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Thread: Op amp myths and........

  1. #11
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    laatsch55's Avatar
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    Halfbiass...Electron Herder and Backass Woof
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  2. #12
    Forum Veteran Netfly's Avatar
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    Thanks Gepetto. Guess that cross reference was not a direct replacement.

  3. #13
    Administrator Gepetto's Avatar
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    Quote Originally Posted by laatsch55 View Post
    Wondered when you were gonna show up ...
    Sure Lee.

    Besides the competing brand differences, there are so many op amps because there are so many differing applications. There is no perfect op amp (although that ideal is being approached more and more). Since there is no perfect op amp, manufacurers optimize one or several functional parameters in each op amp type to suit a particular application. Those could be low power, low offset voltage, low bias current, rail to rail input, rail to rail output, low power supply voltage, single power rail voltage, low noise, high open loop gain, gain-bandwidth product, slew rate, output drive capability, unity gain stability and so on. You either pick the op amp type to suit the current circuit design topology or design the circuit around a particular op amp.

    The NE5533/34 for example cannot be used in applications with a closed loop gain less than three so cannot be used in a unity gain buffer application. The OPA2134 can be as can many other op amp types.

    Choice is good.

  4. #14
    Administrator Gepetto's Avatar
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    Quote Originally Posted by Netfly View Post
    Thanks Gepetto. Guess that cross reference was not a direct replacement.
    No indeed. The LM747 suggested replacement is a horrible op amp designed in the early days of op amps. Op amps have come a long way since the LM741/747 and RC4136. Although many of these got used in early audio designs, hardly any of those designs could be called good by modern standards. The early Crown IC150 pre is a great looking and a very functional pre but the op amp choices available at the time made it sound like fingernails on a chalk board.

  5. #15
    Administrator Gepetto's Avatar
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    By the way, the original article was well thought out and written.

    Another note, Burr-Brown (now owned by TI) and Analog Devices are generally accepted as the king of the hill manufacturers in op amps highly targeted for audio applications. They designed not only for specs but also for sound quality. As we all know, pure specs and SQ do not always go hand in hand.

    The venerable Burr-Brown OPA627 is highly regarded in many audio circles but has some downsides that have to be considered in circuit design to apply it.

  6. #16
    Forum Veteran 62vauxhall's Avatar
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    It looks like some op amp IC's have been around a long time, well one anyway. There are several TL072CP's in APT Holman pre-amps which are give or take 35 years old and those op amps seem to still be in production.

  7. #17
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    Quote Originally Posted by Gepetto View Post
    Op amps have come a long way since the LM741/747 and RC4136.
    Audio Control used the 4136 extensively in their early car audio products in the mid 80's and after. Their products were not what I would call "inexpensive", but they did develop a cult following with good marketing and engineering/technical support.

    Bose uses 4558's in most of their consumer products because they say that this particular op-amp "voices" the product they way they like. Bose could afford to use other op-amps given the price commanded by their product.

    I guess it's like tires... they all are round, made of rubber and roll, but there is a huge difference between various tires.

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