# RB1070 bridged mono??



## Hakka (Sep 10, 2006)

I currently have a Rotel RB1070 power amp driving my mains. I am considering buying another one the same and run them in bridged mono mode (or possibly bi-amped mains).

The RB1070 is rated at 2 x 130w into 8ohms, bridged mono is rated at 330 watts into 4 ohms. In the manual under the 'bridged mono' heading it says that when in bridged mono mode only connect loudspeakers with a nominal impedance of 8 ohms or higher.

Does anyone know what the bridged mono output is when using an 8 ohm speaker?

Thanks.

Harry.


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## Steve Williamson (May 11, 2006)

Someone had the same question at Link and was explained that your amp will see the 8 ohm speaker as 4 ohms when bridged, so your 8 ohm speaker will be given the 330watts quoted for 4 ohm load, it sort of made sense to me.


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## brucek (Apr 11, 2006)

> Does anyone know what the bridged mono output is when using an 8 ohm speaker?


A series bridgable stereo (two channel) amplifier simply phase inverts one input channel and then the output speaker load is placed across the two positive (+) terminals of each stereo channel. This doubles the output voltage available to the load. Since power is the square of the voltage divided by resistance, then the power goes up by x4. So theoretically a 130 watt stereo amp when bridged could produce 520 watts. Most amplifiers would not be able to tolerate the increased current and so they're dialed down somewhat.

Something for nothing? - well there's always a catch......... First, it has to be done well, meaning the phase inverter has to be designed and executed properly or you'll increase your distortion. Checking the RB1070 bridged specification for distortion when bridged, I see it jumps from a respectable 0.03% in stereo up to 0.1% in bridged. Not too good.

Also as explained already, each output channel will see half the load impedance. So if you hook up an 8 ohm speaker to a bridged output, each channel will see 4 ohms. Hook up a 4 ohm speaker and it will see 2 ohms. That's a lot of extra current and the amp will run hotter.

Your idea of biamping would be a better way to go.

brucek


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## Hakka (Sep 10, 2006)

Thanks for the replies, yeah that is a big jump in distortion Bruce. Might look some more into the bi-amp option.

Harry.


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