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Class of amplifiers!

Discussion in 'Amps and Cabs [BG]' started by mettec, Feb 21, 2006.

  1. mettec


    Aug 22, 2005
    I have been reading lately that certain manufactures put a "Class" to their amps for instance... Ampeg's new SVT-8PRO uses a "Class-D" amp, Gallien-Krueger's new Fusion 500 uses a "Class-G" Solid state amp, EA i800 has a "Class-D" amp. What does the Class signify as to how the amp works or is built? Is there a A,B,or C Class amps? Just curious.
  2. Mcrelly


    Jun 16, 2003
    Minnesota, USA
  3. alanbass1


    Feb 8, 2006
    I'm not an expert, but as I understand it, class A amps are generally single ended 'push' only type. These are very inefficient but highly sought after by guitarists (myself included) for their three dimesional soundstaging, harmonic content and musical break up properties. Class A/B and class B are push pull variants which are more efficient power wise but, to many, at the expense of tone. As an example, my Carr Rambler in triode (class A) mode delivers a thunderous...er...14 watts from 2 6L6 power valves. My Victoria Low Powered Twin, which runs in Class A/B, delivers 40 watts of power through the same two 6L6's.

    This is where my knowledge really falls down, but it seems that when the ratings go into D, and beyond, it seems to be how the power delivery is maintained through the power supply. The efficiency seems to be increased with a subsequent increase in power output for the same size (weight) of transformer. It seems that in bass amplification, efficiency, headroom and power delivery takes precedence over the 'musical break-up' properties and therefore are more prevalent in bass amp design.

    As I say, my knowlege is quite sketchy on this and I'm sure others will have a better technical explanation.
  4. seamonkey


    Aug 6, 2004
    Google: Amplifier Classes

    You'll get plenty of hits.

    One amp class shouldn't "sound" different than another if they are designed to be transparent. Some Class-A amps are designed to distort and fool people into thinking they are unique.

    When there's no real measurement of an amp, people start tossing in terms they've heard. "Soundstage" is "when you close your eye's, being able to point to where the instrument is." So for a single channel amp soundstage doesn't make much sense. It doesn't make much sense anyhow as it's subjective, and easily fooled with effects like "Wide sound" buttons on boom boxes. Warm, Ballsy, mean something different to anybody who uses the terms and have to do with signal processing and coloring the sound. You want an amp part that is clean and leave the signal processing to up the chain.

    In general, Class-A - low wattage, inefficient 20% (lots of heat), output devices are in some form of trans-conductance.
    Class-B - higher wattage and better efficiency 50% (lower heat), output devices are only on for half a cycle. Actually designed to be "greener" than Class-A. (Back when batteries were often used)
    Class AB - most common design, lowers crossover distortion.
    Class D (Does not mean Digital), AKA Class-T, Pulse Width Modulation (PWM). Most efficient, some in the 80-90%. Started out in low frequency sub-woofer amps, but full range are widely available.
    Class-H - varies the power supply with the signal. Peaks get more voltage to the amp. Like a class-a/b with varying supply voltage. Efficient. Lot of high end designs right now.

    You'll also see Class C and Class G you can read about on the web.

    The power supply matters quite a bit.
    SMPS = switch mode power supply. What computers use. Lightweight, efficient, usually regulated.
    Linear = Transformer, heavy, easy to design, usually not regulated.

    What everything is moving towards:
    Class-D (Class-T, PWM) with SMPS
    Future proof yourself by looking for one of these.
  5. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    Each type of class has a different efficency and sound. Class A and AB are the most common in instrument amplifiers, and I have only seen A and AB tube amps; the others are in SS amps, even if they are not as common as A or AB. A gets little to no distortion, B gets a sizable in comparison amount of distortion, AB gets some distortion. Class D usually gets some distortion, but are usually really light and efficent. I dunno the specs on the other classes.
  6. Guiseppe


    Oct 26, 2003
    Vancouver, WA
    Is there a place to see what 'class' my gear is? I have an Ampeg SVPCL and SVP1600, but I haven't seen any data on their website or in the Owner's Manual that reflects what they'd be...