There have been questions concerning what is required to “upgrade” the SDA SRS to the SDA SRS 1.2TL. The answer is: NOTHING! Although the original SRS and the SRS 1.2TL look nearly identical to the casual observer, they are entirely different speaker systems. The only things they have in common are the stereo drivers (MW 6503), passive radiator (SW150), and the physical arrangement of the drivers on the baffle board. The cabinets, crossover circuits, SDA interconnect cable, binding posts, SDA drivers, tweeters, and SOUND are different between the two speaker systems.
The set of SDA SRS loudspeakers discussed here was manufactured in September of 1987 and purchased be me in November of 2002. The original owner purchased them in July of 1988 and subsequently sold them to his brother. The second owner was looking to sell them prior to going off to graduate school and moving into a smaller space. I received the speakers in near-mint condition with original boxes, manual, packing material, and sales receipt. The only thing that kept them from being in absolutely mint condition was an easily repaired 8-1/2” long by 1/32” wide crack in the left speaker’s top oak cap.
The modifications consisted of the usual replacement of the grille cloth, binding posts, the resistors and capacitors in the crossover network (Figures 1 through 3), and the replacement of the SL2000 tweeters with the SL2000T tweeters (figures 5a and 5b).
The total parts cost for the modification was $553.45 and was worth every cent. I paid $1400 for the speakers. This price included out-of-state delivery. Therefore, the modification brought my total investment up to a little under $2000.
Parts were sourced from the following vendors:
1. SL2000T Tweeters
Polk Audio Customer Service
2. Mills MRA-12 Resistors
The Parts Connexion
3. Solen PB Series Film Capacitors
The Parts Connexion
4. Ponte Knit Cloth
Can be purchased locally or ordered online
5. Cardas HCBP-S Binding Posts
Figure 1. From front to rear: Cardas HCBP-s binding posts, Mills MRA-12 wire wound resistors, Solen PB series polypropylene film capacitors, and Hancock Fabrics “Ponte” knit grille cloth.
For this modification, I chose to replace the electrolytic capacitors with Solen PB series polypropylene film capacitors. Although I prefer the sound of AudioCap film capacitors over Solen, AudioCap does not make film capacitors in the large values (92 uF and 130 uF) needed for the SRS crossover circuit. I could have connected smaller values of AudioCap capacitors in parallel to give me the larger values I needed, but arranging and securing such a conglomeration on the crossover circuit board would have been a topological nightmare. While the cost of such an arrangement would not have qualified for nightmare status, it would have been a very disturbing dream. I also could have used AudioCaps for the smaller capacitance values and used Solens for the larger values, but I did not want to mix capacitor brands on this particular project.
In comparison tests, the AudioCaps provided a little more detail for a lot more money. However, the Solens are no slackers in the performance area. For example, they were the used by Dunlavy Audio Labs in reference speaker systems costing up to $35,000. Unfortunately, like many well-regarded high-end speaker companies, Dunlavy Audio Labs has ceased operation. While the company was in business, Dunlavy speakers were marketed as “the world's most accurate loudspeakers for discriminating audiophiles and professional recording engineers”. That may have been a little bit of marketing hyperbole, but I will say that I was very impressed with what I heard when I visited the DAL factory in Colorado Springs, Colorado in December of 2000.
Figure 2. SRS crossover circuit board and replacement components.
Although the crossover circuit board of the SRS is luxuriously spacious compared to other SDA models (see Figure 4), the advantage afforded by that spaciousness is moderated by the three large capacitor values required (two each of 130 uF and one of 92 uF).
Figure 3. Comparison of stock electrolytic crossover capacitors with their polypropylene film replacements.
Figure 4. Modified SDA SRS 1.2TL crossover (top) and stock SDA SRS crossover (bottom).
Modifications to SDA loudspeaker crossovers is not an undertaking for the inexperienced, impatient, or fainthearted individual. It is a task that requires the dexterity of a contortionist and the insight and patience developed through solving many difficult jigsaw puzzles.
Figure 5a. SRS speaker with stock SL2000 tweeters. The original SL2000 had a 5 dB resonance at 13 kHz. This added a bit of brightness and "detail" that some listeners liked.
Figure 5b. SRS speaker with upgrade silk dome RD0194-1 tweeters.
Figures 6a and 6b show the stock binding posts and the replacement Cardas HCBP-S posts. With my ears and my equipment, I have noticed no sonic benefit in upgrading the binding posts of my speakers. However, the all-metal, higher quality posts do provide a more secure connection than the stock posts with their plastic retaining nut. Since I have no current interest in bi-wiring and bi-amping, I decided to wire the high frequency and low frequency sections of the crossover to a single set of binding posts. I did leave my options open by drilling larger holes in the binding post plate to accommodate a second set of HCBP-S posts in the future. The upper holes were sealed on the inside with thick plastic adhesive pads and finished on the outside with dark felt circular pads.
Figure 6a. SRS stock binding posts.
Figure 6b. Cardas HCBP-S posts.
The upgrade grille fabric provided both sonic and aesthetic benefits. I tested prospective replacement fabrics by holding the fabric up to the light and by draping a yard of the fabric over my head and having the sales lady stand ten feet away and talk to me. She seemed to really enjoy helping me with my research.
I installed the new tweeters and binding posts in the left speaker and did A/B comparisons between it and the stock right speaker with the SDA cable disconnected. Next, the left speaker crossover was modified and A/B'ed with the stock right speaker, again with the SDA cable disconnected.
The time for all the modifications took a total of 10 hours and 45 minutes. Four hours of this was the time it took to remove, take apart, modify, reassemble, and reinstall the first crossover board. The second crossover board took only 2 hours and 45 minutes since I did not have to figure out how I was going to arrange components on the board. The SDA SRS 1.2TL crossover uses snap-in wiring harness connectors to for the driver wires. The SDA SRS driver wires are soldered to its crossover board. Therefore, the mere removal of the SRS crossover board is a tedious process. All components were resoldered using Cardas high silver content Quad-Eutectic solder.
Figure 7a. Side view of the modified SRS crossover circuit. The resistors that were at the top edge of the board were mounted on the underside of the board in the area above the large inductor coil under the center of the board. Prior to reinstallation, the large capacitors were secured to the board with plastic cable ties and heavy duty packing tape.
Figure 7b. Top view of the modified SRS crossover circuit.
The improvement in sound quality was astonishing! I will post a detailed review of the the modified SRS in two weeks after the new components have had an opportunity to properly burn in. The review will compare the modified SRS to the stock SRS and will compare the modified SRS to the modified SRS 1.2TL.