AI-1 for SDA 1B

SchurkeySchurkey Posts: 1,660
edited August 2011 in Vintage Speakers
Had a thought about isolation transformers for SDA units that can't use the AI-1 or similar transformers.

My (blade/blade) 1Bs use a dual-conductor interconnect cable, each speaker supplies the opposite speaker with a full-range, full-voltage signal to power the SDA drivers in the other speaker. One conductor carries signal left-to-right, the other conductor carries signal right-to-left. All the signal filtering is done in the speaker receiving the SDA signal.

Any reason that TWO isolation transformers couldn't be used to allow bridged or otherwise not-common-ground amplifiers to be used?

The newer pin/blade interconnects have only one conductor supplying signal, the other wire is only used to supply a ground to the isolation transformer (if used).

So perhaps two transformers, one in each conductor for the blade/blade interconnect could serve the same purpose. Grounding the isolation transformer would be easy, just run the cable to that speaker's negative terminal.

I'm not sure how this will affect the overall impedance of the speaker system. Kinda thinking it may drop the impedance. I'm curious, but I don't actually care, the amps I'd use are good to 2 ohm or less.

DOUBLE DREADNAUGHT for 1B and similar SDAs!

Feasable? What am I missing? Comments???
Post edited by Schurkey on

Comments

  • SchurkeySchurkey Posts: 1,660
    edited August 2011
    Captain Obvious wasn't answering his call before I submitted that post.

    A full-range, full voltage SDA signal going through an isolation transformer would essentially short-circuit the speaker. Damn right the impedance would go down.

    Scratch one more idea for driving 1Bs (and similar) with bridged amps.
  • nooshinjohnnooshinjohn Posts: 15,886
    edited August 2011
    I do not know all the tech stuff on this, but I can assume that IF it could be done, Darqueknight would have done so and shared that with the rest of us.
  • Big DawgBig Dawg Posts: 1,950
    edited August 2011
    I do not know all the tech stuff on this, but I can assume that IF it could be done, Darqueknight would have done so and shared that with the rest of us.

    I think that Raife is one of the true gems of this site, very bright, informed, interested, and a gentleman to boot. However, I would never assume that a new idea is no good simply because it hasn't already been investigated.
  • ceg4048ceg4048 Posts: 2
    Hello,
    I apologize for dredging up this 6 year old thread, but searching the forum for "Isolation Transformer" and looking through 50 pages of hits, this one seems to come the closest to my problem. It became obvious that long time members might be annoyed at seeing yet another Isolation Transformer thread. :p

    In any case, I'm the original owner of an SDA SRS purchased around 1987. It appears to be a Gen 3 from what I can glean from some of the documents on the site. The Interconnect cable is a blade/blade and I do recall the salesman touting the features of the SDA as having the "equal and opposite" signal of the stereo array.

    My intent is to upgrade the speakers using some of the items the checklist in the sticky here, i.e., crossover mod, tweeter replacement and so on, however, I do wish to purchase a newer amp such as the Pass Labs monoblocks or the the Levinson high power stereo amps.

    The issue is whether it it possible to devise an isolation transformer scheme so that these non-common ground amps with the SDA?

    I'm not really knowledgeable enough to understand Schurkey's assessment that "A full-range, full voltage SDA signal going through an isolation transformer would essentially short-circuit the speaker."

    I mean, isn't the idea of the transformer that it avoids physical connection so that the speakers are isolated? And of course there is no point in disconnecting the cable as that would defeat the point of SDA.

    If there is no way to use modern fully differential or monoblock amps with these speakers then it seem a real liability. I saw another post stating that the ground terminals of the monoblocks can be connected to create a common ground, but this seems to defeat the purpose of channel separation and differential design of the amp.

    I'd like to determine the cost/benefit of holding on to these speakers. Can anyone clarify this transformer issue for me?

    Cheers,
  • SchurkeySchurkey Posts: 1,660
    Noted...reply coming in a few hours.
  • gimpodgimpod Posts: 1,651
    Welcome to Club Polk,

    As @Schurkey will most likely point out using an isolation transformer with the SDA SRS or any pre 4th gen SDA is a non starter. With this group of guys if there was anyway to use an isolation transformer with pre 4th gen SDA's it would have been done and documented.

    With the Blade/blade I.C. each blade is basically tied to the opposite speakers ground, thus tying both speakers grounds together. The only way to get these SDA' to work with "fully differential or monoblock amps" is to tie the amps grounds together (if possible, and not really a good idea sonically) or don't use the I.C. and if your not going to use the I.C. you should sell them to someone who will and buy some standard stereo speakers.

    Sorry.
  • westmassguywestmassguy Posts: 5,562
    I envisioned using two Dreadnaughts, one for the Interconnect, and a second, smaller one to connect the grounds between the two mono-blocks
  • gimpodgimpod Posts: 1,651
    David remember one lead of the B/b I.C. go's from the +Right to -Left and the other lead go's the other way +Left to -Right so I think using two Dreadnaughts would short them out.
    Schurkey wrote: »
    Captain Obvious wasn't answering his call before I submitted that post.

    A full-range, full voltage SDA signal going through an isolation transformer would essentially short-circuit the speaker. Damn right the impedance would go down.

    Scratch one more idea for driving 1Bs (and similar) with bridged amps.

  • SchurkeySchurkey Posts: 1,660
    Okay. Back with a couple of minutes to reply to this.

    1. The isolation transformer has four leads. The right (or left) side leads go from + to -. This will not work since the blade/blade SDA interconnect carries the ENTIRE full-range, full-voltage + signal. It would create a short-circuit around the crossover and drivers to that channel, and of course the same thing happens at the other speaker cabinet. The impedance of the speaker drops to near-nothing, and little sound would be produced aside from the amplifier blowing-up.

    2. I did re-wire my SDA 1Bs internally to use a single-conductor (like the 1C) style of interconnect. It "works", and you "could" use an isolation transformer...but it also degraded the sound quality. The speakers sounded "off". There's no point to any modification that screws up the sound. I converted back to the two-conductor (blade-blade) interconnect, and waited several years for newer-generation speakers to become available to me.

    Sorry, there's no way I know of to fix this problem in any sort of easy or convenient way. About the best you could hope for is to build newer-generation crossovers, and then update the drivers to match. Not easy, not convenient.

    Or buy newer-generation speakers.
  • pitdogg2pitdogg2 Posts: 6,579
    edited June 8
    Schurkey wrote: »
    Captain Obvious wasn't answering his call before I submitted that post.

    A full-range, full voltage SDA signal going through an isolation transformer would essentially short-circuit the speaker. Damn right the impedance would go down.

    Scratch one more idea for driving 1Bs (and similar) with bridged amps.

    Wondered when you were going to wake up there. Reading that i thought first how my limited electrical knowledge read direct short right off the bat. I have just enough electrical knowledge to be dangerous.... but safe enough to keep myself alive 52 yrs.

    Dang it caught necrothreading again :s
  • ceg4048ceg4048 Posts: 2
    Thanks gimpod and Schurkey for your responses. The difficult choice seems to be to stick with the SRS, do the mods and find high quality amps, which there must be thousands, that are common ground (or just stick with the amp driving them now, or to spend the money for newer generation speakers that can handle non-common ground.

    Greatly appreciate your insights.

    Cheers,
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