SDA SRS 4.1TL Upgrade

F1nut

Awhile back I upgraded the crossovers in my CRS+'s using Sonicaps and Mills Wire-wound resistors along with the new RD0194-1 replacement tweeters. All in all a noticeable improvement over stock, but there was something that bothered me. The vocals usually sounded recessed or too far back compared to the rest and especially when compared to my 2.3TL's. Still, better than stock, but......

Polk had intended to rework the crossover to allow the SL3000 to be used in the CRS+ and from what I understand, it was to be called the SDA SRS 4.1TL. There is even an "Approved" schematic available from Polk with this upgrade noted. So, I decided to try this on mine. The upgrade calls for a 5.8uF cap to be added in the high frequency circuit. I pulled the crossovers and went to work adding the 5.8uF Sonicap in the location marked C5. I soldered the top lead (closest to R2) to the C5 position and ran the other lead to the location marked H (near the small inductor) instead of using the other C5 hole as this eliminated the need for a jumper. While I was at it I decided to change out the 750pF Silver Mica in favor of a Sonicap .1uF cap and I also removed the Polyswitch, replacing it with a jumper. I then removed the RD0194-1's and replaced them with the SL3000 replacement tweeter, the RD0198-1.

After allowing 100 hours of burn in time, it was time to evaluate. Ah, this was much better. The vocals were now up front, as in, in front of the band and were definitely clearer to me than before. In fact, the 4.1TL's now sounded pretty close to my modded SDA 2.3TL's minus the refinements and bottom end of the bigger speaker. After this final upgrade I am very, very happy with the sound quality of my new SDA 4.1TL's.

At the time I wondered why the vocals were recessed using the RD0194-1. Was it the tweeter, the crossover upgrades or the combination of both. Since I did both at the same time I had no way to know for sure and forgot about it until recently when I received a PM from a fellow Polkie asking about CRS+ crossover upgrades. In the PM he mentioned that he had already upgraded to the RD0194-1. He then stated, "The instruments seem to be in the correct location, but sometimes the vocals seem like they are coming from way back behind the wall." Bingo, it's the tweeters! I will say that even with the recessed vocals, the RD0194-1 is a much better tweeter than the SL2000 and that nasty 5dB spike.

The first set of pictures shows the stock crossover and then my first upgrade retaining the Silver Mica and Polyswitch. The second picture shows the fully upgraded 4.1TL crossover from the side, showing the 10uF cap that I had to mount under the board. The last picture shows the 4.1TL crossover from the top.

SDA SRS 4.1TL parts list (for both boards)

Polk Audio tweeter
(2) RD0198-1

Sonicap capacitor 5% or better tolerance
(2) .1uF Gen II (replaces the 750pF Silver Mica)
(2) 5.8uF
(2) 12uF
(2) 20uF
(2) 30uF
(2) 10uF (combine the 30 & 10 to equal the needed 40uF as the largest cap from Sonicap is 30uF)

Mills Wire-wound 5 watt resistor 5% tolerance
(2) 2.7ohm MRA-5

Cardas Quad Eutectic solder

A short piece of 20 gauge solid copper wire (to extend the lead on the 30uF cap)

Hot glue gun (to secure the caps to the board)

Have fun and enjoy!



Edit: This upgrade can also be done to the SDA 2B's as they use the exact same crossover. You can make up a new name, like SDA 2BTL or somesuch.

Zen Dragon

Very nice work and great write-up. Fascinating info there. For the .1uf cap in place of the silver mica, did you use the Gen I or Gen II Sonicap?
Just a theory on the replacement tweeter not quite sounding right on vocals. Polk was not staffed by a bunch of dummy engineers and they had to know there was a spike at the resonant frequency of the SL2000 tweeter. Perhaps their selection of capacitor values were partially aimed at compensation for that spike. It could be designed to repress certain frequencies.
When replacing with a much flatter response tweeter, and still having said frequencies repressed, those frequencies could tend to sit in the backround in the overall sound presentation.
Just thinking out loud.

F1nut

Excellent point and I'd say you nailed it.

It's a Gen II. Thanks, I forgot to include that info.

DarqueKnight

Thanks for the report F1. This is on my "to do" list.

Polk65

This has been on my list of things to try since I read Raife's comment on it. Another is with the SDA 2B.

schwarcw

Very nice Jesse! I was wondering if you considered additionally by-passing the 5.8 uF cap with a 0.1?

I recalled your reply to a thread several weeks ago when I was wondering about using the RD-0198 tweeters in my CRS's. Since the CRS has two tweeters, and even though one of them is in the SDA circuit, would I still have the same "background or set back" vocal image? I'm interested in your perspective.

It would be fun to do a side by side comparison, one speaker with the RD-0194's and simple upgrades of the caps, resistors, etc., and the other using a pair of RD-0198's with the additional cap in the tweeter circuit. Of course this would be a $100+ experiment:(

I am going to get off my lazy but this Summer and upgrade these CRS's. I'm going to get a copy of each schematic from Ken. If you or anyone has a pdf, I would appreciate a copy via email.

Is there a reason Mark didn't put the SDA schematics on the sticky

F1nut

I had not considered that as there is no bypass cap shown in the schematic and I figured the boys at Polk knew what they were doing. Having said that, it certainly wouldn't hurt to try it.

You can't use the RD0198-1 in the CRS's. As for how the vocals would sound using the RD0194-1 in your CRS's, I just don't know. After you install them, let us know.

Zen Dragon

F1nut wrote:

I had not considered that as there is no bypass cap shown in the schematic and I figured the boys at Polk knew what they were doing. Having said that, it certainly wouldn't hurt to try it.

This reverts back to the whole bypassing discussion in general. The smaller cap has a much shorter charge and discharge rate than the larger one and passes transients and harmonic info quicker. It can also smear the signal on the other side due to portions of the signal arriving fractionally quicker, which may or may not be perceived by the human ear as warmth. Anyway Sonicap claims the Gen II is a little more colorful with more mid bloom.
As I read the schematics the 12uf is sort of the gateway capacitor to both the high frequency tweeter circuits. The smaller value cap, which you have changed to a 5.8uf sends the higher portions of the signal to the lower tweeter. As such bypassing it with a Gen II, would change the signature of the sound in the higher part of the high frequencies, if at all.
Might be interesting to try if you were curious, but if it aint broke....

F1nut

As I read the schematics the 12uf is sort of the gateway capacitor to both the high frequency tweeter circuits. The smaller value cap, which you have changed to a 5.8uf sends the higher portions of the signal to the lower tweeter.

Ummmm......I think you're mixing up your schematics. I didn't change the value, I added the 5.8uF and there is only one tweeter in the CRS+.

Zen Dragon

Oh, Duh. I was looking at my SDA-1C schematic. Too many diagrams floating around in my audio folder these days.

BSUfbfan

Good write-up Jesse. I am going to order all of the parts, but do the x-over upgrade first, then swap from the RDO-194's to the 198's(with 5.8 cap). Should be an interesting project.

Is there a website you would recommend to order the x-over parts? I'm assuming most would use Parts Express?

Thanks again.

schwarcw

If your going to use Sonicaps, the website is:http://www.soniccraft.com/ I personally used the Sonicaps with success. You may want to call them and talk with Jeff. He'll spend a little time to tell you about his caps and speaker crossovers in general. Others on the Forum have used Solens for their upgrades. I believe the Parts Connexion has the Solens and Mills resistors. Try this link: http://www.partsconnexion.com/

Zen Dragon

A couple other links for you. First an EBAY seller who stocks many Solen caps and quality resistors at good prices. No affilliation.

http://stores.ebay.com/Precision-Loudspeaker-Components

Also the Sonicaps can also be purchased at GR research in Texas. I beleive they are directly affilliated with Sonic Craft as the prices are identicle and they were able to give me Jeffs phone number at Sonic Craft. I used GR research because they were closer to me so quicker shipping.

http://www.gr-research.com/#

F1nut

I don't know what the results would be using Solens, so I'd recommend using Sonicap.

BlueMDPicker

Great write-up, Jesse. I assume you are still driving them with the MF gear?

Dibs on those nasty "old" RD0194-1s!

BSUfbfan

BlueMD - You've got dibs on the "old" 194's

Talked to Ken at Polk today and got the confirmed 4.1TL updated schematics on the way. After our converstation I will probably start with the 5.8 uF Sonicap and RDO-198 tweeters, spend some time listening, and then upgrade the rest of the x-over to Sonicaps at a later date. This should give me a good evaluation of the sonic difference at each stage of upgrade.

For anyone looking to possibly do this modification/update, Jesse's opinions and comments are highly regarded by Polk CS.

With the backing that Polk gives these "old" speakers, and their generally outstanding customer service, why would anyone not have a set of Polk speakers to grace their listening room?

hoosier21

cool project Jesse, wish I would take the time to do this to my CRS+'s, but I know I never will

Strong Bad

Jesse:

What would you recommend for my 2.3's (non TL version) with the silk domes I replaced out last year? I have the replacement tweeter cutoff switches I got from Ken several years back, but never replaced them.

Talk to me boy!!!!


John

dorokusai

Paul DiComo talked about this project on his CRS's, at the first SC Polkfest. It's kinda neat to have a truly unique speaker.

Rock on Jesse!

schwarcw

John,

Try this link to see what I did with my 2.3's http://www.polkaudio.com/forums/showthread.php?t=35837&highlight=2.3+crossover+upgrade

BobMcG also did his 2.3's, here's his link: http://www.polkaudio.com/forums/showthread.php?t=31294

Very similiar work, different caps.

Carl

F1nut

John,

Good links provided by Carl, if you have any questions or whatever, call me.

BSUfbfan

Well, prior to ordering the Sonicaps for the 4.1TL upgrade, I decided to pull my crossovers out now that my schematics have shown up from Polk, and WOW :eek: , they don't look anything like Jesse's. Apparently Polk made the blade/blade CRS+ from 1986-1988, and these CRS's use (2) MW6510 in-leiu of (1) MW6510 and (1) MW6511 so this portion of the crossover is very different. The tweeter portion of the crossover looks to be the same with the exception of a second 2.7 ohm resistor in parallel with the 0.4 mh coil.

Only the pin/blade schematic shows the "upgrade" to the 4.1TL, so I am hoping you experts can help me decide if it would be acceptable to try it on the blade/blade crossover. I have enclosed some pictures to make it easier to follow what I am saying.

I would like to add a 5.8uF sonicap (for the RDO-198's), replace the 12uF with a sonicap, yank the silver mica (which appears to be piggy-backed to the 12uF) and replace with a .1uF Sonicap. Any other suggestions? Should I remove the secondary 2.7 ohm resistor?

Thanks for any pointers.

DarqueKnight

There were two versions of the CRS+:

1. The blade/blade version made from 1986 to 1987.
2. The pin/blade version made from 1987 to 1990.

The "TL" upgrade was only specified for the pin/blade CRS+. Replacing existing components with higher grade components is fine. I definitely would not advise adding new components or deleting existing components unless specified by Polk. This is especially true of the resistors in the tweeter circuit, which, among other things, prevent the tweeters from receiving too much power.

F1nut

Well, that changes everything.

BSUfbfan

I don't see what it would hurt. Both models were originally designed for the SL-2000, so mimicking the crossover on the later pin/blade schematic can't hurt anything. It would be easy to just upgrade the caps and take a listen, but the results that Jesse has had with his 4.1TL's may prove to be too hard to resist....;)

F1nut

Mike,

I've looked over the schematics and the high frquency circuit is the same except for the extra resistor, also it's unclear what gauge the inductor is, which may be a factor in adding the extra resistor. I would suggest asking Ken Swauger to talk with one of the circuit designers at Polk before trying the TL upgrade. I also noted the use of two 130uF caps per crossover. That pretty much limits your cap selection for the low end to Solen.

honestaquarian

Zen Dragon wrote:

Very nice work and great write-up. Fascinating info there. For the .1uf cap in place of the silver mica, did you use the Gen I or Gen II Sonicap?
Just a theory on the replacement tweeter not quite sounding right on vocals. Polk was not staffed by a bunch of dummy engineers and they had to know there was a spike at the resonant frequency of the SL2000 tweeter. Perhaps their selection of capacitor values were partially aimed at compensation for that spike. It could be designed to repress certain frequencies.
When replacing with a much flatter response tweeter, and still having said frequencies repressed, those frequencies could tend to sit in the backround in the overall sound presentation.
Just thinking out loud.

I was wondering about that in my post about the oil can resonance of the SL-2000 tweeter and whether or not the was a notch filter in the crossover of the SDA-1C's to compensate for this.Every response that i got said there was no such filter.I am not getting recessed vocals now that i am using the RD-0194's however.Any opinions on this F1nut and Zen Dragon?

F1nut

That would be correct, Polk never used a notch filter in any of the SDA's. As for why you don't notice the recessed vocals, I couldn't say for sure. As you well know, there are so many variables involved in sound reproduction that it could be anything from the room, to the gear, to the circuit, to almost anything. One thought on the subject, it might only happen with the single tweeter CRS+, perhaps having two or more tweeters and therefore a different circuit, counter acts or prevents the issue.

reeltrouble1

but you coulda saved the trouble by just setting them up right.;)

Cool.

RT1

F1nut

Waaaaaaaaaaaaaaaaaaaa

schwarcw

BSUfbfan,

I'm curious to know how you proceeded with your crossover upgrade?

I have a pair of CRS's and I plan to upgrade the caps and tweeters, but I don't think I want to ventrue into the project that Jesse did to convert to a 4.1.

My plan is to use the Solen caps because fo the size difference compared to the Sonicaps. I've used the Sonicaps in my SDA-2's and SRS 2.3's. I figured that I wanted to try something a little different. Plus the cost of the Sonicaps for this part time speaker is a little hard to swallow. The RD-0194's alone will cost me more than what I paid for the CRS's.