I had been mildly intrigued by the idea of modding my 1989 version CRS+'s according to the 4.1TL specification since I first discovered it while compiling information for the first edition of the SDA Compendium (way back in the winter of 2002). Similar to the interconnect cable mod, it wasn't something that had a high priority in my audio life.
This simple modification, which only entailed adding a 5.6uF capacitor in parallel with the 2.7 ohm resistor in the tweeter circuit and replacing the RDO194-1 silk dome tweeters (SL2000 replacements) with the RD0198-1 silk dome tweeters (SL3000 replacements), has evolved these 17 year old speakers to a higher level of performance. I was only expecting some modest improvements in high frequency response. What was achieved was a night and day improvement in the overall sound of the speakers. But, before I talk about that, I would like to say a few words about the CRS+'s prior modifications.
This pair of 1989 model CRS+'s, which is one of three pairs I own, was purchased used in 2002. They are currently used in my home office audio/video system. They came with nice light oak veneer cabinets. However, I subjectively thought the cabinets would look better with teak veneer, so I had the cabinets re-veneered at a local cabinet shop. In addition to the new cabinet veneer, I also made the following changes:
1. The stock electrolytic capacitors and cermet resistors in the crossover circuits were replaced with AudioCap polypropylene film capacitors and Mills MRA-12 wire wound resistors.
2. The polyswitches were left on the circuit boards, but were shorted out.
3. The stock SL2000 metal dome tweeters were replaced with RD0194-1silk dome tweeters.
4. The rather thick, rather heavy, coarse textured grille cloth was replaced with a lighter, thinner, silkier textured black knit fabric.
5. The stock binding posts were replaced with Cardas CCGR-S gold plated copper posts.
6. The stock 18 gauge SDA interconnect cable was replaced with a custom SDA interconnect made from Monster Z2 Reference speaker cable (12 gauge conductors).
All modifications except the binding post upgrades and new cabinet veneer provided improvements in sound quality.
The SDA driver (MW6511) of each speaker was removed to gain access to the crossover circuit board. The driver wires and binding post wires are attached to the crossover circuit board with wiring harnesses and easily disconnect. The tweeters and associated wiring harness were removed.
While holding the crossover circuit board with one hand, the circuit board's retaining bolt at the rear of the cabinet was removed with a 5/32" hex wrench.
RD0198-1 tweeters: Polk Audio, $48.00 each.
Sonicap 5.6uF* 200 VDC polypropylene film capacitors: Soniccraft, $12.40 each.
Sonicap 0.001uF 600 VDC polypropylene film capacitors: Soniccraft, $4.00 each.
Buchanan aluminum wide spade clip connectors (part #70072): Home Depot, $0.99 for a pack of six.
*The modification specification calls for a 5.8uF electrolytic capacitor, but 5.6uf falls within the 10% tolerance range of the specified part.
I was initially going to replace the 750pF silver mica bypass capacitor with the 0.001uF polypropylene capacitor, but I decided to just remove the 750uf capacitor altogether. Upon reconsideration, I didn't think that a high quality bypass capacitor was required when using a high quality film capacitor. I removed the polyswitches, since they were shorted out and were not active in the circuit anyway. Finally, I ran a jumper wire from the postive terminal of the input wiring harness to the lead of the 12uF capacitor. This bypassed a wire jumper and the circuit traces for the polyswitch.
Replacing the RD0194-1 with the RD0198-1 required a little improvisation. The RD0194-1 has two narrow metal tabs that are attached to the wiring with narrow spade clips. The RD0198-1 has a narrow tab and a wide tab. No problem with attaching the stock narrow spade clip. I cut off the white wire (negative terminal) narrow spade clip and replaced it with a wider one. I had originally just tinned both the wide tab and the flat back of the other narrow spade clip, then soldered them together. This was quick and easy, and saved me a trip to Home Depot, but I though that I might appreciate quick disconnect capability in the future.
These are my initial listening observations as I just performed the modification yesterday:
1. The bass is cleaner, more defined, and has more impact. Change the tweeters and the bass improves significantly. Interesting isn't it? The RD0198-1 tweeters are evidently a much better match for the existing CRS+ drivers.
2. The speakers sound larger and faster. Vocals have more presence and sound more natural.
3. The overall clarity of the speakers is significantly improved.
4. The soundstage is projected a couple of feet farther in front of the speakers.
5. The treble is smoother, more defined, and more detailed without a hint of edginess or grain.
6. The impedance was raised a little bit as evidenced by my having to increase the volume a little bit (from -44 to -42) to achieve the same pre-mod average sound level of 80 dB. The DC resistance of the speakers measured the same as before the mod: 3.9 ohms.
Prior crossover mods have demonstrated optimum sound quality after two to three weeks of listening (60 to 100 hours). I will submit supplementary observations in a few weeks.
The improvements provided by the CRS+ TL mod were vividly evident, even with equipment of moderate resolving power:
Sony TA-E9000ES preamp/home theater processor,
Sony DVP-S9000ES CD/DVD/SACD player,
Adcom GFA-5500 power amp,
Monster Z3 Reference speaker cables,
Audio Research coxial digital cable,
Monster Z200i interconnect (SACD out).
1. CRS+ with silky black grille cloth.
2. Front-top-side view of teak veneer cabinet.
3. Closeup of teak veneer.
4. Cardas binding posts.
5. Custom 12 AWG SDA interconnect cable.
6. Modification parts.
7. Modified crossover.
8. Sideways view of CRS+'s in home office system.