SDA SRS 2 Crossover Parts list

Systems

inspiredsports wrote: »

EDIT:

I can't tell for sure if Matt said 2.7, or if DJ just assumed because that is the value used in the SDA-2B and CRS+ mods. I guess I should get clarification because I don't want this to be wrong.

Matt wrote, "Yes, that modification should work. The 5uf cap, also known as a "By-pass cap", should only be added across the resistor that is in series with the input signal and not the one that is in series with the small inductor."

OK,then if Matt was refering to the 2B he would have meant the 2.7 R because that is the only resistor in series with the top tweet and input signal.Adding the 5.8uf would effectively do in the 2B what the 2.7R 4.4uf combo is doing in the 1B.IMO you should not add the 5.8uf to the 1B xover as the 4.4uf 2.7R combo are already their for the same purpose.Having 2 such circuits in series will likely cause frequency response issues. IMO.

heiney9

GV#27 wrote: »

Im still not clear what model MP was refering to,was it the 1B?

Me either........I thought DJ was referring to a different model SDA with a different x-over config.

inspiredsports

GV#27 wrote: »

As well as the cap you added,the 3.5R ,12uf ,2.7R and 4.4uf are inseries with the input signal.

(And don't forget those 0.4mH inductors) I don't get continuity from the black post signal input post to any of the three 2.7R's on the board, but I guess it could be my VOM can't power through the 12uf cap ???

Anyway, Disc Jocky was specifically asking Matt Polk about "TL'ing" an SDA-1B (I quizzed him down on it THREE TIMES) and Matt's response leads me to believe we've got it right.

Worst case scenario, I'm out a few buck for the parts, and hour or three of my time, and I get a really wild sound.

If it really gets hairy, I've got 2 of these crossovers, 2 identical amp/preamps, and 5 spare MW6509's and a modded set of SDA-2B's so if the SDA SRS 2's melt down, I will still have tunes while I rebuild from the ashes

ben62670

GV#27 wrote: »

Having 2 paralleled RC combos cascaded in series seems just a bit odd.Adjusting the values in the 4.4uf 2.7R combo would make a lot more sense.


Im still not clear what model MP was refering to,was it the 1B?

If you adjusted the values on the 4.4uf 2.7r combo the lower tweeter wouldn't be 198 compatible. Really the XO could be reworked, but the Polk recommended mod is a simple solution that will work for the dual tweeter SDA's. I have tried many different types of multi tweeter SDA crossovers, and feel a single tweeter is best. The 2.3TL SDA's have near 90% of the power going through a single tweeter, and the 3.1TL's use only one tweeter. The high pass section of the SDA2b-TL modded XO would be my first choice omitting the bottom tweeters in the SDA-SRS2's, or the top tweeters of the 1B's 1C's.

The 1B, 1C, and SRS-2's use nearly the same HP XO.

Systems

inspiredsports wrote: »

I don't get continuity from the black post signal input post to any of the 2.7R's on the board, but I guess it could be my VOM can't power through the 12uf cap ???

Yes you won't get continuity through the cap,but the schem shows them to be in series.

Systems

ben62670 wrote: »

If you adjusted the values on the 4.4uf 2.7r combo the lower tweeter wouldn't be 198 compatible. Really the XO could be reworked, but the Polk recommended mod is a simple solution that will work for the dual tweeter SDA's. I have tried many different types of multi tweeter SDA crossovers, and feel a single tweeter is best. The 2.3TL SDA's have near 90% of the power going through a single tweeter, and the 3.1TL's use only one tweeter. The high pass section of the SDA2b-TL modded XO would be my first choice omitting the bottom tweeters in the SDA-SRS2's, or the top tweeters of the 1B's 1C's.

The 1B, 1C, and SRS-2's use nearly the same HP XO.

Im going to drop the subject because Im being a PIA,I just like to dig deep a try to figure things out.:D

inspiredsports

GV#27 wrote: »

Im going to drop the subject because Im being a PIA, but I just like to dig deep a try to figure things out.:D

Ditto. I've been at this both in the forum and behind the scenes since November. All I have been told is "No, the RDO198-1 won't work in the SDA SRS 2", but I'm a stubborn SOB (just ask my wife ).

The proof will be in the end result and I will report back here as soon as the mod is complete.

I appreciate your asking good, hard questions. You are an asset, and definitely NOT a PIA. Skepticism is the only way the right answer ever really seem to be drawn out (like my questioning DJ with the same question 3 TIMES; he must have thought I was thick, but I wanted it right before I fired up the soldering iron and wrecked these babies)

ben62670

GV#27 wrote: »

Im going to drop the subject because Im being a PIA, but I just like to dig deep a try to figure things out.:D

LOL. You are right, Polk is right. From Polk's perspective to re engineer the XO's would be costly, and not very feasible for the average modder to easily perform. Polk CS is awesome even supporting XO mods. To have to go past the usual replace same value with same value they would be incurring many headaches, and lots of man hours figuring out where people went wrong. The Polk solution keeps the tweeters in proper phase, and is a simple mod:)

inspiredsports

Ben, I know Sal wants to do this too, but also wants to use a non-common ground amp. Did I read a post somewhere where you wrote this ancient SRS 2 crossover could also be made to accomodate the AI-1, or am I hallucinating from listening to my just arrived Shotguns for 4 hours? (they do that to you, you know!)

ben62670

inspiredsports wrote: »

Ben, I know Sal wants to do this too, but also wants to use a non-common ground amp. Did I read a post somewhere where you wrote this ancient SRS 2 crossover could also be made to accomodate the AI-1, or am I hallucinating from listening to my new Shotguns for 4 hours? (they do that to you, you know!)

For him it wouldn't be hard. He has most of the drivers for the mod, and he knows this guy who is owes him a favor;) Seriously the biggest part of the mod is getting the 4 8ohm dimensional drivers.

Edit: had to change the value of the dim drivers...

inspiredsports

ben62670 wrote: »

For him it wouldn't be hard. He has most of the drivers for the mod, and he knows this guy who is owes him a favor;) Seriously the biggest part of the mod is getting the 4 4ohm dimensional drivers.

He's got double digit MW6509's and I have 4 or 5 myself from a buy I made on eBay from a local guy who lives up here right on Lake Erie (house was like 100 feet from the water).

Saw your PM and responded. gw

Conradicles

inspiredsports wrote: »

Lake Erie

Ahhh...brings back childhood memories of catching walleye and going to Cedar Point!:cool:

back to the thread...

inspiredsports...thanks for all of the good pics!

F1nut

Ah, Cedar Point and sailing/fishing/swimming/ice staking on the Sandusky river.......good times.



The rest of this stuff...ugh and good luck.

Disc Jockey

Just for the sake of clarity, here is both the question I asked and the answer I received:

Hello,
I forwarded your question to Matthew Polk:


"Yes, that modification should work. The 5uf cap, also known as a "By-pass cap", should only be added across the resistor that is in series with the input signal and not the one that is in series with the small inductor.

The inductance of the tweeter voice-coil causes the impedance to rise at high frequencies contributing to a gentle roll-off. The by-pass cap modification allowed us to compensate for that roll-off without disturbing the carefully tuned relationship between the tweeter and the drivers in the crossover region."

Regards, Ken, Polk Audio

---

Original Message

---

From:
Sent: Friday, November 21, 2008 2:40 PM
To: Swauger, Ken
Subject: HOME: Customer Service



I was wondering if it is possible to do the so-called "TL" modification to
the SDA 1B to allow it to use the RD0198 tweeters. This would be the one
done to the CRS+, adding a 5uf cap in parallel with the 2.7ohm resistor.
And if I can do this, do I need a cap for each of the 2.7 ohm resistors in
the tweeter circuit or just one of them. Thanks a bunch.
......

As to why I asked about a 5uf instead of a 5.8, I have no idea but my guess is it was simply a typo or error in my part. I can't remember the specifics of a three month old e-mail. I know I did assume that the bypass caps would go across a 2.7 ohm resistor as that's how it was done in the crs. At that time, I did not really understand how a bypass cap works. I understand a little more now, but not nearly enough.

Ben, I don't understand how adjusting the values on the 4.4uf/2.7r value makes the lower tweeter incompatible with the 198. It seems to me that adjusting that value lets the upper tweeter take advantage of a 198's better top end while leaving the lower one unchanged.

I'm thinking about experimenting with this on my 2A's. I've got a couple of 198s around, just need some caps...

Disc Jockey

After reading that again Ben, I think I see what you're saying. The inductance/roll-off would need to be compensated for in both the upper and lower tweeters. But is that the case? I don't know enough to be able to tell if the lower tweeter is reproducing the higher frequencies also. But if it is not, the lower tweeter does not need to be compensated for the inductance/roll-off issue, right?

ben62670

You have good idea of what is going on:). The lower tweeter does roll of the highs before the impedance swing would really have an adverse effect on the performance. The slope wouldn't be as much of an issue as the phasing if someone was modding just one of the tweeters components.

Disc Jockey

That resistor is already modded with a 4.4uf cap, would changing it to a 5.8uf cap affect the phase that much?

inspiredsports

Disc Jockey wrote: »

That resistor is already modded with a 4.4uf cap, would changing it to a 5.8uf cap affect the phase that much?

I'm not well versed from the electronics side of this discussion, but I will share that when I was researching "TL'ing" my SDA-2B's, I was told by multiple sources it was important to get a 5.8uf cap. Sonic Craft has a stock value of 5.6uf, but they can custom value to whatever you need and I was urged to order the .2uf difference from 5.6uf up to 5.8uf. It cost about a buck so there was certainly no financial gain motive behind the advice.

I would extrapolate if that tiny .2uf jump makes a difference, a jump from the 4.4uf cap to a 5.8uf cap would dramatically alter the sound output characteristics of the RDO198-1's.

Disc Jockey

The emphasis on the correct value, I believe, relates to the frequency range that is being passed by the capacitor and I would assume that needs to be as accurate as possible, which is where the insistence on getting the exact value comes in.

Ben's issue was one of phase, which I interpret more as a timing issue. In other words: Would increasing the cap value on the upper tweeter slightly delay its excursion and put it out of sync with the lower tweeter, potentially smearing the sound? What I don't know is if there is much, if any, difference in delay (phase) when switching from a 4.4 to a 5.8.

Systems

Ooops.

Systems

Ok I lied,I'm back to give the horse another kick and to make a comment regarding the purpose of the 5.8 uf cap added parallel to the 2.7 res.
Its purpose is strictly to add a bit of boost at the very top of the tweeters response,it does not change the slope or the frequency of the crossover.

This boost is intended for the main tweeter only,as it would be counterproductive to add this boost to the second tweeter as by design its top end is purposely being rolled off by a coil.

Using the 1B as an example the 4.4uf 2.7 ohm combo will have no affect on the second tweeter.Matts email is rather vague but he may well have meant for the 5.8uf to be in the position occupied by the 4.4uf.This makes the most sense to me,because just adding another boost stage ahead of the 4.4uf 2.7 combo does not seem correct.
Without clearer documentation this merely becomes a guessing game and we are into CL35 cap tweak territory.:D

Disc Jockey;1013078]

I don't know is if there is much, if any, difference in delay (phase) when switching from a 4.4 to a 5.8.

There will be no phase differences between these values,what changes is the frequency range that gets boosted.;)

Disc Jockey

GV#27 wrote: »

Ok I lied,I'm back to give the horse another kick and to make a comment regarding the purpose of the 5.8 uf cap added parallel to the 2.7 res.
Its purpose is strictly to add a bit of boost at the very top of the tweeters response,it does not change the slope or the frequency of the crossover.

This boost is intended for the main tweeter only,as it would be counterproductive to add this boost to the second tweeter as by design its top end is purposely being rolled off by a coil.

Using the 1B as an example the 4.4uf 2.7 ohm combo will have no affect on the second tweeter.Matts email is rather vague but he may well have meant for the 5.8uf to be in the position occupied by the 4.4uf.This makes the most sense to me,because just adding another boost stage ahead of the 4.4uf 2.7 combo does not seem correct.

There will be no phase differences between these values,what changes is the frequency range that gets boosted.;)

Thanks for changing your mind You're right as far as the response being a bit vauge but I think you are correct in where to place the cap. A "double boost" would not make sense to me either. Plus that would require the 5.8uf cap to go over a 2 ohm resistor and not a 2.7, which is what I asked about. I did not think that there would be any significant phase changes so I am glad to hear there wouldn't be any at all I just didn't know enough to assume that.

So there you go inspiredsports. Most likely that's the scenario, but Matt may be the only one who knows for sure.

Systems

Disc Jockey wrote: »

Thanks for changing your mind

Thanks,I tapped out lastnight due to lack of sleep,my bed was calling.

inspiredsports

With my limited EE training, I made the assumption Matt was talking about the first resistor in the circuit (2 ohm on the SDA-1B board and 3.5 ohm on the SDA SRS 2 board) as it registered continuity with the + (input) terminal, not realizing the 12uf capacitor was breaking continuity to the three 2.7 ohm resistor.

After carefully studying the schematic, I agree Matt COULD have been talking about the 2.7 ohm resistor already bridged with a 4.4uf capacitor (he clearly excluded the two 2.7 ohm resistors that are in series with the 0.4mH inductors).

What I'm concerned about is his wording. You would have thought he would have written something like, ". . . the 4.4uf cap should be REPLACED with the 5.8uf cap . . ."

Instead he wrote, ". . . the 5uf (we think should read 5.8uf) cap, also known as a "By-pass cap", should only be ADDED across the resistor that is in series with the input signal . . . ".

Since he said ADDED, that makes me think the 4.4uf was not to be removed. I'm also afraid the 5.8uf not being in the + (input) path to the Bottom Tweeter would be problematic.

Any thoughts?

inspiredsports

Disc Jockey, when you were corresponding with Polk, were you only speaking in terms of replacing the TOP SDA-1B SL2000/RDO194-1 tweeter with the RDO198-1?

I keep looking at the various schematics and it sure does make sense that replacing the 4.4uf would work. That would be "close" to replicating the circuit in the "known good" SDA-2B / SDA CRS+ TL mods that F1 pioneered, but with the exception of the EXTRA (2 ohm/SDA-1B or 3.5 ohm/SDA SRS 2) first resistor in those circuit paths.

If the mod was done REPLACING the 4.4uf cap with a 5.8uf, you would be able to upgrade the top tweeter only with the RDO198-1 as the circuit would not support the upgrade in bottom tweeter location. I wonder if it would sound weird leaving the bottom tweeter alone? It is rolled off several decibels so it may not be a problem that way.

I just wish Matt would have used the word "replace" in his correspondence if that is what he meant.

Recapping, your suggestion only seems to make sense if you are replacing just the top tweeter location.

Disc Jockey

Yes, it would have been nice if Matt were more specific, but his lack of specificity is just a direct reflection of the ambiguity of my questions. It does give us an opportunity to get our learn on though

When I wrote that, I was thinking of replacing both tweeters. There is no reason why you couldn't replace both with only the addition of the one 5.8uf cap. That cap does not really make the 198 "supported", all it does is compensate for the high frequency roll-off by boosting those levels. Since the lower tweet is not reproducing those frequencies anyway, the boost is not needed. The lower tweeter does not need, and should not see, that 5.8uf cap. In fact, as GV pointed out, it would be counterproductive as the top end is supposed to be rolled off.

Replacing the 4.4 with the 5.8 is the only thing that makes sense. The 5.8 was selected to bypass/boost a certain frequency range. If you added that 5.8 to the 4.4, that's now a 10.2uf value and you would be boosting some frequencies that are not called for.

If you placed the 5.8 over the 2 ohm resistor, the full desired frequency would bypass the first resistor, but only a smaller portion would bypass the second resistor with the 4.4uf. So again, you would not be boosting/bypassing the correct frequency range.

This is what makes the most sense to me and "compensates for the roll-off without disturbing the carefully tuned relationship between the tweeter and the drivers in the crossover region."

inspiredsports

Disc Jockey wrote: »

Yes, it would have been nice if Matt were more specific, but his lack of specificity is just a direct reflection of the ambiguity of my questions. It does give us an opportunity to get our learn on though

When I wrote that, I was thinking of replacing both tweeters. There is no reason why you couldn't replace both with only the addition of the one 5.8uf cap. That cap does not really make the 198 "supported", all it does is compensate for the high frequency roll-off by boosting those levels. Since the lower tweet is not reproducing those frequencies anyway, the boost is not needed. The lower tweeter does not need, and should not see, that 5.8uf cap. In fact, as GV pointed out, it would be counterproductive as the top end is supposed to be rolled off.

Replacing the 4.4 with the 5.8 is the only thing that makes sense. The 5.8 was selected to bypass/boost a certain frequency range. If you added that 5.8 to the 4.4, that's now a 10.2uf value and you would be boosting some frequencies that are not called for.

If you placed the 5.8 over the 2 ohm resistor, the full desired frequency would bypass the first resistor, but only a smaller portion would bypass the second resistor with the 4.4uf. So again, you would not be boosting/bypassing the correct frequency range.

This is what makes the most sense to me and "compensates for the roll-off without disturbing the carefully tuned relationship between the tweeter and the drivers in the crossover region."

Thanks again for the good logic,

I guess one thing we are certain of is that the SL3000 / RDO198-1 works very well with the series circuit path of . . . input wire (+) ---> to 5.8uf cap paralleled with a 2.7 ohm resistor ---> to 12uf cap ---> to tweeter. This is the tried and true "F1-Nut" mod now used successfully by everyone when they mod the SDA-2B and CRS+.

I guess the (larger than the SDA-2B and CRS+) SDA-1B has the additional 2.0 ohm resistor in the input path, and the even larger volume cabinet SDA SRS 2 has a 3.5 ohm resistor in its input path as a means of "fine tuning" the tweeters to the larger cabinets.

If that is true, leaving the existing "tuning resistor" in place, replacing the 4.4uf with a 5.8uf, and disconnecting the second (lower) tweeter from the array might be a workable plan.

I'm just still leery of what would happen to the sound of the lower tweeter if you upgraded it to the RDO198-1 without adding the 5.8uf that is always present with the other upgrades that add just one 198.

I could be wrong here, but a last concern is that I believe the SL3000 / RDO198-1 is a higher impedance tweeter than the SL2000 / RDO194-1.

I'm sorry to keep belaboring the points, but I want to get it right the first time and am depending upon these educational posts. As I've said before, I'm a "marketing guy" with a hobby/passion that exceeds his electrical knowledge.

Disc Jockey

My guess is that the 194 and the 198 are fairly similar in the lower part of the impedance curve, and diverge towards the higher frequency range. Otherwise the 2B and crs+ upgrades wouldn't be possible. Ultimately, you're going to have to decide what you want to try, or try and get a definitive answer from Polk CS.

Systems

Disc Jockey wrote: »

Yes, it would have been nice if Matt were more specific, but his lack of specificity is just a direct reflection of the ambiguity of my questions. It does give us an opportunity to get our learn on though

When I wrote that, I was thinking of replacing both tweeters. There is no reason why you couldn't replace both with only the addition of the one 5.8uf cap. That cap does not really make the 198 "supported", all it does is compensate for the high frequency roll-off by boosting those levels. Since the lower tweet is not reproducing those frequencies anyway, the boost is not needed. The lower tweeter does not need, and should not see, that 5.8uf cap. In fact, as GV pointed out, it would be counterproductive as the top end is supposed to be rolled off.

Replacing the 4.4 with the 5.8 is the only thing that makes sense. The 5.8 was selected to bypass/boost a certain frequency range. If you added that 5.8 to the 4.4, that's now a 10.2uf value and you would be boosting some frequencies that are not called for.

If you placed the 5.8 over the 2 ohm resistor, the full desired frequency would bypass the first resistor, but only a smaller portion would bypass the second resistor with the 4.4uf. So again, you would not be boosting/bypassing the correct frequency range.

This is what makes the most sense to me and "compensates for the roll-off without disturbing the carefully tuned relationship between the tweeter and the drivers in the crossover region."

Great post DJ,it nicely sums everything up.

inspiredsports

GV#27 wrote: »

Great post DJ,it nicely sums everything up.

Agreed. In rereading everything over and over today, Matt simply could not have been talking about the 2.0 ohm resistor position. There are three 2.7 ohm resistors on the circuit board and he chose his words to single out the 2.7 that was not sequenced with an inductor.

5.8 caps arrive Friday so sometime this weekend I'm going to desolder the 4.4uf cap, solder the 5.8uf in its place, replace just the top tweeter with an RDO198-1, leave the RDO194-1 in the bottom position alone, button it back up and give it a listen.

After a good listen I will swap out the lower 194 with a 198 to see if that yields any improvement

Thanks to all who offered great insight!