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

    Active Member

    Sep 4, 2010
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    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

    Active 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

    Active 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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