SDA 1C Question

ednjillb

This is my first forum post and I am thankful for any help :-)....I just finished working on an old pair of SDA 2s that I had for a few years, put in new drivers, cherry veneer mdf for the sides, and curly maple tops and kick panel. They were damaged in shipment when I bought them used and it was time to either do something with them or send them to the beyond...

While doing the work on the 2s I came across a pair of SDA 1Cs that were in decent shapeand within a 5 hour drive. Knowing these were held in higher regard and a later generation, I decided to purchase them....my wife is not overly thrilled :-)

For the 1Cs I have taken the following point to point measurements but did not find any table for the 1Cs in the SDA handbook. My measurements curiously are he same for each speaker which is not in keeping with all the others in the SDA series. Infinity was on an Rx1 scale so it may be just taken as out of rangeand being an analog meter the ohm values may not be exact. Note pin 1 is blade and pin 2 is pin.

My readings are as follows.

Reading Left Right
IC Pin 2 to Black 3 ohms 3 ohms
IC Pin 1 to Black inf inf
IC Pin 1 to IC Pin 2 inf inf
IC Pin 2 to Red 4 ohms 4 ohms
Red to Black 5 ohms 5 ohms
IC Pin 1 to Red inf inf

I was wondering if anyone has taken these measurements on a pair of 1Cs? If not would someone be kind enough to take them and post a response. I have checked that polarities of the speaker wiring and plugs to the crossovers and I believe they are wired correctly.

When I A/B test the pair of 2s next to the 1Cs I believe the SDA affect is more pronounced on the 2s which has me a little suspicious. Because the wiring harness and the plugs are all polarized going to the crossover board and each speaker seems to be wired the same, maybe the readings are as expected...not sure. The only way I think they would end up being different would be if the crossover boards were a different PN/design for the left vs right speaker. Thanks in advance for any help.

Later Ed

verb

Hi Ed - Welcome to the forum! Plenty of folks here that should be able to help you. One guy in particular David @westmassguy upgraded my XO's on my 1C's.

ednjillb

Thanks for the welcome. I am hoping someone has the answer to this puzzle. BTW if anyone is looking for some nylon speaker inductor to XO circuit board standoffs that were used on the 1Cs it appears to be a Panduit CBLS50-C available at Digi Key. Mine were broken on one speaker.

westmassguy

What generation is the SDA-2? Original with two horizontal tweeters, 2A, or 2B?
DC Resistance for the 1C should be similar to the 4th Generation SRS-2 since the crossovers are identical, with the caveat that the sub-bass drive inductor is 9.6 mH on the SRS-2 and 16 mH on the 1C.

ednjillb

David, thanks for answering.

My SDA 2s are early transitional models I believe. Had the MDF cabinets covered in walnut vinyl. They had two horizontal SL1000 tweeters and a small pin/pin dimensional array plug with an orientation bar (for lack of a better term) in the round recess kind of like an old mic plug. I do not think that was a common plug but it is original. They have the two fuse arrangement and no poly switches.

Getting back to the SDA1Cs, I have a table that says SDA SRS2 .nc that starts with 1.8 ohms for both sides, then 0, then 1.8, then 3.0, then 3.7, then 3.7 top to bottom. Is that the table that you were referring to?

My SDA1Cs readings do not really follow those. I have ohmed each speaker and checked the harnesses to be sure they are as they should be. Crossovers have no obvious flaws. The measurement I took were with the polyswitches in place which I have removed. They measured about an ohm after my desoldering them.

The fact that both sides have no issues with the speaker resistance measurements and are identical leads me to think they are as they should be. The only way to know for sure is to have someone else measure theirs I think, unless you have some ideas as to
how else to sort this out. Thanks again....
Later Ed

F1nut

The SDA soundstage varies from model to model. Your 2's also have that horrible SDA tweeter creating a phasey effect, so the fact the 1C's present a difference soundstage is no surprise.

A polyswitch measuring close to one ohm is toast. You did well to remove them. Now, upgrade the caps and resistors because they were junk to begin with and those caps are now way past their lifespan.

westmassguy

F1nut wrote: »

The SDA soundstage varies from model to model. Your 2's also have that horrible SDA tweeter creating a phasey effect, so the fact the 1C's present a difference soundstage is no surprise.

A polyswitch measuring close to one ohm is toast. You did well to remove them. Now, upgrade the caps and resistors because they were junk to begin with and those caps are now way past their lifespan.

Ed, this is why I asked what generation SDA-2s you had. They weren't transitional, they are the original 2nd generation 2s.
I can't account for the resistance discrepancies on the 1Cs, other than what's been mentioned already, but I can tell you if you disconnect and safe off the leads going to the dimensional tweeters, the 2s will sound much better. You can also just pull the fuses on the outer tweeters to try it out first.

ednjillb

Thanks David....The quality resistors and caps will have to wait a bit, but it will happen in good time. I have seen your posts regarding the need and agree that it is a good upgrade. Priorities... I have to save a bit and buy an amp/preamp for the 1Cs.

Thanks for clarifying that the SDA2s are early versions. I will try and pull the fuse for the dimensional tweeter and see how that sounds to me. Getting the woodworking done and replacing some needed bass/mid-drivers and tweeters has me ready to take a pause to enjoy them. Attached a couple of photos of the restored SDA2s.

Later Ed

westmassguy

ednjillb wrote: »

Thanks David....The quality resistors and caps will have to wait a bit, but it will happen in good time. I have seen your posts regarding the need and agree that it is a good upgrade. Priorities... I have to save a bit and buy an amp/preamp for the 1Cs.

Thanks for clarifying that the SDA2s are early versions. I will try and pull the fuse for the dimensional tweeter and see how that sounds to me. Getting the woodworking done and replacing some needed bass/mid-drivers and tweeters has me ready to take a pause to enjoy them. Attached a couple of photos of the restored SDA2s.

Later Ed

Nice. Normally would not advise using solid wood for the slab tops. MDF with Veneer is preferred, but they're your babies, so do as you will.

ednjillb

I certainly agree when constructing speaker cabinets that MDF is the material of choice. In this case I am cladding the MDF and took the precaution of foam stripping the interface side and **** them in place. I see no reason to think that this exterior cladding would color the sound in any way.

On another front the Parts Express grill cloth in black has an inexpensive cloth that customers said was not very black and the Mellotone Black cloth which appears to be a better match to the Polk cloth but it is hard to tell. I have to redo the front grill cloths on the 1Cs but not the sides. Anyone have any experience with these cloths and can chime in on which version is a better match?

Thanks Ed

verb

Love the look! Nice contrast on the Top Plate and Kick Panel. Solid wood vs. MDF on the top plates have been discussed often here. As you know, MDF is unidirectional in it's composition, so it's more stable and not susceptible to cracking over time. Natural wood has the risk of cracking. But, if that happens, you can repair or replace.

If I ever get off my arse, I got some Zebrawood side panels that are destined for a pair of 1C's that I'm working on.

https://forum.polkaudio.com/discussion/179960/another-1c-upgrade-path/p1

ednjillb

Thanks for the compliment. I went to your link and went through your process. We can both appreciate how many hours this all takes on a one off project like this. Nice work on your part. You need to get to those panels :-)

Mine started with a two part polyester wood filler to rebuild the shipping damage on the corners of the MDF. You learn a lot with these projects and in some cases new skills. I found that 3M Spray 70 contact cement was a good mount for my MDF cherry veneer. Not sure what would be best for your panels. Be nice if you could come up with some nice removable mounting system. Gluing is not really good for cloth covered panels. Velcro dots or strips?? Your case of wood side panels may be glue..

My 1Cs had one speaker with some water damage at the bottom on one side. The veneer bottom was bowed out with swelled particle board. I plunged cut the bad particle board with a vibrating saw to remove about 1/8 inch of material. I glued and with clamps flattened the bottom back into place. I did not want to get into building 4 new tops and bottoms. I know how much work you did and it really cannot be rushed :-)

verb

Yep. We’re on a similar journey. What got me side tracked a bit is that I picked up a set of minty 1C’s too. Everything was bone stock except for the tweeter upgrade.

And then, I landed a set of SDA SRS’s!

Oh God, I’m in the rabbit hole!

Oh did I mention Monitor 10’s and 5Jr’s? Help me!

ednjillb

It is like Noah's Ark, you need two of everything in the SDA line until there is no room left in the Ark