Controlling volume of an amplifier..

[joseph Degorio]

Hi PICspert!
I'm new to electronics and programming, please guide me where to start on how to control the volume of an amplifier. The amplifier has volume knob already but I want to create two button switch that will increase and decrease the volume.

Thanks in advance,
joe

[T.Jackson]

That's an interesting question -- I have thought about this in the past...

Two orthodox solutions;

1. Discrete IC (yes they do exist)
2. Chain of switchable attenuation resistors

With the resistors, ideally you'll need to formulate something that translates into db. Better still; have the LCD or LED displays show the attenuation level in db. At the end of the day, a lot digital circuits that control audio attenuation induce two undesirable effects into the signal...

1. Harmonic distortion
2. Crossover distortion (bad channel separation)

For superior audio quality; hard-to-beat the good'ol humble POT. Watch out for bandwidth too. I think some of these circuits make an otherwise excellent preamplifier mediocre.

[Jerson]

Two things you can look into

Digital potentiometer (you may find some with pushbutton inputs)
Multiplying DAC (a little more intricate)

[T.Jackson]

http://www.analog.com/en/prod/0,,761...5228%2C00.html
looks interesting. Wonder though how it would effect the .002% harmonic distortion figure on my amplifier. Some DVD players have a distortion figure as much .05% (not necessarily the cheaper ones either)

see; http://siliconchip.com.au/cms/A_109464/article.html

[Melanie]

If it's Lo-Fi, then some Digital Circuitry can be added - there's plenty out there to chose from.

If it's Hi-Fi, then Digital and semiconductors should be avoided due to inherent junction noise. Then do what everyone else does... nail a gear-wheel to the shaft of your Pot and bolt-on a motor.

This isn't exactly rocket science. Until earlier this year, when I just couldn't be bothered wiping fingerprints off black facias anymore, I had a Pioneer Hi-Fi which I bought when I was a teenager that did exactly that... and guess what... the shiny silver TEAK with en-suite DAB and USB port that replaced it, does exactly the same.

But I remember an old uncle that had a Rigonda (USSR) Gramophone from the 1950's/60's (600 layers of laquer producing mirror-finish wood) that ran on valves, steam and things that got hot. Now this had been manufactured at least 20 years before I ever set foot on this planet with not only motorised volume but also motorised tuning as well. As a kid I'd press the AGC button and watch the dial rotate tune into the nearest FM station all on it's own... spooky stuff... Kinda like Captain Scarlets Mysterons...

[mister_e]

All good points Melanie, in some previous project i used those ALPS motorized pot.
http://www3.alps.co.jp/WebObjects/ca.../RMP_RK271.PDF

[loosha]

Hi joe.
You can solve the problem just using a single chip.Just use PT2253B.

Thanks
LOOSHA