Bi-amping using a separate stereo amp?

Discussion in 'Archived Threads 2001-2004' started by Joseph Anlacan, Aug 11, 2001.

  1. Joseph Anlacan

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    I'm thinking of bi-amping my B&W 305. My main amp is an onkyo 838 (90w/ch L,C,R, 50w/ch SL,SR). Can I purchase a stereo amp, hook it to my front L&R pre-out and use this to power the B&W woofers while leaving the onkyo to power the tweeters? What stereo amp (power, specification, etc) would be appropriate for this? In bi-amping, are there different preferred wires running to the woofer and those running to the tweeters?
     
  2. Chuck Kent

    Chuck Kent Supporting Actor

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    Joseph: How are the pre-amp out jacks configured? In other words, do they have jumpers plugged into them so that the main left and right amps are activated? If so, then as soon as you unplug the jumpers, you'll lose the Onkyo's amps and you'll be no better off than you are now.
    If you don't have jumpers, you may still have a problem. Some receivers automatically disconnect the main amps if the pre-amp outputs are used for external amps. So if your 838 doesn't have jumpers, you need to try inserting an interconnect cable into one of the jacks to see if the main amp stops playing. If it stops, you out of luck. If it doesn't stop playing, then you will be able to use the outputs with an external amp.
    You're still not out of the woods yet. If you are able to drive an external amp, you need an amp that has the same voltage gain as your receiver's amps. This is a must due to the fact that in order for your speakers to sound balanced, they need to have the same input level to both the high and low frequency sections. You cannot hookup just any amp and have things sound right.
    IMO, wires, as long as they are of good quality and don't have some kind of deliberate design flaw, are wires. (Others may disagree!!) My advice is if you are able to get to this stage, buy good quality wires that have good quality terminations but don't overpay for them.
    Good luck!
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    [Edited last by Chuck Kent on August 11, 2001 at 10:39 PM]
     
  3. Joseph Anlacan

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    The Onkyo does not have jumper cables and it continues to output even when there are connections on the pre-outs. Now, my problem is finding a matching separate stereo amp. Is it just the gain that should match? Where do I look for the gain specification? How about wattage? Should they also match? Is bi-amping using 2 90w/channel equivalent to a single 180w/channel in terms of power? Thanks!
     
  4. Chuck Kent

    Chuck Kent Supporting Actor

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    {Is it just the gain that should match?}
    Yes, gain or input sensitivity is the key value you should look at. Matching the gain insures that the same volume level comes out of the high frequency and low frequency sections of your speakers (the same as it is now.) You can use an amp that has adjustable input sensitivity but you would need to match your receiver as close as possible so that the speaker's output isn't tilted to the high or low frequency band.
    {Where do I look for the gain specification?}
    If it's not in your receiver's manual (and for receivers it's likely you won't find it) then you'll need to call or e-mail Onkyo to find out. Common values I've seen are from around 25 db to 30 db. But again, gain needs to match as close as possible.
    {How about wattage? Should they also match?}
    Wattage is only important when determining the final volume you're looking for. It's not that big of a deal that the amps match in output wattage. For example, 2-way active amped speakers often have an amp for the tweeter thats half the wattage of the woofer. So if you want more volume from your setup, you would want to drive the woofer section with a bigger amp than what you have in your receiver.
    {Is bi-amping using 2 90w/channel equivalent to a single 180w/channel in terms of power?}
    No, since each section only sees one amp, 90 watts into the high or low section remains 90 watts. (One other thing to remember is that adding more power may not be easily noticeable volume output-wise. To be able to play a speaker just 3 db louder, you must double the amount of power going into it.)
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    [Edited last by Chuck Kent on August 13, 2001 at 07:14 AM]
    [Edited last by Chuck Kent on August 13, 2001 at 07:15 AM]
     
  5. Larry Chanin

    Larry Chanin Stunt Coordinator

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    Chuck:
     
  6. Chuck Kent

    Chuck Kent Supporting Actor

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    Doh!!
    Yes, Larry you could. What I typed is true but yes of course you could use a Y-cable. This is what I get for spending too much time online... [​IMG]
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  7. Larry Chanin

    Larry Chanin Stunt Coordinator

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    Chuck:
    Thanks for the confirmation, its very obvious that you know a great deal about the subject.
    I'm just a newbie, but I've been following this subject at a couple of other forums. Some of the other forum members have confirmed with Lucasfilm that all THX certified power amps must have the same gain (which I'm pretty sure is 29 dB).
    So, if a receiver is THX certified and the external amp is THX certified, especially with an adjustable level control, it seem that you have a pretty good chance of keeping the levels balanced between the higher and low frequency drivers.
    Like you, the more experienced members suggest caution before getting involved in horizontal bi-amping.
    Here's one thread with links to an other:
    Can you biamp use a external amp and the internal of a receiver
    Larry
     
  8. Chuck Kent

    Chuck Kent Supporting Actor

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    Larry: Trust me, I know just enough to be dangerous!!!
    You're right about the 29 db gain for THX Ultra amps. My older THX Carver amp is spec'd at 29db gain (+ or - .5 db.) (Older THX was relabeled Ultra a couple of years ago when THX started the THX Select name.)
    I agree that if you use a THX Ultra amp with an Ultra receiver, and the amp has input sensitivity adjustments available, you are virtually guaranteed to have success matching them.
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