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Bridging power amps....

Discussion in 'audio' started by arthur, Oct 3, 2011.

  1. arthur

    arthur Banned


    Some advice please if I may ?

    I'm making a system for a friend, newly converted to the cause!

    I'm spending his money too, great stuff.

    The question regards power amps. I've seen plenty from Rotel, Nad and others that have adequate power outputs but that can be bridged into more beastly monoblocs.

    But they frequently claim that they can then only drive speakers above 8 ohms. Is this bollocks?

    It seems a little odd to double the power and then say it can't drive a tricky load.

    The system will soon evolve into an audiolab dac/pre and a pair of bridged (probably) Rotels into some bigger Dynaudios.
  2. Plutox

    Plutox Registered Abuser

    It's broadly true - bridging is far from a panacea because you double the voltage swing available but the current drive capability remains unchanged.

    If you need the extra power, get a beefier amplifier. Bridging is not a free lunch.
  3. Michael J

    Michael J CDP3000 1Hz-20kHz ±0.5dB

    I think you'll have to provide links to such claims. My NADs can drive 4ohm loads.
  4. mudlark

    mudlark nearly half a clue

    Go active. you are bridging the amplifiers, sort of.
  5. Darth Vader

    Darth Vader From the Dark Side

    In these scenarios YES!

    To bridge amplifiers they need to be very low almost zero output impedance. This usually means big powerful amps. NAD were ahead of their times and produced amps that really could drive heavy currents = low output impedance
    into speakers. I still have a NAD here in my office/lab for experimental work.

    With the right sort of amp design then bridging is a real possibility. I currently use a pair of Meridian 559s each in bridged mode but here we are in a different playing field.

    If you have 'normal' speakers look for an amp thats powerful enough to drive them without bridging as it'll be cheaper and perform better.

    So what are the speakers?



    ps my amps? >1600wpc into 4 Ohm and 150A peak into 1 Ohm PHZZZZZzzzzzz
  6. martin clark

    martin clark pinko bodger

    Plutox is right on the money. Doubling the voltage swing means each amp 'sees' only half the former load impedance. So a 4-ohm speaker draws current from each amp like it is a 2-ohm speaker. Bad idea.

    Hence even 4-ohm rated amps are only going to be happy into min. 8-ohms or above when bridged.

    Generally - a much more powerful amp in the firstplace is the right answer.
  7. Plutox

    Plutox Registered Abuser

    That may well be so but the point is that, in the general case, whatever load impedance a single power amp is capable of driving, that number is doubled when two identical units are bridged.

    Let the bridger beware ;)
  8. arthur

    arthur Banned

    The speakers will likely be some Dynaudio 1.3's.

    150 amps??????????

    That sounds so absurd I want some :D
  9. Michael J

    Michael J CDP3000 1Hz-20kHz ±0.5dB

    @ Plutox,

    Then it's a good job that mine have a rated "single-ended" peak output into 2ohms. :)

    (You need that if you want to drive two pairs of speakers at once from one stereo amp.)
  10. bottleneck

    bottleneck pfm Member

  11. arthur

    arthur Banned

    Hi Bottle!

    By a spookeroo coincidence, I am indeed watching those very things :eek:
  12. dweezil

    dweezil pfm Member

    i used the Nad C272s and they were much better bridged than biamped into (6 Ohms nom) MA GR60s; bass appreciated the extra headroom and i lost some of the distortion in treble.

    On the big (4 Ohm nom) PMC speakers they were poor, even at very low volume the Brystons were vastly better.

    Look at the specs carefully before you go for a bridged amp.
  13. seyles

    seyles Retired Child

    He'll need a Meridian controller* to get the best out of them or if he has any analogue sources, 562v2 is the minimum.


    *You can plug any digital source into them and they'll work, a Meridian controller or processor will give you more source options and have built in ADCs for analogue sources. 562v2 will pass 24/96 earlier versions won't.
  14. sonddek

    sonddek pfm Member

    Go NADs!

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