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Tech question about SS amps.

Discussion in 'Amps and Cabs [BG]' started by ostrzoskrzydly, Oct 14, 2003.

  1. ostrzoskrzydly


    Jul 1, 2003
    Is there a difference in perceivable volume (or perhaps the proper term is loudness) between SS amps running in Class A and regular ones ?
    And by the way, what is Class AA when talking about SS amps ?
  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany

    The difference lies in effecttivity. A class A amp already uses 50% of its maximum power comsumtion in idle mode (no input signal).

    Class AB is much more effective, so you can build a more powerful amp with basically the same parts.

    AFAIK there's no class AA, but class AB and A/AB.

  3. Actually, a class A amp consumes more than 100% of its maximum output power when idle. It will run cooler when in use, because a part of the idle power is passed to the connected speaker cab(s).

    IMO, pure class A (the above) is a ludicrous (and useless) attempt to lower distortion. class A/AB (I happen to have an amp with this config) is a very good compromise between A and AB. Something like "more A than AB but not quite A" or something; AB with substantially increased idle current.
  4. metron

    metron Supporting Member

    Sep 12, 2003
    Good design principle is to not make an amplifier power section with class A circuits. Basically what it boils down to is that class A involves a design whereby the transistors are on at all times constantly dissipating power. Class B uses transistors that switch and are on half the time of a class A type.

    Preamps may use class A for a more "pure" design because preamp power dissipation is low. The reason that class A is viewed as "pure" by audiophiles is that the signal is continuous. In class B it is required that the transistors be matched in operation because each would pass half the signal.

    Poor class B designs may have an overlap (or a slight loss) in the signal where one turns off and the other turns on, referrred to as crossover distortion. A problem with class A lies in the fact that usually the designer will go out of their way to directly couple the amp stages (no caps, delicate impedance matching between stages) and that results in switching noise due to bias current being able to flow between stages with no signal present.

    I dont know about a difference in volume. Probably all class A would dissipate more power at lower volume. I think class AA may refer to preamp and power amp sections using class A. Hope this helps. :rolleyes: :D
  5. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    Hey Joris,

    Do you see or hear anything inherently wrong with Clss D amps?? what are the dangers, if poorly designed, or has a major component failure? stability of internal voltages etc...

  6. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Class-D can sound great or crappy, depends.

    About NOTHING poorly designed (except an old Fender, etc) sounds as good as a well -designed one. Buts sometimes it all just falls together anyway, and its great.

    Poor design may fail early or never, but it sucks anyhow on an artistic basis.

    Just play through it and see what you think...and see if they drop like flies out in the real world.

    Hey, it's just an amp....you add talent....
  7. Most modern high volume venues and open air stages use digital amps (class D is digital) nowadays. They require less power, are cheaper per watt, more compact, and produce much less heat. That last factor has a tremendous impact on reliability. Most electrical defects involve some form of overheating. Heat is the enemy. I don't know any numbers (I'm not in the audio business) but in my estimation digital amps are much more reliable.

    Digital amps usually have one or several microcontrollers on board. They (should) monitor their own circuitry semi-intelligently, providing much better protection to speakers and ear drums. Some high end amps can be chained to a communication bus on which all units continuously report their status. The tech can view all this info on a notebook computer or the main mixer screen, and can take measures to prevent damage.

    BTW I have not been gifted with ears that can detect any difference between analog and digital amps, sonically.

    As you can see, I'm strongly in favour of digital amps. I embrace new technologies. I'm known for my dislike of tube amps. Not only do I find their sound horrible, I also think such outdated and obsolete technology should be banned (sarcasm).
  8. Class A has the most harmonic distortion of any operating class (B, C, D all have crossover distortion, but within their audio bandwidth are cleaner) and as such, will sound louder, though it will be more a tonal observation than an actual difference in volume. Class A will "cut through" a mix better without being actually louder.

    "Regular" audio operation is usually Class AB or some variation of it.
  9. ostrzoskrzydly


    Jul 1, 2003
    Thanks, that's what I wanted to hear :)
    The question about class AA arose in addition to the main one, because that's what is written on my hi-fi amp. (technics su-v570 afair, i'm at school now)
  10. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Class A in SS particularly will also usually be about 3 to 4 times bigger and heavier for the same power output...if you can get the power out.

    If you are talking about one of those old little square guitar amps, they do rock..and sound pretty cool. Epiphone etc...

    They aren't so big and heavy, but they are also only about 5 watts. A real loud and cool 5 watts in many cases though.

    Got NO low end, won't do much for bass.........
  11. ostrzoskrzydly


    Jul 1, 2003
    i'm talking about the glockenklang bass art head :)
  12. The Glockenklang has a Class A preamp, but the power section is normal Class AB. A 400 watt Class A amp would weigh literally a ton and require its own refrigeration unit to cool it.
  13. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Class-A preamp pretty much means any tube preamp, or, I s'pose, an SS one with no op-amps, like old Randall, etc.

    Probably will be nicer, but it isn't the class-A, its the circuit.......class A can suck too (like really old Crate in the pine boxes).
  14. metron

    metron Supporting Member

    Sep 12, 2003
    Nope. Just because there are no op amps doesnt have anything to do with the circuit class. Its how the devices operate. I dont know squat about tube amp designs but I think its the same thing as semiconductor transistors, depends on how they operate in the circuit.
  15. Yup,you can make Class A circuits with OP-amps. I do it all the time.
  16. ostrzoskrzydly


    Jul 1, 2003
    the bass art is all class A
    and it DOES weigh a ton and is big as hell
    the soul has only class A preamp
  17. When I say literally a ton, that's what I mean. The weight of a 400 watt Class A would approach 2000 lbs once you factored the cooling system and power supply. I don't care what Glockenklang says, the power section is NOT Class A. The heat generated by 400+ watts of idle would toast(literally burn through) ANY kind of output device without a huge and heavy cooling apparatus which would require a power supply equal to or greater than the outputs themselves.
  18. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Quote #1:
    "Nope. Just because there are no op amps doesnt have anything to do with the circuit class. Its how the devices operate. I dont know squat about tube amp designs but I think its the same thing as semiconductor transistors, depends on how they operate in the circuit."

    Well, actually, since most op-amps have class-B output stages, that DOES have quite a bit to do with it.

    You have to work at it to create a class-"anything but A" preamp with discrete parts, PARTICULARLY TUBES, since you really end up making a little power amp if you go with another type.

    And TUBES only come in one polarity, so they are almost always class-A in a preamp, whether common cathode, cathode follower, etc.

    Any LINEAR single-ended stage will be operating class-A, that's just what they do. Class-C is for radio folks, you wouldn't like it for audio.

    Quote #2
    "Yup,you can make Class A circuits with OP-amps. I do it all the time"

    That's a "sort-of" class-A, by putting a resistor or current source off to the supply as a bias. However, the drive is still class-B or A-B, and it will act that way any time the load wants more current than the resistor can supply. Typically on transients...where the sound of most amplifiers is determined.....

    Its a "YOU can DO it, BUT" situation. And 99% of the time the manufacturer hasn't even gone that far.

    Anyway, most any tube preamp is class-A and discrete part SS preamps are almost always class-A.

    Psycho is right on...a ton os probably about right....That's why you got roadies, right?

    And we are getting WAY off in techie-land here....its cool with me, but may not be a mass-market thread....
  19. BTW, I use 347,600 watts of Class C every day. Try hauling around a 1,500 ft tower sometime!
  20. You're right, it is only 'quasi-Class-A' when you take the internal circuitry in the OP-amp into account. I spend so much time with them that I have a tendency to ignore most of the internal stuff and treat them like discrete components....
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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