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Class AB v.s Class H

Discussion in 'Amps and Cabs [BG]' started by metalbass101, Feb 19, 2004.

which one

Poll closed Mar 20, 2004.
  1. Class AB

    5 vote(s)
  2. Class H

    11 vote(s)
  1. metalbass101


    Jan 24, 2004
    Which one would you rather have in your preamp,power amp,amp(head) or combo?
  2. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
    Whichever sounds better
  3. chucko58


    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Class H is most useful at high power levels. It's more efficient and so keeps the amp's cooling and input power requirements down. The only downsides are more complexity and crossover distortion at the rail-switching point(s).

    For anything over a couple hundred watts, I'd say go Class H. Below that point, Class AB is fine.
  4. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD
    Class ALL TUBE. :cool:
  5. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    I'd rather have whichever one is lighter. Gettin' too old to be hauling around SVT's and the like. I love my little Walter Woods, 7 pounds, can't beat that.
  6. Phat Ham

    Phat Ham

    Feb 13, 2000
    For the preamp I'll take class A thank you. For the power amp it really depends on the needs and how well it is implemented. For example, QSC's higher powered amps use class H output circuitry and sound excellent. If I tried to make my own class H amp it would probably sound like crap. And don't forget class D amps such as Peavey's DPC1400. In the end, I'll take the amp that is better (i.e. sounds better, is more reliable, lighter), regardless of what class it is.
  7. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    The eternal pipe dream of a class-less society...
  8. VicDamone


    Jun 25, 2000
    So far, without a doubt, the best power amplifier I've owned/used/heard is the Carver-Pro ZR1600 Tripath processor, purchased and modified by 8th Nerve. This thing provides more detail and control to my Bag End subwoofer than many conventional A/B amps at three times the power.

    The only drawback is that it requires a few hundred hours of break/burn in time for hi-fi use. Of course this is simply my subjective opinion. www.carverpro.com
  9. atldeadhead


    Jun 17, 2002
    I need a quick education. What is the difference between Class AB and Class H amps/preamps? I don't beleive I've ever heard those classifications.
  10. I think the best sound still comes from a led sled (Macrotech). They are fine for fixed applications or for a band with roadies. For a bass rig I like something as light as possible. My next bass rig power amp will be a Peavey DPX1400. Big power and super light weight.
  11. Fuzzbass

    Fuzzbass P5 with overdrive Gold Supporting Member

    My ears say "vintage Ampeg SVT", but my lower back says "Class H". At my age, what the back says goes!
  12. class AB is a traditional amplifier topology that trades some fidelity for some efficiency. class A topology reproduces exactly what is input, just bigger. the benefit of this is high fidelity, but the downside is that it is inefficient and creates a lot of heat. class B looks to solve that by being more efficient and creating less heat, but it is not nearly as accurate. by combining the two, however, you can get sonic performance close to class A with more efficient, cool-running class B thermal characteristics. the result is class AB.

    class H is class AB that has two power supply rails -- a high power rail and low power rail. class H amps track what the input signal is doing and switch between the two rails to optimize power output and heat dissipation. this allows the amplifier to save expense and weight in the power supply and heatsinks while maximizing power output.

    basically, they should sound exactly the same, more or less. most high-power amps these days are class H. the lower powerd amps can still afford to be purely class AB. QSC's PLX series is a perfect example of this: they're class H for the PLX-2402 and above, and class AB for the PLX-1202 and PLX-1602. essentially, they're the same circuit, just tweaked for different power levels.

    you can also see that there's no reason to have a class H preamp. preamps should be class A unless you have a good design reason (read: trying to achieve a certain sound) to use anything else. but since class H is a high-power tweak of class AB, it has no purpose in preamps.

    hope this was helpful to everyone. personally, i think the poll is a bit silly. if it were between amps with switching power supplies and low-frequency power supplies, it would make sense. after all, getting rid of the big power transformer is the real difference in weight. from there, it's about shaving the weight of the amp from 20 lbs. to 15 lbs. by playing with different output topologies. that's nice, but once the amp is 20 lbs., i'm more concerned with getting the best sound instead of losing 5 more pounds. so if it takes a switching amp or a dissipative amp to get good sound, i'd prefer that over the lighter of the two.

  13. atldeadhead


    Jun 17, 2002
    Thanks so much for the thorough explanation Robb. :)
  14. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Not necessarily. Class A just means that current flows in the transistor or tube throughout the entire signal waveform, but it doesn't necessarily mean that the transfer function is exactly linear. It may or may not have less distortion than class AB, H, or others. For example, the first single-transistor class A circuit I built in EE 10whatever lab had a substantial asymmetry that changed the sinusoidal input signal into something of a cross between sine wave and epicycloid; the effect varied depending on the signal amplitude and where I biased the transistor. But the harmonics generated by that distortion were both even- and odd-order. I'll have to recreate it sometime and see what it sounds like on audio.

    I agree that the poll is a bit silly.

    In addition to saving transformer weight, class H's efficiency boost allows an amp to put out more power and still operate from a standard AC mains outlet. Even higher-power amps with switching supplies can and do benefit from class H technology.
  15. Bob -- i know that, but i was trying to make it make sense to the layman -- keep it simple! and in that respect, i guess it wasn't boldly obvious that by making the output stage more efficient, you're allowing for a smaller power supply. but i still think using a SMPS will reduce the weight far more effectively than class H vs. strictly class AB. your own RMX series amps can attest to that! ;)


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