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Biamping or Bridging?

Discussion in 'AV Receivers & Amplifiers' started by Bassbin, Apr 26, 2003.

  1. Bassbin

    Bassbin
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    I've currently got a RC870/RB870 pre power set up and a pair of huge Infinity Kappa 8s in a CD/Phono system. I'm looking at adding another RB870 power amp to the set up. Just wondered if anyone has got any thoughts on the best way to use it.

    The RB870 provides 100W per channel into 8 Ohms and can deliver up to 50 Amps peak current. In bridged mono mode the power is 320 Watts. So I can either biamp each speaker with 2x100 Watts per channel or use the amps in bridged mode with 320 Watts per channel.

    I'm not hung up on the numbers but that's all I've got to go on just want to know which is likely to give the best results before I buy the required cables. I've read in a few reviews of other Rotel amp that the bridged mode is not much better than the standard out put to each channel. Any thoughts?

    Thanks,

    BB
     
  2. buns

    buns
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    I have actually read that bridging is bad.......
     
  3. Sunday Ironfoot

    Sunday Ironfoot
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    I'd have thought that bridging would just increase the power output, so that they go louder. Whereas bi-amping will actually improve the sound quality (one amp for each set of speaker cones instead of one amp driving both sets of cones).
     
  4. buns

    buns
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    im not sure why im thinking it, but i was of the beleif that bridging was likely to cause difficulty driving any sort of tricky impedences..... its too late im afraid for me to work out why!

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  5. Steve.EX

    Steve.EX
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    Bi-amp.

    Better stilll buy a better amp which will give better resulkts than either of the other options.
     
  6. Bassbin

    Bassbin
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    Thanks for the replies look like biamping it is. I'd been watching an RB870 on ebay and managed to get it for a little over £100 earlier this evening.

    I'm not keen to buy a different amp in the medium term as none of the friends ones I've compared mine against (up to £500) sound any better IMO. I also looked at amps from the Rotel 900 series a few years ago and found the pre didn't have the CD direct function which turns the amp into a passive pre-amp and the power amps (RB970/971 were very similar but had been engineered down to a price.

    Hopefully get the new amp by next weekend and be able to try it all out.

    Thanks,

    BB
     
  7. Phil43

    Phil43
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    Sorry to be thick but when you 'Bridge' a stereo amplifier do you just SUM the stereo output plus to plus and minus to minus ?
     
  8. Bassbin

    Bassbin
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    Ok so I'm going to Biamp. I've had a look at my spare cables and I think I've got just about enough speaker cable to do. I've also got spare interconnects. However, is there a tried and tested way of spliting the preamp signal into two? I'm guessing that you can get leads made up for this but ideally I'd like a 1 into 2 adaptor without any cabling - any ideas?

    Thanks,

    BB
     
  9. buns

    buns
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    dont the rotel amps have a loop through facility? so you can pass the signal to the next power amp in a chain type fashion?

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  10. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    The reason bridging is worse, usually, is that the power supply is not designed to cope with the current delivery bridged. It's a current limited design. That's why they say it is bad for difficult loads. The amp will measure more power but sound worse. I've never heard a bridged amp sound better than unbridged IMHO.

    I'm with Steve EX on the whole deal anyway.

    Have fun

    Gordon
     
  11. Nic Rhodes

    Nic Rhodes
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    Just to add to Gordon and Buns, the ability of bridged amps to deal with low ohm loads is GREATLY restricted, therefore only brdge with the easy to drive speakers. I would bi amp or buy a better amp.
     
  12. Steve.EX

    Steve.EX
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    For the sake of simplicity:

    In Rotel bridged "mode" the amp only "see's" half of the speaker resistance, hence the BIG warning labels stating 8 ohm ONLY.
    On a Rotel if you use 4/6 ohm speakers in bridged mode you will start knocking out internal fuses within a very short period of time.

    Steve.
     
  13. Bassbin

    Bassbin
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    I'm not at home at the moment but I'm pretty sure that the Infinity Kappa 8 is 6 Ohms and could be quite a heavy load so I'm not even going to try bridging the amps. The RB870 doesn't have the daisy chain feature so I'll need to split the pre amp output. I still really don't want to change the amps outright though as the system I've got gels very well together (the thinking on the extra power amp is just more of the same). When I do upgrade I'm thinking that I'll need to spend about £1,000 split between amp and CD so it will be over a year before I can do it at least.

    Thanks,

    BB
     
  14. banman

    banman
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    Hi BB,

    Just wondering how you got on with all this?

    I bought recently a 870 and am waiting to get a 200C (KEF.) I was contemplating whether to just bi-amp the 200C with the one 2-ch amp.

    My other option was to think about geting another 870 and bridging them to run my fronts Kef Ref. 3...

    So am wondering how you got on?

    I hate reading posts that start "I read...", "I thought...", "I'd imagine..." or "I heard..." - sorry guys!! - I'd rather hear from the horse mouth so to speak.

    Many Thanks,
    B.
     
  15. Bassbin

    Bassbin
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    I've still got a pair of 870s and use them to biamp my big infinity speakers and really like the results. At the moment I'm deciding on whether to change the infinity speakers for some Tannoy R3s and add an old Rel storm.

    I think I paid £200 for my first 870 brand new back in 1988 and since I've added another used one for £100, an RC972 pre for £100 and an RQ970 phono stage for £35. So at used prices the whole kit would cost about £300-350. I guess a very good £500 intergrated could beat my amp in some respects but my room is about 30' x 25' so the extra power on offer is quite important for me.
     
  16. banman

    banman
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    Thanks for the update. It's nice to see a follow-up. Thats a large room indeed. A friend of mine has an integrated Yammy (old but top of the range, I'm checking for reference...) on Kef Q35's in a room of say 18'x12'. Blows the pants off my 985MkII on Kef Ref 3's in terms of grunt - nothing biamped in each case. So I've seen an integrated amp do wonders.

    I'm a bit concerned about the ability of the 870 to run the 200c let alone thinking about bridging it! Its a 4-Ohm unit. So I will be testing running the 200c straight of a single channel off my 985 MkII (100Wpc into 8-Ohms) then bi-amping it using the 870 (60Wpc into 8 Ohms).

    Steve.EX
    so I guess it will run 4-Ohm speakers. We'll see.

    I'll post results back here! :)

    Regards,
    B.
     
  17. Bassbin

    Bassbin
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    An 870 should be 100W into 8 ohms and 300W bridged according to my manual. I think the later 970 was 60W though.

    I've also got a 985 MKII for movies and although I've not tried it I think that 1 channel on the 870 would easily equal 1 channel on the 985. Also if the 985 is running 4 or 5 channels I think it would start to lag behind a pair of 870's.
     
  18. banman

    banman
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    Just for reference.

    http://europe.rotel.com/support/owners-manuals-archived.htm
    (watch for the cunning deception plan there are 2 rb870 links and an 870bx link. The top 870 link is to the 870bx manual! :oops: )

    The RB870 is 60wpc the RB870BX is 100wpc.

    I guess you have RB870BX amps?

    I have RB870, def 60 wpc in the manual.

    Cheers,
    B.
     
  19. Bassbin

    Bassbin
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    I stand corrected. Yes mine are the BX ones. :blush:
     
  20. Dfour

    Dfour
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    Even a reasonable quality intergrated can benefit from bi amping as I found out when I added my Rotel RB981 to my setup.:D
     

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