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I am considering the purchase of a new preamp/processor, and an amp(s). I was wondering if someone could describe some of the pros and cons of bi-amping.



Scenario 1 -


What are the pros and cons of lets say, a given brand's 200w/ch amp, versus using two weaker amps (bi-amped) that are the same brand. By same brand, pretend I mean that their sonic characteristics are the same. The only difference is power.


Is there any sort of gain in seperating like this? Is there any sort of loss?


Would I be just as well off getting a 200W/ch amp?



Scenario 2 -


Is the common idea behind bi-amping to use two different sounding amps to get the best of both worlds?


Like using a sweet, warm sounding amp for your highs/mids, while using a more punchy, bright amp to power your lows? Does that make sense?





BTW - How does one figure out how many watts are needed when bi-amping, in order to get the volume correct betwixt the highs/mids, and the lows?


Do you generally need amps with gain control?
 

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I have bi-amped my Martin Logan Odysseys using a Classe CA200 for the woofers and a Counterpoint SA-220 for the panels. I am not completely happy with the results - I have found it a bit difficult to get the gains matched. (Using a subwoofer isn't helping this part either, even though the sub is adding a lot of value.)


Perhaps because the SA220 is a fairly powerful amp in its own right (200 wpc @ 8 ohms, close to 400 wpc @ 4 ohms), and because it is a tube/transistor hybrid rather than a pure tube amplifier, it really wasn't running out of gas when it was powering both cones and panels. So when the CA200 was introduced to take the load off the main amp, it obviously didn't do that much.


I have found that both of my amps are powerful enough to run the full speakers without assistance - I suspect that this would NOT be the case in some other configurations. For example, had I ended up with a Conrad Johnson MV60 power amp, I am pretty certain that offloading the bass to the considerably more powerful CA200 would pay a big dividend.


I prefer the tone of the Counterpoint, so I am considering putting back the SA220 as the only amp up front, and bi-wiring the speakers to it.
 

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I think the benifit is less distortion. The disadvantage is your reciever or pre processor will have to work a liitle better for the extra needed signal strength. I use bi amping for my main left and right surrounds. Bi amping does wonders for music. BTW mine does not count as biamping if using both a stereo amps A and B channels is not what you consider tow seperate amp sources. I use a Denon POA5200's a and b channels. If that doesn't count than I take back what I said about music but the rest stands. I have tried multiple mono blocks on the same floor standing speakers with the same improved results.
 

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Bi amping increases headroom and reduces distortion. If you bi amp for instance with dual 100wpc amps, the results will be more like using a 500w amp than a 200w amp in non bi-amped mode.


The drawbacks, beside cost and complexity, is the difficulty in matching the low level crossovers ahead of the power amps to what the speaker designer has in mind.


You need the right slopes in and out of the driver in question as well as the correct crossover center frequency.
 

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Stevemo:


I believe if you bi-amp each speaker with the same amp (stereo amp, 1 channel for low's the other for high's) it's still considered bi-amping. The reason why you might think it's different is because usually people bi-amp with a specific type of amp for running the highs (we'll say a tube amp, because they sound sweet) and a more powerful amp (solid state) running the low's. Either way, you are bi-amping.
 

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Unless you are using active crossovers then I feel biamping (passive) is not a significant improvement (i.e. you are better off getting a larger amp). On the other hand, active biamping is a significant improvement but you'll want speakers that are designed for this (i.e. they include active crossovers).
 

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I compared a pair of Magnepan MG-III's (which I still have) both with a single and bi-amped with both a passive (the one Magnepan supplied for bi-amping) and active xover (Bryston) between the woofer and mid-range/tweeter panel amps.


The main value in bi-amping, I believe, is getting the large LC xover out of the speaker. In particular, inductors are a large source of distortion. To me, the improvement of bi-amping the MG-III's is significant but not huge. The speakers sound a bit more transparent, the bass has a little more impact, and imaging has more depth.


Since mid-range needs almost as much power as woofers (and there is much less value in tri-amp'ing the tweeters), both amps should have similar power capabilities.


The key question, though, is the one the poster asked which is whether one gets a better value spending money on double the amps plus an active xover or put that amount on a better single amp (or some other part of the system). Unfortunately, this is not easy to answer and depends your speakers, the rest of your system, your budget, your ears and your preferences.


The MG-III's like a fairly large amp. A single large power amp would probably sound better than bi-amping with a two inexpensive under-powered amps. On the other hand, I'm in the camp that believes there is only a small sonic improvement going from a decent moderately priced amp and a high-end amp of the same power capability. In this case, I'd go for bi-amping with two good mid-priced amps rather than one high-end amp, assuming there isn't something else in the system that would benefit you more with the additional money.


-David
 
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