Dreadnaught Avel-Lindberg 1000VA Transformer Group Buy?

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  • Inthefade
    Inthefade Posts: 180
    edited July 2014
    nspindel wrote: »

    Inthefade, you're supposed to be paying me today, correct? That will make 13.

    Just send payment and info Neil. Thanks!
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    I thought it might be useful in the interests of drumming up more participants to put up a good post explaining what this group buy is all about, with a few links to some highly useful threads.

    The original SDA design worked only with common ground amps. Some non-common ground amps allow you to strap the negative poles together, essentially making it a common ground amp, without a problem. Others do not, and very very bad things can happen if you do. You certainly couldn't use mono blocks with SDA's. Polk's later design iteration of the SDA's allowed for the use of a new cable they sold called the AI-1. You can still find them for sale on occasion on eBay or they come up here every now and then. The AI-1 allowed the SDA signal to pass between the speakers without requiring the grounds to connect by using an isolation transformer. However, like other parts of the crossover design, this cable was manufactured to meet a price point by using less expensive (i.e. inferior) components. It worked, and allowed you to use SDA's with non-common ground amps, but it didn't sound as good as using a straight cable.

    Enter DarqueKnight and his research into using much better isolation transformers. His original intention was to replace the original AI-1 he needed in a scenario where he was not using a common ground amp. He researched several different transformers and settled in on an 800VA transformer from Avel Lindberg for his original Dread:

    http://www.polkaudio.com/forums/showthread.php?73304-AI-1-Dreadnought-Preliminary-Results
    http://www.polkaudio.com/forums/showthread.php?74472-The-AI-1-Dreadnought-Project-Pt.1

    DK later discovered that improvements continued using an even bigger 1000VA transformer from AL, however these were not a stock part and required a minimum purchase of 10 units, hence these group buys:

    http://www.polkaudio.com/forums/showthread.php?131537-Plitron-1000VA-Transformer-Evaluation
    http://www.polkaudio.com/forums/showthread.php?129829-The-AI-1-Dreadnought-Project-Pt.2-Upgrade-to-1000VA-Transformer

    Somewhere along the line, he experimented with the Dread using a common ground amp, and discovered that when built with a boutique audio grade transformer like we're ordering here, the original AI-1 design actually sounds considerable better than a straight SDA connection when used with a common ground amp as well. That's when a lot of interest in these transformers came about, a lot of people including myself are using a Dreadnaught (either 1000VA or 800VA) with common ground amps and are loving the results.

    So this group buy is for the transformer. Sounds expensive for a transformer, but this thing is a massive hunk of audio grade copper. You'll need a case to mount it in. Save yourself time and get Larry's. You'll need to consider what kind of connectors you'll need. Save yourself time and get Speakons:

    http://www.polkaudio.com/forums/showthread.php?142058-A-slightly-different-take-on-the-Dreadnought

    Finally, you'll need to consider cables, and how they terminate on the speaker side. Personally, I replaced my pin-blade SDA connector with a Speakon and haven't looked back. You can also use a single binding post, connect the positive Dreadnaught cable, and connect the negative to the same negative post that you connect the negative speaker cable coming from the amp. Helps to use both a spade and a banana on the same terminal. I'd recommend going Speakon though!

    Hopefully I'll get paid three times today and we'll be at 15 paid units. Then we try to recruit 5 more over the weekend and get to 20!
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    Received payment from Inthefade. 13 paid units.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • voltz
    voltz Posts: 5,384
    edited July 2014
    Kudos to Neil & Larry and everyone making this happen!!

    I joined in knowing I may never find some SDA's to use this with, but if I did.....I didn't want to try and find this stuff later, plus Larry making the cases. and maybe making his famous rings, this is a good time to be a Polkie :)
    2 ch- Polk CRS+ * Vincent SA-31MK Preamp * Vincent Sp-331 Amp * Marantz SA8005 SACD * Project Xperience Classic TT * Sumiko Blue Point #2 MC cartridge

    HT - Polk 703's * NAD T-758 * Adcom 5503 * Oppo 103 * Samsung 60" series 8 LCD
  • Sea
    Sea Posts: 317
    edited July 2014
    ^^^^^^what he said!
    Main-Carver TFM35(2),Carver C11 ,Carver SD/A 360 CD,Carver TX11 ,Grace Digital Tuner, Pioneer PL707 TT,Polk SDA1C
    Downstairs -Carver M1.5t, Carver C1 Pre, Carver TX10 Tuner, Carver TL3200 CD Player, Dual 1009 TT,Polk SDA SRS 2.3tl
    Study - Carver AV634 Amp, Carver CT7 Pre, Carver DTL50 CD Player, Polk RTA12c
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    South Dakota Po and scubasteve4sq I need to hear from you.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
    Sent you an email Neil. I'll have payment out in the morning when I get off work.
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    Yup got it. So you're going to pay tomorrow, at which point we'll have 14 paid, and hopefully I hear from South Dakota Po. If I don't, I'm still going to put in the order for 15 units, since it's actually cheaper to order 15 than it is 14. Someone will show up in the next 12 weeks who will want it before they're actually built and shipped.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • DarqueKnight
    DarqueKnight Posts: 6,642
    edited July 2014
    nspindel wrote: »
    Someone will show up in the next 12 weeks who will want it before they're actually built and shipped.

    I expect they will show up a day or two after the group buy has concluded just like the previous group buys. I know the stragglers will appreciate your consideration.

    Polk should order about 50 of these to avoid broken hearts in the future.
    "So hot it burns Mice!"~DK
    "Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
    "Knowledge, without understanding, is a path to failure."~DK
    "Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
    Well I can only afford 1 at the moment but I may grab that second one as well next week.
  • F1nut
    F1nut Posts: 46,494
    edited July 2014
    Polk should order about 50 of these to avoid broken hearts in the future.

    You know, if Al Ballard was still there he would have made that happen. Don't hold your breath now though.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
    And also Larry make that 2 cases for me with speakon. If I can't swing 2 of the 1000 I'll settle for an 800
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    Confirming payment received for 14th unit. So I will definitely be ordering 15 on Monday, and assuming someone comes along and pays me for it, you'll all be getting a bit over $26 back.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
    And also Larry make that 2 cases for me with speakon. If I can't swing 2 of the 1000 I'll settle for an 800

    im assuming that the 800 would fit into the same case since the 1000 is larger correct?
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    Correct.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    South Dakota Po payment received. We are good to go for 15 units.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • GlennDog
    GlennDog Posts: 2,519
    edited July 2014
    Neil,
    What's the harm in waiting 1 more week, so more can "pile on" the opportunity?
    The Polk purchase of 50 is quite good, but it'll prolly never happen. I will commit if it will helps to make it to 20

    G
    Power Rogue M180 monos & Adcom GFA 5802
    PS Audio PerfectWave Power Plant 10
    Rears Salk SuperCharged Surrounds
    Source PSA PWT into NSD Supremo
    Pre/Pro Integra DHC 40.1
    LCD Samsung LN46B750
    Mains Salk HT2-TL
    Center Salk HT2C
    Pre Cary SLP-05
    Wires WW & MIT
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    It's up to you guys, I'm in no rush. I have one already :)
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • Sea
    Sea Posts: 317
    edited July 2014
    I am ok with waiting.
    Main-Carver TFM35(2),Carver C11 ,Carver SD/A 360 CD,Carver TX11 ,Grace Digital Tuner, Pioneer PL707 TT,Polk SDA1C
    Downstairs -Carver M1.5t, Carver C1 Pre, Carver TX10 Tuner, Carver TL3200 CD Player, Dual 1009 TT,Polk SDA SRS 2.3tl
    Study - Carver AV634 Amp, Carver CT7 Pre, Carver DTL50 CD Player, Polk RTA12c
  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
  • nspindel
    nspindel Posts: 5,343
    edited July 2014
    Well, you guys get almost $50 back each if you get 5 more units.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
    Worth the wait in my opinion. I'm sure there are other people who will want to get in on this.

    Especially considering it's been almost 2 years since the last buy.

    Here are some quotes from Matthew polk to consider

    "The original isolation transformer was successful at eliminating the issues of SDA with non-common ground amps but at the cost of a significant compromise of the SDA sound stage. We later figured out how to do this right with the transformer incorporated into the SRT controller.

    The transformer is a 1:1 ratio and allows the L-R and R-L SDA signals to be derived while isolating the grounds of the two amp channels. The inverted portions of the SDA signals only need a bandwidth from a little below 100Hz to 1.6kHz. It's helpful if the transformer has more bandwidth on the top end since the high-end cutoff is controlled by a low-pass in the cross-over. At the low end, however, it's best if the transformer windings have a very high inductance as measured with the secondary open, around 14mh, and a very low DCR.

    In the mid-range where SDA operates, the SDA drivers on one side operate in series with the SDA drivers on the other side with the signals passing through one set of SDA drivers then through the transformer and then through the set of SDA drivers on the other side. However, at low frequencies the positive part of the signal passes through the SDA drivers and is shunted directly to ground by an inductor in parallel with the transformer. The result is that the SDA drivers operate in parallel with the stereo drivers at low frequencies but operate in series with the other side to produce the SDA difference signal in the mid-range. If the DCR is too high, as it was in the original isolation transformer, it will reduce the level of the SDA signal and alter the bandwidth. If the inductance isn't high enough, also the case in the original, it will raise the low-end cutoff of the SDA signal further reducing the SDA soundstage and allow the SDA drivers to produce too much upper bass thereby muddying the sound.

    The transformer in the SRT controller had a DCR around .3 ohms and an inductance around 14mh as best I recall. Current carrying capability before saturation is also an issue and was not adequate with the original. I think it was only about 3 amps which would be about 60 watts to the SDA drivers and not enough. I don't recall exactly what it was in the SRT but seem to recall something like 10 amps which would deliver about 600 watts to the SDA drivers.

    As a practical matter we found the only way to get a low enough DCR was with a 1:1 toroidal transformer. These are available off the shelf but expensive. Because of the efficiency of the toroid the cores must be much larger to avoid saturation.

    Hope that helps.

    -msp

    Yes, I did mean 5 amps. The transformer will have to handle nearly the entire amplifier output for any signal that is primarily in one channel or the other. The impedance of the sda drivers in series is around 6.5 ohms. So, a 5 amp rating will deliver up to about 160 watts to the sda drivers before saturation. The inductance determines the frequency at which the transformer will shunt low frequencies to ground allowing the sda driver to produce the same low frequency signal as the strereo driver in that cabinet. 14mh puts that point well below 100 Hz. That means that the sda signal will be preserved at full strength down to 100 Hz which is important for best imaging. Higher DC resistance just attenuates the sda signal and the bass. I think the transformer in the SRT system had a DCR of 0.3 ohms, 14mh inductance and saturation current around 7.5 amps.

    -msp
  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
    I'm pretty sure this transformer is a 10amp rating correct? The 800va is a 7amp

    Either way it should provide more than enough headroom for your amplifiers on the sda dimensional drivers.
  • jonicont
    jonicont Posts: 262
    edited July 2014
    No rush
    SDA 2BTL, VPI Prime, Soundsmith Zephyr MKIII, Rogue Ares Magnum, McCormack DNA 0.5 Gold, ARC LS-17se, Cambridge cxn v2, MIT AVT MA ic’s and speaker cables, ps audio stellar power plant 3

  • voltz
    voltz Posts: 5,384
    edited July 2014
    No Rush!! As I do not have speakers yet :) just planning for the future. If you think you may get some SDA's in the future I would jump in.
    2 ch- Polk CRS+ * Vincent SA-31MK Preamp * Vincent Sp-331 Amp * Marantz SA8005 SACD * Project Xperience Classic TT * Sumiko Blue Point #2 MC cartridge

    HT - Polk 703's * NAD T-758 * Adcom 5503 * Oppo 103 * Samsung 60" series 8 LCD
  • Sea
    Sea Posts: 317
    edited July 2014
    I remember seeing a post, maybe in this thread, from F1Nut, recommending that the SDA interconnect cable be the same as the stereo speaker cable. I also remember hearing or reading that some people shield the SDA interconnect cable. Opinions?

    I also noticed that there are variety of female speakon connectors for case mounting. I truly have not compared to see if the hole patterns are the same. Does anyone know which type or types the Larry cases are precut for?
    Main-Carver TFM35(2),Carver C11 ,Carver SD/A 360 CD,Carver TX11 ,Grace Digital Tuner, Pioneer PL707 TT,Polk SDA1C
    Downstairs -Carver M1.5t, Carver C1 Pre, Carver TX10 Tuner, Carver TL3200 CD Player, Dual 1009 TT,Polk SDA SRS 2.3tl
    Study - Carver AV634 Amp, Carver CT7 Pre, Carver DTL50 CD Player, Polk RTA12c
  • scubasteve4sq
    scubasteve4sq Banned Posts: 72
    edited July 2014
    I believe the holes are all the same size because the connectors are cross compatible. Ie:you can use a speakon 2 conductor in a 4 conductor socket.
  • F1nut
    F1nut Posts: 46,494
    edited July 2014
    The face plates are drilled out for a D size chassis connector, but there are many choices and they are not all the same. This is the one you should use, http://www.neutrik.com/en/speakon/speakon-chassis-connectors/nl4mp-uc

    It's sealed (very important at the speaker end) and high current rated unlike the rest. Make sure the cable connector is also rated for high current, such as this one, http://www.neutrik.com/en/speakon/stx-series/nlt4fx-bag

    You will also need M3 (metric) screws, lock washers and nuts to properly mount the sockets. I recommend stainless steel. They are available from Fastenal.

    To mount the transformer use either a brass or stainless steel bolt, fender washer, lock washer and nut.
    recommending that the SDA interconnect cable be the same as the stereo speaker cable.

    Only makes sense to me, but not required.
    I also remember hearing or reading that some people shield the SDA interconnect cable.

    Speaker cables are generally not shielded. I believe you are thinking of the original AI-1, which sounds a lot better wrapped in ten layers of aluminum foil, aka the baked potato.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • F1nut
    F1nut Posts: 46,494
    edited July 2014
    Forgot to mention, these flanges give it a nice finished look. http://www.neutrik.com/en/speakon/speakon-chassis-connectors-accessories/scdp
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk