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Amp Classes

Discussion in 'Amps and Cabs [BG]' started by BulbousMoses, Apr 15, 2014.

  1. I always see references to this amp being a Class D amp or that amp being a Class A etc etc..but I have no knowledge of what the different classes mean and why you might want one over another. Is there anyone who can explain this in layman's terms. I'm not an electronics guy so if you get into heavy jargon, I'll be lost!
  2. experimental bassist

    experimental bassist

    Mar 15, 2009
    It's a letter designation that is basically referring to the "power amp" side of an amplifier.

    Letters are typically assigned in the order that the generation was developed, and one shouldn't really read anything more into it than that.

    Specific links:



    What it means to you as a musician:

    Class A : very musical, precise, lower output power. Can be solid state or tube.

    Class AB : what we think of when we talk about the typical musical amplifier, can be tube or transistor (solid state). Good sound, high output power.

    Class D : lightweight, efficient. These are the micro amps that everyone is talking about that only weigh a few pounds. Solid state all the way, unless it has a tube in the preamp or something but that would be it.

    Anyway, hope this is helpful.
    Old Garage-Bander likes this.
  3. Very helpful. When you say, with regards to Class A, that it is "precise", what does that mean in musical terms? The amp I have recently ordered is a Class A amp and from the videos and sound clips I have heard, it seems to be a very clean, uncolored amp (which is what I want)
  4. Class A amps are very rare. You are probably reading spec's for the preamp.

    Class of amp really means very little. A well designed amp of any class will add or subtract very little from the tonality of an amp of any type.

    Class D amps have become very popular due to their very high efficiency and light weight. Virtually all PA type amps are now class D, due to the wonderful ratio of power and performance to heat, weight and power consumption.

    Most 'micro amps' are class D, although some are the more traditional class A/B, with switch mode power supplies (another issue in amp design) to keep the size and weight down.
  5. experimental bassist

    experimental bassist

    Mar 15, 2009

    Class A : the transistor (or tube) amplifies positive and negative sides of signal.


    Class B: one transistor (or tube) amplifies positive side of signal, and another transistor (or tube) amplifies negative side. So you see how the output can be much louder, but there is a tiny amount of distortion right in the middle where the positive and negative signals don't exactly match up (crossover distortion).


    Class AB amplifiers are engineered to minimize this crossover distortion.

    Class A amplifiers do not have crossover distortion to begin with, therefore they can be thought of as more "precise".

    Of course these drawings are simplified, amp designs can contain many multiples of transitors (or tubes).

    All this is generalizing of course, there are good amps and better amps and they can vary wildly based on engineering and components and applications, etc etc etc. :cool:
  6. Yes, in fact the preamp is Class A. So does that mean that this is not a Class A amp? I realize that this probably makes no difference. If you like the amp, you like the amp. I'm just curious.
  7. Correct. If it is a very small, lightweight amp, it is probably class D. If it is a regular sized solid state amp, it is most likely class A/B. The full size GK and EBS use class G/H amps.

    None of it really matters IMO and IME, since the class of amp is just a small part of what makes an amp sound like it does (preamp, hi passing, preamp voicing, baked in voicing of the preamp, power management design, limiting design, absolute wattage, etc, etc., etc., etc.).

    What amp are you talking about?
  8. experimental bassist

    experimental bassist

    Mar 15, 2009
    Rare for bass amps, pretty common for some smaller wattage tube guitar amps.

    I have a little Epiphone Valve Jr. tube amp that I use for guitar, and it is class A. A simple class A, sure, but still. ;)

    Agreed. :cool:
  9. +1 Talking about bass amps and PA power amps.
  10. It's a Warwick BC80.
  11. Not really familiar with their amps. Don't see them much in the States. Again, if it sounds good, it sounds good! I wouldn't sweat the details!
  12. Thanks. Again, I'm not concerned or anything, just curious. You hear these terms thrown around by manufacturers and bass players all the time and I, for one, have never really known what it was all about.
  13. I just read the spec's and marketing description of the combo you are getting. I see your confusion, since they say that the preamp is class A (not unusual), but then later on in the marketing blurb, describe how 'more pure class A amps are versus class A/B', which connotes the power amp.

    My guess is, a bit sloppy on the copywriter's part. No way that combo's power section could be class A, given the power output, weight and cost. Not sure though, but again, just play and enjoy!

    On way to somewhat know for sure is to look at the INPUT power listed on the back of the amp (the power consumption). If it is only a little bit higher than the 80 watt output, that suggests class D. If it is quite a bit higher (double or so), that suggests a class A/B. If it is WAY higher, then maybe it is a class A, which I believe are very inefficient.

    Looks like a nice little combo to me! Enjoy!
  14. Cool. If you look at some of the official Warwick videos on YouTube, I see that Andy Irvine demos the BC80 and BC150. I think he's a Warwick endorsee. They sound nice to me. Check them out if you have a chance.

    By the way, I checked the input power on the back of the amp as you suggested and it is 160 watts so it looks to be class A/B based on your criteria.
  15. I'll check those out. Thanks!

  16. bass_case

    bass_case Maintain low tones. Supporting Member

    Oct 23, 2013
    Miami, FL
    I used to work in high-end hifi in the 80s, my company sold the old Mark Levinson ML-2 mono amps, these were solid-state class A, weighed about 50lbs each and delivered 25 watts into 8 ohms.

    Class A = heat, these had massive heat sinks. Sure sounded good thru a pair of Quad electrostatics.
  17. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    In a simplified nutshell:

    Class A draws the same amount of current no matter how loud it gets.

    Class B draws no current at idle but draws more and more current as it gets louder. you see this Class more in transmitters, The high crossover notch eliminates the Class from audio use.

    Class AB draws a little current at idle up to a certain point set by the bias. After that, it kind of "switches" into Class B. This eliminates the cross over notch. This is what me mostly use in our business. There are also subsets AB1 and AB2 that are slightly different but operate in basically the same manner.

    Edit: These classes apply equally to tube or solid star devices.
    spankdaplank likes this.
  18. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    There are some notable small Class A amps around, and they've been a 'fad' amongst small amp boutique makers and buyers...think the old Fender Champs and the like.

    I'd like to point out that while people generally assume Class D means small and light, that's not necessarily the truth. There are great examples of class A/B micros. And not all Class D are superlight, although that topology does lend itself to that form factor.
  19. +1. Again, guitar amps are a bit of a different thing.

    Also, +1 that lots of design decisions define the ultimate size of the box used to house a bass amp for sure (power supply design, preamp design, marketing considerations, etc.).
  20. teemuk


    Mar 1, 2011
    The output device dissipates least amount of waste power when it's in cutoff (no conduction) or in saturation (full conduction) state. That pretty much explains the main deal behind amp classes: Efficiency. Distortion and such in a well-designed amplifier are negligible regardless of class of operation.


    Classes G and H refer to amplifiers with modulated supply voltages. Under idling and with output signal voltage swings below certain threshold the output devices are hooked to low voltage power supply rails. When a certain threshold voltage is exceeded a higher power supply voltage is switched in or a higher power supply voltage alternatively "tracks" the output signal within a few volts.


    Generally, in such amplifier the "inner pair" of output devices usually works in class A or AB as usual, while the "outer pair" (with switching action) is either a switch or operating in class C.

    Classes D, E and F use switching output devices and some suitable modulation scheme to control the switching, usually PWM (Pulse Width Modulation). The pulsating signal is then low-pass filtered for demodulation. Class D amplifiers are generally all-analog but there are few rare examples of "digital" class D amplifiers too. E and F refer to different types of filtering arrangements.



    Other amplifier "classes" (T, Z, I a.k.a. BCA, J, BD, XD, TD, etc.) are not really amplifier classes at all but simply trademarks.
    agedhorse likes this.