SDA 2B troubles

[strider]

I don't belive that my dimensional drivers are working as they should be. When changing the balance from centered to all right, there is some sound from the left channel dimensional driver, but it's so low I need to put my ear up to the driver to hear it. When the balance is back to center, I can't discern a difference with the SDA cable hooked up or not.

My set up is pretty simple, but my amp is non-common ground. Thus, I constructed my own AI-1 cable. My cable is the blade/blade design, from what I've read I think I have the '87 version of the 2B's. The serial numbers are within the range that should be able to use the AI-1, but the left and right side serial numbers are markedly differnt from one another, somewhere in the area of 1500 apart. When I first got my speakers I also was told I needed to attach the negative terminal from the speaker binding post to the larger pin, which I have. Here's a link to the post where I asked questions when I built the cable, I haven't changed anything in regards to the hook ups on the transformer, etc.

http://www.polkaudio.com/forums/showthread.php?t=44518

Any help is appreciated.

Ben

edited out unclear portion

[DarqueKnight]

I am not sure what you mean by "I also can't discern a difference with the SDA cable hooked up or not". Do you mean that, with the balance control turned all the way to the right, you hear sound from the left speaker's dimensional drivers whether the SDA cable is connected or not? Assuming this is what you meant...

You should not be getting any sound from the opposite speaker's dimensional drivers if the SDA cable is disconnected UNLESS the balance control on your preamp is the type that never completely attenuates the other channel when the balance is turned all the way to one channel. My Adcom GFP-750 preamp had that type of balance attenuator. With the SDA cable disconnected, the stereo drivers can still induce movement (and thereby generate sound) in the dimensional drivers through fluid coupling with the air inside the sealed cabinet.

You can test to hear if your preamp completely attenuates the opposite channel by disconnecting one speaker (SDA cable and speaker cables) and then turning the balance control all the way to the disconnected speaker. If you hear sound from the connected speaker, you know that your preamp does not completely attenuate the non-selected speaker.

If the balance control is the type that fully attenuates the non-selected speaker and the balance control is turned all the way to one channel with the SDA cable connected, you will hear sound from the dimensional drivers of the opposite speaker because the active speaker is still sending an inverted signal to the the opposite speaker.

[strider]

Sorry, I re-read that and see that it was somewhat vague. I can't hear a difference between when I have the cable connected vs when it's disconnected when the balance is set to the center. When I disconnected the speaker and turned the balance to the unhooked speaker I heard no sound whatsoever.

My concern began after reading various people rave about the soundstage seeming as if it were so wide sounds were coming 5 feet outside the edges of the speakers. I don't hear it. When I have the balance switched, say, all the way to the right, I have a very low signal from the left side dimensional driver. So low I need to get my ear about 6 inches from the driver to tell it's definitely coming from the speaker. In my mind, that is what is keeping me from having a huge soundstage. From my understanding, this low output would cause a diminshed SDA affect. To compound this dilemna are a couple of thing: I have never heard any other SDA's besides my own and I don't have a discerning ear (or a lot of audio experience, for that matter.)

I tried to do a little testing, trying the test outlined on the bottom of page 66 of your compendium (which is a great resource, even moreso then I imagined)and had no sound at all from either speakers when the negative wire was unhooked from the speakers. Is this because I have a blade/blade cable?

[F1nut]

Madmax and I both pointed out that since you don't have a ground connection on the larger blade, you're not going to get the SDA drivers to work.

[strider]

Madmax and I both pointed out that since you don't have a ground connection on the larger blade, you're not going to get the SDA drivers to work.

That's what I thought I had done when I attached a lead from the back of the large blade to the back of the negative binding post.

[F1nut]

Ah, you've done that. Sorry, I missed that. Where are you in B'more, I may be able to swing by one day and take a look.

[strider]

Ah, you've done that. Sorry, I missed that. Where are you in B'more, I may be able to swing by one day and take a look.

No need at all to apologize, I've always appreciated and valued your input. I live just inside the Beltway off of Bel Air Rd, about a mile or so from where 95 hits 695 to the northeast of the city. My biggest concern is I've got unrealistic expectations. I'd hate to waste your time if that were the case.

One thing I noticed when I re-read that post I referenced above is that I had listened to the speakers without hooking up that ground. Am I correct in my understanding that the lack of a ground there would just not complete the SDA circuit? Rather, would I have fried some type of component in the SDA crossover because I negated the AI-1 interface without having the ground from the negative binding post to the larger blade?

[DarqueKnight]

SDA soundstaging can be affected by the following:

1. Soundstage dimensions for the same recording can be reproduced differently by different amps and source components.

2. Lateral imaging can also be affected by room conditions, especially one or both SDA's is too close to a side wall.

3. How much difference there is between the left and right channels of the recording. Typically, the more difference there is, the more spacious the SDA effect. The less the difference between channel content, the closer the recording gets to mono, where all the sound comes from between the speakers.

At the rear of your SDA 2B manual there should be a list of recommended recordings for demonstrating the SDA effect. Do you have any of those recordings and, if so, have you demoed any of them?

When I turn the balance control in my 2 channel rig all the way to either side, I can still clearly hear the dimensional drivers of the opposite speaker at my listening position which is 12 feet from the front of the speakers.

I went back and read your post from September of 2006. This may be your problem: If you refer to the SDA AI-1 compatibility chart on page 32 of the Compendium, it states:

"Some early units of the SDA-1C and all units of SDA-2B require plug adapters and some internal modifications to the crossover to be used with the Non-Common Ground Amplifier Interface."

I assume that this means that early blade/blade SDA-2B's must be converted to the pin/blade configuration. I have no idea what would need to be done to pin/blade SDA 2B's, but it does say that all SDA 2B's require some modification work.

I assume from what I read in this post and in your 09/2006 post that you have not done this modification. I recommend contacting Ken Swauger in Polk's customer service department regarding what is required for your SDA 2B's.

[F1nut]

Nah forget it, I don't go there..........j/k

Am I correct in my understanding that the lack of a ground there would just not complete the SDA circuit? Rather, would I have fried some type of component in the SDA crossover because I negated the AI-1 interface without having the ground from the negative binding post to the larger blade?

That would be correct, no ground, no SDA.

It's possible, but hook up the ground wires and see what you hear. If that doesn't do the trick, I'd be happy to stop by and help.

[DarqueKnight]

Am I correct in my understanding that the lack of a ground there would just not complete the SDA circuit? Rather, would I have fried some type of component in the SDA crossover because I negated the AI-1 interface without having the ground from the negative binding post to the larger blade?

I don't think you blew up anything. If you didn't hear any howling, smell any ozone, or see any smoke or flames, and if the speakers still sound ok outside of the SDA issues, I think you are still good.

[F1nut]

"Some early units of the SDA-1C and all units of SDA-2B require plug adapters and some internal modifications to the crossover to be used with the Non-Common Ground Amplifier Interface."

That's correct, but the adapters are used for plugging in the pin/blade cable ends into the blade/blade socket and since he's built the AI-1 with blade/blade ends the adapter wouldn't be needed. The only modification needed would be running a ground wire from the large blade to the negative speaker post.

[DarqueKnight]

I am disturbed by the statement in the AI-1 compatibility chart that "all units of SDA 2B" require a plug adapter and crossover modification.

The chart may only be referring to SDA 2B's from the 1987 model year, of which the early production was blade/blade and the later versions were pin/blade. However, the same crossover is used in the 1987 and 1989 versions of the SDA 2B and SDA CRS+. If all units of the 1987 SDA 2B required a crossover modification to use the AI-1 interface, it seems like the 1987 SDA CRS+ should have required the same modification. I'll ask Ken to pass this question along to Polk's engineering department.

I'd also like some clarification on when the compatibility chart was written.

[F1nut]

I'll ask Ken to pass this question along to Polk's engineering department.

I'd also like some clarification on when the compatibility chart was written.

Good idea.

[strider]

Darqueknight- I couldn't find a listing of recordings in my owner's manual, but going from the SDA playlist sticky in the Vintage Speakers forum I've got a few of the recordings. The one I typically turn to is DSOTM, which seems to be the standard most refer to. I've had the speakers hooked up to my HK AVR before; when this was set up I had jerry rigged the transformer out of my interconnect and the ground straps in between the binding post and the large blade were removed. "Run" is the track I usually compare the SDA effect with. When I was using the AVR without the AI-1 set up the person running down the hall did sound as if it were moving from outside the left speakers, to the middle, then past the right speaker.

As for my speaker placement, it's not perfect, but I don't believe it's that bad. Speakers are approx. 6 feet apart, 2 inches or so in front of the plane of my rack, 15 inches from the wall behind. The left speaker is about 4 feet away from a wall, the right 3.5-4 feet away. I do have the arm of a couch about even with the front plane of the right speaker, but it is just under the horizontal plane of the dimensional driver. Typically I sit between 7 and 8 feet away, equidistant to the right and left speakers.

I saw that the crossovers in my speakers were the same model as those used in the pin/blade CRS+, with the big difference between the 2 models being the termination of the interconnect table. The schematics of the 2 different models are indentical, far as I can tell, with the exceptions of the cable interface and the lack of connection between the negative binding post and the large pin on the 2B. If I'm able to give Polk a call Monday I will; if you're able to speak with Ken directly and have the opportunity to do so I'd be very interested to hear your findings.

Thanks again for your assistance and effort.

[dudeinaroom]

with my 2a's the left interface socket has lost some of it's grip and I had the same problem after wiggling the connector a bit all is well. Just a thought.

[strider]

with my 2a's the left interface socket has lost some of it's grip and I had the same problem after wiggling the connector a bit all is well. Just a thought.

Definitely something to look into, thanks.

[DarqueKnight]

My original question:

"Ken,

Please pass this question along to your engineering department.

The AI-1 compatibility chart states that "all units of SDA 2B" require a plug adapter and crossover modification.

When was the compatibility chart was written?

The chart may only be referring to SDA 2B's from the 1987 model year, of which the early production was blade/blade and the later versions were pin/blade. However, the same crossover is used in the 1987 and 1989 versions of the SDA 2B and SDA CRS+. If all units of the 1987 SDA 2B required a crossover modification to use the AI-1 interface, it seems like the 1987 SDA CRS+ should have required the same modification."

Here is Matthew Polk's response:

"Any SDA using the series connected SDA drivers and
Full-Complement-Sub-Bass-Drive circuitry would be able to use the AI-1. I dimly recall that prior to the AI-1 being available the interconnect plugs were not wired to the correct points on the crossover to make use of the AI-1. The crossover modification simply changed the connections on the interconnect plugs on each speaker to accommodate the AI-1.

-msp"

[strider]

Jesse (F1nut) left my house an hour or two ago after comfirming what I had feared- I did something wrong. The connections at the transformer of the AI-1 were backwards, I thought I had tried all possible combinations. While he was here he was nice enough to give me a bunch of pointers on the 2B's, the different transformer options for the AI-1, etc. etc., all without making me feel dumber then I did already. Thanks again, Jesse!

Darqueknight- Thanks for your time as well; your info here, as well as in your Compendium, are an invaluable resource.

I continue to be impressed at how helpful and knowledgeable folks are around here.

[schwarcw]

Jesse to the rescue!!! Your lucky that you live close enough he can do house calls. Congrats! at least the problems is diagnosed and you have some potential solutions!

Carl

[F1nut]

Ben, it was a pleasure.

I dimly recall that prior to the AI-1 being available the interconnect plugs were not wired to the correct points on the crossover to make use of the AI-1. The crossover modification simply changed the connections on the interconnect plugs on each speaker to accommodate the AI-1.

That bears further examination.

[F1nut]

Too follow up on the proper wiring method mentioned by MSP. After conversation with Ben in which he checked the connections, his blade/blade SDA 2B's are wired correctly with the addition of the ground wire run between the large blade and the negative binding post being the only change needed, which he has already done.

Even though the Stancor transformer is now wired correctly I believe it to be the limiting factor. It's my understanding that Ben will replace it with an Avel, so we'll have to wait and see. However, I am confident that the Avel will result in a vast improvement over the Stancor.

[DarqueKnight]

Even though the Stancor transformer is now wired correctly I believe it to be the limiting factor.

I was considering building one of these last year because I was looking at several non-common ground amps. I decided against getting an amp that required the AI-1 because I did not want to invest in a good amp and then find that it's performance was compromised by the transformer. Matthew Polk said that the AI-1 is a "workaround" for the common ground amp requirement and that it could cause some loss of high frequency detail. Experience has taught me that "workarounds" are usually less than optimal in performance. Some people have reported no sonic difference with the AI-1 and others have. I opted not to take a chance on ending up in the second category.

[DarqueKnight]

My original question:

"Ken,

Please pass this question along to your engineering department.

The AI-1 compatibility chart states that "all units of SDA 2B" require a plug adapter and crossover modification.

When was the compatibility chart was written?

The chart may only be referring to SDA 2B's from the 1987 model year, of which the early production was blade/blade and the later versions were pin/blade. However, the same crossover is used in the 1987 and 1989 versions of the SDA 2B and SDA CRS+. If all units of the 1987 SDA 2B required a crossover modification to use the AI-1 interface, it seems like the 1987 SDA CRS+ should have required the same modification."

Here is Matthew Polk's response:

"Any SDA using the series connected SDA drivers and
Full-Complement-Sub-Bass-Drive circuitry would be able to use the AI-1. I dimly recall that prior to the AI-1 being available the interconnect plugs were not wired to the correct points on the crossover to make use of the AI-1. The crossover modification simply changed the connections on the interconnect plugs on each speaker to accommodate the AI-1.

-msp"

I was not entirely satisfied with that response. Hence this follow-up:

Ken,

OK. Looking at an SDA schematic, how would I identify the "Full-Complement-Sub-Bass-Drive circuitry"?

The response from Polk's engineering v.p. Stu Lumsden:

"The SDA drivers form a cross-coupled series connection between L+ and R+. The SDA drivers are also connected to ground by a low-pass filter. Since the SDA information that is presented to the SDA drivers (L-R and R-L)is high-passed only the L and R low-passed signal will flow through the left and right SDA drivers respectively to ground."

[peckgary]

Too follow up on the proper wiring method mentioned by MSP. After conversation with Ben in which he checked the connections, his blade/blade SDA 2B's are wired correctly with the addition of the ground wire run between the large blade and the negative binding post being the only change needed, which he has already done.

Even though the Stancor transformer is now wired correctly I believe it to be the limiting factor. It's my understanding that Ben will replace it with an Avel, so we'll have to wait and see. However, I am confident that the Avel will result in a vast improvement over the Stancor.

I was wondering if somebody could share how to make a proper A1 connectorer for a pair of SDA 2B's that have a pin/blade layout. Also where could a person get the Avel. I have a Stancor right now and can not seem to get it to work. Probably because I do not have the wiring correct :)

Thanks,

Gary

[strider]

RT1's build with the Stancor:
http://www.polkaudio.com/forums/showthread.php?t=23442

This link (I think it's this one :o ) is from Ken at Polk
http://polksda.com/A1_Interconnect.pdf

The Avel ,AFAIK, is only available from them. Here's their response when I inquired regarding the price, etc:




We are pleased to offer:



Type: Y236906

1 : $97.90 each

Delivery: Stock

FOB: CT (Shipping based on your location and final weight)



MasterCard and Visa accepted.



Please call 800-979-1022 or fax 860-3548597 to order.



We look forward to meeting your transformer needs.



Melanie Roman

Avel Lindberg Inc.

47 South End Plaza

New Milford, CT 06482

860-355-4711, ext 41

Fax: 860-354-8597

[F1nut]

http://www.polkaudio.com/forums/show...highlight=avel

[F1nut]

So Ben, did you get it yet?

[strider]

No, not yet.:( Those things went up a bit since I last heard a price. Between work being real slow and trying to pay for a wedding, it's gotten pushed to the back burner a bit. They sound worlds better now that you get 'em wired correctly, so I'm enjoying that for the time being.

[F1nut]

Yeah, the price of copper keeps rising. Anyway, like you said, they are better than before.