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Rotel RMB1075 & RMB985MkII How compatible for Bi-Amping?

Discussion in 'AV Pre-Amp/Processors & Power Amps' started by Mark Ward, Feb 12, 2003.

  1. Mark Ward

    Mark Ward
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    Having sold my PA2400 Sig Power Amps, I've just bought a rotel RMB 985MkII off the forum for use with my surrounds.

    It has occurred to me that since the high frequencies don't require the same amount of amp power as the low frequencies I could use the RMB985 for the Highs and the 1075 for the Low freqs when Bi-Amping. How similarly matched are they? I don't have ANY specs on the 985 yet so I can't make an on paper comparison.

    With 10 channels of amplification available it makes sense to Bi-amp the front 3 and have 4 remaining channels for surrounds.

    Just a thought,

    Mark.
     
  2. garyc

    garyc
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    Mark,

    Have you tried the rotel web site it has the manual if thats of any help.

    Hope you will be happy with your new 985.

    Gary

    PS. What phono leads you using between your lexi and amps?
     
  3. russraff

    russraff
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    I have had both, and the only difference that I could make out was the size of the case! Well, not quite, but they both sounded the same and both have the same power output (the 985 was conservatively rated, whereas the 1075 is realistically rated). What I did notice was that the capacitors in the 985 were of a higher spec than those in the 1075 but, as I said, this didn't seem to make much difference.

    Russell
     
  4. Mark Ward

    Mark Ward
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    Sounds encouraging. The idea was put into my head by a guy who has a high degree of knowledge on these things, his caveat was that the amps had identical gain patterns.

    I did take a look at the Rotel Site, however it appears to b e under construction for Worldwide. I wasn't sure whether the US sight information would be the same. Specs from some companies change for US models.

    Thanks,

    Mark.
     
  5. garyc

    garyc
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    Mark,

    Just downloaded the manual from the USA web and it looks like one manual for all. its give a full specification

    Gary
     
  6. GaryG

    GaryG
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    Ideally, both amps should have the same gain. Rather that scratch your head with the specs just connect them up and have a listen, then swap them over so that the one that was driving the tweeter is now driving the bass. If the gain's the same you wont notice a difference in volume. You may notice a difference in timbre and quality etc so just go with whichever sounds best. On the other hand the gain may not be the same, but you may find that you are happy with the mismatch anyway if it's less than around 3db, you can probably correct it with a tone control if your amp has one.
     
  7. Steve.EX

    Steve.EX
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    Tone control??????
    Lexicon??????

    Damn your eyes man! How dare you sir!
     
  8. GaryG

    GaryG
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    :D

    At least it doesn't degrade the signal on a Lexicon as it's in the digital domain.:zonked:
     
  9. Steve.EX

    Steve.EX
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    Tone Controls???? Cough - Splutter!!

    TONE CONTROLS????

    I fear my dear sir that medication is the only respite from your madness!

    Sreve.
     
  10. GaryG

    GaryG
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    Well you guys will insist on bi-amping/tri-amping your system instead of buying a really good quality monobloc.:D

    Short of building a resistor dividing network to balance the gain it was the best I could come up with!

    I'm going to crawl back under my rock now.:blush:
     
  11. Steve.EX

    Steve.EX
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    Gary.
    Rotel Bi/Tri-Amping is the direct result of wife/mortgage induced poverty!
    Gain curve/matching is a little bit more invovlved than simple input impedances (especially when using 2 different amps) am i teaching you suck eggs?
    However as you have stated whether you are actually able to hear any mismatching will most likely be down to the individaul/imagination.
    There may be more obvious differences when placing the amps under some strain.

    Now let me hold your rock up for you.

    Steve
     
  12. GaryG

    GaryG
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    :D I've got an egg in my gob right now!:D

    I'm glad I got out of electonics, it's so bloody boring!
     
  13. Steve.EX

    Steve.EX
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    Gary.
    I see from another thread you too are a 4x34ds type of guy, what have you got as a front end??

    Steve.
     
  14. GaryG

    GaryG
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    Steve you have a PM.
     
  15. Plump

    Plump
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    Mark, I would not do that.
    Amps should have same gain but Rotels are sort of funny there. I read a lot of diverse mesurements where deviation was pretty big.
    Sometimes even if they put those THX stickers on they do not match exactly. And in your case you need ideal gain curves because your room is huge.
    So, unless you use same model from the same series (here you don't) don't do it.
     
  16. Mark Ward

    Mark Ward
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    OK, I won't :)

    I actually bought this amp to use for the rears anyway, I just thought it may be more convenient for me to use as I suggested.

    Bi-Amped Rears is is :)

    Thanks,

    Mark.
     
  17. mick23

    mick23
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    mark i have the offer of 985mk1 for £295 including postage ,its just a matter of me sending a cheque, i have sought info for 985mk1or mk2, how they compare with 1075, seller who seems genuine , and has 1075 does not think there is a great differance between "985 and 1075"

    a dealer has told me that the 1075 is more (refined in sound quality than the 985 models)

    could you give me yours feelings on your 985 vs1075 i will be trying 985 vs my denon 3802 amplification.



    hoping you can give me some idea which way to go, as i cannot demo the 985 befor purchase and will be using with cdm1 nts as front pair (av and sterio)

    i was going to try biamping my fronts using (985 for powering fronts and center) 3802 for rears and surrounds)

    but have not got a clue on how to connect this all up, if there is a digram somewhere or link would be helpfull thank you
     
  18. CYRUStheVIRUS

    CYRUStheVIRUS
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    MARK having had a demo of big ROTEL 1095 again recently i really think you should get one on loan and compare with bi amping the two you have, im convinced it will be better and you can sell me back my amp;) ha ha
     
  19. Mark Ward

    Mark Ward
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    For £295 Incl Shipping the 985mk1 would be a very good buy. As far as how similar the 985mk2 is to the 1075 I'm really not sure. I have both and asked the question here because I was considering using the 985 for the high freq and 1075 for the low freq channels bi-amped.

    I would say that both perform very well and at very similar power levels, although I have noticed that neither are as refined as the Harman/Kardon 2 Channel power amps I just sold. With a potential 14 channels need for my room 2 channel amps just aren't possible.

    Someone on these very forums suggested the opposite was true. Better quality Caps in the 985mk2. I really don't know which is true.

    If I had the money I'd go for the 1095, but I have so many items to buy and limited funds. I am comfortable with my current setup but I am looking for another 1075 or 985mk2 to give me the extra channels I need.
    I bet the 985 will sound great, the only test is your ears. For the price it sounds a good buy though.

    If it is from a dealer then a why can't you demo? Too far away?

    Hmmm, Denon have a very distinct warm sound, the rotel is more in your face. Don't get me wrong I like both, I'm really not sure how they would work together. What would be more important is how well timbre matched the surround speakers are to the new fronts.
    It's really easy, the only thing you will need you may not think of is a phono splitter lead or adaptor to enable 2 power amps to be used with each bi-amped speaker.

    Maplins do a very good short adapter in their "Shark" range, but I use gold "Monster" 1RCA to 2RCA adapters that are a lot more expensive. Don't forget to budget for analogue interconnects for the pre-amp to poweramp channels.

    Good luck :)

    Cyrus Said:-
    The big rotel is just too much money for me right now. I'm still on the lookout for a third 5channel amp.
    Ok...Part ex against my Servo15 when your other half tells you it's just too big after all?:devil:


    Mark
     
  20. mick23

    mick23
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    thanks mark i will go ahead with purchase and try denon vs 985 ,i did try the denon poa-t10 running front pair ,but (to me) this was worse than denons internal amps for 2 channel sterio,

    mark what phono lead and where to purchase do you use for "amp to say 985 for the center channel as this is a single mono feed or do you use "just one side of interconnect"


    thank you
     
  21. nathan_silly

    nathan_silly
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    Will using a splitter lower the output to each amp though?

    My amps have a link mode. I take the C out from the processor into the L input. Then I take a short phono from the L load, into the R input.

    I noticed a -1 dB increase in output. I think a Y splitter would do the same?

    Nathan
     
  22. Mark Ward

    Mark Ward
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    I have to say that -1 or -2 db on output can be easily corrected with levels.

    I've never really noticed anything adverse bi-amping. For me I bi-amp to get more power and therefore theoretically more control.

    Higher rated power amps 200W+ seem to be disproportionately more expensive than Bi-amping smaller ones. I would expect a single channel of say a 250WPC and would drive the speaker just as well as 2 X 125W channels bi-amped, if not better. In my case 2 S/H RMB1075 5 Channel amps are cheaper than 1 X RMB1095 5 Channel amp.

    I'm also using 40p a metre wire (Maplins HiFi cable 100M Roll Price) right now until the Van Damme bi-wire cable comes into stock. It already sounds good enough to me so I'll now think twice before that upgrade too.

    I like the idea of pass-through facilities an power amps, my friend's Arcams have this. I don't expect it'll be any better or worse that a decent splitter, just tidier.

    If anyone else has a good bang-for-bucks solution to this I'd also be interested. I use Puresonics co-axial analogue interconnects because I bought some cheap. I'll be replacing them when I'm sure how short they can be (tidyness not performance issue).

    Mark.
     

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