Is this true?

mdk5068

I was readying about this in an Elite Receivers comparison between what some people consider to be the top five receivers. In the commentary, this caught my attention:


I'd probably just get an Onkyo 805 with an Emotiva XPA-5. The 805 can put out nearly 170 wpc with only two channels (use for the 2 back surround channel)s being driven and just run the other 5 channels on the XPA-5.

If you can break 1500 dollars, an Onkyo 875 with the HQV Reon video processor would be even better with an XPA-5."

Is it feasible to direct the majority of the power in the receiver to only two channels, and allow the external to power the rest? Is this done automatically? I am simply surprised if it is, because it would mean most people in a 5.1 setup could get away with only buying a 3 channel external as apposed to a 5 (other two channels just using the amp from the receiver). Any comments would be great, I was simply curious.

--Thanks,

Mark

Toolfan66

As far as i know it is done automatically, My SC-07 runs my surrounds and my XPA-3 powers my center and fronts (R-L) 200 watts per channel running all three, and 250 watts running two channels. This helps the receiver to not work as hard if i was running all seven channels. This setup works very well.

If i am missing something here someone will chime in to educate us.

I also beleive this is only the case if the amp is common ground.

Fongolio

If you are asking if the receiver will "bridge" or automatically direct all the power from the unused channels to only the ones being used, the answer is no. Most receivers will only output the rated per channel wattage. Some, when running in two channel mode will output slightly more power to the front two channels. Read the manual for a full explaination.

ahorvitz

When using most HT receivers for 2 channel, you'll typically get a little more power (per channel), automatically. You're right - you could step things up by adding just a 2 or 3 channel amp.

The Onkyo 875 can be bridged (front and SB channels), but will only drive two speakers when configured this way. It's an interesting feature. I haven't found it useful, but it's interesting. I assume the same can be done on the 805, per OP.

mdk5068

That is interesting that the channels can be bridged. I have heard the term but never really understood it until now. So for a guy that was only desiring to run a 5.1 system off of a 7.1 receiver (100wpc), he could grab a three channel amplifier (200wpc) for the front three channels, and bridge the back two channels to hit around 150wpc? If it was an onkyo, of course, such as the 805. I was only curious because there typically is a big difference between the prices of a 5 channel and a three channel amplifier. One might dampen the cost by using the bridging feature.

greymatter

mdk5068 wrote: »

That is interesting that the channels can be bridged. I have heard the term but never really understood it until now. So for a guy that was only desiring to run a 5.1 system off of a 7.1 receiver (100wpc), he could grab a three channel amplifier (200wpc) for the front three channels, and bridge the back two channels to hit around 150wpc? If it was an onkyo, of course, such as the 805. I was only curious because there typically is a big difference between the prices of a 5 channel and a three channel amplifier. One might dampen the cost by using the bridging feature.

interesting indeed

mmadden28

When using a reciever to power the surrounds and an external amp for the mains and center, you just have to keep in mind the possible gain difference between the amp and the AVR. If there is a difference (or at least a big difference), when you turn the volume up, the avr and ext amp volume may increase at a different 'rate'. This may or may not be noticeable, esp when comparing the mains to the surrounds, but should be noted.

If this change is implemented (wether mixing the AVR and ext amp, or going all external), be sure to recalibrate the system, either using an SPL meter or the automated feature of the AVR (Audyssey, etc)

I would say that whether or not all power would be realized by the two channels vs. the 5 channels of an AVR highly depends on the AVR itself and how its designed (esp with the capability of the AVR power supply transformer).
The Onk 805 is rated as follows:

130 watts minimum continuous power per channel, 8
ohm loads, 2 channels driven from 20 Hz to 20 kHz,
with a maximum total harmonic distortion of 0.05%
(FTC)

Note that the rating is for 2 channels driven. So if you're only using the AVR amp for the surround channels, you will have the full rated power available if the speakers demand it-not a fraction of the rated power.

It should also be noted that even if you choose to externally amp all of your speakers; the AVR's amps (in the 805's case at least) can still be put to use to power Zone 2 for another room or outdoor speakers.