bless.

 

[audioguru2]

Maxim and TI make volume control ICs that use MCU control. Then you'll need to make your own A to D converter for the MCU to sense the levels.

 

[nolram]

ok audioguru. thanks a lot.