New Polk SDA-2Bs: looking for Polk expert in Seattle area

Moofy

BTW, the extraneous photo is the second woofer. Trey at VR3 mods was wondering if perhaps it was different from the first one.

VR3

It looks like you have late 2A's right before they changed to 2B

Moofy

OK, I did the best I could (see attached, and don't laugh). The capacitor(?) on the bottom of the two on the upper crossover is hard to read through the orange glue, but I think I got it pretty close. Looking forward to advise and next steps.

SethCrossovers.pdf

nspindel

Is it possible to "turn them into" 2B's? Tony's boards, build a 2B TL crossover, buy two new stock 6511's and the 198's. Or are the cabinets considerably different so it wouldn't work?

agfrost

nspindel wrote: »

Is it possible to "turn them into" 2B's? Tony's boards, build a 2B TL crossover, buy two new stock 6511's and the 198's. Or are the cabinets considerably different so it wouldn't work?

Could be done. Drivers on the 2B's are 2x 6503 and 2x 6511. IIRC the 6503's have a replacement available from Polk, but the 6511's are somewhat hard to find as they must be sourced used (from someone parting out other speakers). All four would need to be procured.

The other issue is the inductors--I haven't studied the schematics closely, but I believe a couple of them have different values so different values would have to be sourced.

A committed person could make it happen; he would have to decide whether the extra time (researching and part-hunting) and money were worth the results (2B & RD0-198 vs. 2A/194). I suspect the OP might be happier with the simpler path of upgrading his 2A's with a part-for-part replacement, but maybe he's all in for the whole hog! 2A-to-2B doesn't seem like the simplest job for a new modder.

nspindel

Polk sells 6511's, I just bought two of them for my 4.1TL's.

agfrost

Apparently IDRC.:redface:

zingo

I would suggest a regular crossover upgrade with RDOs as it will produce a significant improvement in sound quality on its own; too much time and money tied up in 2A-2B-TL transformation.

nspindel

I don't want to stick my nose where it doesn't belong, you're going to be doing the work and it's not my wallet. But other than the 6511's, which will cost $100, is this really a lot more involved than if these speakers were 2B's already? If they were 2B's, I'm guessing you'd be using Tony's boards, figuring out a way to mount the boards, and buying all the 2B components. To me it doesn't seem like a whole lot more that needs to happen than if they were 2B's to begin with. Of course, if you're not using Tony's boards, it's certainly going to be much simpler to just replace like for like and upgrade the tweeters.

agfrost

zingo wrote: »

I would suggest a regular crossover upgrade with RDOs as it will produce a significant improvement in sound quality on its own; too much time and money tied up in 2A-2B-TL transformation.

Agreed.

Moofy

Ok, I finally got up the gumption to mess with the innards. The top capacitor (closer to the front of the cabinet) says 130 UF. The other says 100 VNP. Does that make sense?

Jake, Trey and others: does this give you enough information to develop a parts list for the upgrade path Jake recommends above? What other upgrades are recommended, e.g., spikes, Larry's rings, etc.? Thanks.

Seth

F1nut

The schematic for your 2A's is posted here. You have two 130uF, two 20uF and one 12uF cap per speaker. There are two 2.7 ohm resistors per speaker. The 750pF silver mica cap should be removed and not replaced.

Moofy

Thanks to everyone for the guidance. Trey just sent me the list of items I need for the castle stack design:

- Mix of Clarity Cap ESA (Tweeter) and SA (midbass/SDA)

- Solen large value caps

- Mundorf Mox resistors

Jake, if your offer to help is still open, please let me know if I should go ahead and place the order. Is there anything else I need?

Cheers.

Seth

zingo

Nice parts list. You will also need to order two small resistors to replace the poly-switches, but I don't remember the value...

I have plenty of Cardas solder and an iron if you don't have one; I can also bring my DMM if you don't have one.

VR3

You don't -have- to put a resistor there :-P

Moofy

But -should- you?

VR3

Out of every SDA mod I have done I have never put a resistor there and no one has ever complained... :-P

I think it makes them sound veiled but YMMV

It would only add $5.00 to the cost and you can always take them out to see, it is a .5 ohm

Moofy

Trey, are you saying including or excluding the resistors makes the speakers sound veiled?

Moofy

What are your thoughts on Dynamat, etc.? I'm kind of thinking when I do this, I'd like to do everything (that truly makes a difference) at once.

nspindel

That damn 0R5 resistor is probably one of the most hotly debated topics on this forum. Here's the deal - the polyswitch has a dcr of 0R5. So one would have to imagine that these speakers were voiced with that resistance in the circuit, and removing the switch should require replacing it with a 0R5 resistor rather than a straight jump. Some have done extensive tests and say it makes a difference, that the speakers are too bright without it. Some have said it has no effect. I have rebuilt three pairs of SDA's. The first two I did not use a resistor, just a straight jump. On my 4.1TL's I used a 0R5 Dueland. I've not done any back and forth testing. All I can say is that I loved my 2BTL's without the resistor. I loved my 1C's without the resistor. And I love my 4.1TL's with the resistor! As Trey said, he's never used the resistor in any of his rebuilds, and I've never heard anyone say that his crossovers sound like crap, but I've heard plenty say that they sound great My advice - flip a coin....

nspindel

Dynamat is a must. Do it on the MW's and the PR. See post #8 in my 4.1TL thread that I pointed you to at the beginning of this thread.

inspiredsports

Moofy wrote: »

But -should- you?

I've done a bit of experimentation with different resistors in the circuit. If you choose to add resistance, don't add a separate resistor (adds solder and an additional component; noise), just increase the initial 2.7 value a bit. I do feel 2.7 covers it and the response curves look good, but my first removal of the polyswitch (and accompanying resistance) in several Polk models did approximately coincide with my ears turning 50 .

P.S.: adding too much resistance would make a tweeter sound veiled.

gimpod

Of all the poly-switchs I've measured they've been in the 0.1 - 0.2 Ohm range. It really does come down to a matter of taste and in most cases I'd doubt if you would even notice it. If they sound to bright with a jumper (after burn in) you can always replace the jumper with a resistor, I would start with a 0.2 Ohm and go from there just don't go over 0.5 Ohms.

Moofy

Any thoughts on the best bang-for-the-buck spikes? Should I plan on placing a spike at each spot where a plastic "foot" is now (i.e., four spikes per speaker)? The speakers will be on carpet, so I don't need cups, right? Thank you.

Seth

Moofy

I'm over 50, so I guess it's no polyswitches for me...and I didn't even need to flip a coin.

Seth

Moofy

So, the plan now is for Trey's castle mod, Dynamat, spikes, and RD0 tweeters. Any good arguments for Black Hole, upgraded wires, upgraded connectors, etc.?

Seth

VR3

I have some brass spikes that came from some Tyler Acoustics - very heavy duty...

You would just need the threaded inserts for them, I will throw them in the box for $15.00 :-P

Easily a $30-35.00 set of spikes!

F1nut

Too bright to my 50+ old ears without that 0.5 ohm resistor. I highly recommend them.

Moofy

Guess I'm back to flipping a coin!

WRT to the spikes, any idea where I can get the inserts?

Thanks.

Seth

Moofy

Guess I'm back to flipping a coin!

WRT to the spikes, any idea where I can get the inserts?

Thanks.

Seth