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About fedeleluigi

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  1. I'm afraid it has happened?

    Hello Tom Pete said the tweeter che tested had ferrofluid. If the ferrofluid was still in place (in the magnet gap) when measurements were carried out, it sealed the magnet gap and consequently the space behind the dome. So, in the 200011-1 tweeters with ferrofluid the air behind the dome can't escape from under the dome into the pole-piece/magnet cavity. On the contrary, this is possible for the early 200011-1 tweeters because they don't have ferrofluid sealing their magnet gap. Luigi
  2. AR12's Restored-A few Pics

    Hi Glenn, I was referring to the 12 inch woofer. The moving mass of the 10 inch woofer is much lighter and its Xmax is smaller than the 12's. Moreover the 10 inch ferrite woofer has a bumped black plate. For all these reasons the crack of the voice coil support is rather rare in AR 10 inch woofer. As I do not usually shim woofers when I refoam them, I do not know when AR exactly changed the former for its voice coils. I usually disassemble woofers only when their voice coils or spiders are broken. Anyway in some 2ax 10" alnico woofer using foam surrounds I found NOMEX. They were dated about 1972. Nomex is a meta-aramid material developed by DuPont in sixties and is completely different from paper. It seems plastic. I do not know if AR continued using it also after the indroduction of the ferrite magnet for the 10 inch woofer. This is also why I asked you what material you had found when you shimmed your woofers. Later in some date of 1977 AR began to use aluminum for all its woofer voice coils. As regards AR 12 inch ferrite woofer manufactured from about 1970 to 1977 untill now I have never found Nomex former (but only paper former) in their voice coils . Luigi
  3. AR12's Restored-A few Pics

    Thank you Roy, I thought that the change had occurred later, around the middle of 1977. Anyway, one of the pictures posted by Glenn shows a woofer manufactured on the 33th week of 1977 and one of his woofers would seem to have a paper voice coil just like he remembers. Imho, the paper voice coil former used in the 12 inch woofers from around 1970 to around 1977 and the use of a not bumped back plate was the "Achille's heel" of those excellent woofers. Apart from the possibility of a hard bottoming for the flat back plate of the magnet , Imho, at the voice coil "collar" (I mean the former space between the cone and the first voice coil winding) the paper former was not "strong" enough to bear the big forces caused by the wide and violent oscillations of the heavy cone (at high volume) during many years . I do think that at AR they never imagined that there would be lovers and enthusiasts for their speakers after more than 40 years! Luigi
  4. AR12's Restored-A few Pics

    Hi Glenn, I hope Roy C. can chime in as he uses to shim woofers when refoaming them. Thanks again Luigi
  5. AR12's Restored-A few Pics

    Hi Glenn, Excellent job and thank you for sharing it! Could you please tell me what is the voice coil former material used in the woofers (200004-2 ) you shimmed? In one picture it seems aluminum, in the other one it seems paper or nomex. I'm interested in it as AR began to use aluminum for its voice coil at some point (I suppose about the middle or the end of 1977) and in one of your woofer is printed the manufacturing date (33th week of 1977) . Thanks. Luigi
  6. A lurker steps out!

    Thank you Chris, When you have your LSTs repaired, I would appreciate it if you could let me know how they perform using both the ML-11 and ML-9. If I remember correctly these Levinson amplifiers were designed by Tom Colangelo. Unfortunately, I've never listened to the Levinson amps designed by him. I only listened to Levinson amps designed by Madrigal's engineers. In any case, if I were you I would also try the "little" Radford STA 15. If its caps, resistors and tubes are OK and if your listening room is not very big or your listening position is not very far from speakers, it could work very well with LST despite its low power. Once I listened to a pair of LSTs driven by a 35 Watt tube amp (the Unisis by "Tube Technology") and the sound was very good and enjoyable. Luigi
  7. AR 11 Diagram

    Yes, that's right! Obviously, tweeter and midrange switches are completely independent of each other and can be used to independently get different attenuation of sound pressure in high- and mid-range frequencies. Luigi
  8. A lurker steps out!

    Hi and welcome Chris, Which are the best sounding amplifiers you have used (or listened to) to amplify AR loudspeakers ? Luigi
  9. AR 11 B schematic

    I've drawn the AR-11 MKII (B) crossover schematic. I've preferred to use old style types and drawing. Hope it can be useful. Luigi
  10. AR 11 Diagram

    I've drawn the AR-11 MKII (B) crossover schematic. I've preferred to use old style types and drawing. Hope it can be useful. Luigi
  11. Here is the AR 10 Pi schematic coming from a copy of an AR original drawing sheet. Unfortunately the copy I have is not complete and a part of the AR drawing sheet is missing. I couldn't find this schematic in the "AR Drawings" section, so I hope it can be added to the other files somewhere in the Library in order to allow everybody to see it. I think it's a rather rare document even if, unfortunately, not complete. I have scanned it as TIFF format then I've converted it to JPEG to insert it directly into this post. To get a higher resolution, save the attached file in Tiff format. Differently from LST, in the AR 10 Pi the auto-transformer and the 3 dB step switches permitted the listener to have more flexibility with a total of 27 different combinations of driver output level (that is 27 different frequency responses) without using any attenuation resistor. The auto-transformer enabled the user to control bass output by a 3 step switch as well. Differently from midrange and tweeter, the woofer switch (Woofer Environmental Control switch) is actually not a 3 position +/-3dB step switch but a 0dB (4Pi), -5dB (2Pi) and -8dB (Pi) switch. Luigi PS: I had already posted this schematic in the Acoustic Research forum pages but I think that the most appropriate place is probably here. AR10 Pi original schematic TIFF.tif
  12. AR-9 Restoration - Pete Basel

    Pete, could you post some pictures? Luigi
  13. AR3a Tweeter Voice Coil Wire Gauge

    Hello David, The AR drawing (DRG. NO. 202029, ISS. C of 14 May 1982) reports the use of N. 38 AWG insulated copper wire for the 3/4" lamda driver voice coil. It also reports 22-24 turns in all and a DC resistance from 3 to 3.7 ohms REF. Taking into account that AR 3a tweeter voice coil has about 20 turns, (that is 10-20 % less than lamda driver's), using the same wire gauge, the resulting DC resistance should be OK. Examining some AR 3a voice coil by a biomicroscope, I have counted about 8 and 12 turns for the outside and inside layer respectively. Luigi
  14. AR-3a / AR-91 Combo Build

    About the risk of overdamping the last generation 200003-0 woofer by using 20 oz of fiberglass, you can read this other John O'Hanlon's post:
  15. AR-3a / AR-91 Combo Build

    Hi ar_pro, You did not post a picture of the woofer magnet you used but your AR woofer seems the last production of the 200003-0 woofer with round magnet. So, if I were you, I would also try about 8.82 oz of the "white" polyester wadding as the last production of AR11 or 10 Pi that used the same woofer as yours. As far as I've observed in Italy, AR11 and 10Pi never used fiberglass with the last generation 200003 woofer. Moreover, it seems that the real enclosure volume of the ar 3a is exactly the same as AR11 or 10 Pi's , read Johnieo's (John O'Hanlon's) post here: http://www.classicspeakerpages.net/IP.Board/index.php?/topic/1194-ar3a-vs-ar11-cabinets/&do=findComment&comment=55341 . So, using the last generation 200003 woofer, the amount of polyester to be used in the 3a cabinet should be the same as in the last AR11 or 10 Pi (using the same type of polyester). I don't know the precise "physical" characteristics of the white polyester wadding AR used in AR11 or 10 but, if available, I'd try the polyester used in the AR 9 or LS series as all of them look identical. I think your 3a/91 balance between bass, midrange and treble could improve. I would also try polyester wadding even if I had the 200003-1 square magnet woofer. Luigi