Audio opamp question

Discussion in 'General Electronics Chat' started by stoppage, Aug 29, 2013.

  1. stoppage

    Thread Starter New Member

    Aug 29, 2013
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    P { margin-bottom: 0.08in; } I'm looking for a tone control circuit based on the LM324 chip or at least on an op-amp that uses single-supply +15V., no negative rail, no „virtual earth“. Ive found plenty online using dual-supply rails, I want one that operates on +15V., 0Volt earth.
    Also a question on the circuit in Attach.....does this circuit in itself attenuate the signal (i.e. op amp has no gain)?
    If anybody can help here, much obliged, if not, don't suggest a Google search
     
  2. wayneh

    Expert

    Sep 9, 2010
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    That circuit should solve your single supply needs.

    Can't help you with your gain question.
     
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  3. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Did you ever turn the BASS and TREBLE controls on your radio? What did that aural test equipment, your ears, tell you about the signal?

    The posting sounds like a homework problem. That tone control is called a baxandall tone control.

    What is the source of that circuit?
     
    Last edited: Aug 30, 2013
  4. #12

    Expert

    Nov 30, 2010
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    I would like to point out a different way to label the voltage supplies. You seem adamant about not using a virtual ground, but audio signals are always changing their voltage direction and you just can't get an op-amp to work without a reference point between its two supply terminals.

    This one will still work with its labels changed (as well as a 741 op-amp can work) but the idea of a "split" supply is inescapable in one form or another.

    As for gain, tone circuits always cause a loss of voltage and the op-amp is referred to as a tone recovery amp in this case. It doesn't recover tone, it recovers the original amplitude if it's designed correctly. Problem with me is that I can't tell if this one winds up with about the same amplitude of output as its input when the controls are set to mid-range. I will bet it has a loss if you turn both the controls down as far as they will go.
     
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  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Here's an image from ESP on the baxandall tone control. The gain of the OP's circuit is different .... however, at mid-point the gain is 0 dB.

    [​IMG]
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    If you are going to use an LM324 for audio signal processing you will need to stick needles in your ears to make sure your hearing is ruined because the LM324 is not an audio grade device.
     
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  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    +1 Just set up some kind of midpoint, even if it's just a Zener diode that isn't important. Capacitor couple the stages. A TL071 is a good choice.
     
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  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    The circuit has a "virtual ground" because the + input is tied at 1/2V through a resistive divider. The input is capacitor coupled so it should work. Using a 741 indicates the designer knows nothing about audio or the circuit is about 40 years old.
     
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  9. stoppage

    Thread Starter New Member

    Aug 29, 2013
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    I'm not building a radio.
    Source of the circuit....http://www.edutek.ltd.uk/Circuit_Pages/OpAmp_ToneControl.html

    Looks like I'll be going for a split-supply after all. Gulp!
     
  10. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    No, but the tone control works the same as you are working with an audio amplifier.

    You should know the gain/loss question by drawing on your previous experience of twisting the bass and treble controls on a radio. A radio is probably your first experience with a bass and treble controls.

    Other than the 741, the single supply circuit works fine. The 741's performance specifications included split supplies.

    What OpAmp do you intend to use?
     
    Last edited: Aug 30, 2013
  11. stoppage

    Thread Starter New Member

    Aug 29, 2013
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    I've decided on TL072
     
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I see you decided to go with ESP's baxandall circuit.
     
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