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Thread: Altec Big Red Monitors

  1. #16
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    mastering Lab Crossover

    Hello,
    First thank you guys for sharing all the info here regarding the Mastering Lab crossover. It was very helpful for me in my attempt of recreating it.
    I was able to come across a great pair of Super Big Reds - the ones with a bass helper. Unfortunately they came without the original ML crossover - but only with the Altec N-1500 crossover. I read everything I could find about various crossovers and made several attempts in making different iterations of original 604 Altec crossover. I read somewhere that someone said that Altec N1500 crossover is excellent crossover but needs something to be done to tame shouty mids. And I completely agree with that statement.

    But I really wanted to try Mastering LAb's crossover and I did it. As we can see from conversation here there were some unanswered questions about the orientation of 1.5 mH coil. I will post here measurement so you could all see the difference. I could say with the absolute confidence that bigger portion of that coil goes toward junction of 20 ohm resistor and 2.3 uF cap. Not vice versa as it was shown in this schematic posted above. Here are the pictures and measurements. I did electrical measurements ( not acoustical ) on AP with the crossover and speakers connected. I measured it both ways so you could see the effect. I also measured effects of the pots so one could see exactly what and how much they affect the sound. At the end I am really happy with this crossover. It addresses very successfully the issue of over pronounced mids and shoutiness.
    Attached Images Attached Images      

  2. #17
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    And here are the speakers.
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  3. #18
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    If those posted images of measurement are not visible here they are as PDFs.
    Attached Images Attached Images

  4. #19
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    You are running the Utahs too high.

    The Mastering Labs put a big choke on it for a 1st order slope. The crossover even cost more because of the choke.



    My Super Big Reds are triamped with passive eq units between the horns and their amp. This is in all probability a "one-off" created by The Mastering Labs.




    These are the slopes:

    HF (no passive eq added):


    604 woofer:


    Utah woofer (no bass boost engaged):


    https://youtu.be/iGa9259pz-I

    https://youtu.be/4MWmYYV1bg4

  5. #20
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    Quote Originally Posted by toddalin View Post
    You are running the Utahs too high.

    The Mastering Labs put a big choke on it for a 1st order slope. The crossover even cost more because of the choke.



    My Super Big Reds are triamped with passive eq units between the horns and their amp. This is in all probability a "one-off" created by The Mastering Labs.




    These are the slopes:

    HF (no passive eq added):


    604 woofer:


    Utah woofer (no bass boost engaged):


    https://youtu.be/iGa9259pz-I

    https://youtu.be/4MWmYYV1bg4
    Thank you for your comments and details. I understand why it creates the wrong impression. I made the image when I just have finished construction. Measured curves are only for Altec. I actually run Utah's and Altec biamped through the software / hardware active digital crossover crossed pretty low - around 80 - 100 Hz. Altecs are run through the class A Nelson Pass's J2s and Utahs are driven with small 2A3 tube amps. I wanted to drive them reversed but they sound much better in the configuration I mentioned due to top end roll off on Altecs. You have a great set up !

  6. #21
    Senior Member eso's Avatar
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    Quote Originally Posted by Ar2 View Post
    Hello,
    First thank you guys for sharing all the info here regarding the Mastering Lab crossover. It was very helpful for me in my attempt of recreating it.
    I was able to come across a great pair of Super Big Reds - the ones with a bass helper. Unfortunately they came without the original ML crossover - but only with the Altec N-1500 crossover. I read everything I could find about various crossovers and made several attempts in making different iterations of original 604 Altec crossover. I read somewhere that someone said that Altec N1500 crossover is excellent crossover but needs something to be done to tame shouty mids. And I completely agree with that statement.

    But I really wanted to try Mastering LAb's crossover and I did it. As we can see from conversation here there were some unanswered questions about the orientation of 1.5 mH coil. I will post here measurement so you could all see the difference. I could say with the absolute confidence that bigger portion of that coil goes toward junction of 20 ohm resistor and 2.3 uF cap. Not vice versa as it was shown in this schematic posted above. Here are the pictures and measurements. I did electrical measurements ( not acoustical ) on AP with the crossover and speakers connected. I measured it both ways so you could see the effect. I also measured effects of the pots so one could see exactly what and how much they affect the sound. At the end I am really happy with this crossover. It addresses very successfully the issue of over pronounced mids and shoutiness.
    So then, this should be correct orientation for tapping the inductor at 10%?

    I've got a set of 604E that I need networks for and I used a coil winding calculator to design the needed coils.

    Does anyone have dimensions/plans for a big red cabinet?

    Name:  Corrected M_L_604_Xover.jpg
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    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

  7. #22
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    Mine are ~15.5 cu ft exterior dimensions. IIRC, they were speced at 12 cu ft interior volume. Shapes varied.

  8. #23
    Senior Member eso's Avatar
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    So I finally came up with a pair of Audiotechniques Inc. Mastering Labs crossovers.

    Based on a few measurements and tracing my way through the units I can say pretty certainly the schematic that has been floating around the internet is wrong, very wrong.

    I've got to dig into it a bit further, but so far L1 is a tapped inductor, but only uses the tapped portion, L2 is much greater value, C1 is smaller, R3 is non-existent, ATT1 is a greater value than listed, L4 is a tapped inductor but the tap is not connected, and L5 is much smaller than listed...

    I'm going to fully dig into these and come up with a correct schematic.

    "You can't believe everything you read on the internet" – Abraham Lincoln


    eso
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    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

  9. #24
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    Very cool... keep us posted!


    Widget

  10. #25
    Senior Member eso's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    Very cool... keep us posted!


    Widget
    Going further down the rabbit hole I'm looking for any internal pictures of a Crossover for Super Reds. The resistor not in these could easily be omitted with an extra woofer since the HF would not need as much pad to match the LF output.

    And these do have leads for the added woofer. I know there are significant differences in the HF sections of Urei networks between 811, 813 and 815 configurations.

    eso
    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

  11. #26
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    The electronic crossover for my Super Big Reds is dead on 1,500Hz with (IIRC) 2nd order slopes on both sides. The Utah is crossed over at ~100Hz with a 1st order slope.

  12. #27
    Senior Member eso's Avatar
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    Quote Originally Posted by toddalin View Post
    The electronic crossover for my Super Big Reds is dead on 1,500Hz with (IIRC) 2nd order slopes on both sides. The Utah is crossed over at ~100Hz with a 1st order slope.
    I'm specifically looking for the Mastering Labs Crossover alterations between the Big Reds and Super Reds. The Mastering Labs crossovers I picked up last week have and extra set of leads for a second woofer and have a few differences from the schematic that is the main reference on the internet.

    The two resistors not in my pair of crossovers would amount to less padding of HF which would be consistent with increase LF output.

    eso
    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

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