Free Shipping on All Orders 1-866-764-1801

Vist our Online Store
+ Reply to Thread
Results 1 to 4 of 4
  1. #1

    Member Sales Rating: (0)

    Join Date
    May 2006
    The Seasonally Frozen Wastelands

    Default 2B and EARLY 1C AI-1 modifications

    Quote Originally Posted by heiney9 View Post
    IF you have late enough serial number 1C's you can build/buy an AI-1 interphase cable which allows all non-common ground amps to be run with SDA's (mono or not)
    I decided it would be better to start a new thread than to derail the other thread:

    I know there's a list of serial numbers for 1Cs and 2Bs that deals with the ability to use the AI-1 isolation transformer. The nicest scan of that list that I found in a search, was provided by F1nut a long time ago in a thread far, far away.

    The bottom of the instructions says that "plug adapters and some internal modification" are needed.

    WHAT were the "internal modifications" needed?

    First Guess: "Plug adapters" were to convert the blade/blade interconnect jacks to a pin-blade configuration. Polk used up leftover jacks from the earlier-generation speakers on the first of the later-gen speakers. ONE of the blades was actually used to transfer the SDA signal between the cabinets, and I bet the second conductor in the jack was simply un-used--not connected to anything inside the cabinet. The "modification" is nothing more than connecting the second "slot" of the blade/blade jack to the negative binding post. Polk would perhaps have supplied a plug-in adapter so a pin-blade cable end would attach to a blade/blade speaker jack.

    The sum total of the Polk-approved modification is a pair of adapter jacks (or, perhaps, the proper pin/blade socket as used on the later-production speakers???) and maybe eight or twelve inches per cabinet of whatever wire Polk was using to connect the previously-disconnected blade to the negative binding post.

    This could be EASILY electrically reproduced using non-stock parts. Wouldn't even have to be expensive, although I'm sure there are expensive ways to do it.

    My point being that the early 1C and the 2B are completely compatible with the AI-1, with very minor changes.

    What part(s) of my guess are not correct?
    Last edited by Schurkey; 04-15-2012 at 06:02 PM.

  2. #2

    Member Sales Rating: (22)

    Join Date
    Oct 2008
    Directly over the center of the earth in Olathe Kansas


    Are there schematics on the sticky under vintage speakers? If there are that may shed some light. For some reason I think it is more than that to it but I have no data to back that up. Just considering there is serial number range tells me something specific changed that allowed an AI.
    Speakers: SDA-1C (most all the goodies)
    Preamp: Joule Electra LA-150 MKII SE
    Amp: Wright WPA 50-50 EAT KT88s
    Analog: Marantz TT-15S1 MBS Glider SL| Wright WPP100C Amperex BB 6er5 and 7316 & WPM-100 SUT
    Digital: Mac mini 2.3GHz dual-core i5 8g RAM 1.5 TB HDD Music Server Amarra (memory play) - USB - W4S DAC 2
    Cables: Mits S3 IC and Spk cables| PS Audio PCs

    Ofc: Wright WLA12 preamp: Anthem Amp 1: Pio Elite DV-79AVI: Airport Express: CAL Sigma II DAC: PA LS90 sonicaps and mills

  3. #3

    Member Sales Rating: (0)

    Join Date
    May 2006
    The Seasonally Frozen Wastelands


    Quote Originally Posted by thsmith View Post
    Are there schematics on the sticky under vintage speakers? If there are that may shed some light.
    Yes. Thanks for the kick in the ass. Proved most illuminating. There are two versions of the SDA 2B. Early 2B has a blade-blade socket, and according to the schematic, the second blade is not connected to anything.

    Newer 2B has a pin-blade socket, and is already AI-1 compatible.

    AT THE TIME OF PRINTING, the scan provided by F1nut posted above was correct--2Bs shipped with the older, leftover blade/blade sockets, and so "all" 2Bs (to that time) needed the modification. AFTER the above document was released, Polk began using the "correct" pin/blade socket, properly wired and suitable for AI-1.

    The situation was almost certainly the same with the 1Cs that fell within the specific serial number ranges.

    It would take MINIMAL work and expense to convert them to be fully AI-1 compatible. Parts needed would depend on the cable ends used with the AI-1-style device. Since I expect the majority of isolation transformers will be of the Dreadnaught variety and not using the "stock" pin/blade cable ends, aftermarket choices are nearly limitless. One conductor to the crossover via the original blade, or tied in using an added speaker binding post and a bit of wire--and the other conductor routed directly to the negative binding post already on the speaker. Done. $5.00 on the cheap, or sky's-the-limit for "audiophile" connectors and wire.
    Last edited by Schurkey; 04-16-2012 at 02:51 PM.

  4. #4

    Member Sales Rating: (0)

    Join Date
    May 2006
    The Seasonally Frozen Wastelands


    [EDIT to above]
    Well, technically, there are THREE versions of the 2B, but the third is exactly the same as the second except for a change to the polyswitch, and the schematic has added notes on parts quality. Inconsequential.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)


Similar Threads

  1. Need Help Speaker ID; Suspected EARLY EARLY Model 10/ Monitor 10
    By JohnLocke88 in forum Vintage Speakers
    Replies: 31
    Last Post: 09-03-2009, 10:56 AM
  2. SDA CRS modifications
    By maandjojo in forum Vintage Speakers
    Replies: 15
    Last Post: 05-20-2009, 01:23 PM
  3. 10B modifications
    By specialidiot in forum Vintage Speakers
    Replies: 8
    Last Post: 10-05-2007, 01:22 PM
  4. Modifications
    By Zero in forum The Clubhouse
    Replies: 7
    Last Post: 03-08-2003, 02:03 AM
  5. Any Modifications
    By DungBoi in forum Car Audio & Electronics
    Replies: 1
    Last Post: 10-25-2001, 09:45 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts