Differences in power sections

Discussion in 'Amps and Cabs [BG]' started by MoonQuake, Sep 20, 2016.


  1. MoonQuake

    MoonQuake Supporting Member

    Jan 1, 2011
    Montréal, Qc.
    Hi folks,

    Currently checking out different class-d micros to provide power for a Noble preamp and was wondering what differences are there, other than power ratings, between different power sections.

    I've narrowed it down to the following choices so far :

    Mesa Boogie Subway D-800
    Darkglass Microtubes 900
    Form Factor Audio Bi 400/1000
    Aguilar TH 500

    So.... Like I explained, not considering power ratings, what differences would I hear between these amps' power sections?

    Thanks!
     
  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Major differences in how each amplifier handles power amp overdrive (both tone & feel), the recovery from overdriving, and the ability to drive 2.67 and 2 ohm loads safely and robustly.
     
    wcriley and MoonQuake like this.
  3. MoonQuake

    MoonQuake Supporting Member

    Jan 1, 2011
    Montréal, Qc.
    I will risk sounding like a total noob but if one sets the external preamp volume accordingly, should there not be any overdriving of the power amp? If so, does how a specific amp handles overdriving means available power/headroom available before said overdriving occurs?
     
  4. JGR

    JGR The "G" is for Gustav Commercial User

    Jun 29, 2006
    Maryland
    President, CEO, CFO, CIO, Chief Engineer, Technician, Janitor - Reiner Amplification
    When comparing power ratings, also pay attention to the specified THD and frequency/frequency range.
     
    Old Garage-Bander and MoonQuake like this.
  5. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    If you take an amp and drive it hard (like they are often used in the real world), it is not only easy but common to overdrive the power amp. Some folks like the sound that SOME amps achieve being driven this way, and much of this comes down to how well the amp behaves.
     
    ThisBass and MoonQuake like this.
  6. MoonQuake

    MoonQuake Supporting Member

    Jan 1, 2011
    Montréal, Qc.
    Those stats are not always readily available.

    Can't find them in the case of Form Facto Audio and had to dig into B&O's website for Aguilar.
     
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Also note that the distortion may not be a factor of the power amp, but a byproduct of the design of the preamp that meets the desired "character" that the designer intends (and that many players demand).
     
    Al Kraft and MoonQuake like this.
  8. MoonQuake

    MoonQuake Supporting Member

    Jan 1, 2011
    Montréal, Qc.
    And with these different stats, can someone know which amp would be the most neutral and translate the preamps voice the best without trying it?

    Cause it's impossible to have them all side by side at the same time to sonically compare.
     
  9. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    If the signal crest is knocked down a lot at the preamp section it's rather unlikely to get decent power amp overload coloring.
    If the signal passes the preamp with nearly full dynamic range it's very likely the power amp will run into overload situation in (real world) practce thus will contribute coloring to the sound
    Both "concepts" are different and do sound different. Personally I prefere some/little power amp "grind" cause it can interact nicely with drivers.
    btw personally I wouldn't suggest pedigree low drivers doing it this way!
     
    Last edited: Sep 21, 2016
  10. Buy a standalone power amp
     
    seamonkey likes this.
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Are you talking about an external preamp (Noble) or using the preamp that's part of each of the amps you originally mentioned? The reason I am asking for clarification is that when comparing integrated preamp-power mp combinations, there are things that can be more tightly interactive between the two.
     
    Al Kraft likes this.
  12. MoonQuake

    MoonQuake Supporting Member

    Jan 1, 2011
    Montréal, Qc.
    I'm talking about using the Noble as an external preamp through the effects return/aux in of one of these amps.
     
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Ok, in this case, and I can speak only for the Subway D-800, the tone will be neutral but if you drive the amp hard (beyond rated power), there is additional circuitry that emulates some of the overdriven characteristics of a tube power amp, specifically clipping behavior and unobtrusive recovery from the overdriven territory.

    So, it really depends on what you need, how hard you intend to play the amp, and if graceful (power amp) overdrive characteristics are important to your particular application.
     
    fdeck, Al Kraft and MoonQuake like this.
  14. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    The only coloring these "standalone" amps may contribute to the sound is the coloring that limiters can contribute if the amp is pushed hard.
    IME a limiter can't substitude a well designed "musical" charatersitic at overload range. These are totally different animals.
     
  15. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    In the case of the TH500 (according to the manufacturer) you can't overdrive the power section. The protection circuits keep it from clipping. So that's one difference in implementation. I don't know how the protection circuit contributes to the sound signature when you're pounding on it.

    (There's a clip indicator light that causes some confusion; this shows clipping in the preamp's final gain stage)
     
  16. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    Crest number of different signals is the key to understand WHY.
    3dB crest for MI signals means very lots of distortion so if the amp refuses to amplify those very "optimistic" 3dB crest signals at bench mark test, so what.
    The sine wave can't be substituded for MI bass guitar in practice and the bass guitar signal can't substitude a meaningless bench mark.
    Hope the myth that clean sine power would directly translate to clean MI power, hope this myth would die.
     
    Last edited: Sep 21, 2016
  17. seamonkey

    seamonkey

    Aug 6, 2004
    There aren't many schematics around from makers using the ICepower modules, but Fender has some at it's site
    Here's one
    http://support.fender.com/schematics/bass_amplifiers/Rumble_350_2010_schematic_Rev-B.pdf
    Not the same ICEpower but you can get an idea that it's wrapped in a custom circuitry, looks like a limiter, and a diode clipper in there.
    Diodes are used for soft clipping even some well known tube amplifiers.

    If you like the sound directly out of the Noble all this extra stuff may not be for you.
    Head makers aren't in it to sell just power amps.
    A power amp may do the Noble the best justice.
     
  18. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    I'm no expert on designing bass amplifiers, but thankfully we already have one who has shared his insights. All I can add is that as someone who owns both the TH500 and D-800, and is an engineer who understands conceptual design trades and options in architecture for things that most would see as being very much the same, I can't imagine there would be a lot similarity beyond the AC power cord on those two units.

    I like the sound of both, but they are very different animals and I can only imagine that those differences started in basic architecture and led to fairly different choices in design execution, including how the overall sound would be shaped with the preamp and power amp sections working in a synergistic/complementary manner. My sense is that your best bet might be to find a good clean amp that was optimized to be a "wire with gain".

    Hoping that half an equation you don't have all the parameters for will yield a good result probably isn't your lowest risk option. The TH and D-800 are great as a system, but in my mind would not be the most cost effective way to get that preamp signal that's just right to your ear to a level that will drive will speakers. If I had to guess on one of the two being most likely to please it would be the D-800 - it seems more clean and transparent to me, albeit with some design magic that addresses over-driven signals.
     
    MoonQuake likes this.
  19. 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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