SDA 1B crossover mods

kidglove13 wrote: »

FYI I know nothing about soldering.

Here is a link to a video that will give you the basics of how to solder. Once you know the basics, do a lot of practicing on something else before starting on your crossovers.

Learn How to Solder

http://blip.tv/make/learn-how-to-solder-skill-building-workshop-130343

Marvelous thread from member inspiredsports from some time ago.
http://www.polkaudio.com/forums/showthread.php?74946-SDA-SRS-2-Crossover-Parts-list

The first few pages are a lot of confusion, experimentation, verification, argument...and not that helpful. The later pages are TERRIFIC.

Recognize that the SDA 1B is the SAME electrically as the SDA-SRS 2 (early version--blade/blade) with one resistor per speaker different. The SDA 1C is the similarly the SAME electrically as the SDA-SRS 2 (later version--pin/blade) but we don't care about those in this thread.

Anything that applies to the SRS 2 having the blade/blade interconnect jack will work with the 1B.





Suffice to say that if you simply replace all the capacitors except two per speaker with exact- or near-exact value FILM caps, replace all the resistors except one per speaker with exact-value replacements, eliminate the poly switch (safety device) along with eliminating the very tiny 750pF silver-mica bypass cap, and replace the tweeters with the RD0-198, you're in for a real treat. You think the speakers sound good now...just wait! You're gonna soil yourself.

You will want to yank out a 4.4uF capacitor in each high-frequency crossover board and replace it with a 5.8uf (5.6 is easier to find and close enough) This and a different crimp-on terminal on the wire harness allows the use of the 198 tweeters.

You will want to buy a small selection of resistors to replace the MAIN high-frequency resistor. This single resistor is the only difference in the crossover between an SRS 2 blade/blade and an SDA 1B. The 1B already has a resistor that's closer to optimum--2 ohms instead of the 3.5 ohm unit of the SRS 2. You may want to experiment with resistors ranging from 1.5 ohms to 2.5 ohms. Buy a selection, see what happens. If I were doing mine again, I'd use a 1.5 ohm or 1.75 ohm. The 2-ohm is still too large even with the polyswitch bypassed for my taste.

You can argue with the others here about the brand and grade of capacitors. I used 1% tolerance Daytons in the high-frequency crossover, and 5% tolerance Dayton and 3% tolerance Erse capacitors in the low-frequency crossover.

ANY ANY ANY film cap you buy will be better than the worn-out, degraded electrolytic caps in there now.

The Mills brand resistors are well-recommended, reasonably inexpensive, and EASIER TO INSTALL than the resistors I bought from Erse. Buy the Mills resistors.

There is a pair of capacitors (130uF and 55uF) on the low-frequency board that are coupled. Together, they provide 185uF of capacitance. I used two 91uF caps per board to total 182uf, easily close enough to 185 considering the original caps were probably + or - 10-to-20 percent. The original wide-tolerance 34uF caps were replaced by tighter-tolerance 33uF caps. Again, not an important difference. The new film caps will be huge in comparison to the cheap electrolytics used by Polk. Finding space on the circuit boards is the biggest challenge of the whole endeavor.





Inductor changes are less easy. I have--but have not installed--replacements for the big inductor in this photo. I'll have to un-wind a few turns off of it to get to the correct value; but the reduced DC resistance should make for better bass, and will require more current from the amplifier. If you have a marginal amp, this probably isn't for you because it's going to significantly reduce speaker impedance. Changing the other inductors is probably not something I'll get into.

Sorry, I was too dumb to take photos of the high-frequency circuit board.

This is VERY do-able if you have some practice at soldering.

To the OP, If you decide to do these yourself after learning how to solder here are some VERY important tips. Before soldering anything arrange and test fit your components once you have everything in place and know where everything gos then start soldering but don't clip any leads off until your sure everything fits. At first it can seem a bit confusing and a daunting task but it really is not that hard it just takes some planning and patience. Take your time and have fun doing it. And if you get stuck ask questions most of us here are more than willing to help out if we can.