It might sound good

December 11, 2014
 by Paul McGowan

… but nothing’s perfect, not even live music; it has imperfect venues to be played in.

We were discussing complementary transistors: PNP and NPN devices. They too are not perfect. Each alone has its own quirks but they are different. And that’s a problem when we try and divide the top half of the sine wave using an NPN and the bottom half using a PNP as we do in a full complementary circuit. Were they identical it shouldn’t be a problem. But they are not and try as we might, as designers, to match their characteristics we can only get close, not perfect.

To our rescue comes things like negative feedback – which some designers use while others eschew. No, designing circuits is always a challenge involving compromise, careful listening to the results of fixing one thing while breaking another. It’s just the nature of what we do.

On a personal note I like and use complementary symmetrical devices for output stages, and have for years. They are the best of the compromises we have.

And that’s important, knowing which are the best, which to stay away from. And perhaps most important, knowing what to listen for when designs are being evaluated.

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4 comments on “It might sound good”

  1. Hello, Paul.

    Again I put the question what you are listening for when evaluating a circuit topology?
    Do you really listen to the amp? Or are you listening to the interaction between your specific listening room, your specific speakers and the new amp?
    How can one transfer your listening results to other speakers and listening rooms?
    Or do you listen via a closed headphone design?

  2. Imagine the lousy sounding venues that the great European composers experienced in the eighteenth/nineteenth century. I can confirm that first-hand having attended concerts in some old palaces and salons. Even among contemporary concert halls, how many deliver that extraordinary sound,let alone decent sonics ? And nothing sounds worse than the exhibition rooms at the HiFi shows.

    As audiophile consumers, we appreciate all the manufacturers’ efforts to achieve perfection in their equipment. But don’t lose sight of the real world in which they play. There never is and never will be perfect sound, whatever that means.

  3. It seems to me audiophiles and electrical engineers have a different view of what an ideal amplifier is supposed to do. Audiophiles want amplifiers that sound good…to them…in their own sound systems. Electrical engineers want amplifiers that perform a specific idealized electrical function based on their understanding of electricity as closely as they can get it no matter how it sounds. If it doesn’t sound good but performs well by their criteria they look for the root cause of problems and fixes elsewhere.

    It is true that nothing performs perfectly. However, mathematicians have given engineers a tool called an asymptote. Stated verbally this is a notion of something that continually approaches an ideal more and more closely but never reaches it. The question then becomes how close does it have to get? The engineer’s answer is close enough that humans cannot distinguish the difference between the engineered product and the ideal. This threshold is determined by experimentation performed by clinical psychologists who study the limits of human perception. The audiophile’s answer often seems to be that no nearness of approach is good enough and that usable improvement is possible and therefore justified indefinitely.

    What does this mean in practical terms? To the engineer there is a point where he stops. The only improvements of value are cheaper, smaller, more reliable, more efficient, easier to use. To the audiophile it means an endless search, often one that is increasingly expensive and never has a satisfactory end point. I’m glad I’m not an audiophile.

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