SDA 2B "TL" mod

mhollida

Gentlemen

Great forum, really glad I found it and all the great suggestions to improve the SDA speakers.

I recently dug out my old SDA 2B speakers (Been stored for 10+ years) and hooked them back up. I bought them new and enjoyed for many years. Moved on and did the HT thing. But now I have a dedicated room and set up for 2 channel music and want to upgrade by 2B.

My plan (Per the advise on this forum) is to:
> Redo the crossovers with new caps and resistor (considering several types)
> Dyna mat and Mortite for the drivers, probably do t nuts for driver mounting
> New binding posts both inputs and SDA cable
> Build a MDF base with spikes
> New 198 tweets (TL mod) also remove the poly switch
> Any other suggestions (Willing to put some $ into them)

This is where my question comes in
TL mod for the new 198 tweeters:
My understanding is that a 5.8uf cap need to be added
Seen several posts on this mod but only one "schematic"
This schematic shows the 5.8uf cap in parallel with the 2.7ohm resistor in the tweet crossover.

+......poly...X....2.7ohm.....X....12uf.............tweeter

X.....5.8uf......X

So X is where the new capacitor parallels with the 2.7 ohm resistor.
Is this correct?


Also removing the polyswitch. Read where this is roughly .5ohm so should the resistor be changed to 3.2ohm (2.7 + .5) to compensate for the removal?

Im one who likes to work with schematics as to be fully clear. I will probably build new boards for the crossover's and separate them form the large inductor to minimize any filed affects.

I still remember the dropped jaw look on friends faces when I played Pink Floyd Dark side and the clock bells sounded like they came from way outside the walls of my room. These were my first "high end" speakers driven with a Carver M1.0 and NAD preamp. Really great memories. Looking forward to bringing them up to the next level.

Thanks for your help

Mark

inspiredsports

Welcome to the forum Mark.

When I did mine, I started a post at http://www.polkaudio.com/forums/showthread.php?t=74945. There are quite a few photos in it that will help you out and post #54 has a few of the finished product.

Schematics for the 2B are in post #3 of this thread http://www.polkaudio.com/forums/showthread.php?t=55888

In the schematic from the + (black) pole, it shows "jumper", "safetyguard", and then the 2.7 ohm resistor that is the one that gets the 5.8 bypass cap to "TL".

I've heard it 2 opionons concerning making up the .5 ohm value of a removed polyswitch:
1) just bypass with good quality wire and don't worry about it
2) add a quality .5 ohm resistor in its place

I dont think you want to increase it to 3.2 if you are TL'ing as that is the 2.7 ohm cap that gets the 5.8uf bypass added to accomodate the RDO-198 tweeter used to complete the "TL" mod (RDO-194 is the direct replacement for the stock SL-2000 if you are not adding the 5.8uf bypass cap)

Greg

F1nut

Do not use T-nuts! Use these instead unless you can get Larry's rings. http://www.parts-express.com/pe/showdetl.cfm?PartNumber=081-1080

With the use of the hurricane nuts or Larry's rings, you do not need Mortite.

Build a MDF base with spikes

Why build a base?

This schematic shows the 5.8uf cap in parallel with the 2.7ohm resistor in the tweet crossover.

Yep.

Also removing the polyswitch. Read where this is roughly .5ohm so should the resistor be changed to 3.2ohm (2.7 + .5) to compensate for the removal?

You could do that.

I will probably build new boards for the crossover's

Forum member gimpod is selling custom SDA boards at a very resaonable cost. You can always remote mount them if you don't want to attach it to the inductor.

On3s&Z3r0s

mhollida wrote: »

...Im one who likes to work with schematics as to be fully clear. I will probably build new boards for the crossover's and separate them form the large inductor to minimize any filed affects.

Welcome! These custom boards get my vote too. I just did a 2B TL with them, and they are about the most foolproof solution you could imagine.

I did everything you described less the mortite, and however you do it I think you'll like it when you're done. It's a pretty substantial difference. Good luck!

Also, mentions of the removal of the "Silver Dipped Mica" cap in the schematic seem to be pretty rare. But it seems to be universal that in any crossover rebuild that is removed/not replaced.

mhollida

Great info!

Thanks all who responded.

I will go forward with the project. Those new CO boards look really nice.

BTW I have a pair of SDA 1 (not sure of series) 15" passive, 2 drivers, 2 sda drivers, 2 tweeters (1 sda) I think these would be 1A maybe?

I bought them off Ebay several years ago and they are in storage in the loft of my garage.

Worth doing any mods to?

Thanks
Mark

On3s&Z3r0s

My first pair of SDAs were the original 2's with two side-by-side tweeters (one dimensional). Pretty much the same as the SDA 1's, but with one less MW driver. I asked how much upgrading I should do to them, and the answers were mixed. The dimensional tweeter can make them sound a little echo-y, so the dominant answer was that it wasn't worth the $200 to upgrade all the tweeters. I still have them, but I haven't done anything to upgrade them yet.

Joe08867

On3s&Z3r0s wrote: »

My first pair of SDAs were the original 2's with two side-by-side tweeters (one dimensional). Pretty much the same as the SDA 1's, but with one less MW driver. I asked how much upgrading I should do to them, and the answers were mixed. The dimensional tweeter can make them sound a little echo-y, so the dominant answer was that it wasn't worth the $200 to upgrade all the tweeters. I still have them, but I haven't done anything to upgrade them yet.

They are very much worth upgrading. I love my original SDA2's. The third driver changes the feel of this speaker and I prefer it to the SDA2b's.

I upgraded all the tweeters and have gone back and forth with them hooked and unhooked and with the new RDO it isn't as echo-y as you would think. With the SL tweeters there was a ton of peaking issues that made the dimensional very fatiguing but the RDO cured all of this.

I also feel they have better bass response than the 2b. The lower mid is something they should have kept.

On3s&Z3r0s

Joe08867 wrote: »

They are very much worth upgrading. I love my original SDA2's. The third driver changes the feel of this speaker and I prefer it to the SDA2b's.

I upgraded all the tweeters and have gone back and forth with them hooked and unhooked and with the new RDO it isn't as echo-y as you would think. With the SL tweeters there was a ton of peaking issues that made the dimensional very fatiguing but the RDO cured all of this.

I also feel they have better bass response than the 2b. The lower mid is something they should have kept.

I like them a lot too, better than the stock 2B's on some stuff. Definitely agree about the bass, but I didn't really get the bass I wanted out of them until I fed them 200wpc. The 2B TL's have pretty outstanding bass so far on the 55wpc receiver I have them hooked up to for burn-in. I just don't know if it's quite as tight. I was planning on bringing the 2's back when the 2B's are burned in and doing a side-by-side comparison.

Also going back to the OP's question, I've been told that XO mods can be made to boost the volume on the stereo tweeter and disconnect the dimensional tweeter. I'd imagine that would be possible on the 1/1A's too, which would definitely eliminate the echo issue and would make upgrading much less expensive.

Tronman

On3s&Z3r0s wrote: »

I like them a lot too, better than the stock 2B's on some stuff. Definitely agree about the bass, but I didn't really get the bass I wanted out of them until I fed them 200wpc. The 2B TL's have pretty outstanding bass so far on the 55wpc receiver I have them hooked up to for burn-in. I just don't know if it's quite as tight. I was planning on bringing the 2's back when the 2B's are burned in and doing a side-by-side comparison.

Also going back to the OP's question, I've been told that XO mods can be made to boost the volume on the stereo tweeter and disconnect the dimensional tweeter. I'd imagine that would be possible on the 1/1A's too, which would definitely eliminate the echo issue and would make upgrading much less expensive.

On3s&Z3r0s - Did you ever do this and was wondering what your listening results were?

"I was planning on bringing the 2's back when the 2B's are burned in and doing a side-by-side comparison"

I just purchased a set of SDA-2A's and am going to do the TL mod to them. Already ordered the RDO-198's and the 5.8uf and also the 12uf cap for the tweeter
Got these from the Original Owner, he bought them back in 1984 and he kept them in immaculate condition - felt like I had to get out of there before he changed his mind as he was already have sellers remorse before I got there.

I'll let you know how the TL Mod goes but I need to finish up restoring my SDA-1C's before I start that one.

westmassguy

mhollida wrote: »

Gentlemen

Great forum, really glad I found it and all the great suggestions to improve the SDA speakers.

I recently dug out my old SDA 2B speakers (Been stored for 10+ years) and hooked them back up. I bought them new and enjoyed for many years. Moved on and did the HT thing. But now I have a dedicated room and set up for 2 channel music and want to upgrade by 2B.

My plan (Per the advise on this forum) is to:
> Redo the crossovers with new caps and resistor (considering several types)
> Dyna mat and Mortite for the drivers, probably do t nuts for driver mounting
> New binding posts both inputs and SDA cable
> Build a MDF base with spikes
> New 198 tweets (TL mod) also remove the poly switch
> Any other suggestions (Willing to put some $ into them)

This is where my question comes in
TL mod for the new 198 tweeters:
My understanding is that a 5.8uf cap need to be added
Seen several posts on this mod but only one "schematic"
This schematic shows the 5.8uf cap in parallel with the 2.7ohm resistor in the tweet crossover.

+......poly...X....2.7ohm.....X....12uf.............tweeter

X.....5.8uf......X

So X is where the new capacitor parallels with the 2.7 ohm resistor.
Is this correct?


Also removing the polyswitch. Read where this is roughly .5ohm so should the resistor be changed to 3.2ohm (2.7 + .5) to compensate for the removal?

Im one who likes to work with schematics as to be fully clear. I will probably build new boards for the crossover's and separate them form the large inductor to minimize any filed affects.

I still remember the dropped jaw look on friends faces when I played Pink Floyd Dark side and the clock bells sounded like they came from way outside the walls of my room. These were my first "high end" speakers driven with a Carver M1.0 and NAD preamp. Really great memories. Looking forward to bringing them up to the next level.

Thanks for your help

Mark

Gimpods boards are nice, but not a requirement. Sonicaps will fit just fine on the old board.
Dynamat, yes, Mortite, no. Larry's rings, or Hurricane nuts, and Armacell, ONLY if the existing gaskets were damaged during removal.
New Binding Posts, yes. You can go expensive with Cardas or Vampire, but Parts Express has some nice alternatives, for a lot less.
Use SpeakOn Plugs and Sockets for the Interconnect, not Binding Posts.
New Spikes can be mounted to the existing cabinet bottom, no need for additional MDF Base.
The 5.8uf is a shunt for the 2.7 ohm resistor. I would keep the 2.7 ohm resistor, and the .5 ohm Polyswitch replacement resistor separate. It's easier to replace the .5 ohm if you need to adjust the overall tweeter level.
Consider Blackhole5 damping material behind the woofers.
Consider replacing the 16mh "Full Compliment Sub Bass Drive" Inductor with a lower DCR type, such as Erse SuperQ, for better low bass response.

westmassguy

Joe08867 wrote: »

They are very much worth upgrading. I love my original SDA2's. The third driver changes the feel of this speaker and I prefer it to the SDA2b's.

I upgraded all the tweeters and have gone back and forth with them hooked and unhooked and with the new RDO it isn't as echo-y as you would think. With the SL tweeters there was a ton of peaking issues that made the dimensional very fatiguing but the RDO cured all of this.

I also feel they have better bass response than the 2b. The lower mid is something they should have kept.

The third Woofer is there to make up for the lack of low bass from the Dimensional woofer. This was corrected in the 3rd generation 2As and 4th generation 2bs, when they added the "Full compliment Sub Bass Drive" circuit. A 2A or 2B, fully upgraded with low resistance Dimensional Inductors will easily match the 2s for bass response.

Schurkey

mhollida wrote: »

> New 198 tweets (TL mod) also remove the poly switch...
...TL mod for the new 198 tweeters:
My understanding is that a 5.8uf cap need to be added
Seen several posts on this mod but only one "schematic"
This schematic shows the 5.8uf cap in parallel with the 2.7ohm resistor in the tweet crossover.

You are not really "adding" a 5.8uF cap.

You are REPLACING an existing 4.4uF cap with a 5.8uF cap. It's a spec change, not an outright addition.

westmassguy

Schurkey wrote: »

You are not really "adding" a 5.8uF cap.

You are REPLACING an existing 4.4uF cap with a 5.8uF cap. It's a spec change, not an outright addition.

There's no 4.4uf shunt cap in a 2B crossover. the 5.8uf IS an added component

Schurkey

westmassguy wrote: »

There's no 4.4uf shunt cap in a 2B crossover. the 5.8uf IS an added component

My apologies. I'm thinking of the SDA 1B.

Tronman

Westmassguy

In order to get the "Consider replacing the 16mh "Full Compliment Sub Bass Drive" Inductor with a lower DCR type, such as Erse SuperQ" I assume you have to purchase a 17mh or 18mh and unwind some of the coil. Just wonder if anyone has done this before and has a suggestion such as - "buy a 17mh and remove five turns of wire."
Here is the 17mh: http://www.parts-express.com/erse-super-q-17mh-16-awg-500w-inductor--266-956 - ERSE Super Q 17mH 16 AWG 500W Inductor. Any info would be great as I would like to do this mod :-)

TennMan

Tronman, I don't mean to speak for Westmassguy but below is a copy of my comments from another thread about installing the ERSE Super Q 17mH 16 AWG inductors and unwinding them. You might find it useful.

TennMan wrote:

After spending some time listening to my 2BTLs with the Erse Super Q (17mh 16awg) inductors installed I can highly recommend them. They made a significant difference in the sound of my speakers. Not only did this mod improve the bass, it also seemed to make the mid range much more open sounding. Almost as if a curtain has been pulled back so you can clearly hear the speakers the way they were meant to sound. The highs are crisp and clean. Air core inductors might be better but these inductors (laminated steel core) are really a good bang for the buck. I think they should be installed at the same time anyone is doing the TL upgrade to a pair of 2Bs. The RDO-198 tweeters and the Erse Super Q inductors seem to compliment each other and make the 2BTLs sound much more balanced.

Getting the inductors right without a meter didn't work too well for me. After reading all the posts here on Club Polk about using these inductors I unwound 15 turns of wire off when I first received them thinking they would be close to where I needed to be (16mh). I didn't cut off the excess wire. Then I installed them and tested them out. At 15 turns unwound they just didn't sound right to me. The bass, although pretty deep, was weak to my ears and the SDA effect was not good. Thinking more was better I unwound another 5 turns off the inductors bringing the total to 20 turns unwound. That improved the SDA but the bass still just seemed wrong. At that point I realized I shouldn't continue flying blind so I ordered a meter capable of measuring LCR.

Once I had the new meter in hand I checked my stock inductors and they measured close to 16mh as specified in the schematic. That told me the meter was working correctly. Then I checked the Erse inductors. To my surprise the LCR was just slightly over 14mh for both inductors so I began the job of winding turns back on the inductors. Let me tell you. That is hard on your hands if you keep the windings straight and tight. By the time I added enough turns back on both inductors to reach 15mh my hands were aching and cramping. At that point I decided it was time to do some testing to see if I was going the right direction to get the sound I was looking for. At 15mh the SDA was back to normal but the upper bass was a little too strong and the vocals were a little too much "in your face" for my liking.

Then I pulled the inductors back out and wound enough turns back on to get me up to 16mh (as specified in the schematic) and installed again for more listening tests. At 16mh the SDA was still good but I felt I had lost a too much punch in the upper bass that was excessive with the inductors set at 15mh. With that in mind I removed the inductors one more time and adjusted the LCR again. This time to 15.5mh (+- .05mh) and reinstalled. I know second guessing Polk might not be the best thing to do but for me that is where I feel they sound the best. I would agree that me thinking .5mh made a difference one way or the other might be psychological but hey, getting speakers to sound the way you like is what modding them is all about. At this point I have no intention of making more changes.

Thanks to all the forum members who wrote articles about using these inductors. Special thanks to westmassguy and OldmanSRS for convincing me to do this mod. You guys have helped me a lot with these speakers.

Here are a few things I learned from installing these steel core inductors.

1.) In my experience it would be hard to get the LCR right without a meter. It is a hit or miss proposition but it could be done.
2.) You need a good amplifier to drive your speakers with these inductors installed. The DCR of my 2bTLs dropped to 3 ohms, which was expected.
3.) Unwinding turns from the inductor is not linear. Each turn removed from the inductor doesn't change the LCR by the same amount across the inductor.
3.) You shouldn't use the meter to determine when your speakers sound the best. That is what ears are for.

Tronman

WOW now that is what I call the "Perfect" answer :-) thanks Tennman. I will use my meter when I do mine as that does not sound like fun at all rewinding a inductor. I have some some caps and resistors on order for the TL mod for the 2A's so look forward to the upgrade - should be a quick and fun mod.
I noticed the SDA 2BTL · Sonicaps · Mills resistors · RDO-198s · New gaskets · H-nuts · Erse inductors!!! How do you like them??

Tronman

sorry double post :-(

westmassguy

Tronman wrote: »

Westmassguy

In order to get the "Consider replacing the 16mh "Full Compliment Sub Bass Drive" Inductor with a lower DCR type, such as Erse SuperQ" I assume you have to purchase a 17mh or 18mh and unwind some of the coil. Just wonder if anyone has done this before and has a suggestion such as - "buy a 17mh and remove five turns of wire."
Here is the 17mh: http://www.parts-express.com/erse-super-q-17mh-16-awg-500w-inductor--266-956 - ERSE Super Q 17mH 16 AWG 500W Inductor. Any info would be great as I would like to do this mod :-)

TennMan is correct, you'll need an accurate LCR meter to unwind the larger coil. I've done it many times, on many different SDA Models

Phasewolf

When I did mine I just went with the 15mh inductor and was happy with how it sound. But that was me your results may very.

westmassguy

Phasewolf wrote: »

When I did mine I just went with the 15mh inductor and was happy with how it sound. But that was me your results may very.

I did that with my CRS+s, and was able to get the 14 gauge. The change in low bass from them was astounding.

TennMan

double post

TennMan

Tronman wrote: »

... I noticed the SDA 2BTL · Sonicaps · Mills resistors · RDO-198s · New gaskets · H-nuts · Erse inductors!!! How do you like them??

I love them. They bring a smile to my face every night when I listen to them. Best sounding speakers I have ever owned.

Westmassguy did the crossover upgrades. I can highly recommend his work. He does professional work and the turn around time on getting repairs done is really fast.

The 2BTLs fead with the Adcom GFA-555 is a great combination when you add the Super Q inductors. You must have a good amp when you install the low DCR inductors that can handle a load of 3 ohms without problems.

Tronman

Got my RDO-194 and RDO-198's from polk today :-) but I'm sure as you guys know there is no markings on them as to which is which. Did my DCR measurement and I get 5.6 ohms and 6.6 ohms on the two pairs. Would you happen to know which one is which?? They are pretty looking I'll tell you that much - but they did no include the poly switch's for the crossover that I asked for. I will be ordering more stuff from them any way so will try next time.

Oh Tennman received the crossovers for the SDA-2B today for the bay look nice. They are from a sda crs II but what is neat is they actually have the SDA-2B sticker on them as they are the same crossover :-) so I could use those instead of the SDA-2A crossover - less expensive to upgrade.
Thanks for the input on the meter and the other values for the inductor I will give the values some thought or as an option.

Tronman

Forgot to mention that I will be changing one of the drivers to a MW-6511 if I do the 2B upgrade.

pitdogg2

Tronman wrote: »

Got my RDO-194 and RDO-198's from polk today :-) but I'm sure as you guys know there is no markings on them as to which is which.

the RDO198 has bigger tabs or A bigger tab.(connector)

westmassguy

The ground on the 198s is 3/16" the other is 1/8"

nspindel

Once upon a time a 16mH Erse Super Q was available, I used a pair several years ago. Cheaper to buy a more expensive inductor that's available in 16mH than to buy a meter. There are Jantzens, Northcreeks, and Solens all available in this size.

Stew

Phasewolf wrote: »

When I did mine I just went with the 15mh inductor and was happy with how it sound. But that was me your results may very.

Same here. Punchier mid bass and more deep bass. I like it!

Tronman

Ahhhh thanks for the help guys, once I knew what to look for I found this.