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Class A/B Preamps with a Class A/B Power Amp

Discussion in 'Amps and Cabs [BG]' started by DrakeWeiss, Oct 6, 2018.


  1. DrakeWeiss

    DrakeWeiss

    May 14, 2012
    Wisconsin
    It's difficult to find Class A/B Preamps with a Class A/B Power Amp. Where are they? Which ones are worth their weight in gold? How far back in time do I have to go? The only one that I can find is an Orange 4-Stroke 500 for $1100 new, but made in China ugh. I would even go for a pa amp that is class a/b at this point, and use pedals for preamps. Basically, anything that doesn't recreate the signal would be ideal for me. I'm really struggling trying to avoid digitally processed signals. Any suggestions?
     
  2. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Most solid state bass amps uses op-amp chips in the preamp stages, which have Class-AB output. So pretty much any mainstream amp would do the job. Very few bass amps have digital processing, and the ones that do are probably identified as such. Digital processing circuitry turns out to cost more than analog.
     
    nbsipics, mbelue and agedhorse like this.
  3. What are you after in A/B that you can’t find with other classes?
     
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  4. DrakeWeiss

    DrakeWeiss

    May 14, 2012
    Wisconsin
    I was under the impression that most preamps and power amps were analog. That is not the case nowdays. I thought my ampeg pf800 and genz benz streamliner 900 were totally analog. I read the manuals. They're both digital devices. That means the signal is an imitation of the real thing, cause it gets turned into ones and zeros. Here is what GB stated in the manual:

    "The Class D amplifier uses digital PWM (pulse width modulation) techniques similar to those in more familiar digital to analog converters to reduce the size and weight by a factor of 10 times that of a comparably rated conventional Class AB amplifier. Essentially, a Class D amplifier converts the analog signal into a logic level PWM digital signal with a digital to analog converter, level shifts this PWM signal up to a higher voltage and current and then reconstructs the analog signal by passing it through what is essentially a power digital to analog converter. Additionally, we developed our own, proprietary 3DPM™ 3-Dimensional Power Management signal processing techniques to give a distinctly analog feel and sound to the Class D platform."

    I guess I've become a purist. Yeah, the GB900 has the Class A tube preamp, but the power amp is what is re-creating the signal and digitizing it. I am very disappointed, and realize the music industry has been hijacked into digitization. The old amps are heavy and huge. Some are mid-weight, and it is difficult to find the power class for its power amp. I'm trying to find more options in addition to the Orange 4-Stroke 500 bass amp that's out right now. When reading about that one, it states and brags about its A and AB classification for both the preamp and power amp within it.

    From the Orange manual...
    "Featuring all-analogue circuitry throughout, these amps are all about powerful, full-bodied tones with an organic delivery that has passed by a generation of players confronted with an array of lifeless digital offerings."

    Digital technology is great, but I don't need it to totally re-create my signal, and that is what happens with class D power amps, no matter what the preamp class is. I play electric bass guitar, not digital bass guitar. LOL, at least that is what I was bamboozled into believing.
     
  5. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    The definition of "digital" is poorly understood, endlessly debated, and made more confusing by marketing departments. Most class-D amplifiers contain no digital circuitry, and reconstruction is simply a matter of filtering out the switching waveform, which is inaudible anyway. I don't know the state of the art today, but a few years ago, it was the "self oscillating" circuit as described here:

    Self Oscillating Class D

    There were some early attempts to improve the performance of Class-D amps by incorporating digital elements, but the fully analog circuits won out, probably due to their simplicity, and because engineers gained a better understanding of how they work.

    At the same time, every amplifier "re creates" the sound, in a way. Every mainstream power amp does pretty much the same thing: Produce an output voltage that is proportional to the input voltage, virtually instantly. In my view, if two amps produce the same output voltage for a given input, then the speaker will produce the same sound, and I'm satisfied.

    Still, we live in a time when virtually all historical amp technologies remain available, and it's easy to choose something that meets your needs. My GK Backline 600 is a conventional amp, and those are still widely available. I would still happily use it, but I prefer the lightweight gear.
     
  6. Jack

    Jack

    Sep 6, 2003
    Newcastle, UK
    So does your amp sound deficient or is it just a principle thing?
     
    Old Garage-Bander likes this.
  7. JimChjones

    JimChjones

    Aug 6, 2017
    SE England
    Excuse my ignorance, but I was under the impression that all preamps (except true digital I suppose) were effectively class A, because they just don't require enough power for anything else to be of use. I understood that the Class B types were power stage only. Or am I hideously out of date? What value would class A/B bring to a preamp stage?
     
    Jeff Scott likes this.
  8. DrakeWeiss

    DrakeWeiss

    May 14, 2012
    Wisconsin
    If digital only enhanced the signal, that'd be pretty reasonable, and that's how it is with many digital pedals that have the option of blending it with the dry analog signal. I suppose none of it really matters if it is going to be digitally processed in a class D power amp stage. It matters to me though, so I'm going to keep my eyes open and hopefully pick up something that won't re-create the whole signal into ones and zeros. Artificial tones don't excite me as much as authentic ones do. I need some real eargasms! LOL Thanks for mentioning the GK Backline... I'll check those out.
     
  9. DrakeWeiss

    DrakeWeiss

    May 14, 2012
    Wisconsin
    The amps sound very good and gets lots of compliments for good tone. Mainly, my issue is a matter of principle, but I also feel that some muscle is missing... like it should be thicker or more beefy... it's very warm but kind of hollow.
     
  10. DrakeWeiss

    DrakeWeiss

    May 14, 2012
    Wisconsin
    It's all new to me lol. I probably meant to write just class A for preamps. Class B devices is a digital thing for FCC... still absorbing what it all means and trying to sort it out. I mixed it up pretty good I guess lol. Sorry!
     
  11. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Apr 11, 2006
    That's what I always though, too. Digital preamps, however, are a totally different ball of um, digits.
     
  12. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    You are not understanding what you are reading and why is was stated that way. You were not bamboozled, you just are not understanding the context of the explanation.

    I designed the Streamliner amp, it is 100% analog from the input through the output.

    Using digital techniques does not mean a digitally processed signal.

    Class D is a non-linear analog process, the generation of the PWM signal uses a process similar to digital in that there is a clocked pulse train, but not the same as the digital signals used in digital audio where each audio value is represented by a digital word that can have computations performed on. PWM is a series of time variant pulses that do not have any computation capability.

    There are 3 types of signals:

    - Linear analog
    - nonlinear analog
    - digital

    Nonlinear analog signals share properties with both analog and digital but is a purely analog process.
     
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  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    There are no ones or zeros in PWM class D, there's nothing artificial, it's 100% authentic.
     
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    So you are going off on this topic like a bat out of hell, yet you haven't the slightest idea about what you are so high on your horse about.

    The FCC class B statement nothing in the freekin world to do with class B amplifiers. Zero, zip, nada.

    FCC class B refers to Part 15 in the FCC's EMC regulations, and not to audio amplifiers in particular.

    Would you please learn more about the topics that you are making such rash and absurd judgements about, your arguments will completely evaporate once you understand what you are talking about!
     
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  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Jim, you are hideously out of date by about 50 years. ;)

    Preamps are typically a combination of class A and class AB stages depending on the devices used and the needs of the designer. Typically, tube preamps are class A (in part due to cost) but I have seen class AB stages used for unique applications in a tube preamp.

    In solid state, it's often a mix of both, there are significant benefits to class AB when the cost penalty is small,
     
    Last edited: Oct 6, 2018
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  16. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Apr 11, 2006
    Thanks for that explanation, Andy.
     
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  17. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    Yup. Class D does not mean ‘digital’.

    If you are an old iron or led sled affecianado (IOW, a large heavy power transformer) many of those typically use class G or H power amp, nothing wrong with those topologies all.
     
    Last edited: Oct 6, 2018
    Mvilmany likes this.
  18. fast slapper

    fast slapper

    Dec 11, 2001
    Fresno, CA
    To get to the point. A well engineered product is a well engineered product regardless of specific technologies.

    Forget the specifics and leave it to people who know what they're doing. Look for reputable brands, try them, buy what fits your needs and enjoy life.
     
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  19. Pocket4

    Pocket4 Supporting Member

    Dec 9, 2013
    New Hampshire
    I think a little more listening to amp rigs would beat the hell out of alphabet soup and conspiracy theory. I play some of each topology, and to each his or her own.
     
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  20. Class D does not digitally process the signal. There is nothing artificial about it.
    The D does not stand for digital anymore than the A in class A stands for analog.

    You don’t have to like class D. I’ve got no argument with you not liking class D. But I will respectfully request that you not continue to spread misinformation about class D.

    One could use the same argument that class D is digital because of the switching that happens and apply that logic to class B amplification. Class B also introduces switching to the signal, does that make it digital?

    Thank you sir.
     
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