A1 Interconnect for SDA-2B ??

inspiredsports

I own a pair of SDA-2B's with Serial Numbers R 14683 and L 14926 and they are BLADE / BLADE. Interestingly, I note this system is configured where only 1 blade connects via the Interconnect Cable to the blue wire connected to the bottom, narrowest blade within each speaker cabinet.

I note with interest a recent ebay posting for for an A1 Interconnect at . . .

http://cgi.ebay.com/Polk-Audio-SDA-amplifier-interface-interconnect-cable_W0QQitemZ300269007939QQcmdZViewItem?hash=item300269007939&_trksid=p3286.c0.m14&_trkparms=72%3A1420|66%3A2|65%3A12|39%3A1|240%3A1318

The sellers states the Interconnect will work with SDA-2B serial numbers HIGHER than R 14124 and L 14115.

By Serial number these appear to work with my cabinets, but I thought A1 Interconnects were all PIN / BLADE.

Does anyone know more about this. I would really like to be able to use a non-common ground amp with my speakers and this looks like the answer.

ben62670

Well I hope you didn't "win" it. $255. Ouch. There were some in between models that used as you said just one of the blades as an IC connector. It is the same as the pin blade, but just different ends. An A1 can be made. What amp are you using that needs the A1?
Ben

inspiredsports

ben62670 wrote: »

Well I hope you didn't "win" it. $255. Ouch. There were some in between models that used as you said just one of the blades as an IC connector. It is the same as the pin blade, but just different ends. An A1 can be made. What amp are you using that needs the A1?
Ben

Hi Ben,

No, I wasn't involved in that bidding. I'm just amazed to see that it shows my SDA-2B Serial Numbers as working with it. My speakers are BLADE / BLADE and only 1 wire connects between the 2 cabinets. I just flat out don't see how the AI-1 Amplifier Interface works with my speakers. I thought they were all Pin / Blade and used both conductors.

The group consensus is that there is no way use a non-common ground amp with my original SDA SRS 2's, so I started researching the possibility with my smaller SDA-2B's and found this information.

I have a vintage NAD 7600 Receiver that I love, and found a "can't pass it up" price on it's separate 2600A Amp. When bridged the NAD's become non-common ground. That's where my interest in the AI-1 came up.

And yes, I understand building one from scratch with high quality cable, connectors, transformer, aluminum case, etc. like DarqueKnight and other have is the best idea. If this 2600 purchase goes through for sure, I will be in the market for an AI-1 clone once I verify that my 2B's are 100% capable of working in non-common ground mode without blowing something up.

Thanks,
Greg

danger boy

you can use a NAD 2600A amp without any problem with the SDA 2B's. I do every day without any problems. I don't know anything about mating it with a NAD receiver though.. that's over my head. Mine are blade/blade

strider

With some help I was able to get my blade/blade 2B's to work with the AI-1. There's a post around here somewhere with my serial numbers in it, I'll try to dig it up if I get the chance.

Come to think of it, what I did was documented to a degree on the forum; poss in a couple different posts. IIRC I needed to connect the neg binding post to the small blade socket inside the cabinet to complete the circuit.

inspiredsports

danger boy wrote: »

you can use a NAD 2600A amp without any problem with the SDA 2B's. I do every day without any problems. I don't know anything about mating it with a NAD receiver though.. that's over my head. Mine are blade/blade

Hi Danger,

The 7600 is a receiver that incorporates the 2600A and the 1700 Preamp and Tuner into 1 Box, so I essentially have a 2600A.

What I'm basically talking about is using TWO amps (my 7600 [2600 inside] plus another separate 2600A), both set in "bridged" mono mode, one for each stereo channel. This PROFOUNDLY CHANGES the amps circuitry from COMMON GROUND in stereo mode, to NON-COMMON GROUND in mono mode. This is not a problem for other brand speakers that are isolated from one-another, but a 100% no-go with the IC Cable that SDA's use.

The work-around is that Polk built the AI-1 Aplifier Interface (an IC Cable with a transformer in it) that works with the cirtruitry configuration of a few select Polk models. I'm trying to make sure my 2B's allow for this use, but like all Polk's, revisions, etc. even withn the same model year make for confusion.

inspiredsports

strider wrote: »

With some help I was able to get my blade/blade 2B's to work with the AI-1. There's a post around here somewhere with my serial numbers in it, I'll try to dig it up if I get the chance.

Come to think of it, what I did was documented to a degree on the forum; poss in a couple different posts. IIRC I needed to connect the neg binding post to the small blade socket inside the cabinet to complete the circuit.

Thanks strider,

I've searched the forums extensively and did not find your post yet so any help you could provide would be helpful.

I was just on the phone briefly with Polk and they confirmed the AI-1 is no longer available from Polk. The rep vaguely remembered that at the time there was a Pin/Blade to Blade/Blade Adapter available where 1 of the blades on the adapter had a wire on it that was to be connected to the Amplifiers output ground lug. He couldn't remember which blade (wide or narrow).

I do know that on the SDA-2B, it is the NARROW blade on the normal IC Cable that connects to the blue wire of the crossovers, and the WIDE BLADE DOES NOTHING (it's not connected to anything).

What kind of amps are you bridging?

Greg

inspiredsports

I went ahead and bought the 2600A today and it's on its way so I will definitely need to learn how to interface the AI-1 to my SDA 2B's.

Ben, I'd rather pay you to build custom than buy the less than stellar stock part on eBay. I will be mailing my SDA SRS 2 low-pass crossovers to you as soon as Sonic Craft sends (out of stock 17uf's). Maybe if we are lucky we can get everything in order price-wise/parts-wise so you can send it back in same box. PM sent.

strider

This post should help.

Poee7R

Not to stir the pot, but Ive never heard an amplifier bridged that sounds that great. I would instead of bridging two stereo amps, use them in stereo pairs with one driving the highs of both speakers, and the other driving the mids/lows. The 2600's are nowhere near weak amplifier's and you probably wouldnt need anymore than they will give with just one amp running your sda's, not to mention bridging amps of that age would probably lead to undue stress and a shortened lifespan.

Not to say what you are planning wouldnt work, and work just fine. But I dont think it will sound better, which leads me to wonder why to do it in the first place.

Good luck in your search, audio is fun isnt it.


Dave

DarqueKnight

Dave brings up an excellent point. The sound quality of some, maybe most, maybe close to all, brigeable stereo amplifiers significantly diminishes when they are switched to bridged mode. The sound of my Adcom GFA-555II's and Carver M1.0t's was cold and hard in bridged mode.

It wasn't the bridging that caused the deteriorated sound, but rather how the bridging scheme was implemented in those particular amplifiers. There are many bridged designs that sound excellent, but most of these are straight bridged designs rather than switchable stereo/bridged designs.

inspiredsports

I am so thankful for this group and the way members are so courteously and patiently willing to share.

I think I've beaten this idea to death and am now convinced by those of you with way more knowledge that I'm better off in all respects to concede that bridging in my situation is not a great plan.

I already had plan "B" in that I and purchased a nice NAD 1700 preamp / tuner (identical tuner and preamp as parts inside the 7600 Receiver I own) that will mate perfectly with the 2600.

My SDA-2B's and SDA SRS 2's will now each have lots of NAD power in 2 separate rooms installations.

(I'm still going to bridge briefly without the Interconnect just to see what effect that does impart to the sound of these amps)

BrettT1

inspiredsports wrote: »

(I'm still going to bridge briefly without the Interconnect just to see what effect that does impart to the sound of these amps)

I'm interested in hearing the results.

inspiredsports

BrettT1 wrote: »

I'm interested in hearing the results.

I'm hoping to test for several hours on Sat 20th or Sun 21st and will definitely post.

I'm going disconnect my IC BEFORE bridging and listen to some very familiar passages with varied characteristics first to get a baseline, and then bridge and listen again to get a good comparison.

inspiredsports

BrettT1 wrote: »

I'm interested in hearing the results.

I got a chance to bridge my NAD 7600 / 2600A. I removed the IC cable and listened to several varied and familiar recordings to get a baseline using JUST the 7600.

SIDE NOTE: I don't remember ever listening to these SDA-2B's without the IC cable, but was pleasantly surprised at how good they still sounded with the two 6.5 SDA drivers silent.

I then carefully bridged both units, using the 7600 to drive the left side and 2600A to drive the right.

I'm ruined for life !!!!!!!!!

The treble and midrange opened up a bit and sounded slightly clearer, but it was the bass that impressively both tightened up and seemed infinite, not that it really seemed strained before. But I gained a sense that I could just keep turning the dial up to the point of damaging my body before damaging the speakers.

I'm monitoring with a decent quality Extech Sound Level Meter on a tripod at the apex of the sweet spot triangle, and had been listening at up to 80-85 db with the 7600 alone. I'm not sure how to best qualify this, but the bridged amps easily pushed 95db with a quality of sound that really did not seem any louder than the single amp at 80+ db. It was just an astounding, pleasing, enveloping sound.

NEW QUESTION: With new RDO198-1's and Sonicaps (just hit 48 hrs. burn in but have used IsoTek Special Burn in Disc for more than 14 of those hrs. so maybe equivalent to 90 hrs), is it OK to push them this hard? And I wonder just how much sound these relatively small SDA-2B's can make?

At any rate, the bridged sound is very, very good. NAD literature states their amps are optimized for 4 ohm loads. I believe the SDA-2B's nominally pulled 5 ohms stock, but the RDO198 tweeter/crossover upgrade might have pulled that closer to 6. Assuming they were in fact at about 6 ohms stereo, the amps are seeing 2.5 to 3 ohms bridged which could account for the good sound. NOTE: there was absolutely no measurable heat increase over 4 to 5 hours of listening at 70 to 85 db with short durations of up to 95 db. Soft clipping LED's never flickered and output transistors never sounded even close to saturation. Plenty of headroom into a tough load with those 21 year old bad boys running cool.

I will qualify that I don't think I am in a great position to judge the qualitative part as I have listened to nothing but SDA's (with crossover connected) for 21 years. The bridged sound I think would have been even better with SDA in play.

Now I really want to hear these bridged with the AI-1.

F1nut

NAD literature states their amps are optimized for 4 ohm loads.

In bridged or stereo mode?




Going back to your original post. I believe Polk offered an adaptor for those blade/blade SDA's that can use the pin/blade AI-1, although I've never seen one.

inspiredsports

F1nut wrote: »

In bridged or stereo mode? In your original post. I believe Polk offered an adaptor for those blade/blade SDA's that can use the pin/blade AI-1, although I've never seen one.

The old literature states my NAD 7600 Receiver and matching 2600A Amplifier are optimized for 4 ohm in STEREO MODE (so they would theoretically be "happiest" with 8 ohm speakers when bridged). However, the literature goes on to say that these amps are capable of driving 2 ohm loads at all but the highest listening levels. Last, they state driving a PAIR of 4 ohm speakers in PARALLEL appears to the amp a 1 ohm and may cause thermal protection to engage or internal fuses to blow at high listening levels. These particular vintage model NAD's amps feature a SOLID high current design with a VERY heavy and robust power section. They did not heat up in 4 hours of moderate to high volume testing into what I believe was about a 2.8 ohm load when bridged.

#######

I did find an old post from 2005 called "Custom AI-1 By Ken Swauger" at http://groups.yahoo.com/group/mikespolkpage2 (you have to have a yahoo membership to see posts) with an image of the special AI-1 adapter leading from the wide blade to a 1' long wire that he explained was a ground wire. It said "Spades go onto the negative posts."

I know the narrow blade is the only blade used on my Blade/Blade SDA-2B's, so the ground wires are internally connecting to the "other" wire in this modified AI-1 cable.

#######

It looks like this is the rig I need if I decide to pursue using my Blade/Blade SDA-2B's in bridged mode with my NAD amps that become non-strappable, non-common ground in bridged mode.
.
.

ben62670

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