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Pros and cons of Bridged configuration?

roog

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Hi you knowledgeable techies, I wonder if I could benefit from your knowledge about Bridged power amplifiers please?

I note that some designs are offered with bridged configuration as an option, what are the pros and cons to doing this?

And given the plethora of low cost class D amplifiers doing the rounds at the moment does anyone know of one that can be bridged to give circa 200W rms in to 8 ohms per channel ?
 

jae

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I believe some manufacturers have been bridging the Purifi 1ET400A modules although Purifi does not expressly suggest this. Thermals are the main concern here and with adequate heat exchange perhaps most of the existing modules can pull it it off. But it would simply make more sense to buy NC2K.
 

sergeauckland

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The pro of bridging is that output power is nominally quadrupled (in practice a bit less) over a single output.
Con is that each half of the bridge sees half the load impedance, so puts an extra strain on the amplifiers, which have to be comfortable with low impedance loads.
Minor con is that both sides of the load are driven, so one has to be careful not to ground one side inadvertently.
Further con is that a bridged amplifier of whatever output is likely to be more expensive over a single output, especially if the bridged amp is a converted to mono, and one needs two of them. From the dealer's point of view, of course, this might be a pro!

S.
 

jae

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Forgive me what is a NC2K?
Hypex NC2K module, or an amp containing such a module, for example: https://www.audiosciencereview.com/...-hypex-nc2k-monoblock-amplifier-review.16892/ if you need big wattage w/o going into the professional PA/home theater rackmount type stuff (which usually doesn't measure as well).

NAD's bridgeable Purifi-based amp: https://www.audiosciencereview.com/...er-with-purifi-eigentakt-amplification.15881/. An unbridged Purifi 1et400a amp should be able to handle about what you require. The NAD I linked is rated at 185W continuous, but NAD is fairly conservative with with ratings and that particular amp does not have anything impressive as far as cooling is concerned, so I don't doubt a DIY or other Purifi-based solution with better heat exchange could be able to handle the 200W continuous you require (Purifi datasheet more or less says the thermals are the limiting factor.)
 

DonH56

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Quick overview, mostly echoing what has already been said:

Pros:
  • Twice the voltage swing yields four times the power if not limited by current or thermal (heat) capacity;
  • Improved SNR since noise is in general uncorrelated so does not scale linearly (but output signal - hopefully - does);
  • Potential cancellation of some odd-order distortion and common-mode noise so overall THD may be lower;
  • Allows higher power without doubling power supply rails (higher-voltage components cost more and so forth); and,
  • If switchable, flexibility in being able to run as a two- or single-channel amplifier.
Cons:
  • Each amplifier "sees" one-half the load impedance so an 8-ohm load looks like 4 ohms to a bridged amplifier, so requires more current output and ability to dissipate additional heat;
  • SNR is higher but so is the actual noise floor (from two amplifiers) so there may be more "hiss";
  • Output impedance is doubled (thus damping factor is halved) due to two amplifiers in series with the load thus minimum rated load is usually doubled (this also leads to greater load sensitivity and potentially reduced stability);
  • No true ground terminal -- both (+) and (-) terminals float so must be careful not to ground an output during testing or whatever, and potentially more sensitive to EMI/RFI without a "true" ground path for the signal;
  • Two independent amplifiers means duplication of circuitry so generally less efficient than a single amplifier.
There is more, of course, but that's what I thought of off-the-cuff. - Don
 
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