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    Prefered load alternatives vta m-125

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    Dahlberg

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    Prefered load alternatives vta m-125

    Post by Dahlberg on Mon Oct 03, 2016 3:50 am

    I have different load alternatives to choose from since I'm using
    six drivers for the work at hand. I have the possibility to connect
    them as 2x8/3=5,33ohm or 3x8/2=12 ohm.
    The first alternative will have a smaller missmatch to the 4ohm
    output tap (1,33ohm) but the 12ohm load will be equally missmatched
    to either the 8 or 16ohm tap (4ohm).

    Any thougths on this ?


    Last edited by Dahlberg on Mon Oct 03, 2016 11:47 am; edited 1 time in total
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    Bob Latino
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    Re: Prefered load alternatives vta m-125

    Post by Bob Latino on Mon Oct 03, 2016 7:05 am

    You should probably try it both ways to see if your speakers sound better one way over the other way. The other option is to use an active crossover. Check the link below for a good explanation of differences between active and passive crossovers.

    Active and passive crossovers for speakers

    Bob
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    Dahlberg

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    Re: Prefered load alternatives vta m-125

    Post by Dahlberg on Mon Oct 03, 2016 8:02 am

    Well I already have the active filter  Cool  The M-125 amps will be used for
    midbass (50-350hz). There are six Seas "8" inch drivers in the midbass panels.

    This filter is up for a rebuild with all tube outputs (John Broskies "Unballancer").



    The active part comes from "WAF-audio" it's called Najda and I'm using
    half of it, the dsp resources only (the wiring looks better now than in this picture).



    Most of the set-up.



    It's quite a task to rewire the speakers, that's why I'm asking Smile
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    Kentley

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    Re: Prefered load alternatives vta m-125

    Post by Kentley on Mon Oct 03, 2016 1:18 pm

    That looks like a system with incredible potential! Do us all a favor and publish some more details, please.
    The article(s) from Bob make abundantly clear how complex impedance matching is, among other things. My limited experience, backed up incidently by a major independent speaker builder, is that one is generally both better off sound-wise AND safer using taps that are somewhat less in impedance rating than the nominal rating of the speaker, rather than the other way around. This seems to increase "tightness" of sound perhaps by influencing the damping factor favorably. It is safer, presumably because there should be less chance of current over-draw on the amp. Now, what with your using active crossovers, one problem is eliminated - the impedance swings around passive crossover points. But speaker impedance is a complicated matter. Take a look at real-time impedance curves of any model speaker out there - they're all over the place. Nominal ratings are somewhat arbitrary.
    In fact, Bob is correct - in the real world, the only way to determine the "best" loading is by careful experimentation. I imagine the Seas are already wired up at 5.33 ohms. Should be quite satisfactory on the 4 ohm taps as is. I know I wouldn't wish to open up those towers and rewire them. Not today or any other day. affraid
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    corndog71

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    Re: Prefered load alternatives vta m-125

    Post by corndog71 on Mon Oct 03, 2016 1:34 pm

    Dahlberg wrote:I have different load alternatives to choose from since I'm using
    six drivers for the work at hand. I have the possibility to connect
    them as 2x8/3=5,33ohm or 3x8/2=12 ohm.
    The first alternative will have a smaller missmatch to the 4ohm
    output tap (1,33ohm) but the 12ohm load will be equally missmatched
    to either the 8 or 16ohm tap (4ohm).

    Any thougths on this ?

    Who designed this speaker?
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    Dahlberg

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    Re: Prefered load alternatives vta m-125

    Post by Dahlberg on Mon Oct 03, 2016 2:39 pm

    Thanks for the input on wiring. Seems that 5,33 connected to 4ohm or 12
    connected to the 8ohm tap is what should be tried then.
    The speakers are my own design with a ribbon driver fairly simular to the
    ones described at my homepage. And no, they are not for sale  Smile  .
    These ribbon drivers are supplied with even more powerfull neo magnets
    (magnetic assembly weight 40kg). They are driven by a pair of
    C3m/KR300b xls/Hashimoto amplifiers.
    Midbass drivers comes from Seas and are modyfied by removing the dustcap
    and instead adding a solid aluminum fase plug. Subs are a cross from
    AudioArtistry Bethoven and the "Ripole idea", Dayton "15" inch drivers (4/ch)
    wired as 16ohm driven by A pair of Hypex ucd2K/regulated psu +/-90v.
    Got some of the inspiration from Monte Kay's subwoofer towers but 12x15  Shocked x2  affraid
    Everything gets their signal from the dsp in the first picture.
    It has 2ch (hardwired) John Broskie "Unballancer" and one balanced output from "Twisted Pear".

    I'm rebuilding the dsp with 3 new pcb's from John soo there will be tube outputs for all channels soon (I hope).

    I can't ad any links yet but you will probably find most of what's mentioned with a quick search anyway.
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    Dahlberg

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    Re: Prefered load alternatives vta m-125

    Post by Dahlberg on Mon Nov 21, 2016 8:06 am

    This is the simulated (close enough) impedance curve. Resistance drops to 4,8 ohm but
    is never above 10 ohms in the 65-400hz region. Speakers are actively crossed over 2/order
    at 65 and 350hz today and I will most likely not change that.

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    Kentley

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    Re: Prefered load alternatives vta m-125

    Post by Kentley on Mon Nov 28, 2016 11:59 am

    This is a P.S. to my post here of Oct. 3 concerning preferred impedance taps.
    As my new Tyler Acoustics speakers have continued to settle in and blossom, I thought I'd once again test the 8 ohm taps of my ST-120. Lo and behold, now they sound much better - more open sound with no hint of the out-of-control quality I had first experienced. Response at the extremes of low and high is improved. So I guess the message is - Don't stop experimenting. Things change over time, whether it's the equipment or simply the ears! Exclamation


    Last edited by Kentley on Mon Nov 28, 2016 12:00 pm; edited 1 time in total (Reason for editing : speiling)
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    Dahlberg

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    Re: Prefered load alternatives vta m-125

    Post by Dahlberg on Wed Jan 11, 2017 8:12 pm

    So I have tried the 4 and 8ohm taps with speakers still wired as 5,33ohm
    and the 4ohm tap came up a clear winner. If we round it of to 6ohm there
    is a 50% higher nominal speaker impedance than the tap used says.
    There would be the same ratio if I would rewire the speakers to 12 ohm
    and then use the 8ohm tap.

    Question, would this load draw less current from the output tubes ?

    Next question, is the 16ohm tap dedicated for feedback only or is it
    possible to use that for speaker connection as well ?
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    Bob Latino
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    Re: Prefered load alternatives vta m-125

    Post by Bob Latino on Wed Jan 11, 2017 8:49 pm

    Dahlberg wrote:
    Question, would this load draw less current from the output tubes ?

    Next question, is the 16ohm tap dedicated for feedback only or is it
    possible to use that for speaker connection as well ?

    Not really sure if the current draw would be more or less (or similar) from the 4 ohm tap? The 16 ohm tap is not dedicated for the feedback line. You can use the 16 ohm tap for a speaker connection also. After you run the yellow (16 ohm) wire to the red binding post, you just run an additional wire from the red binding post to the NFB eyelet on the driver board.

    Bob
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    Dahlberg

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    Re: Prefered load alternatives vta m-125

    Post by Dahlberg on Thu Jan 12, 2017 5:31 am

    Sorry but I belive that I was a bit unclear about what the two alternatives are Embarassed .

    Alt 1: Speakers wired as 6 ohm connected to the 4 ohm tap.

    Alt 2: Speakers wired as 12 ohm connected to the 8 ohm tap.

    And wish one of these would draw more or less current ? (if there is a difference).

    Thanks for clearing up about the 16 ohm tap Smile

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