IC TDA7294 audio amplifier problem

Discussion in 'General Electronics Chat' started by Linus, Apr 21, 2009.

  1. Linus

    Thread Starter New Member

    Apr 21, 2009
    4
    0
    Hi!

    got a problem with a amplifier I built.

    the amplifier is the kit from kitsrus nr 106 :http://kitsrus.com/pdf/k106.pdf consisting mainly of the IC: tda 7294


    I get sound out of the circuit. BUT after a short while the sound deteriorate and gets very poor and distorted. if I disconnect the power and immediately connect again the sound gets clear but again distorted after a short while.

    if I turn up the volume on the input pins it also clears for a short while. why?

    anyone got any clues what this might depend on?

    I power it from 3st 12v batteries because its used in a portable soundsystem. I use the 2 pins called +34v and -34v but leaves out the middle 0v. I gues 0v is used for some kind of stabilising if using unfiltered DC current?

    Would be great with some support! my knowleadge of audio amplifiers are very limited.

    thanks! //L
     
  2. bertus

    Administrator

    Apr 5, 2008
    17,843
    3,316
    Hello,

    The circuit needs the 0 Volt connected to the powersupply.
    If this is not done the 0 Volts connection will "float" to an unwanted value.
    (you noticed the distortion).
    You could use 4 X 12 Volts batteries in series, the middle point connected to 0 Volts.
    (So 2 batteries for V+ and 2 batteries for V-).

    Greetings,
    Bertus
     
  3. Linus

    Thread Starter New Member

    Apr 21, 2009
    4
    0
    Thanks for the advice!

    what puzzles me is that when I connected 2st 21,6v batterypacks that way the ic exploded. it might be because of some earlier error with the power, but I dont know what reasons there could be for the IC to explode?

    but great to know that the symptom of deteriorating sound comes from undefined ground!

    any further ideas what could have caused the IC to explode is very welcome.


     
  4. bertus

    Administrator

    Apr 5, 2008
    17,843
    3,316
    Hello,

    Did you use a cooling frame like in the PDF ? (It says it has to be bought seperately).
    Without the cooling frame the IC will get hot very soon and can explode.

    Greetings,
    Bertus
     
  5. Linus

    Thread Starter New Member

    Apr 21, 2009
    4
    0
    hi!

    yes i used a cooling frame, but the IC also got heat protection cut off.

    the IC immediately exploded when I connected the batteries so I dont think thats the problem.

    I just noticed that the copper to pin 8 has burnt of maybe that happend before when I shorted it and then when I connected the batteries in suggested way without contact to pin 8 it shorted it self out...

    so my next step should be to repair the pcb and try the same setup with batteries.

    is it possible to use another source as defining voltage at connector marked 0v? if I like to use 3 12v batteries and therefore dont have any centerpoint in the batterypack?
     
  6. bertus

    Administrator

    Apr 5, 2008
    17,843
    3,316
    Hello,

    In the datasheet it is said the IC works from ± 12Volts to ± 45 Volts.
    See attached datasheet for more details.
    At ± 12 Volts the power will be much lower.

    Greetings,
    Bertus
     
  7. Linus

    Thread Starter New Member

    Apr 21, 2009
    4
    0
    thanks!

    waiting for my new IC now.
     
  8. aravindlm386

    New Member

    Mar 17, 2018
    1
    0
    hello sir.how to check weather my ic tda7294 works or not by using simple me
    thods??pls reply sir!!
     
  9. nigelwright7557

    Distinguished Member

    May 10, 2008
    519
    73
    I built up a similar circuit and it oscillated badly.
    Turned out there were 2 problems.
    1/ Feedback resistor needs a very short path as tracks have inductance and cause instability.
    2/ I had just used a gain of 10 and the amp needs at least a gain of 22 to be stable.

    It must have a good sized heat sink on the amp.
    Also it needs 3 power rails, +,- and zero volts or it will probably die.
     
  10. Audioguru

    Expert

    Dec 20, 2007
    10,002
    1,073
    How can you get +36V and -36V from only three 12V batteries??
    You can use three 12V batteries to make +36V and use another three 12V batteries to make the -36V. Then you need six 12V batteries with 0V at the middle of them.
     
  11. MisterBill2

    Active Member

    Jan 23, 2018
    503
    77
    Exploding ICs are almost always the result of far too much current which is often caused by a reversed polarity connection. With many of these audio amplifiers there may also be a condition of oscillation at some much higher frequency, even in the megahertz range, if there is inadequate bypass capacitance or a poor bypass connection.. Read the manufacturer's application notes on the device for an additional explanation of what I am telling you. The application notes can be very useful.
     
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