Controlling volume of an amplifier..


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  1. #1
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    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.

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    Two things you can look into

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

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    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
    Last edited by T.Jackson; - 14th December 2007 at 11:32.

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    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...

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

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    There's no problem, only learning opportunities.

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    well yes and no, but yeah they're good for most case.

    VCA such as SSM2164 produce better results.. well for much sensitive ears...
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.

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    They're very good figures for thd (total harmonic distortion) Willing to bet that PCB layout would play a key role in obtaining them though.

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