Several weeks ago, with the help of my long time friend Bill, I completed an upgrade of the crossovers on my SDA-2’s. I used a thread by Aadvark1 as a guide for my project. Aadvark1’s thread was extremely valuable to me in this project. [thread] http://www.polkaudio.com/forums/show...tion+Crossover [/thread] Aadvark1, thanks a million! With Aadvark1’s permission I am going to use several pictures of the “before” pictures of the crossovers. I didn’t take any before shots since Aadvark1’s were so good. Aadvark1 use Solen caps and Mills resistors for his upgrade. I decided with a lot of angst to go for the more premium Sonicap capacitors. These caps represented a significantly larger investment over the Solens, which are popular among Polk members performing these mods.
I made my decision after several conversations with Jeff Glowacki at SonicCraft. Jeff immediately impressed me with his knowledge of speaker crossovers and his experience with capacitors in these circuits. Jeff’s primary message was to eliminate the fuse protection as these were viewed as the weakest link from the sound source to the crossover boards. My tweeter fuse filaments were smaller that the diameter that a typical human hair. Barely visible under light with my glasses removed to view up close. According to Jeff “Why people are spending good money on thick speaker wire, expensive cable, only to be limited by this tiny wire is beyond me. By pass those fuses with a solid copper wire and you should notice an immediate improvement”.
The other departure from the Polk schematic was to eliminate the 750 pf silver mica by pass capacitor from the 0.5 uF capacitor and the 12 uF capacitor. The 750 pF by-pas capacitor from the 0.5 uF capacitor was eliminated completely. For the 12 uF capacitor Jeff recommended replacing the 750 pF by pass capacitor with a 0.1 Gen II. The elimination of the 750 pF by-pass capacitor was also a hotly debated discussion with in the Forum [thread] http://www.polkaudio.com/forums/showthread.php?t=32685 [/thread] He recommended the Gen II over the Gen I. He felt the Gen I might be a little too transparent and the Gen II might offer a little color that you might expect from a tube amp source. Since I was using solid-state equipment, Jeff thought this might be a better choice, offering a softer cap with a little color.
I chose the Mills MRA-5 resistors and the Vampire brand binding posts. When I received the Sonicaps I was a little alarmed at the size of these caps compared to the Polk originals and the Solens. My fear was these caps would have a hard time fitting through the back of the speaker cabinet into the speaker enclosure. I decided to go for it.
I have attached several pictures depicting the comparative sizes of the original caps vs. the Sonicaps. We removed all of the speakers, carefully numbering the wire leads and the speaker terminal. Little adhesive numbers worked great for this labeling process. We had no trouble soldering the new components to the boards of fitting the newly assemble boards into the cabinet. The size of the cap left us a few blind spot for reattaching the wires to the spade lugs. Additionally, I used ring terminal to attach the main leads to the binding posts as opposed to soldering these wires to the new Vampire binding posts. I used the steel ring terminal, as I didn’t want to spend all afternoon trying to run down some gold ring terminals. All the boards and components went back together without much effort. Bill had a nice set of hobby tubes of various diameters that were very useful to compress the plastic “trees’ that held the circuit boards to the mounting blocks that attach to the speaker cabinets. These allowed effortless removal of the boards without the use of pliers or other hand tools. The whole project took about 5 ½ hours with the two of use working together. The attached pictures show the original boards, a side beside view of the original capacitors with the new Sonicaps, a picture of the SDA board assemble with the new Sonicaps, and a look inside the cabinet with the refurbished boards installed.
I notice a change in the sound of the speakers immediately. Initially, it was not profound. I noticed a wider soundstage and more punch to the bass. The midrange was more detailed. I was happy. However after more than 50 hours of “burn in” of these components, the changes are much more pronounced. Greater detail, softer detailed highs, more bass and overall a moderate improvement. I have very happy with the results. Whether or not I would have realized a similar or even beer improvement with the less expensive components is a mater of debate that I cannot offer any objective opinion. I am very satisfied with this result and would recommend these to any SDA owner contemplating this upgrade. The overall cost of this upgrade with Sonicaps, Mills resistors, Vampire binding posts, postage etc. was a little under $300. This upgrade could have been done with Solens, Mills and Vampires for about $100, or the cost of my upgrade was about three times the typical upgrade done by may other Polk owners doing the same project.
Your comments and feedback are welcome! Enjoy the pictures and happy listening!