To bi-amp or not to bi-amp???

Discussion in 'McIntosh Audio' started by kln138, May 3, 2017.

  1. kln138

    kln138 AK Subscriber Subscriber

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    I have a stack of McIntosh gear (MC2505, C26) powering Altec 604e's through the Altec passive crossover.
    I love my set up. However, that opportunity came along and I acquired two MC60 mono blocks in pristine condition. I don't want to break up my 2505 and C26 set. Should I bi-amp?

    From the research I've done 60's for the high's, 2505 for the lows. What's the best way to go about this?
    No crossover wired direct, through the passive crossover, or through an active cross over? I have no bi-amping experience and I'm seeking your wisdom to get the most out of my system. I guess not wanting to part with any of these components is what is driving me, with an eye toward great sound.
    Thank you all! This forum always helps me!
    Keith
     
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  2. Mike Gibson

    Mike Gibson Modulator Super Mod Subscriber

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    Many years ago I went through the same thing. Except my speakers are Altec Valencias and not 604's. I bought a used Rane electronic crossover and made my own cables. Figuring it was the least expensive way to try this bi-amp business and see (read hear) what all the fuss was about. So after I had it all working I was impressed enough I've never looked back. Being able to adjust the crossover point on the fly and experiment with fine tuning it has been priceless.

    The Rane eventually died so I bought another crossover and life is sweet once more. I too put a tube amp on the horns and SS on the Woofers. I'm sure you are aware of the musicality of Altecs since you own a pair. Now female vocals and guitar, sax and all that are even better. If you have any questions send me a PM and I'll do my best to help you. I'm not a tech and know little about gear. However, I do know what sounds good to me. If you try a Rane or any other inexpensive crossover and decide you like it then you can always pick a Marchand or other audiophile crossover. I'm not convinced that spending a lot for a crossover is necessary unless you want one with a S/N ratio like the Black Hole of Calcutta. :)

    The easiest way I've found to set it up is to use a SPL meter and balance the left & right and also the hi & low. Then you can fine tune it by ear. The meter will get you close enough to where you can tune it to your liking. Which is the real beauty of going electronic. There are a lot of Altec owners on this site. Quite a few of them have gone with bi-amping and the electronic crossover. Hopefully some will add their experience to this thread.
     
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  3. shelly_d

    shelly_d Not An Audiophool

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  4. kln138

    kln138 AK Subscriber Subscriber

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    Thanks Mike!
     
  5. kln138

    kln138 AK Subscriber Subscriber

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    I'll have to open a cold one and sit for a while on this one. Thanks!
     
  6. Bob

    Bob AK Subscriber Subscriber

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    IMHO always active and a separate component.

    reasons
    1. you need to control the crossover point to separate out the bass and treble to match
    the speakers. for example, treble speakers that are small may need a higher (say 100hz+)
    crossover.
    2. you need to control the bass output (or input to the amp) to match the treble/amp combo
    you can use the amp's input volume control also.
    3. once you start using a bi-amped system you may find you need adjusting the bass
    (Madonna's Shanti is very bloated bass on my system, vs classical music) and its
    easier with an up-front single control
    4. the crossovers will have differing slopes on the treble and bass for better integration

    you will have a system that keeps the bass intact as you lower the volumes - kind of
    like a loudness switch.

    In any case, enjoy the music!
     
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  7. twiiii

    twiiii Super Member

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    Bi-amping was developed to more efficiently provide power to speaker systems that were large complex and with drivers with differing efficiencies. Passive crossovers have to dissipate large amounts of power to match the level of a Multicell horn versus a pair of 515's in an infinite baffle or a 515 in an 825 enclosure. Some times 6 to 10 db of power. If you need 10,000 watts for the woofers in a large hall , throwing a large share of 7,000 watts away for the horns and taking the power away from the woofers in a full range system seems like a waste. Plus big crossover coils for woofers keep amps from controlling the woofer cones that well. And of course its a lot easier to design different slopes with different frequencies with different combining circuits in a processor than using passive networks.

    Then some consumers folks like the sound of tube amps for the highs and SS for the woofers. We bi-amped all our large PA systems for Churches, Cathedrals, Basilicas, Sports stadiums and sport arenas, and convention halls and theatres.
    As we were also a Bozak dealer and we sold lots of Symphonies and Concert Grands that were Bi-amped. They were easy as they used identically rated amps for top and bottom.

    Altec is a different story with the HF section being more efficient than the woofer. Lets see 98 or 99 for the woofer to maybe 104 in a horn enclosure and 110 db for the HF Horn. I would recommend a few choices. First your 2505 on the bottom as it doesn't have Power Guard, with either a 752 or a 502 on top. Another choice would be sell the 2505 and find a 4 channel 7104. Its a great amp. but not much in demand so you can usually get a great price. Another choice would be a pair of MC-30's for the top if you don't mind breaking the bank. I owned MC -60's , but would not use them for the bottom. They didn't do my Carmels or Coronados any favors, though they preformed rather well with Symphonys and 302's from Bozak. If you want a smooth sound try the 60's on top. Remember the 2505 and MC 60 clip at about the same power, 2505 around 72 watts as I remember and MC 60 around 75 watts. The woofer can take an occasional clip better than the tweeter. Do your 604's have percussion caps covering the HF diaphragm? They protect Altec driver diaphragms if crossed below 1000 HZ.

    You might want to contact the guys at Great Plains Audio, that are still manufacturing two versions of the 604 and ask them which electronic crossover they would recommend. A couple of Musicians I went to college with owned 604 E's that they bi amped. One used Marantz tube amps. 8b's as I remember and the other used Citation amps. The 40 watt model. I only heard them a few times, but I like the sound. They built there own 6 to 8 cu ft ported enclosurers. One pair resembled Altecs 612 enclosure. The other had tall enclosures reminding me of something Tannoy builds now days. I preferred the tall enclosure with the tweeter at ear height. I copied the design for a friend that was using 619's Coax. instead of 604's. He -uses MC 60's quite successfully by the way.

    A friend at work wanted 4 portable speakers for his disco. So we started out with a 604 HPLN as the tweeter and mid woofer, added Mr994 horn with a 908 as the mid, and a 3184 as the sub. The system was tri amped. with a passive crossover for the Hf section of the 604 at 9,000 hz. He used a pair of Crown PSA2 for the bass, a MC2200 for mid 604 woofers, and a Mac 2120 for the 908 and HF section of the 604. The sound was quite spectacular. They easily out performed A-7's and we half as big, though much heavier. .

    A few systems we installed we used two 604's mounted in 817 enclosures for stronger than the average Disco systems. The systems were basically 40, to 18,0000 Hz systems with four of the boxes suspended over the perimeter bi amped using three 2255 power amps. Two for the 8 woofers and 1 for the 8 tweeters. We would get close to 118 db on the dance floor. Stanel Sound use to mount a 311 with a 291 driver on top of two 817 boxes with 4 604 HPLN tri amped as entertainment stage speakers and behind the screen speakers for multi channel sound to support slide shows and movie presentations in large halls. He used mostly Yamaha professional amps or Altec 9440 amps for All Altec systems.

    I do go on. But a 604 was a favorite of mine. I've always wanted to try a tall enclosure with a 604 mounted between two 416's . I think they would be fantastic. Or how about 5 604's stacked in a Bessel configuration. You'b be surprised how well speakers of an type perform in a stacked Bessel Configuration of 5 speakers.
     
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  8. kln138

    kln138 AK Subscriber Subscriber

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    .
    Do your 604's have percussion caps covering the HF diaphragm? They protect Altec driver diaphragms if crossed below 1000 HZ.

    twiiii, You used a new term on me. What a percussion caps? Protection capacitors in line with the horn?
     
  9. kln138

    kln138 AK Subscriber Subscriber

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    Does anyone run their tweeteters through the active crossover and passive crossover? Would that provide DC protection?
     
  10. whoaru99

    whoaru99 Epic Member

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    Using a DC/low frequency blocker cap in series with the tweeter is not too uncommon, Probably not a bad idea at least until you get the hang of things. :)
     
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  11. kln138

    kln138 AK Subscriber Subscriber

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    How does one determine what capacitance to use?
     
  12. damacman

    damacman Blown and Injected Subscriber

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    Xc = 1 / (2pi f C)
     
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  13. Seamaster

    Seamaster AK Subscriber Subscriber

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    I am throwing a monkey wrench in here. I have a pair tannoy that crossover point is at 1kHZ, do I get any benefit if I bi-amp those speakers with TWO pairs of MC30? More control or effortless?
     
  14. kln138

    kln138 AK Subscriber Subscriber

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    From what I've been reading having a speaker tied to one amp is the way to go. i.e. one tweeter to Mc30, one woofer to Mc30 etc etc

    With an active crossover of course,
     
  15. twiiii

    twiiii Super Member

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    We used protection capacitors calculated one octave below the electronic crossover, when using any SS amp without DC protection . Bur most of the time we used Mcintosh amps with autoformers so that wasn't an issue as they had power guard in addition. QSC has there own form of power guard and DC protection so we didn't use caps there either.

    The Percussion caps I was referring to is made of a black plastic and is designed to physically mount over the back of the diaphragm to form a seal very close to the diaphragm. It prevents physical damage from frequencies below 1000 Hz when using a 500 hz crossover frequency. This allowed the 902 and earlier 802 drivers to almost double their power handling with out physical destruction. 20 to 25 watts pink noise.

    I really liked Mcintosh amps with Power guard. You could take two 291 drivers with 16 ohm diaphragms and connect them to one channel of a 2120 8 ohm tap. These amps put out close to 150 watts before the Power Guard activated preventing clipping. Then set the crossover at 500 Hz and drive the two 40 watt rated diaphragms would function all day with the limit lights flashing with out failure. That almost a 3 db increase in out put. If you raised the Crossover frequency to 770 Hz. . You could run one 8 ohm diaphragm all day on the 2120 as long as you kept the power Guard lamp from just starting to flicker. Power Guard circuit compares the input to the amp with the output and if there is more than a 2% difference reduces the signal until the wave form is corrected. Which means if you loose an out put transistor for example or DC appears before being blocked by the autoformer the out put of the channel is instantly shut down as the output signal doesn't match the input. Now some folks didn't like the idea because they were so use to hearing their amps create distortion at high levels that not having the distortion meant the Mac amps could not play as loud as the conventional amps. It was the same level the distortion wasn't there.

    Now if you pushed the Mac amps to far making the power Guard work over 25% of the time the circuit begins to act like a peak limiter and if pushed further a compressor. That makes for and easily heard though not unpleasant distorted signal. Today with cheap big amps with similar circuits from Crown, QSC, etc they are no longer pushed as previous amps were in the 70's and there fore the limiting circuits are very seldom used. But back in the day when a watt was very expensive, everyone wanted more power. To get as much level as they could. And to hell with the distortion just as long as you didn't blow the speakers. Mac changed all that. Today Mac owners buy their amps with large amounts of head room and speakers that can handle lots of power with very low distortion. Which means if a power guard light flashes once a week or year its only preventing the listening experience from being shattered on rare occasion. or to protect a tweeter from mishap from a dropped phono tone arm and the like. I have 250 watt per channel amps and I seldom listen over 2 watts. With maybe a 30 watt peak once in a great while in the HT mode. But Power Guard is always there to protect my valuable hard to find drivers.

    Your Altec 604 are special speakers and fortunately cones and diaphragms are available in case of a mishap. But that doesn't means you want to abuse them so take care. 75 watts for the cone and 20 watts for the diaphragm would be all I would plan on, That does;t mean you want to use small amps, far from it it just means thats all the power I would use. How you determine that is up to you. I like the meters on my Mac amps, but if thats not an option then There is always an Oscilliscope to give you a visual reference until you get a feel for things not being played to loudly.,
     
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  16. Seamaster

    Seamaster AK Subscriber Subscriber

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    What if I just want to use the existing passive crossover in the speaker?
     
  17. Mike Gibson

    Mike Gibson Modulator Super Mod Subscriber

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    Here is a better explanation for using a active crossover than I can articulate. :)

    Active Bi-amping
    Active bi-amping involves the use of an active crossover which splits the electrical signal into high and low frequencies before it reaches the amplifiers, consequently allowing each channel to only reproduce the range of frequencies required of it. In terms of audible differences, ditching the passive crossover boards in your speakers for an active bi-amping setup certainly has the potential to make a change, though whether this is positive or negative depends on the quality of implementation, as well as the quality of the passive crossover you’re replacing (generally speaking, we feel it’s difficult to meaningfully improve upon a very good passive crossover). Be warned: converting a passive loudspeaker to an active model is not an undertaking for the faint of heart due to the complexity involved as well as the costs (active crossovers as well as additional amplification and wiring).

    From a technical standpoint, aside from possible improvements afforded by active crossovers, active bi-amping allows an amplifier to be directly coupled with a driver, having it to deal with a much more benign load than what a typical passive loudspeaker represents. This can also result in a more efficient system given that no energy is wasted as heat in passive crossover components. Intermodulation distortion in the amplifiers is reduced given that each amplifier channel is reproducing a smaller portion of the audio spectrum, and the split load also dramatically reduces the likelihood of tweeter destruction as a result of overdriving an amplifier. Last but not least, active bi-amping allows for a more efficient allocation of power, i.e. it’s possible to place a smaller amplifier on a relatively sensitive tweeter, and reserve the 1000W monster for the power hungry woofers.

    [​IMG]
     
  18. shelly_d

    shelly_d Not An Audiophool

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    You can do that, BUT you MUST remove the woofer off the crossover network and tie it to one of the amps directly. If you leave all the speakers on the crossover, then you end up tiring the outputs of the two amps together and that causes all sorts of failures, certainly in the amps and possibly in the speakers too.

    The whole idea of biamping is to separate the highs and lows to delay the onset of clipping. Earlier in this thread I posted a link to Rod Elliot's excellent article on the subject. It explains the "what to do" and "why it works" much better then I do.

    Shelly_D
     
  19. whoaru99

    whoaru99 Epic Member

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    As long as the speakers have separate terminals for LF (+) (-), HF (+) (-), and the jumpers are removed there should be nothing common to cause problem for amp or speakers.

    If there is a common ground, e.g. three terminals on the speaker ( common (-), LF (+), HF (+) ) then maybe there could be some weirdness if the amps weren't common ground.
     
  20. 62caddy

    62caddy AK Subscriber Subscriber

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    Altec 604s have two full sets of terminals for LF & HF drivers so there shouldn't be any cross amplification issues.

    I think it would be more worthwhile exploring alternative dividing networks (there are several specifically designed to be used with the Altec 604 duplex).

    Given the extreme sensitivity of the 604 duplex (not to mention the many fine passive crossovers available), bi amplification seems rather [Rube] Goldberg way of doing it, not to mention the potential for opening a can of worms and the expense.

    As twiiii said, multi amplification's main advantage is that of being a more efficient way of powering large & complex arrays such as used in concert venues. Not so much for a 100 dB speaker in a home setting.
     
    Last edited: May 10, 2017

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