single control, two output op amp design

Discussion in 'The Projects Forum' started by jameslee, Sep 9, 2010.

  1. jameslee

    Thread Starter New Member

    Sep 8, 2010
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    :) hello everyone, i'm new here, i was trying to google for reference and i found this site.

    I was looking for a op amp design such that two op amp gain can be control by a single potentiometer, however the op amp must be able to receive and amplify their own signal independently.

    I'm looking for this design because i wish to control the gain of my stereo speaker, now im stuck because i dont wish to use two potentiometer to control two separate op amp,because this leads to unbalance volume between left and right speaker. I know there are sophisticated IC such as TDA8424 that capable of doing this, but i just wish to implement a very simple volume control using potentiometer instead of a audio IC+microcontroller to achieve this goal.

    Had anyone came across such design before? would you share the design?
    thanks in advance for all your help.

    James
     
  2. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010
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    34
    Have a look at transductance opamps.
    Most of those have two methods of contolling gain ....
    Front end equilisation diode current and a programming voltage that directly relates to the current gain of the transductance output.
    I think that right anyway ... I will look up a spec sheet for you.
    What I do remember is that both inputs represent an attenuation of the gain which govened by a conventional feedback arrangement .....

    I'l get back to you when I find the sheet
    Al
     
  3. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010
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  4. jameslee

    Thread Starter New Member

    Sep 8, 2010
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    hi Dyslexicbloke,

    i having lots of op amp such as u741 and MCP6044, so im thinking whether i can make use of them to build a single control dual output buffer amp instead of buying an additional component like the IC you suggested,
     
  5. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Would a dual potentiometer do the job?
     
  6. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010
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    windoze killa is obviously right on the money, you need a pair of variable resistors working together.
    I assumed a pot wasnt the solution you wanted based on your initial post, I probably should have asked.

    I dont know much about audio circuits I just remembered the example 'vertual pot' circuit in the spec sheet from the last time I used one.

    I could postulate for hours on possible methods to attenuate an AC signal but I wouldnt have a clue what sort of abberations they would impart to the sound.

    Can't offer anything else sorry, i'l be interested to know the answer though.
    -----------------------------------------------
    Would shifting the signal so it is DC biased, attenuating it with partially on FET's and then re applying AC coupling work?
    Do FETS make noise?
    --- Just asking not offering this as a solution ---
    Al
     
  7. jameslee

    Thread Starter New Member

    Sep 8, 2010
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    yes indeed, a dual potentiometer can achieve this, i didnt knew there is dual potentiometer, now that i can control the gain of two op amp simutaneously, then i can control the volume in a single knob, indeed a low cost solution, i try that out.thanks man
     
  8. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Yes. Thats the idea of a dual pot. they are ganged together on the one shaft so one knob will rotate both.

    Having said that You could also use a single pot to control the gain of 2 amps. I will try and do a circuit over the weekend.
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Why not just use those dedicated DC controlled volume control ICs? They're made by several manufacturers and vary their gain by a DC input voltage that could be fed to more than one. For all I know they're made in stereo now as well.
     
  10. jameslee

    Thread Starter New Member

    Sep 8, 2010
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    it work!!! dual potentiometer works, now i can control two channel volume simutaneously.

    cost me $1 to achieve this,indeed a low cost solution. But no bass & treble control. i look into the datasheet of audio processing IC, many of them can control bass, maybe i should give a try, let me study a bit of these IC.
     
  11. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Well done. There is always a simple answer for most problems. Just have to work out what the real problem is in the first place.
     
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