Deleterious effects of bridging ??


I am considering the following two options for purchase, both being approximately equal in price.

(1) NAD C370 integrated and C270 power amp in bridged mode (300 wpc @ 8 ohms, 70 amps peak)

(2) Parasound PLD1100 pre and HCA1500A amp (205 wpc @ 8 ohms, 60 amps peak)

I cannot biamp with the NAD amps because my Magnepan SMGa's are not biampable nor biwireable. Thus, the NAD's must be run bridged.

According to the salesman, bridging stereo amps has undesirable consequences by "trashing the damping factor of the amplifier." Thus, he suggests going with the Parasound separates.

Given that I believe in so little that I hear in regard to either audio or politics, my question is simply is there any foundation to the salesman's claim, or is he just talking out of his ass, so to speak?

The remainder of my equipment is as follows:

Adcom GDA 600 DAC
Monarchy Audio DIP Super Drive
Pioneer Elite PD-F27 CD Changer
Apogee Wyde Eye 75 ohm & 110 Ohm digital cables
MIT T2 interconnects and speaker wire
Monster Power HTS2500 Power Center

Any feedback that you can offer would be most graciously appreciated.

Mil Gracias
Ag insider logo xs@2xdocwarnock
IMHO, I'm not sure the NAD advice is correct above. If the 370 and 270 offer the same output power you should be ok and better off. I can't offer anyting re: Parasound vs NAD.
Bridging will obviously increase the power by a factor of three or four. However, it also increases the distortion and, in addition, limits the ability of the amplifier to drive lower impedance loads. With many bridged amplifiers, 8 ohms is the preferred load. However, with those precautions in mind, I have used bridged amplifiers several times in the past 36 years and never had a problem; and did in fact enjoy the markedly increased power delivery. Also keep in mind that the hook-up instructions for some bridged amps can be a bit tricky, so read the instructions very carefully.
Bridging will mean that because each "channel" of output is seeing only half of the loudspeaker load (the + or the - terminal), the amp will see the loudspeaker as half of its actual impedance if both channels were driving it. This means that if your Maggies are a nominal 4 ohm load, the amps will see them as nominal 2 ohm loads. This can strain the power supply, since it has to deliver a pretty healthy amount of current without any voltage increase. This is why higher impedance loudspeakers are a better match for bridging. Be careful to make sure that the amps are up to it, especially at higher listening levels. If the speaker dips lower at any point, you'll be straining the amps quite a bit.
I was told recently, by two knowledgable people, that bridging does in fact degrade an amp's damping factor. This is probably yet another case of "try it yourself to see what happens" esp. in light of positive experiences (ie: Hifiexpert) shared above.
Bridging does not result in seeing half the speaker impedance. There is no complete circuit to just the + or - terminal. Bridging puts the outputs of the two amps in series, effectively doubling the available output voltage swing. The same gain setting will result in supplying twice the current to the SAME load, if the amp has the current capability. That results in four times the power. That is why some mention the problem of an inherently low impedance speaker with the additional voltage swing of a bridged amp applied. Often the amp can not supply that much current. That is why 3 to 4 times the power is correctly claimed in a previous post. How much current does your speaker take to drive it to adequate listening levels and what is its nominal impedance? Does your unbridged have high enough voltage output to drive it to that level? Those are the questions. If it doesn't play loud enough and the amp is voltage limiting, then bridging is a possible solution. If it doesn't play loud enough and the amp is current limiting, then you need a higher current supplying amp or a more efficient speaker. Bridging won't help because if the amp is current limiting unbridged, it will just limit at a lower gain setting when bridged. I know, a lot of words, but there are 3 current threads on bridging and a lot of misunderstanding. See BIAMPING under Speakers, for example (it includes bridging). :)