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Newbie stupid suestion No.11

Discussion in 'AV Receivers & Amplifiers' started by UselessPratt, May 8, 2003.

  1. UselessPratt

    UselessPratt
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    I see that some amplifiers can allocate unused channels to different things. I also see that on the back of the sub-woofers, you can bypass the amp. Can AV amps drive the sub too, if they have an unused channel?
     
  2. Mylo

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    I have a question for you. If you buy an active subwoofer that a company has spent time designing and developing. Why on earth would you want to bypass the dedicated mono (bass) amp module to drive it from an external source? :rolleyes:
     
  3. UselessPratt

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    For the same reason they put the connections on the back to allow it...

    :rolleyes:


    I suppose the answer is to allow you to "upgrade" the amplifier at a later date without having to change the entire unit.

    I must admit that it is unlikely I ever would....but it is just interesting to know what the possibilities are with those extra channels....
     
  4. Ian J

    Ian J
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    Why am I getting messages from people this morning asking me if you're a wind up merchant.
     
  5. UselessPratt

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    Guys if you haven't asked questions like this before then you know less than I do. I am new to AV, so I have to ask lots of silly questions. But have been in the hi-fi world for many years. The practice of bypassing the sub amp is well known in the hi-fi world. It bascially allow you to use the same amplification as the rest of your speakers, which improves the integration of the sub. I was only wondering whether this was accepted in the AV world or not....I guess not..... :)
     
  6. UselessPratt

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    Actaully the real reason I asked this is becasue I really want to buy a particular AV, but it's one downfall is that it is only five channel. So I was wondering what I was missing out on - if anything ( other than the obvious two rear speakers).
     
  7. Jase

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    Add a decent powered subwoofer and you'll be fine.:)
     
  8. Ian J

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    If you can't utilise the two extra rear speakers you won't miss out on anything. Tell us which AV amp you are thinking of and you will get loads of opinions on that instead.
     
  9. UselessPratt

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    I was looking at the Rotel RSX1065.
     
  10. MikeK

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    The practice of bypassing the sub amp is well known in the hi-fi world. It bascially allow you to use the same amplification as the rest of your speakers, which improves the integration of the sub. I was only wondering whether this was accepted in the AV world or not....I guess not.....


    Never heard of this before, either in hifi or AV!
    Which active subs allow you to bypass the onboard amp?

    I suspect you may be getting confused by the presence of speaker level inputs on the back of many active subwoofers - these do not bypass the subwoofer amplifier. They simply provide an alternative means to connect the subwoofer to amps lacking a dedicated line-level sub-out phono, such as most stereo amps (I know, you can use the tape loop, but many people are using that already).

    As for AV amps driving a passive subwoofer - yes, some can (by utilising the surround back channel and reconfiguring it as sub channel), but it's not a very good idea - few AV amps have the capability to drive a subwoofer properly while driving the main 5 channels at the same time.
    You may get way with it if you are using a small sats/midwoofer combination though!
     
  11. alexs2

    alexs2
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    Not sure which hi-world that would be...I've been involved in HiFi for over 25 years and have not come across this one....bypassing the sub's internal amp would require a fair degree of internal surgery and also bypassing the electronic crossover and filtering.

    For sure there are a number of passive subs around,but once you've added a power amp,filtering and crossovers,you're almost back to an active sub.
     
  12. Jase

    Jase
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    Do you not mean bypass the subs internal crossover ? rather than the subs internal amp. This is far more common.
     
  13. UselessPratt

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    Oh, you are right, I did misinterpret the "speaker level inputs". And have for many years, in that case. I always though by the size of them, they handle power. But then, I have never been interested in subs before. BUT GOOD JOB I ASKED THE QUESTION THEN!

    Would it be difficult to bypass the internal amp? I wouldn't have thought it would.

    And why would you want to bypass the crossover?
     
  14. UselessPratt

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    Having said ALL THIS, I can't actually find a supplier for the 1065 so the seconf choice will be a Denon AVC-A11SR ( Which of course is not limited to 5 channels)
     
  15. Jase

    Jase
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    Gives you a cleaner signal path for one thing. e.g if you have all your speakers set to small and all bass to the sub the amp/processor will be controlling the cutoff frequency e.g 80hz so you don't need to have another crossover in the way.
     
  16. alexs2

    alexs2
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    To feed a power amp level input into a (previously) active sub and drive the sub direct from the external power amp you would have to bypass the internal crossover,which is of course a low level active crossover,not designed for,nor capable of handling high power inputs.

    The speaker level inputs you refer to are heavily attenuated before being fed to the subs active crossover.
     
  17. UselessPratt

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    Sounds like a good idea...
    :)
     
  18. UselessPratt

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    What confused me is YES they would be heavily attenuated, so why the need for huge speaker terminals? Your speaker cable could be really fine. I suppose it must be to keep the purists happy.

    Yep, I suppse it would be a low level crossover too.....
     
  19. alexs2

    alexs2
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    I think you'd be very unhappy with the results of tinkering with an active sub in that fashion.

    The terminals on most subs aren't so large,and simply allow the use of reasonably sized cables with a good area for the terminals to grip on.

    A number of subs(REL's for instance) use a simple voltage feed from the power amp via a Speakon connector to permit the crossover to sense the power amp's LF output...this uses a fairly thin cable.
     
  20. UselessPratt

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    oh! Don't worry, all these questions are hypothetical only. I never tinker!
    Anyway, thanks everyone. The main point here is that no, I am not really missing out if I only have five channels ( of course, provided I do not want two rear speakers)
     
  21. MikeK

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    Would it be difficult to bypass the internal amp? I wouldn't have thought it would.


    Not really - but bypassing the amp will also bypass the crossover etc etc. Simply open the sub (by removing the driver usually), and remove the wires connected to the driver. Then connect up some new wires, which will need the other ends connected to some speaker binding posts which you'll have to install somewhere on the rear panel usually. Don't forget to tape up the removed original wires, and remove the mains input - not needed anymore. And voila, it's now a passive sub.

    However, I can't think of any worthwhile reason why you'd actually want to do this (if the plate amp on the sub isn't good enough just replace the plate amp - but in all probability, you'd probably need to replace the driver as well, hence it's all a bit pointless IMO)


    And why would you want to bypass the crossover?


    If you are using the bass management of the AV receiver, the signal is already filtered (ie crossed over) by the AV amp.
    So, the simple answer is there's no point filtering it again.

    In fact it's not quite that simple - filters have a cumulative effect, so filtering the signal again at the sub will affect the sound, both in terms of phase shifts, level, etc etc. Now, it depends on the various slopes/characteristics of the filters/subs in question, but generally speaking, it's probably best not to filter at the sub when the AV amp is doing it - but that doesn't necessarily mean that's "always" the best way.
    Bottom line is to do whatever sounds best with your kit in your room. Setting up subs is a bit of a black art anyway, given that the playing field is always changing - the room is never the same (and room couplingis a big issue with subs), the position within that room isn't usually the same and is often compromised (what do you do when the best position is right in the middle of the floor :) ), the kit it's used with is often different, and so on.....
     
  22. UselessPratt

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    Oh! And while this conversation was ongoing, I found a supplier for the 1065.
     
  23. Reiner

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    If you want to bypass the internal amp I wouldn't buy an active subwoofer in the first place. Just get a passive one - but keep in mind AV amps are not designed for this, they don't have dedicated subwoofer amplification and using the amplification of the other channels would increase the load too much, especially budget amps will struggle then.

    High-Level inputs on active subs are there for two purposes: to connect to AV amps speaker outputs in case you do not want to use line level (for whatever reason) or for connecting to traditional stereo amps.
    That said some subwoofers allow both connections in combination with AV amps, usually with different options for the x-over settings - thus allowing to switch e.g. between AV use and stereo use. Some REL models have this function I recall.
     
  24. 50/50

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    suestion?
     
  25. bob1

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    That name can't be helping
     
  26. UselessPratt

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    This is true.
    You know it's funny really - if you call yourself AmazingExpert, everyone thinks you are a pratt. If you call yourself UselessPratt, everyone still thinks you are a pratt. I should have stuck to my real name - Oswald Perambulator....but then, maybe not.
     
  27. bob1

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    so what are you useless or just a pratt:D
     
  28. lynx

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    [​IMG]
     
  29. polaco

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    Well, you could use the extra channels to drive a pair of speakers in another room. Some 7 channel receivers will even allow you to play a stereo input through two of the channels at the same time as you play another input through the other five channels (multizone capability).
     

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