Rotel amp classification?

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  • doodleboytoy
    Member
    • Jun 2003
    • 30

    Rotel amp classification?

    Just wondering how are Rotel amps classified? Class A? A/B? B? :?:
  • greggz
    Senior Member
    • Jun 2002
    • 317

    #2
    I know the 1075, 1090, and 1095 are Class A/B. I'm not sure about the rest.




    Gregg
    Gregg

    Our Home Theater

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    • Aeromos
      Senior Member
      • Jun 2003
      • 192

      #3
      Can someone please clarify for me the differences that specifies an amp to fall in each class? Thanks!!




      Aeromos
      Enjoy life, it's too short to waste!!
      My Collection
      Aeromos
      Enjoy life, it's too short to waste!!
      My Collection

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      • Danbry39
        Moderator Emeritus
        • Sep 2002
        • 1584

        #4
        From audiofaq.

        11.18 What is Amplifier Class A? What is Class B? What is Class AB?
        What is Class C? What is Class D?

        All of these terms refer to the operating characteristics
        of the output stages of amplifiers.

        Briefly, Class A amps sound the best, cost the most, and are the
        least practical. They waste power and return very clean signals.
        Class AB amps dominate the market and rival the best Class A
        amps in sound quality. They use less power than Class A,
        and can be cheaper, smaller, cooler, and lighter. Class D amps
        are only used for special applications like bass-guitar amps and
        subwoofer amps. They are even smaller than Class AB amps and
        more efficient, yet are often limited to under 10kHz (less than
        full-range audio). Class B & Class C amps aren't used in audio.

        In the following discussion, we will assume transistor output
        stages, with one transistor per function. In some amplifiers,
        the output devices are tubes. Most amps use more than one
        transistor or tube per function in the output stage to increase
        the power.

        Class A refers to an output stage with bias current greater than
        the maximum output current, so that all output transistors are
        always conducting current. The biggest advantage of Class A
        is that it is most linear, ie: has the lowest distortion.

        The biggest disadvantage of Class A is that it is inefficient,
        ie: it takes a very large Class A amplifier to deliver 50 watts,
        and that amplifier uses lots of electricity and gets very hot.

        Some high-end amplifiers are Class A, but true Class A only
        accounts for perhaps 10% of the small high-end market and none
        of the middle or lower-end market.

        Class B amps have output stages which have zero idle bias
        current. Typically, a Class B audio amplifier has zero bias
        current in a very small part of the power cycle, to avoid
        nonlinearities. Class B amplifiers have a significant advantage
        over Class A in efficiency because they use almost no
        electricity with small signals.

        Class B amplifiers have a major disadvantage: very audible
        distortion with small signals. This distortion can be so bad
        that it is objectionable even with large signals. This
        distortion is called crossover distortion, because it occurs at
        the point when the output stage crosses between sourcing and
        sinking current. There are almost no Class B amplifiers on the
        market today.

        Class C amplifiers are similar to Class B in that the output
        stage has zero idle bias current. However, Class C amplifiers
        have a region of zero idle current which is more than 50% of
        the total supply voltage. The disadvantages of Class B
        amplifiers are even more evident in Class C amplifiers, so
        Class C is likewise not practical for audio amps.

        Class A amplifiers often consist of a driven transistor
        connected from output to positive power supply and a constant
        current transistor connected from output to negative power
        supply. The signal to the driven transistor modulates the
        output voltage and the output current. With no input signal,
        the constant bias current flows directly from the positive
        supply to the negative supply, resulting in no output current,
        yet lots of power consumed. More sophisticated Class A amps
        have both transistors driven (in a push-pull fashion).

        Class B amplifiers consist of a driven transistor connected
        from output to positive power supply and another driven
        transistor connected from output to negative power supply.
        The signal drives one transistor on while the other is off,
        so in a Class B amp, no power is wasted going from the
        positive supply straight to the negative supply.

        Class AB amplifiers are almost the same as Class B amplifiers
        in that they have two driven transistors. However, Class
        AB amplifiers differ from Class B amplifiers in that they
        have a small idle current flowing from positive supply to
        negative supply even when there is no input signal. This idle
        current slightly increases power consumption, but does not
        increase it anywhere near as much as Class A. This idle current
        also corrects almost all of the nonlinearity associated with
        crossover distortion. These amplifiers are called Class AB
        rather than Class A because with large signals, they behave like
        Class B amplifiers, but with small signals, they behave like
        Class A amplifiers. Most amplifiers on the market are Class AB.

        Some good amplifiers today use variations on the above themes.
        For example, some "Class A" amplifiers have both transistors
        driven, yet also have both transistors always on. A specific
        example of this kind of amplifier is the "Stasis" (TM) amplifier
        topology promoted by Threshold, and used in a few different
        high-end amplifiers. Stasis (TM) amplifiers are indeed
        Class A, but are not the same as a classic Class A amplifier.




        Keith
        Keith

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        • greggz
          Senior Member
          • Jun 2002
          • 317

          #5
          There is also a Class G starting to show up more and more as space gets tighter and tighter. The new Outlaw Audio slimline Monoblock amps are Class AB/Class G.

          Class G amplifier - Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.



          Gregg
          Gregg

          Our Home Theater

          Comment

          • Zzap
            Member
            • Sep 2003
            • 50

            #6
            Class D amps are only used for special applications like bass-guitar amps and subwoofer amps
            Apparently there is a Danish company that has produced a class-D digital amplifier.

            For the curious:

            but don't get too excited - it costs $10k!

            (Edit
            Bang & Olufsen have a variation they call ICEpower:

            These have shown up in various products
            /John

            Comment

            • doodleboytoy
              Member
              • Jun 2003
              • 30

              #7
              Sorry... kinda getting confused with all the classes :LOL:

              Are you saying that a class AB will sound better than a class A for stereo/HT or is it just better value with marginal benefits? I am comparing the Rotel 1080 (200w) or 1090 (300w) with 1055 as receiver pre pro vs. Musical Fidelity A3.2 pre-amp plus two A3.2 amps (at 130w each - bi-amped).

              Musical Fidelity's A3.2 is class A and from another forum they said that it would be better than the Rotel set-up.

              :?:

              Comment

              • Danbry39
                Moderator Emeritus
                • Sep 2002
                • 1584

                #8
                Here's what I would say. Class A amps are the best overall sonic performers, but with the downside of the amps getting very hot and being energy hogs. A class A/B amp usually will sound just as good at low to moderate volumes due to the fact that it is running like a class A amp before the class B kicks in. For instance, my Parasound amp runs class A for the first 5-10 watts, which means that it will be running class A up to and above 90 decibels, afterwhich class B kicks in.

                I should mention that I'm not the authority here and could well be off in what I'm saying, but this is my understanding (misunderstanding?) My impression is that Class A/B amplifiers try to take advantage of the positive aspects of both Class A and B amplifiers, which eliminating or reducing the negative aspects of these types of amps. The definition I cited above said:
                Briefly, Class A amps sound the best, cost the most, and are the
                least practical. They waste power and return very clean signals.
                Class AB amps dominate the market and rival the best Class A
                amps in sound quality. They use less power than Class A,
                and can be cheaper, smaller, cooler, and lighter.
                All that said, Musical Fidelity has an outstanding reputation and people here at HTGuide have spoken highly of Musical Fidelity components that they've owned.

                Is it possible for you to audition both and also to compare the performance of each to your Rotel pre-pro? Again, I'd want to do so personally before buying as I'd want to make sure the improvement in two channel sound justified the expense. The performance of Rotel pre-pros in two channel is generally excellent as is.




                Keith
                Keith

                Comment

                • Danbry39
                  Moderator Emeritus
                  • Sep 2002
                  • 1584

                  #9
                  Just found an explanation that simplifies the understanding of the categories. It states:
                  Think of three cars at a stop light. The class A car keeps the engine running at full power and full RPMs ready to take off at any time. The class B car shuts off the engine entirely and must re-start and get in gear before it can take off at the green light. The class AB car keeps the engine running at idle with the gear in drive using some power but not as much as the class A car and being much quicker off the line than the class B car. Class AB amplifiers are the most commonly used amplifier designs thanks to their attractive blend of reasonable efficiency and high-quality output (low distortion and high linearity close to but not equal to class A amplifiers).



                  Keith
                  Keith

                  Comment

                  • Scarp
                    Senior Member
                    • Mar 2003
                    • 632

                    #10
                    So, if its a B class amp, there would not be much idle power comsumption right? If its A it would be half of its power rating. If its AB it would be somewhat less than half.

                    Look at the idle comsumption figures then:
                    http://rotel.com/support/techups/techup-10-2.htm

                    Comment

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