more bass from a "class A" amp?

Discussion in 'AV Receivers' started by Geno, Oct 21, 2003.

  1. Geno

    Geno Supporting Actor

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    I used to run all 5 channels thru my "class a-a/b"
    b&k video 5 "5 channel x 105" amp and I had split my LFE to both channels on my "class a/b" nikko "2 channel x 120" amp.

    as an experiment, I am now using 2 channels on the b&k for my sub and the nikko is now running my mains.

    From the few days of listening that I have had it setup this way, I have noticed that the low bass seems to come out cleaner or less restrained. I really dont know what it is but I thought it had something to do with the circuitry.

    can anyone else explain this?
     
  2. JohnSer

    JohnSer Stunt Coordinator

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    I know B&K makes a marketing point about being class A -A/B, but it is my understanading that almost all class A/B power amps use class A for the initial stages, and only class A/B on the final output stage. You are probably hearing just minor differences in the amps.

    JohnS
     
  3. Geno

    Geno Supporting Actor

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    yes the b&k only uses the a/b AFTER 25 watts, which I rarely have it that loud.

    I guess Ive got myself trained to hear the sublte differences now. but now I have to get a good class a amp for my mains [​IMG]

    darn upgraditis [​IMG]

    anyone else have explinations?
     
  4. JohnSer

    JohnSer Stunt Coordinator

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  5. Geno

    Geno Supporting Actor

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    lets hope that doesnt happen.

    mass marketing has already pulled the wool over many peoples heads about quality, design, and clarity.
    IMHO Bose, mp3's, NAFTA, THX, all have contributed to the downfall of mainstream audio.
     
  6. Yogi

    Yogi Screenwriter

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    Class A amps have very high slew rates because they are always on for the full waveform and because of lack of switching between the complimentary stages. So they generally have well defined bass.
     
  7. Yogi

    Yogi Screenwriter

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    Also remember MOSFET amps in general have better bass response and perhaps thats what you are hearing from the B&K.
     
  8. Geno

    Geno Supporting Actor

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    I believe the Nikko has Mosfet amps too though
     
  9. Yogi

    Yogi Screenwriter

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  10. Michael R Price

    Michael R Price Screenwriter

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    I don't think high slew rate has much to do with bass performance. I don't have any idea what contributes to good bass performance. My guesses would be a good power supply, high power and high damping factor.
     
  11. Chu Gai

    Chu Gai Lead Actor

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    Perhaps adequate current in reserve in the way of good power supplies and substantial capacitors. The DF for low output impedance devices is pretty much irrelevant.
     
  12. Khoa Tran

    Khoa Tran Supporting Actor

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    just look at a pass lab amp, pure class A, THEY ARE REALLY BIG!
     
  13. Michael R Price

    Michael R Price Screenwriter

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    What damping factor is good enough to be irrelevant? 20, 50, 100, ?
     
  14. Yogi

    Yogi Screenwriter

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    Taking into account real speaker cable impedances any damping factor over 100 is good. Has anyone done a level matched DBT to see if there is an audible difference between a DF of 100 and 1000? [​IMG] Sorry couldn't resist throwing that in.
     
  15. Chu Gai

    Chu Gai Lead Actor

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    Consider the following article by D. Pierce on DF.
     
  16. Brad_Harper

    Brad_Harper Stunt Coordinator

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    The class of an amplifier has nothing to do with it's bass response. Elimination of crossover distortion is the main reason for using a Class A amplifier. This comes at the expense of efficiency. That is why they are often bigger then a class A/B or class b because they need larger heat sinks. Chances are your new amp just has a better power supply (it had better if it's class A) so there is just more current available for those low frequencies.
    Now as far as MOSFETs go. They also have no bearing on frequency response. MOSFETs are just a more robust transitor then a BJT (Bipolar Junction Transistor). The truth is MOSFETs actually increase distortion. [​IMG]
     
  17. Yogi

    Yogi Screenwriter

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    Nice article Chu. No wonder my tube amp with a damping factor of 20 sounds as taut as my B&K amp with a DF of several hundred. I always thought that anything beyond a DF of 100 would be irrelevant but I guess it is even lower than that. Makes me feel good even though I am not into specs.

    Thanks again Chu.

     
  18. Geno

    Geno Supporting Actor

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    well whatever the reason, it sounds better. i might just have to upgrade that stereo amp to a good a a/b amp too
     
  19. Yogi

    Yogi Screenwriter

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    B&K amps are pretty high current. My Ref7250 does [email protected] and [email protected] In HT mag it was measured to put out (with 2 channels driven) over [email protected] and a little over [email protected] So as we can see it almost doubles its output with half the impedance. Thats a good indicator of a robust power suppply. That in itself would make a whole lot of difference in handling of bass frequencies.
     
  20. Chu Gai

    Chu Gai Lead Actor

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    Yes, that article, as well as others, basically debunks the myth that the damping factor of an amp somehow controls the performance of a speaker to any signficant degree. It's contribution is orders of magnitude less than say of the dampening effect of the back emf that's generated by the voice coil. However Yogi, since damping factor and output impedance are intimately related, as your DF goes down the output impedance of your amp can rise to a significant enough degree such that it does result in a non-linear FR in conjunction with your speakers. Old news though. I seem to recall reading somewhere that the lower limit for audible interactions was somewhere around 20 or so.
    My good man, you should be into specs!! After all, a pair of Aces beats a pair of Kings, and IMHO, a pair of 38D's beats a pair of 32A's.
    I agree with your B&K assesment fwiw.
     

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