stereo power amplifier

Discussion in 'The Projects Forum' started by devgorkha, May 2, 2011.

  1. devgorkha

    Thread Starter New Member

    May 17, 2010
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    I start new project name as "digital display sterio woofer". we can supply a signal from audio source and from MIC too. we add equalizer for each signal and mix signal of sterio(audio and mic input). so that it become complicated.i use bjt as preamp of mic and to mix signal i use buffer using op amp741,equalizer also using opamp 741. this circuit work properly but problem is in power amp, i use sterio ic 2822 as power amp i also work in audio input but it makes very noisy sound when its connected to MIC input. i thing mic peak noise or problem in power amp part so pls .... suggest me where i have to change ???

    one confusion !!! can we drive sterio ic as mono mode by using single switch?? but loudness of speaker must not change.
     
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    If you post a schematic you may get some comments from people who know more about this sort of thing.

    For a start though, I would say that a 741 was a poor choice far any audio project, apart from anything else it cannot cope with higher audio frequencies. Is this project really a woofer, concerned only with bass frequencies?
     
  3. devgorkha

    Thread Starter New Member

    May 17, 2010
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    thank for ur suggestion.... as far as i know LM 741 has frequency limitation is 100kHz which is out of audio range. without any slew rate limitation we can achieve gain with in audible range but i don't know about noise factor.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    We might suggest you compare the data sheet of a 741 with that of an OPA134. You really would be wise to use a more modern op amp.
     
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  5. devgorkha

    Thread Starter New Member

    May 17, 2010
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    i attach block diagram of my project, this is my own block diagram.... it is not perfect .
    pls... suggest me how can i make it better.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    The datasheet for the LM741 shows that its poor slew rate limits its full output frequencies to only 9kHz. Most audio opamps go easily to 100kHz.

    The LM741 opamp is 43 years old and was designed to use only a plus and minus 15V supply. Some do not work from a 10V supply. It is very noisy (hiss).

    Please describe the noise that you hear. Is it hiss? Hum because the mics do not have shielded audio cables? Acousical feedback howling because the mic can hear the speaker?

    Do you have earphones or loudspeakers?

    Your block diagram is missing a stereo volume control at the input of the TDA2822 IC. Is it a TDA2822M IC instead?

    The word for two sound sources is STEREO, not sterio.
     
  7. devgorkha

    Thread Starter New Member

    May 17, 2010
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    thanks guru
    yes it is hiss. i think it may not be the hum and acoustical feedback. actually i want to construct it in such a way that it is connected to loudspeaker when we plug in earphone jack, speaker turn off.

    it is better idea if i start to discuss each part of my circuit.
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    If the TDA2822 power amplifier has a stereo volume control at its input then you can turn it down to see if the hiss comes from the preamp or from the power amp.

    The LM741 has a lot of hiss and should never be used for a mic preamp. Use a more modern and low noise opamp instead.

    Why don't you post the schematic so we can see if something is wrong?
     
  9. devgorkha

    Thread Starter New Member

    May 17, 2010
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    this is my equalizer part
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    Your equalizer is the same as this circuit except you use a lousy old 741 opamp.
    R11 and C5 should be removed (they add hiss).
     
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  11. devgorkha

    Thread Starter New Member

    May 17, 2010
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    thank guru ...
    this equalizer circuit is very good in simulation . i connect this circuit on coming Sunday in hardware. Could you tell me that what is frequency range for bass,mid and treble ?
    I attach my preamp part of mic which is not very sensitive. how can i make it more sensitive?

    dev
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    I guess that the equalizer has 50Hz to 500hz for bass, 500Hz to 4kHz for mids and 4kHz to 20kHz for highs. It is really a simple tone controls circuit (not an equalizer) that has gradual slopes for the filters.

    Your simple mic preamp is a transistor with a lot of negative feedback, a fairly low input inpedance that loads down the signal from the mic and a fairly high output impedance that is loaded down by the equalizer.
    If an audio opamp is used instead then it can have a fairly high input impedance that does not load down the mic and a very low output impedance that is not loaded down by the equalizer. It can easily have as much gain as you need.

    Your simulation of the equalizer shows the pots set to 100% which is maximum boost of about 6 times. Normally all pots are not set for maximum boost. Maybe one or two pots are set for boost or cut.
     
  13. devgorkha

    Thread Starter New Member

    May 17, 2010
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    guru... i want mix left and right audio signal to make mono and also mix with vocal sound coming from mic. So i made a circuit using bjt and op-amp (mixture- buffer) which one is better ?
    ( I had already posted my block diagram) Guru.. i made control switch that control each output ( only mono output of mix R & L from audio source, only MIC output & both music with vocal) I will post diagram .. suggest me.
     
  14. Audioguru

    New Member

    Dec 20, 2007
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    The opamp is a perfect mixer.
    But your transistor is biased wrong so it is almost cutoff. A very small signal level will cause its collector to smash into the +15V supply voltage with severe clipping distortion.
     
  15. devgorkha

    Thread Starter New Member

    May 17, 2010
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    (i made mistake in transister circuit.)
    Can i connect like in this diagram?

    thank audio-guru ... i design all part except stereo power amp. First i select TDA 2004 as stereo power amp. but its volume is very loud even in on input. and i decided to use TDA 2822 but its volume is low . It (TDA 2822) heated in max volume.
    :rolleyes: what happen when i connect mono signal in both i/p of stereo ?
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    All stereos have a volume control. Yours does not have a volume control.

    You did not say what is the impedance of your speakers. You also did not say what is the supply voltage. Then we cannot calculate the output power at clipping.

    Did you try a big TDA2822 or a little TDA2822M amplifier IC? What were the speaker imedances? What supply voltage?

    Why do you show a 47k balance control? Instead use two 22k resistors to make a simple stero to mono mixer.
     
  17. devgorkha

    Thread Starter New Member

    May 17, 2010
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    i used stereo pot as volume control (i.e. 22K)
    My speaker impedance is 5 ohm D0305 (D0305 - but i don't know the meaning of this number ) It has - / + indicated terminal.
    I thing my power supply may be the problem. i made 12V-0-12V power supply.(my transformer max. current limitation is 1 amp). when i use TDA 2004 my power supply heated as i increase volume and its sound is distorted. my circuit diagram is attached.

    Then I use TDA 2822 M. i use 9v and 8 ohm 1 W general speaker( one of them is damaged).

    i used 47k pot for balance control but it output is not satisfactory event in 22K and 10k because audio mix mono out put is hight then mic input so i boost up mic input and use 22k pot it is working.
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    12V-0-12V is an AC transformer, not a DC power supply. If you connected the 0V tap to the amplifier ground and used two rectifier diodes feeding a high value filter capacitor then the resulting DC power supply will be +16VDC at 0.71A. the transformer is rated at 12V x 1A= 12W. The 17V peak voltage of the transformer x 0.71A= 12W.

    With a 5 ohm load and a 16.0VDC supply, a TDA2004 amplifier IC produces about 4.6W at clipping and heats with about 3.0W. Then two channels use a total of 15.2W from the power supply so your power supply is overloaded if the music is blasting all the time.
    It is normal for an amplifier to produce severe clipping distortion if the volume is turned up higher than clipping.

    I do not understand your broken English.
     
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