SDA 2 Identification Help

Rand

Hello Polk Pros,

I recently picked up a pair of SDA 2 speakers and am trying to find out exactly what I have. I'm hoping someone can assist in identifying these. I plan on creating a baseline and then upgrading/restoring as needed. Thanks in advance for your help!

I had a pair of SDA 2's in the 90s and have been chasing the sound ever since selling them which was not one of my finer moments. After finding a pair locally last weekend and listening to them, I picked them up and am very excited to hear that wonderful SDA sound again. I have not opened them up yet to see exactly what's inside for cross-overs, etc.

Serial #'s: Left: 23749, Right: 23473
Tweeters: Appear to be SL3000
Drivers: All four have this number stamped onto the outside ring: SR 142/17
Radiator: SR 278/6
Audio Connect Cable: Custom made by a PO






Thanks for your expertise!

Rand

Gardenstater

Do you have a link to the Polk SDA History Manual? That's a good resource for info.

Questions for you to help answer your questions:

1) What are the MW model #'s which are on the label affixed to the magnet pole piece?
2) Are the IC connectors blade/blade or pin/blade?
3) What is the actual model# on the tweeter label, which is also affixed to the magnet pole piece?
4) What is the date on the crossover PCB?
5) Do they have oak or walnut end caps that cover the top and bottom of each speaker? It looks like they do not from your pics.

I'm thinking they are SDA 2A and those are probably RD0-194 tweeters.

The SDA Handbook (2011, Rev. 2):

https://us.v-cdn.net/5021930/uploads/editor/qx/d5a14j8apinc.pdf

pitdogg2

SDA connection is in the cup. More than likely pin blade therefore I'll take SDA 2b.

All blade/blade models I've seen SDA socket was outside the cup.

Rand

Thank you, Gardenstater. Much appreciated and great info. I do not have a link to the Polk SDA History Manual.

These have clearly been worked on/modified. There are sound deadening mats placed on the speaker metal baskets and inside on the walls of the cabinet. The radiators appear to be siliconed in place and are difficult to remove. Any tips on how to pry them up without damaging the cabinet?

Answers:
1) What are the MW model #'s which are on the label affixed to the magnet pole piece?
> 6511 & 6503 in each speaker
2) Are the IC connectors blade/blade or pin/blade?
> Modified by PO. See pics.
3) What is the actual model# on the tweeter label, which is also affixed to the magnet pole piece?
> No label or markings on the back of the tweeters. See pic.
4) What is the date on the crossover PCB?
> Trying to remove the radiator now...stay tuned.
5) Do they have oak or walnut end caps that cover the top and bottom of each speaker? It looks like they do not from your pics.
> No top or bottom caps. I had those in the past and these are different.

Rand

Thanks pitdogg2, good to know.

bigmontana

For the passive radiators, try removing the terminal cups and reaching inside the cabinet to push them out instead of prying from the front. It should at least limit the damage that prying on the front would create.

Gardenstater

Wow I have never heard of anybody siliconing the PR's in place. A painter's 5 in 1 tool used carefully would be my choice of tool if it weren't for the fact that they are recessed into the baffle. Gonna be tough!

I'm thinking maybe you have SDA 2A cabinets with SDA 2B innards (MW's and Crossover). The proof will be to look at the crossovers and compare to schematics in the SDA manual and in the reference section of this forum.

Those should be RD0194-1 tweeters unless the previous owner did a TL mod to the crossovers and then they could've used RD0198-1. From the SDA Manual:

bigmontana

The photo looks like a new connector has been crimped onto the white tweeter wire. I'm betting it's a TL modded 2B.

I'm not 100% on this detail, but I believe the riser on the bottom of the 2B studio models is black, whereas the riser on the 2A's is wood grain.

Gardenstater

In one of your pictures it looks like there are 2 rivets that are located below the crossover/binding post cup that were probably where the original SDA 2A IC connector was located (or the old one is still there?). Also, according to the SDA Manual the studio version of the SDA 2B, while it is true that it didn't have end caps, it was fully clad in black vinyl and you appear to have walnut vinyl so it still looks to me like SDA 2A cabinets. I agree with bigmontana that the faston for the white/negative wire appears to be replaced hinting at maybe a TL mod and RD0198-1s. Check the DCR for confirmation.

bigmontana

Gardenstater wrote: »

Also, according to the SDA Manual the studio version of the SDA 2B, while it is true that it didn't have end caps, it was fully clad in black vinyl and you appear to have walnut vinyl so it still looks to me like SDA 2A cabinets.

I have a pair of 2B studios that are finished in oak vinyl. I'm pretty sure I've seen examples in the darker walnut too.

F1nut

Those are 2B Studio in vinyl walnut. Someone has replaced the original SDA socket with a strange one.

Rand

Thank you F1nut, bigmontana, and Gardenstater! Your help is truly awesome and appreciated.

The radiator will not come out even when pushing from the inside due to the silicone or whatever was used to seal it. I could probably force it more but will not at this time unless necessary. This entire cabinet has been sealed and lined with dynamat. Is the brace in one of the pics OEM or added by a PO?

Can you tell from the crossover pics what has been done? Sorry, best images I could get stuffing my phone through the cup opening.

In the 4th image I can read:
Dayton Audio Grade
2.7ohm 10W 2% on the white board compenent

F1nut

Whomever worked on those is a hack. Lining the cabinets with Dynamat Xtreme was a huge mistake. Best to remove it.

The crossover work looks like a 2 year old did it. Not sure what's up with those 2 smaller caps or that cheap block resistor. You need to pull the crossovers for a better look.

They likely used Mortite as a gasket for the PR. If you push really hard from the rear it will pop free. It would be a good idea to have someone in front to catch it. Once you get them off remove the Mortite and replace with a proper gasket.

The crossbrace is stock.

audioluvr

Like F1 said. I'd pull the crossovers to make sure components of correct values were used in the right place. Also get rid of the electrolytic cap paralleled with the resistor and replace the Dayton sandcast resistor with a mills resistor. The big Dayton caps with the yellow and white ends are acceptable and better than stock but if you can afford Sonicap capacitors I'd go that route. At least for the tweeter circuit.

Rand

Thanks F1nut - good and bad to know. Looks like I have a good project to work on.

I tried to remove the PR again and it won't budge. What the hell did this guy use on these?! I'll recruit some help and push harder.

Curious: What are the negatives about the Dynamat on the cabinet?

Thanks audioluvr - good info and will do once I get these removed.

Who would you guys recommend to send the crossovers to for rebuilding?

tonyp063

Rand wrote: »

Who would you guys recommend to send the crossovers to for rebuilding?

Contact forum member @westmassguy
http://www.dhsspeakerservice.com

Rand

Thanks tonyp063!

F1nut

Curious: What are the negatives about the Dynamat on the cabinet?

Highly reflective surfaces are the last thing you want inside a speaker cabinet. Dynamat Xtreme's soul purpose is to dampen vibrations on metal surfaces. It is not an acoustic damping material like BH5 or Sonic Barrier, which help to reduce unwanted sound reflections.

Rand

That makes sense. Will remove and replace with BH5 or Sonic Barrier.
Thank you!

F1nut

Rand wrote: »

That makes sense. Will remove and replace with BH5 or Sonic Barrier.
Thank you!

Hang on. You do not want anything on the cabinet walls around the PR. The only place to install BH5 or Sonic Barrier is a 4 inch square directly behind each mid-driver. The factory poly fill should remain.

Rand

Fantastic and great to know. Will do!

Any reason not to pick up a NAD C370 to run these? I can get one for $200 and would get it reconditioned. I've read about the issues but no idea how the 2Bs would sound with this amp.

Schurkey

Rand wrote: »

Any reason not to pick up a NAD C370 to run these? I can get one for $200 and would get it reconditioned. I've read about the issues but no idea how the 2Bs would sound with this amp.

I would not put the reconditioning money into what I suspect is a Chinese amplifier.

I think you'd be better off to put the reconditioning money into a better amp to begin with.

Gardenstater

NAD amplifiers make the claim of high current reserve power supplies and high dynamic power ratings, as well as their full disclosure power ratings (FDP):

https://support.nadelectronics.com/hc/en-us/articles/360000158988-NAD-Full-Disclosure-Power

NAD's approach, on the other hand, is to optimize its power supply to properly drive real-world loudspeakers. This means a properly regulated, high-current power supply is supplied in all NAD amplifiers and receivers. Thus we can rate our receivers with a difficult 4-Ohm load, with ALL channels driven simultaneously, over the FULL frequency bandwidth (20Hz - 20kHz), and at rated distortion. This is the Full-Disclosure rating method on which all our amplifier and receiver specs are based, and it's a far cry from the FTC's minimal requirement of using an 8 Ohm load, any channel (singular), at an easy 1 kHz frequency, with no distortion specified!

Another aspect of power specification long championed by NAD is dynamic power. Since real-world program material requires short bursts of very high power rather than the continuous power normally specified, we also include dynamic power ratings at 8 Ohms, 4 Ohms, and even 2 Ohms! Most receivers will go into full protection mode when presented with a 2-Ohm load, but NAD's high-current power supplies, sonically transparent protection circuitry, and heavy duty output stage are easily up to the task. So to further distinguish our Full-Disclosure ratings from the barebones FTC standard, and give the consumer the most realistic description we can of real-world performance, we also specify the dynamic power our amplifiers deliver to speakers of varying impedances. And to maximize this real, useful power in daily listening, we've developed an amplifier circuit we call:

POWERDRIVE
To meet the diverse requirements of high current drive and high dynamic power, our patented PowerDrive amplifier circuit will build further on our reputation for amazingly effective power. By adding a second high-voltage rail to our well regulated high-current power supply, we get an "overdrive" that can nearly double the continuous power on a short term dynamic power basis. This is a further development and refinement of our renowned Power Envelope circuit, utilized by NAD in the 80's and 90's. PowerDrive differs from Power Envelope in that it offers greater amplifier stability and low impedance drive capability, resulting in less distortion when driving real speakers with real program material.

pitdogg2

Dynamic power ratings are phooey. You can never rob peter to pay paul

Gardenstater

I would like to see the FTC require it, along with the full power rating across the entire audio band with distortion into lower impedances besides 8 ohms. Then we'd see how amps really compare.

Schurkey

Gardenstater wrote: »

...it's a far cry from the FTC's minimal requirement of using an 8 Ohm load, any channel (singular), at an easy 1 kHz frequency, with no distortion specified

Since when did the FTC permit advertising power ratings with no distortion specified?

I've seen power and distortion rated at 1KHz; which as said is an "easy" load; and I've seen power and distortion rated from 40Hz-20KHz rather than 20--20KHz on crappy amps that have poor current (amperage) capacity. (i.e., no current-hungry bass allowed!)

The way I remember it, "Stereo" amplifiers must be rated with both channels driven. "Multi-Channel" amps can be rated with some or all channels driven, which means they're usually rated with only one or two channels operating.

It is therefore cheaper to build a multi-channel amp than it is to build a "stereo" amp; because the FTC has screwed-up the protocol for rating multi-channel amps. The stereo amp is rated more stringently, so it has to be built better to generate the same "rated" power.