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Bi Amping with tube amplifier

Discussion in 'Home Theater Projects' started by Jef_DC, May 17, 2003.

  1. Jef_DC

    Jef_DC Auditioning

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    I'm considering to use my tube amp to bi-amp the center speaker.
    As I sometimes read that it is a bad idea to power up a tube amplifier without speakers ...
    (why exactly ? The primary of the transformers present a resistance I would think)
    ... I consequently wonder whether it is possible to use it for bi-amping because one channel will not be able to dump the lower frequencies into the speaker and the same for the higher frequencies in the other channel.

    Best regards ... Jef
     
  2. Brett DiMichele

    Brett DiMichele Producer

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    I am in no means an expert here (not even a dumbass in fact)

    But what I gather is that without an output load on the
    output tubes they can run rampant and fry..This is if you
    send them a signal.. Powering them up with no signal and no
    speakers, I am unsure if that will kill them also..
     
  3. Jef_DC

    Jef_DC Auditioning

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    Hi Brett,
    meanwhile I learned that some tube amplifiers can go into oscillation (and self destruct) when powered without a suitable load (4 - 8 ohm) attached - even without input signal.

    Question remains : will they oscillate when only a tweeter or a woofer is attached. I guess not, but confirmation by 'those in the know' would be nice.

    Thanks for your reply.

    Jef
     
  4. Michael R Price

    Michael R Price Screenwriter

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    Jeff,

    They won't oscillate with only one driver connected, unless something is really wrong. Don't worry about it... lots of other people biamp with tubes successfully. Start out using both your active crossover and the passive one in your speakers, to make sure you don't damage a driver or something with the wrong frequencies. Then you can remove the speaker level crossover, which should make a pretty big difference in sound. Your speakers won't have the same tone as they did before unless you carefully tweak the crossover, though.
     
  5. Mark Leitch

    Mark Leitch Stunt Coordinator

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    I have biamped (tubes on top, solid state down below) and there is nothing to worry about... other than cost and the dangers of rethinking the speaker designer on the crossover ;-)

    M.
     
  6. Greg Monfort

    Greg Monfort Supporting Actor

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    >As I sometimes read that it is a bad idea to power up a tube amplifier without speakers ...
    (why exactly ? The primary of the transformers present a resistance I would think)
    ====
    When the tube conducts, and it's conducting even with no load, it stores energy in the OPT in the form of an electromagnetic field. In fact, quite a bit of energy is stored while the amp is idling, so no load = no damping of the tranny, which means that the back EMF could create thousands of volts at the plate of the tube, damaging the tube and the insulation of the tranny.

    GM
     
  7. Jef_DC

    Jef_DC Auditioning

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    Thanks for all the replies.
    Meanwhile I have bi-amped the Center speaker and the sound changed more than I anticipated - in the positive sense.
    A lot more detail - maybe even a bit on the bright side now.
    But I still have multiple options to fine tune the timbre - which was not optimal so far - by playing with the 4 & 8 ohm tabs of the amplifier.
    Looks and sounds very good.

    Thanks ... Jef
     
  8. Judy Y

    Judy Y Stunt Coordinator

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    Question, how do you use a tube amp and a solid state OR ANY two different amps to bi-amp? Don't you have to, some way, match the levels being sent to the speakers? Is there a unit one can buy to do this? (I would really like to use a small tube amp on my tweeters but am very happy with the sound I am getting on my woofers and mid range with solid state amplification).
     
  9. Brett DiMichele

    Brett DiMichele Producer

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    Judy,

    I run a pair of tube monoblocks on my towers which are bi
    amped. I run the Tubes to the Tweeter/Mid (HF) section of
    the internal crossover and I run a big solid state plate
    amp with it's own gain control to the Subwoofer (LF) side
    of the crossover. I can match levels this way.

    Most any S.S "Power amp" will have gain control over the
    channels so matching isn't an issue really.
     
  10. Judy Y

    Judy Y Stunt Coordinator

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    A plate amp?? Wow, I hadn't even considered that....... I use a plate amp for my SVS.... it sounds great for the sub..

    Hmmm, and I wouldn't need two BIG plate amps. I could get a couple of small ones for next to nothing, add a tube amp for the front two channels and VOILA, instant home theater and music nirvana? (Do I exagerate?)

    How many watts are your tube mono blocks? How many watts would you recommend?

    Thanks for the info!!!!

    Judy
     
  11. Brett DiMichele

    Brett DiMichele Producer

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    Judy,

    I wouldn't use a plate amp for anything but a sub woofer
    and that is my useage. The low side of my crossovers connect
    to a pair of 10" subs and that is what the 500 watt plate
    amp feeds.

    If you had a Bi Ampable set of mains that used say a pair
    of 6.5's or something on the low side I would say to use
    better amplification (a good 2 channel amp with gain control)

    My tube amps put out 20 Watts Class A per channel
     
  12. Brett DiMichele

    Brett DiMichele Producer

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    Judy,

    I forgot to address your question about what amount of power
    to use.

    With tube amps power rarely comes affordably. Most of the
    "cheaper" tube amps are very low wattage SET's that only
    develop 3-9 watts per channel. I wouldn't even consider
    using something like this with anything less than a 100+Db
    Sensitive speaker.

    A good 20 watts per channel mated with a reasonably efficient
    speaker (say 89 to 93 Db Sensitive) should get you more
    than adequate listening levels. You should be able to easily
    exceede 100Db.
     
  13. Judy Y

    Judy Y Stunt Coordinator

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    One more stupid question........ "gain" control = "level" control? I was actually just looking at some 2 channel amps and none say "gain" but almost all have "level" control.

    I was also thinking 30 watts or so- and looking at a Jolida integrated. (My speakers are rated at 89db)

    Thanks again for your replies!
     
  14. Brett DiMichele

    Brett DiMichele Producer

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    Yep "Level" is gain..

    The Jolida sounds like a good choice.. Also check out the
    offerings from Antique Sound Labs (Divergent Technologies)
    and there are even some very nice kits if you was so inclined
    to build your own.. There is a nice kit called the Ella I
    am not sure who makes it (Michael Price knows if I am not
    mistaken.)
     

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