Rotel Mono-blocks for 6 ohm speakers

[gilphilbert]

Hi everyone, My current setup consists of: Project Debut III, Rotel RA-920AX and a pair of Wharfedale Diamond 9.1's - I'm looking to upgrade the speakers and amplifier. I like the sound of the Rotel kit, so I'm looking to upgrade it, but stay more or less with the more classic kit. I know the mismatched impedence question has been asked hundreds of times, but what I'm struggling with is whether I can use two Rotel RB-970AX power amps with the Wharfedales (the Wharfedales are only a stop-gap while I save up for something more exciting, probably B&W CM1, Focual Chorus or B&W 685 S2) but I'd like to get the amps in place so when I get the new speakers I'm ready to go. The Rotel RB-970AX is rated for a minimum of 4 ohms in stereo mode, but in bridged mode they're rated for 8 ohms. Is this going to be a real problem? The Wharfedales have a nominal impedence of 6 ohms and are rated for up to 100 watts.

 

[chelstondave]

Hi - have you some form of preamp as you won't be able to use the power amps without one?

 

[gilphilbert]

Sorry, yes. I left that off - I'm planning on getting the matching Rotel RC-970AX to go with the power amps.

 

[davedotco]

The general rule when using bridged amplifiers is that you get 'twice the power into twice the impedance', so ig the amps are rated down to 4 ohms in stereo, that will be 8 ohms when bridged.

Realistcally these figures have are not totally exact, there is a bit of 'wriggle room' so your 870s should be fine providing you use a little common sense, ie don't drive them flat out and keep an eye on how warm they run.

For what it is worth I used to use 870s and mostly 860s in modest background music type systems in bars, shops and the like. We would usually run 2 pairs of speakers off each amp, ie a 4 ohm load, with no issues whatsoever.

Not quite your situation, but testimony to the ruggedness and reliability of these models when worked quite hard.

 

[gilphilbert]

Sorry for the belated thank you for your advice everyone.

In the end I actually settled for to Rotel RB-971 power amps with a Rotel RC-970BX pre-amp connected to a pair of Tannoy Mercury V1 speakers as my "temporary solution" which are 8 Ohm speakers anyway.

I'm so impressed with this setup that I might keep it like this for a lot longer than I planned! Now I just need to add a good DAC and phono pre-amp, a pair of speaker stands and... 🙂

 

[BryO]

Nice, I have a pair of 980BX power amps with an 870 pre amp. They sound great.