4.1TL Modification for 1989 version SDA CRS+

[DarqueKnight]

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.

Modification Procedure

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.

Parts-Vendors-Prices:

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.

The Sound

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.

Associated Equipment

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).

Picture Captions

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.

[ESavinon]

As usual, this is just another excellent post coming from raife.
Bravo! I'm waiting on the opportunity to purchase a pair of crs + to perform these modifications.

[DarqueKnight]

I'll sell you my newly modded CRS+'s for $5,995.14. This price includes a Club Polk discount of 20%.:)

[ESavinon]

I'll sell you my newly modded CRS+'s for $5,995.14. This price includes a Club Polk discount of 20%.:)

Is that $5,995.14 in mexican pesos? ;)
I'll add .85 for shipping to ny.
Do we have a deal? :D .

[DarqueKnight]

I'm sorry. I stated the initial price in US dollars. I meant to specify Euros.

[F1nut]

Excellent!!!

[DarqueKnight]

Jesse,

Did you experience an improvement in bass response when you did your 4.1TL mod?

[amulford]

Excellent play by play. I've bookmarked this for reference. I'm curious as to how you know the 1989 manufacture?

[DarqueKnight]

If you look at the picture of the crossover in my first post, you will notice a little white sticker near the front edge of the circuit board. That sticker has a date of "2/6/89". The 6-1/2" drivers also have 1989 date stamps on the rear. The 1989 CRS+ is the only version that used the combination of a MW6510 stereo driver and a MW6511 SDA driver.

This mod might work with the 1987 version CRS+, since the only difference between the 1987 version and the 1989 version is that the 1987 version used a MW6503 stereo driver and the 1989 version used a MW6510 stereo driver. If someone wanted to try this mod with the 1987 CRS+, I would recommend asking Polks engineering department if it is feasible.

[F1nut]

Jesse,

Did you experience an improvement in bass response when you did your 4.1TL mod?

Yes, quite a bit actually.

[Zap Rowsdower]

I just completed this modification last night on a stock pair of '89 CRS+ I recently inherited from my father.

The difference is amazing, just like F1nut & DarqueKnight noted.

I encourage anyone who is thinking about performing this upgrade to do so. And don't be discouraged if you've never done any soldering before - Last night was my first time!

*Many* thanks to F1nut & DarqueKnight for their informative posts!!

[BobMcG]

Dang they're beautiful! Nice work.

[Dennis Gardner]

Would a version of this simple upgrade be available for my SDA1Cs since they have the same 6510 & 6511 drivers used? I haven't been into the crossovers on my speakers yet, but would consider doing it instead of the common RD0194-1 tweeter change.

[nadams]

DK- Those speakers are beautiful! Now you have me interested in trying to get my SDA's refinished... how much did the refinishing cost you?

[DarqueKnight]

Would a version of this simple upgrade be available for my SDA1Cs since they have the same 6510 & 6511 drivers used?

Polk's engineering department would have to answer this.

[DarqueKnight]

... how much did the refinishing cost you?

Cabinet refinishing: $175.
Crossover capacitors and resistors: $208.
Three pairs of Cardas CCGR-S binding posts: $96.
RD0198-1 tweeters: $96.
Custom SDA interconnect cable: $107.
Grille cloth: $5.

Total modifications/upgrades: $687.
Increase in aural satisfaction: Priceless.

[DarqueKnight]

Based on the remarkable results from modding the CRS+'s in my home office, I gave my other two pairs of CRS+'s the treatment. A pity I didn't do this sooner...such good sound.:D

[Deadof_knight]

The wood work in the ole homestead is nice ..........




Big fan of wood everywhere !!!

ps. was the house built for the speakers or vise versa ?

[DarqueKnight]

A little bit of both.

[dcoil]

DarqueKnight, I should be getting a pair of SRS's (original, in every way). I've read about your 2nd edtion compendium and I'd like to get a copy. Can't pm yet (almost there), so I'm posting to this thread. I know you moded your 1.2 TL's, and I was wondering how my upcoming project would compare - both to work to be done, and how you think the finished product will compare?

[DarqueKnight]

See this thread: Improvements to the SDA SRS

I have sent you a PM.

[Lasareath]

I had been mildly intrigued by the idea of modding my 1989 version CRS+'s according to the 4.1TL specification

DarqueKnight,

Your CRS+'s look MEGA SWEET!,

How much would you charge to do that conversion on my pair?

Lasareath

[DarqueKnight]

I prefer not work on other people's speakers, but I will be happy to answer any questions you have. There are a couple of forum members who have expressed interest in doing such work (Madmax is one).

[Refefer]

Whoever re-vinyled your speakers did a knock up job. How much does something like that cost anyways? I'm interested in doing that to a couple of my speakers.

[DarqueKnight]

See post #16 for costs. BTW, the speakers were redone in real wood veneer, not vinyl.

[Refefer]

See post #16 for costs. BTW, the speakers wereredone in real wood veneer, not vinyl.

Explains why it looks so good. I gotta do some priceshopping, that's impressive.

[hoosier21]

this mod would work with a pair of 2B, right? They share the same crossover.

[DarqueKnight]

I don't know if this mod is applicable to the SDA 2B. Two things to consider:

1. This mod was only specified for the 1989 version CRS+. While it is true that the 1989 versions of the SDA CRS+ and SDA 2B used the same crossover, they also used different stereo drivers. I would check with Polk's engineering department to see if this mod is applicable to the 1989 version 2B.

2. If the mod is applicable to the 2B, you would need to make sure you have the 1989 version rather than the 1987 version, which used a different crossover.

[Stew]

Hi all! Life's been hectic and haven't been here in a while. Looked around the other day and this thread caught my eye. It sounds like one of the big improvements from this mod is bringing the vocals forward. I've never noticed recessed vocals on my 2B's (1989 version). Is this only an issue with the CRS+ or have other 2B owners noticed recessed vocals? What are the differences between the RD0194-1 and the RD0198-1, other than the impedance difference, that would contribute to the difference in sound?

[F1nut]

While Raife is correct that the '87 and '89 versions use a different stereo driver, the basic crossover remains the same and since this mod is strictly for the high frequency circuit, I can see no reason it can't be done to any of the pin/blade CRS+'s or 2B's regardless of year.

Stew, not sure where you got that the vocals are brought forward, it's the entire soundstage that is. Having said that, I did notice a vast improvement in the vocals with the use of the RD0198-1 vs the RD0194-1, but to use the RD0198-1 you must change the crossover as Raife describes.