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Class A mic pres?

Discussion in 'Pro Audio Equipment' started by planet red, Sep 23, 2001.

  1. planet red

    planet red Active Member

    What does something have to have or be to be classified Class A? Does it pretty much guarantee decent quality or is it more of a marketing thing?
     
  2. audiowkstation

    audiowkstation Active Member

    The classification of "A" is a technical classification.

    Class A amplification, be it mic pres, line pres, or power amplifiers means that the top half and the bottom half of a single cycle is reproduced by the same output device continuiously.

    In most electronics, you have transistors (or tubes) that hand off 1/2 of the wave to a simalar device to do the other half of the wave. In a "Push Pull" amplifier, one set of transistors (PNP) does the top half of the wave, then the other set (NPN) does the bottom half of the wave. This is called the switching Output circuit of amplification. Take a frequency of lets say 10,000 Hz. or 10,000 cycles per second. (10KHz.)

    In a push pull or non class A design, this is switching 40 thousand times to produce the 10K note in 1 second. (Switch on PNP, Switch off PNP, Switch on NPN, Switch off NPN) This switching causes what is called "zero crossing notch distortion" as the switching causes a small (most of the time inaudible) "blip" in the waveform at zero crossing.

    Class A devices do not switch at all and produce the entire cycle, giving a smoother flow to the waveform. The result should be a more accurate reproduction of the wave and smoother, more coherent sound.

    Since class A output devices do not receive the 50% rest state as non class A circuits, they run much hotter as far as temperature. Also the raw components designed to be used this way are more expensive and thermodynamic coupling in the physics of the design must be considered.

    Hope this helps.

    Do a web search on different classes of amplification. You have Class A, AB, B, D, G, H, H+...many different topograpic choices avalible to designers. Class A/B and class B units' can be designed to sound great given the proper capacitor coupling and filtering.

    Beware of the cheesy companies that could possably (although I do not know of any) use the term class A for something else.

    A popular audiophile magazine classifyes equipment quality in classes of A,B,C..etc.. that has absolutly no bearing on the circuit design, causing confusion amongst other things, to some.
     
  3. atlasproaudio

    atlasproaudio Active Member

    Most class A designs seem to be very good from my experience, but in no way does it guarantee quality. Take each piece of gear on it's own merit for sound quality, and leave the rest to the designers. :cool:
     
  4. tubedude

    tubedude Active Member

    Hey Nathan
    What do you think of the Presonus class A preamp? Just wondering, seems like a decent sounding pre for a good price. Not a 1st choice, but good "extras" like for toms and stuff. The Burr Browns make a difference, too.
     
  5. atlasproaudio

    atlasproaudio Active Member

    The Presonus that I heard (the blue 8ch) at a friend's home place sounded decent. I would rate them slightly better than a Mackie VLZ Pro preamp. First off, it depends on your situation. Depending on what level you view yourself and your available finances that can go toward gear, is how you should spend accordingly.

    If you all you have for preamplifier's is a 16 channel VLZ, then you are going to feel the need to expand for one of two reasons...for increasing the quality or flexibility of either a commercial situation, or a personal situation where you will derive satisfaction from that improved quality (and of course they can go hand in hand).

    I don't think for "extras" you are going to hear a fundamental difference in the quality of your recording between a vlz and a presonus. For fundamentals with overdubs, probably a slight quality increase. I would rather have a small variety of condensers for toms and a mackie than 57's and a presonus in the rack. That is just me though.

    I find the Drawmer mid range line to fundamentally hold up quite nicely to higher end gear greater in price. I think they did a great job of listening to the product before it was released, which I don't think all manufacturers do
    :cool:
     

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