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Regarding volume gain circuit

  1. Jun 16, 2017 #1
    The above is a circuit i found on the net regarding amplification of volume.
    I needed to know if increasing the potentiometer resistance (between "cold" and "wiper"; terminal 1 and 2?) in the circuit would increase "volume"
    Also, i could use a potentiometer resistance ( between "cold" and "wiper" ) to volume equation of the above circuit, given that the equation should consist of C1 (= C2) and R1 (= R2)...
    Also would having multiple 9V batteries in series make the sound louder?
    I'm just troubles with this circuit lately partly because i don't know much about electronics ( maybe im even wrong in using some of the words the way i used above ) but... i hope to figure the questions out!
  2. jcsd
  3. Jun 16, 2017 #2


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    To see which direction increases the gain, just use the equation for the gain of a non-inverting opamp, and think about how the voltage divider changes at the inverting input as the wiper moves. :smile:

    BTW, that circuit has a fundamental problem, and you should not use it, IMO. Potentiometers need to have a minimum wiper current to keep the wiper contact from developing problems over time. Having the wiper go straight into only the input of an opamp is a fundamental circuit design error.
  4. Jun 16, 2017 #3


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    Likith D, I think your arrangement is not going to work as you hope. Varying the pot changes the DC gain here, but you really need the output DC level to stay fixed at ½Vcc to accommodate the output AC swings.

    I think you need a separate feedback network for DC, and use capacitor isolation so the pot is giving variations to feedback only at AC.

    Increasing the voltage powering the op-amp will allow greater output, but you must stay within the manufacturer's voltage (and power) ratings for this particular IC, otherwise it may be destroyed.
  5. Jun 16, 2017 #4


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    It is not a good idea to have that pot configured in the manner it is. With the wiper all the way in one direction there will be a gain of 1, which is fine. However, in the other direction the gain goes to open loop, or infinity if you prefer to think in that manner. This of course is separate from the issues previously posted in this thread.
  6. Jun 16, 2017 #5
    What is the op amp part number?
    Few op amps have the ability to drive a speaker very loudly.
  7. Jun 17, 2017 #6

    jim hardy

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  8. Jun 17, 2017 #7


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    Likith D shows an amplifier that drives a speaker.
    That suggests the common or garden LM386.
  9. Jun 17, 2017 #8

    jim hardy

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    What a GREAT little amplifier !
    Its inputs are ground referenced so there's no need for that "Virtual Ground" R1-R2.

    For a typical 8 0r 16 ohm speaker Likith's C2 needs to be a LOT bigger.
    Last edited: Jun 18, 2017
  10. Jun 17, 2017 #9


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    @Likith D
    as a number have stated, this is not the way to go

    initially .....

    1) you have given no part number or pin numbering --- so we don't even know if you are dealing with an op-amp or an actual audio amplifier ?
    2) if it is an op-amp, forget it and have a close look at the PDF that @jim hardy provided in post #8 ( the one before this post)
    it will get you out of trouble and have a good little amp working for you
    3) Figure 10 in the datasheet Jim provided shows how to connect a volume control

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