New SDA 2B owner

nathanso

Greetings all.

I am the new owner of a pair of 2Bs in natural oak. These had their tweeters replaced with SL2500s and are in 9/10 condition. They even included the original boxes, plastic bags, and packing styrofoam. And two interconnect cables were included, one NIB. $325, which I though was decent considering the condition, location, and extras.

A few questions:

o All four black fabric side panels fell off over the years but were included in the sale and are in excellent condition. Can anyone recommend the proper adhesive or other method for reattaching them?

o I've read some things about SDAs and common ground amps. Does anyone know if an Aragon 8002 will have difficulty with 2Bs?

o Instructions were not included.. are they available anywhere online or elsewhere?

danger boy

Congrats on your SDA 2's.

sorry i can't be of any help to you. others will chime in shortly though.

enjoy

schwarcw

Welcome to the Forum! The SDA-2B's are real nice. The price you paid is fair, they sometimes seel for a little less, but $325 is a good price for a great pair of speakers. I don't have any experience gluing the cloth side, but someone on the Forum will reply. There are upgrades you can perform to the tweeters and crossovers if you so desire. Research the threads for "1st Generation SDA Crossover Mods" aaharvel did a nice job on the posting with pictures, etc. Welcome and enjoy your Polks!

BlueMDPicker

Welcome and congrats on your "new" speakers. SDA 2B was my first SDA and still a favorite.

The side panels can be reattached with a good grade carpet tape (adhesive both sides.) Get the variety that will handle irregular surfaces (usually cloth-based.)

Put a VOM across the negative binding posts of your amp. 0 ohms indicates a common ground amplifier.

Ken Swauger, at Polk customer service, can send you a copy of the manual/instructions by mail. See the "Contact" icon at the righthand top of the site for a toll free number.

$325 is a good price for 2Bs in excellent condition with all original packing materials. Does one of your two interconnect cables have a transformer inline in it? If so, it can be used with non-common ground amplifiers.

dorokusai

Welcome to the forum.

If you would like a more permanent solution....

I use a metal putty knife to remove residual glue from the cabinet and ensure that the panels are free of glue as well. Be careful upon removing the glue from the panel as it's cheap pressboard. I always use Liquid Nails for Paneling and/or Floors to reattach the panels. After you get the panel glued and mounted, cover with a towel and drop as much weight as possible on the panel overnight. Pay close attention to the ends as they will typically warp out before the rest of the panel.

Have fun.

Tour2ma

Yup, as BMDP stated, good price... especially if an AI-1 (transformer utilizing) interconnect is there. Some 2B's included blade-blade SDA connections; some used pin-blade.

Welcome to the Club....

nathanso

My Aragon 8002 measures 20-ohms across the R and L negative outputs.. does that mean I need the transformer cable or not?

Somewhere on the web today I came across the plans for making that SDA isolation transformer/cable.. I should be able to Google it up again. But I also recall seeing something that said the 2B in particular was different in that it was more flexible in which kind of amp could drive it. Any truth in that?

My 2Bs have blade-blade interconnect cables.

nathanso

The Aragon 8002 is a dual mono amp, fwiw. (It's new here too, please forgive my ignorance.)

Tour2ma

It means that you your very likely cannot use your 2B's with your Aragon because:
- No blade-blade SDA's are compatable with the AI-1; and
- Your Aragon is not common ground.

One ray of hope... call Aragon and ask if you can strap the negative terminals of your amp together. Some dual mono's can accomodate this.

nathanso

There's this I just found: Click Here

My serial numbers are both above those listed. I guess my question now is, is Polk still supportive of these old speakers were I to call them and try to obtain the instructions that, at one time, seem to have been dealer-only info?

Tour2ma

Good hunting there...

I'd say your 2B's fall under that special note about the early models. Give Polk CS a call and they'll give you whatever info you need.

But also call Aragon...

BobMcG

Welcome to the forums and the world of SDAs.

Some of the earlier B/B 1Cs and 2Bs could make use of a custom AI-1 like this one...

http://www.polkaudio.com/forums/attachment.php?attachmentid=8335

nathanso

Here's the skinny straight from Ken at PA CS:

The A1 cable is no longer available, but for Twin-Blade cables it's a simple matter to cut the stock cable somewhere along its length and splice in an audio isolation transformer with a 1-amp minimum rating, see below..

From http://www.polksda.com/A1_Interconnect.pdf

An isolation transformer such as:
SPC Technology 81N5406, 2" x 3 !/4" x 1 3/4", $15.99 or;
Stancor 01F043, 2" x 3 V? x 1.8", $20.04 or,
Magnetek Triad 03F1017, $16.46.
These can be bought from Newark catalogue parts company at 1-800-463-9275.

However.. Ken is still researching what crossover mods might be needed per document http://www.polkaudio.com/forums/attachment.php?attachmentid=12280

This does not apply to Pin-Blade cables so don't try this solution for those as both wires in Pin-Blade cables are connected to the same pin!

BobMcG

nathanso wrote:

This does not apply to Pin-Blade cables so don't try this solution for those as both wires in Pin-Blade cables are connected to the same pin!

You'll notice the custom AI-1 I linked you to is a B/B model made a long time ago by.........




........yup, Ken himself. No crossover mods were needed to work on an earlier B/B pair of 1Cs that had serial numbers within the accepted range.

nathanso

Well here's some good news.. according to Aragon tech support's Steve Donalson (a vintage Polk fan!), the Aragon 8002 -- depite having 20-ohms resistance across its negative binding posts -- can have its negative binding posts jumpered effectively making the amp common ground and well suited for driving SDA 2B's. Apparently the 20-ohms comes from the fact the the negative binding posts are tied to chassis ground via 10-ohm resistors. He warned against jumpering the negative binding posts on the Aragon Palladium amp as its circuitry is different.

Tour2ma

There you go...

Couple random thoughts popped into my head:
1. It seems like it's a common ground already
2. Interesting that they design in the resistors, but it's fine to operate without them.
Did you happen to ask about either of the above?

nathanso

Got the Aragon 8002's negative binding posts jumpered but that introduced a hum in my speakers. I spent a couple of hours last night diagnosing the source and it seems to happen when *any* device is connected to the amp's input with both RCA interconects; use just one RCA interconnect and the buzz doesn't occur. Remove the jumper across the amp's outputs and the buzz doesn't occur, with either one or both inputs connected.

I have an ongoing dialog with Aragon support underway but they have already indicated that it's not the amp. My theory is that the output jumper somehow makes the amp more sensitive to reproducing ground loop/RFI induced hum. I may be dropping $150+ on a Jensen transformer.. anyone got a CI-2RR for sale?

F1nut

On a side note, you mentioned the tweeters are now SL2500's. Those are not the proper tweeters for the crossover, so you might want to consider either the original SL2000 (can be had used) or the new replacements, the RD0194-1, which I would recommend.

Forum member Reeltrouble1 made a AI-1 and if memory serves, found that only one of the listed isolation transformers actually worked properly. I'd suggest you contact him first.

RuSsMaN

BlueMDPicker wrote:

Put a VOM across the negative binding posts of your amp. 0 ohms indicates a common ground amplifier.

0 or open, would indicate non common ground. Any other reading, showing continuity, would indicate common ground. Have I lost my mind?

I have a 'dual mono' Aragon 2004, and ran my blade/blade SRS 2's on it with no problems (hum).

Cheers,
Russ

Tour2ma

Yup... Mind has been lost... 0 ohm, AKA continuity, indicates common ground. Infinite resistance would be an open circuit...

But on the Aragon, if the 20 ohms he's reading is due to the two 10-ohm resistors going to the common chasis ground, then it's a common ground amp, just as yours is.

RuSsMaN

You will get SOME reading, if there is continuity - .3 ohm, .03 ohm, SOMETHING. I've never seen a straight '0' reading on a VOM, period. 0 would be no resistance - and even the small amount of wire from the posts to the ground would cause SOME sort of reading.

OL is non common, any other reading (greater than 0) is common.

Are we nit picking, getting crossed on terms, and saying the same thing?

Tour2ma

... and good catch on the tweeter, Jesse. No SDA used the 2500 that I am aware of...

RuSsMaN

The 2500 was the original 2000 replacement (iirc), the RD0 now replaces them both.

BlueMDPicker

nathanso wrote:

My theory is that the output jumper somehow makes the amp more sensitive to reproducing ground loop/RFI induced hum.

Have you tried lifting the ground from all components except one? Use two prong to three prong adapters, or physically remove the ground prong from some old IEC cords (old PC power cords are great for this.) If the hum persists, I believe you are looping between the amp sections.

Are the 10 ohm resistors critical to the circuit design of the amp? Ask Aragon if you can try a jumper around them.

F1nut

I thought the SL2000T was the original SL2000 replacement, that the SL2500 was entirely different, no?

Tour2ma

RuSsMaN wrote:

You will get SOME reading, if there is continuity - .3 ohm, .03 ohm, SOMETHING. I've never seen a straight '0' reading on a VOM, period. OL is non common, any other reading (greater than 0) is common.

Are we nit picking, getting crossed on terms, and saying the same thing?

LOL... Well, I touch the leads together and zero my meter. Then when I find clean contact on the amp's neg terminals, I've seen zero...

But you're right, I overstated things when I equated 0-ohms and continuity. A reading of >0 also indicates continuity. But 0 and "open" are not the same. An open circuit has infinite resistance.

I've not seen infinite resistance, even in a non-common ground "stereo" amp, because there always will be continuity via some path in the direction of the positive terminals.

Tour2ma

One more conversation and we're gonna need a traffic cop...

Mike,
Strapping the negatives is what is introducing the hum... so wouldn't bypassing the 10-ohms give the same result?

BlueMDPicker

Tour2ma wrote:

Strapping the negatives is what is introducing the hum... so wouldn't bypassing the 10-ohms give the same result?

I really don't know? What are they for, to eliminate any stray DC in the output?

On the issue of a VOM and what constitutes continuity, there's a fundamental difference between an analog and digital meter. My digital will show 0F if the leads are touched together and (sometimes) a small reading that fades to 0F on something I know is continuous. The analog always shows infinity for leads separated and goes to zero (other end of scale) for continuity.

nathanso

BlueMDPicker wrote:

Have you tried lifting the ground from all components except one? Use two prong to three prong adapters, or physically remove the ground prong from some old IEC cords (old PC power cords are great for this.) If the hum persists, I believe you are looping between the amp sections.

Are the 10 ohm resistors critical to the circuit design of the amp? Ask Aragon if you can try a jumper around them.

Yes, I tried lifting the ground on the amp with a cheater, no help. Then I regrounded the amp and tried lifting the ground on the pre-amp, no help. I also tried removing the pre-amp and using my CD player (without any disk) interconnected directly to the amp, and as soon as the second interconnect is made the hum begins.

Adding the SDA interconnect cable also makes the hum increase which makes me wonder if removing the jumper across my Aragon 8002's negative binding posts would help as RuSsMaN's post may have implied (but I'll try it.. nothing to lose).

Aragon tech support emailed me again and said the 10-ohm resistors are there to prevent cable ground loops. They suggested I short the shield of the R + L inputs together as an experiment.

nathanso

Hum problem solved.. I simply removed the jumper across the Aragon 8002's negative binding posts as suggested here. No hum, no problems (so far). The Polk SDA effect is working almost too well in my 20x24x18 (tall peaked ceiling!) hardwood-floored room. Reverb anyone? I may stick with my DQ-20s.

danger boy

Disconnect the SDA cable and see how they sound.. this will lessen the SDA effect. but is usually still very pleasing to listen to.