Yamaha 663: # of channels vs power/channel

[josko]

If I drive my front two channels with a separate amp, will the power/channel (on a yamaha 663) into the remaining three channels increase or stay the same? Yamaha specs say it will be the same, but I've seen some reviews that claim the power per channel varies inversely with the number of channels driven. Since I assume the amp has a separate power amp for each channel, I'm not sure how the power would increase.

If it does increase, is the increase noticeable or just measurable with instrumentation?

Thanks in advance

 

[oppman99]

I'm pretty sure that the 663 does not have a separate amp for each channel. So driving your mains with an external amp should allow more power to be channeled to your remaining three speakers. It will definately make it so the 663 won't have to work as hard. If you are planning on adding an amp anyway, why not go with a 5 channel?

 

[MDS]

Multi-channel AVRs typically do have a separate amp for each channel; however, they are all driven from a single shared power supply.

This leads to the all channels driven controversy. Manufacturers advertise their receivers as 100 x7 (for example) but the power measurements use the FTC standard of 2 channels driven. When bench tested with all channels driven simultaneously, the results will be far less than 100 wpc for each channel and that is why you may have read that 'power per channel varies inversely with the number of channels driven'.

Don't worry about that because a) real music will never drive all channels simultaneously at the same level and b) the shared power supply allows the receiver to allocate power where it is needed most on an instant to instant basis. That is why the 'dynamic power' of such a receiver is often greater than one that was rated using all channels driven simultaneously (such as H/K).

If you use an outboard amp to drive the front channels, that will reduce the burden on the shared power supply because now it only has to allocate power to 3 channels instead of 5 (or 5 instead of 7). The max power per channel will not increase or decrease but the power supply will be better able to supply the power needed for the sharp transients (think sudden loud cymbal crash or an explosion in a movie).

In practice will you notice a huge difference? Not so much...unless you are really driving the system hard at very loud levels.

 

[j_garcia]

If you are pushing the receiver to the point where it is struggling now, then you will hear an improvement. If not, then as MDS said, the difference will be less noticeable. What you will find is, additional headroom which should allow you to play at higher levels than what you are currently capable of with less distortion (or that is the goal anyway) due to the fact that the amp should be capable of providing more power to the speakers than the shared power supply of the reciever. Even though you will usually not have a lot of things going on in all speakers, during times where there IS a lot of activity (action scenes w/big explosions, etc...) you could see a benefit with an amp because the power supply is dedicated only to the speakers it is driving.

With my receiver the difference is quite noticeable though my amps are 150wpc vs the receiver at 120wpc. The difference being that the amps have much larger power supplies dedicated to what they are doing compared to the receiver powering everything.

 

[GlocksRock]

This confirmed what I was thinking, and I'm doing the exact same thing with my RX-V663, since I got a free 2 ch. amp from my dad, I'm using it to drive my BP7006 towers, and the receiver to push the remaining 3 channels.

 

[Unclepauly]

I heard the 663 really only does about 40w per channel so if you can offload the front 2 or 3 channels I think you'd be good for dynamics as the back channels use very little power.

 

[PENG]

I heard the 663 really only does about 40w per channel so if you can offload the front 2 or 3 channels I think you'd be good for dynamics as the back channels use very little power.

You are quite right, the 663 may do well enough for most situations with the help of even 2 or 3 channels, according to:

http://www.ultimateavmag.com/avreceivers/608yam663/index7.html

“This graph shows that the RX-V663’s left channel, from Multi input to speaker output with two channels driving 8-ohm loads continuously at 1 kHz, reached 0.1% distortion at 166.7 watts and 1% distortion at 190.7 watts. Into 4 ohms, the amplifier reached 0.1% distortion at 218.0 watts and 1% distortion at 245.9 watts. With five channels driven continuously into 8-ohm loads, the amp reached 0.1% distortion at 60.0 watts and 1% distortion at 74.9 watts. With seven channels driven continuously into 8-ohm loads, it reached 0.1% distortion at 47.3 watts and 1% distortion at 57.8 watts.
Yamaha's stated distortion of 0.09% was reached at 46.9 watts with seven channels driving 8-ohm loads. This is roughly half of the 95Wpc specified by the manufacturer, which could be why the AVR seemed to run out of gas at higher listening levels. “

So while it would run out of gas at high listening levels continuously, it would have plenty of power in terms of dynamics for typical 2 channel stereo music listening.