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Do amps running at 8ohms have more headroom?

Discussion in 'Amps and Cabs [BG]' started by pulse, Oct 16, 2013.

  1. pulse


    Apr 10, 2007
    Berlin, Germany
    Its funny I have two trace elliot 1153 cabs and a HH V-S BASSAMP from the 70s that I love.

    They actually sound really good together... funny thing is when ever I run only one cab into the amp (so 8 ohms load only) said cab kinda sparks to life.... when I run both there is presence drop in both cabs,

    SO I recently picked up a second HH amp on ebay (Power amp only) and now each HH Head runs an 8 ohm trace elliot cab and sounds great.... :hyper:

    the Cabs are punchy and sound happy :bassist:

    My question is what is happening here. cos when I plug both cabs into one head there is a kind of "presence drop" I need to dig in more to get the same grind and turn the amp up to get the same fatness....

    Am I imagining things, or is there some technical rule behind this ?

    Thanks for any info!
  2. 4-string


    Jul 23, 2006
    Cabs out of phase?
  3. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    +1 if everything was working properly, the 4 ohm load with the 2 cabs should be noticeably louder, deeper, and fuller sounding. If the 2 cabs are wired out of phase with each other, the result is as you described.
    Test the cabs with a 9VDC battery to find out.
  4. Yes, but if the cabs were out of phase with one amp, they'd still be out of phase with two.
  5. Maybe the output jacks are in series?
  6. pulse


    Apr 10, 2007
    Berlin, Germany
    thanks - I did the Phase test, both speakers moved in the same direction with a 9Volt battery.
    The speakers are different types tho....With different sound characteristics

    I mean each HH amp is only 100watts (mind you 1970s watts which are pretty darn loud)
    so maybe it matches up better to one 8 ohm cab...(each has a max power handling of 200 watts....) either way the cabs seem pretty happy that way....
  7. Two things that can cause an amp to underperform with a heavier load (4 ohms) if the amp was designed to operate fully to that load is weak power supply caps and incorrect output bias.
  8. seamonkey


    Aug 6, 2004
    So when you have two heads, each going into it's own cabinet - yes you have more "headroom"

    You have twice the headroom of a single head feeding two cabinets.

    Headroom is some term where the power supply can push out a little more than rated power when needed, but only for a short burst.. With 2 power supplies you have twice the capacitance, twice the theoretical headroom.
  9. I think I've about heard it all now. we have "tube watts", Trace Elliot watts" and now 1970 Watts. H&H made very good equipment. I still own a 100W Professional power amp and the remains of an IC100. Both are 100W into a 4Ω load. About 60-70 into an 8Ω load.

    If you are experiencing difficulties running into a 4Ω load quite possibly your amp could do with having its forty year old capacitors replaced.
  10. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Is that because volts were bigger or amperes were bigger?
  11. Jim Carr

    Jim Carr Dr. Jim Gold Supporting Member

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    In the 1970s, people were smaller, so the watts seemed bigger then.
  12. ric stave

    ric stave

    May 6, 2006
    Buffalo, NY
    What about 'Texas watts'? Cuz, you know...
  13. I did not know that the scientific community got together AFTER the 70's, and re-defined how watts are measured :eyebrow:
  14. Amperes were bigger because volts were smaller ;)
  15. pulse


    Apr 10, 2007
    Berlin, Germany
    dudes dont ask me why 1970s watts just sound more pleasant to my ears....

    I am constantly perplexed why modern 1200 watt rigs can sound so sterile ... and a nice Vintage 70s amp like this has such a pleasing loud sound with such a lower power rating...

    mind you they were competing at the time with Tube heads, so I guess they had to make sure the sounds coming out held up.... either way these power sections sound delicious....

    But I am not complaining.... I would say HH are amazing bang for the buck heads...

    I have paid a total of 200 euro for both these amps, and a total of 350 for the two cabs... for 550 euros I am plenty happy and its an easy to move rig

    minirig by James Welburn, on Flickr
  16. chienmort


    Aug 15, 2012
    I have both an HH VS Bassamp and an HH Bassamp 100.

    Both are rated at 100 Watts into 4 Ohms and 80 Watts into 8 Ohms. So the gain in absolute power is only 25%. The real gain should be in adding the extra cabinet but this would not be earth shattering.

    The best way to use the two cabs is one on each amp. These amps have a slave output and if I remember rightly the you can use the Echo return input so that you just use the power amp of the slave amp.
  17. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Then it's self-defeating, because P=IE.
  18. chienmort


    Aug 15, 2012
    I must admit I have changed the caps in mine but they are only 4700uF. That is quite low by today's standards. A modern class amp would have 10000uF caps.
  19. pulse


    Apr 10, 2007
    Berlin, Germany
    Yeah Chienmort, its comfortable to use---- I go slave out of the V-S Bassamp into the the power amp's input on the front panel....

    then the V-S Bassamp's master controls the volume of both amps....

    You are right, it sounds pretty darn glorious this way....
  20. Yep ;) :D

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