SDA2b life support

[jcandy]

I am trying to revive my uncle's SDA2Bs that suffer from (at least) the blown-tweeter problem. These speakers have great sentimental value: in fact, I drove them home myself in 1990, in a 1986 Honda Civic hatchback. I lost contact with him in the period 2002-2010, but recently he had a stroke :(. Now I am helping him to sell some items, and since I am a DIY audio fanatic, I offered to deal with the complete setup (also includes the high-end NAD pre-amp-tuner-cd from that era). The entire system was ridiculously expensive when purchased in August 1990 (seems like yesterday ...), and oddly enough, hasn't really been used for about 10 years. My uncle doesn't really like music!

Over the years, I believe two sets of replacement tweeters were ordered, but all tweeters he can locate are *dead*. I tested a random spare tweeter and this produced a roughly correct SPL, so I know there is a signal to the tweeters. The inner 6.5 driver is making NO sound, but I suspect this is because I don't have the SDA interconnect.

What should I do? Attempt to locate replacement tweeters, upgrade the crossover (I am comfortable with that), just sell them as-is, what

[helipilotdoug]

Welcome to Club Polk. :) Those 2b's are very good speakers, and can be fixed very easily. Polk Audio sells replacement tweeters for $48 each plus free shipping for Club Polk members. There are many tweaks and upgrades that can be done to them, which will make them outstanding speakers. The interconnect cable is very important, so try to find it. If you can't, you can find one, make one yourself, or get with ben62670 who makes them. Unless you really need to sell them, I'd keep them and do the upgrades below.

Here are some links that I have found very helpful and great reading. I'm sure there are more.

Most of the tweaks are covered in this great post started by TOOLFORLIFEFAN:
http://www.polkaudio.com/forums/showthread.php?t=97719

And another thread by nspindel that covers several tweaks:
http://www.polkaudio.com/forums/showthread.php?t=62106

Mortite:
http://www.polkaudio.com/forums/showthread.php?t=74524

Dynamat:
http://www.polkaudio.com/forums/showthread.php?t=52810

Hardware Rings:
http://www.polkaudio.com/forums/showthread.php?t=103241

SDA2B Crossover upgrade:
http://www.polkaudio.com/forums/showthread.php?t=87121

Hope this helps.
Doug

[inspiredsports]

Welcome to CP.

I have been down your exact path and will be glad to help as best I can.

I have TL'd 2B's (that I bought stock in 1987), an NAD 7600 receiver I bought the same day (7600 Receiver incorporate 1300 preamp, 4300 tuner and 2600 Amp in the same package). plus have owned and sold a 4300, and later purchased a 1700 preamp/tuner (incorporates 1300 and 4300) and a separate 2600A!

I've performed (with help) all mods possible on the 2B's, and all of my NAD components have been sent out for mods/caps/power upgrades within the past 12 months.

The gear in your photo can provide you with EXCEPTIONAL sound reproduction :)

Can you post images of the back with a closeup on the terminals / SDA interconnect socket?

[jcandy]

Here are some links that I have found very helpful and great reading. I'm sure there are more.

Thanks very much for the comprehensive reply! I appreciate it.

[jcandy]

I have TL'd 2B's (that I bought stock in 1987), an NAD 7600 receiver I bought the same day (7600 Receiver incorporate 1300 preamp, 4300 tuner and 2600 Amp in the same package). plus have owned and sold a 4300, and later purchased a 1700 preamp/tuner (incorporates 1300 and 4300) and a separate 2600A!

First of all, thanks so much for the speedy reply. Sadly, the CD player powers up but does not play, and the preamp has some contact problems when the tone controls are active.

Can you post images of the back with a closeup on the terminals / SDA interconnect socket?

Sure.

[inspiredsports]

Great, photos. You have the 1987 Pin/Blade model.

If you ever need to look at a schematic, go to http://www.polkaudio.com/forums/showthread.php?t=55888 and open up the SDA 2B 1987-pb Sch.pdf file.

[jcandy]

Status report: took one speaker apart and had a look at the internals and crossover. Yikes, what a MASSIVE air-core inductor -- 16mH! I suspect a proper replacement would be > $100.00, if somebody was willing to wind it for you. Someone on this forum, in describing a crossover tweak for the SDA2B, replaced this with a steel-laminate (SL) inductor. I am very suspicious of such a change, as the lower DCR of the SL inductor will alter the very-low-pass filter characteristics, perhaps for the worse, although I need to stare at the crossover schematic a little longer to make complete sense of the dimensional bit. Also, in the original crossover design, the huge magnetic field of this inductor will affect the other inductors. This was probably taken into account somehow in the original design. Has anyone seen FR plots for the unmodified and modified SDA2Bs? I wouldn't in a million years attempt to modify the crossover without such data. The SDA feature would be difficult to sort out in the measurement process, which is usually based on a mono MLS analysis.

That said, I pulled out the dead SL2000s and popped in a pair of Vifas I had lying around, and also built a temporary IC with some spare pin/spade connectors. The system sounded roughly correct, although bright (the Vifas are probably more efficient than the SL2000s). I didn't push the system hard, as cabinet leakage would muck up the bass response significantly.

Now I am re-gluing the side panels which had all but fallen off. I am a little afraid that the fit won't be super tight, but I'll know for sure tomorrow.

I guess the next step is to order a pair of the RDO-194 ...

[Joe08867]

Replacing the Air Core Inductor is really a waste of time. Replacing the caps is more the way to go.

The replacement RDO-194 is a very efficient speaker as well. If you decide to do the TL modification then you would want to replace the tweeter with the RDO-198. Considering your tweeters are shot I would vote you go that way.

[mmadden28]

^^^^ +1

Welcome to Club Polk

[Bobsama]

Replacing the Air Core Inductor is really a waste of time. Replacing the caps is more the way to go.

The replacement RDO-194 is a very efficient speaker as well. If you decide to do the TL modification then you would want to replace the tweeter with the RDO-198. Considering your tweeters are shot I would vote you go that way.

Though to add, iirc, you'll need to add resistance so that the RD0198's will play at the correct levels. Also take a few notes on where you set the speakers up. Placing them close to a wall reinforces bass response so you'll want to play around with them until you are happy. Also to note, the speakers are not to be toed in.

[mmadden28]

Though to add, iirc, you'll need to add resistance so that the RD0198's will play at the correct levels..

Correct-That is part of the TL mod.

[jcandy]

Replacing the Air Core Inductor is really a waste of time. Replacing the caps is more the way to go.

Yes, I can understand replacing the capacitors because of the tendency to degrade over time. Replacing the air-core inductor with steel-laminate could really be an *error*, since the two will differ significantly in DC resistance. Generally speaking, if you switch from air-core to SL in a low-pass filter, you will raise the level of the low-pass transfer function, accentuating the bass. Maybe this is the "bass slam" people spoke of :(

To put it another way, that massive air-core is a thing of beauty, one of the key components for the SDA effect, and will not degrade over time. I wouldn't mess with it.

The replacement RDO-194 is a very efficient speaker as well. If you decide to do the TL modification then you would want to replace the tweeter with the RDO-198. Considering your tweeters are shot I would vote you go that way.

Right. Maybe I just need to flip a coin! I really would prefer to leave the crossovers stock, as they appear to be functioning properly. The RDO-194 is a drop-in replacement as I understand it, and corrects the main fault of the SL2000, which was high-frequency peaking somewhere. It would be nice to see SPL traces for the SL2000, RDO-194 and 198 tweeters, otherwise its a bit like shooting in the dark.

[jcandy]

Correct-That is part of the TL mod.

Are there FR plots showing "before" and "after" the modification?

[inspiredsports]

. . . I really would prefer to leave the crossovers stock, as they appear to be functioning properly. The RDO-194 is a drop-in replacement as I understand it, and corrects the main fault of the SL2000, which was high-frequency peaking somewhere. It would be nice to see SPL traces for the SL2000, RDO-194 and 198 tweeters, otherwise its a bit like shooting in the dark.

RDO194-1's are a fine tweeter in their own right, but in my opinion, not as smooth and refined as the RDO198-1.

You could drop in the 194's without touching anything else, but then all you are doing is smoothing out the obnoxious (tiring) high frequency peak the SL2000's present. However, you would be missing much of the sound that was originally there when those now degraded 20 year old (and cheap) caps were new, plus listening to the noise even one cycle of protection imparted by the polyswitches.

In my humble opinion, just dropping in 194's won't give you much for your $100 investment.

At a minimum, the polyswitches should be replaced (or most including me would advise snipping and bypassing). But . . . snipping and bypassing requires adding back the .5 oms of resistance they imparted to the circuit, Now you need a higher impedance resistor (increase the 2.7 to 3.2). IF replacing, Polk will generally send them for a song.

What the heck, now that you're in that deep, it's easier to spend the same $48 on 198's and replace the caps too.

If you are keeping them stock, why not find 2 SL2000's for about $40 delivered and then you are economically back to 1990. (and can sell the SL's for the same $40 when you decide 198's are the right answer) :D

PS.: Remember, the SDA-2B "TL" mod was a Polk approved mod. Overall sound pressure levels with SL2000 and RDO198-1's, to my recollection, was very similar, but it has been a couple of years.

[jcandy]

RDO194-1's are a fine tweeter in their own right, but in my opinion, not as smooth and refined as the RDO198-1.

Please forgive my skepticism, but unless I see an FR plot showing the difference I would be afraid do it. What does smooth and refined mean in terms of frequency response, power response, and directivity? Once I get the speakers working I desperately want to do some far-field FR measurements. This will establish a sort of baseline performance. Maybe the RDO-194 just needs some minor response shaping or attenuation, which may be possible by just adding a series and shunt resistor (L-pad).

Um, sorry if I am coming across as a bit of a jerk here. I really do appreciate your feedback, information, etc :o

You could drop in the 194's without touching anything else, but then all you are doing is smoothing out the obnoxious (tiring) high frequency peak the SL2000's present.

Are you aware of any measurement which shows the location and magnitude of the peak?

However, you would be missing much of the sound that was originally there when those now degraded 20 year old (and cheap) caps were new

Yes, I am a little worried about degradation of the capacitors. This would be the main reason to make new crossovers.

In my humble opinion, just dropping in 194's won't give you much for your $100 investment.

Well, now I have no tweeters period (both originals are dead), so I will certainly get something! And I see people dropping ridiculous $$$ on "boutique" capacitors when simple Dayton/Bennic or Erse would be indistinguishable.

If I decide to modify the crossovers, what I would do is make new boards, leaving the original boards intact. I would only reuse the monster inductor. However, I would also mount the new boards on the bottom of the enclosure, rather than atop of the monster SDA inductor, so as to reduce the field interaction:

http://techtalk.parts-express.com/sh....php?p=1500176

Cheers!

[inspiredsports]

I hope you don't think I'm being critical and I hope I didn't come across that way.

I will say that I used to be from Missouri (the "Show me" state :D) and I have absolutely learned now to trust my ears versus empirical testing which in my opinion provides only a hint as to what you will hear.

I spent a lot of time (and money) trying to "snip the dog's tail off an inch at a time". Then at some point I just started to trust the guys here, especially F1 who may come across differently than the genuine Polk guru that he is, and others too numerous to mention so this does not become a CP commercial.

I now have some of that "boutique" stuff, and I won't bore you with details. However, here we are talking about Sonicaps (http://www.soniccraft.com/sonicaps.htm) where you get 93-100% (an A grade on any curve) of what the boutiques offer for just a few dollars more than caps you mention.

I don't know if Face has some of the quantitative stuff you are asking for, but if not you should get his qualitative opinion. There a probably 4 dozen guys here who have been around the block with Polk who can tell you much more than I. But if anything, next time I ABSOLUTELY will go with the boutique stuff, because the Polk SDA-2B design sounds absolutely that good.

[jcandy]

Lately I have been using Erse ($7.47 for 20 uF) capacitors:

http://meniscusaudio.com/20uf-250v-p-369.html

This is almost a factor of 4 cheaper than the equivalent SoniCap. For the large values needed by the SDA2B, I would probably go with Solen:

http://meniscusaudio.com/20uf-400v-p-321.html
http://meniscusaudio.com/40uf-400v-p-326.html

which are only slightly more than the Erse.

[Joe08867]

I am a big fan of Sonicaps. For the price they are tops in my book.

To go back a little. The SL2000 tweeter has a harsh spot in the upper end of its range that is irritating at best and annoying to most. I am sure this has something to do with Age and design but I prefer the sound of the RDO194.

Now as far as the RDO198 is concerned the TL modification we talked about changes the resistance to match that tweeter and really opens up the sound of those speakers.

I would look at the capacitors like mini batteries. Would you use a battery that was 20 years old or would you replace it with a brand new one? I would replace it. Even if it worked it is nowhere near the efficiency they get nowadays and will almost guarantee the speakers work well for another 20 years.

[Joe08867]

I was searching some older posts and it looks like the peak would be at 13khz on the SL2000. It has been noted in most magazine tests of the speakers back in the day and is attributed to the SL2000.

The SL3000 fixed this issue later on, but it was never made available for the SDA2's. And should not be used unless you do the TL mod.

[heiney9]

Lately I have been using Erse ($7.47 for 20 uF) capacitors:

http://meniscusaudio.com/20uf-250v-p-369.html

This is almost a factor of 4 cheaper than the equivalent SoniCap. For the large values needed by the SDA2B, I would probably go with Solen:

http://meniscusaudio.com/20uf-400v-p-321.html
http://meniscusaudio.com/40uf-400v-p-326.html

which are only slightly more than the Erse.

Except the Sonicaps are 7 times better sounding.

H9

[inspiredsports]

Except the Sonicaps are 7 times better sounding.

H9

+7 to that :D

[inspiredsports]

jcandy,

If you were to walk into a showroom (or find online deals) for brand new gear comparable to the stack of NAD's plus the SDA 2B's in the image in your first post, you would probably be laying out 6-7K.

Saving a few dollars on caps is admirable, but it does not do the system, especially the speakers justice.

But . . . I certainly do respect your desire to save money.

[inspiredsports]

Vintage SL2000's may be for sale here if pending sale fell through ... http://www.polkaudio.com/forums/showthread.php?t=105249 . . . and he's a very trustworthy Polkie if they are available

[jcandy]

Except the Sonicaps are 7 times better sounding.

H9

Really? When I am designing a crossover, how do I account for this dramatic variability in capacitors, other than by its capacitance? Let's assume we are talking about modern polypropylene capacitors. Is there a nonlinear shift in the capacitance or something?

It seems to me fiddling with inductors is probably worthwhile, since just rotating an inductor will change its inductance, as well as the inductance of all surrounding inductors. In designing my own speakers I tend to separate the woofer and tweeter filters so as to maximize inductor-inductor spacing. From this POV, the modified crossovers I see here, with hyper-expensive capacitors along side poorly-oriented inductors is telling.

I am ready and willing to believe there are audible differences between capacitors as soon as someone can "show me the measurements" as it were. In the meantime, its Erse/Dayton all the way.

[F1nut]

As long as you are stuck in the show me the measurements state of mind, audio nirvana will never be obtained.

Anyway, this is a great read. http://www.humblehomemadehifi.com/Cap.html

[jcandy]

jcandy,

If you were to walk into a showroom (or find online deals) for brand new gear comparable to the stack of NAD's plus the SDA 2B's in the image in your first post, you would probably be laying out 6-7K.

Saving a few dollars on caps is admirable, but it does not do the system, especially the speakers justice.

But . . . I certainly do respect your desire to save money.

Its not really about saving money, its more about not throwing it away. There's a significant difference. You see, when I look at (and in) the SDA2Bs, I see a very clever, innovative speaker, but with some problems that cannot be solved with the use of boutique capacitors, such as: inadequate bracing, poor inductor placement, 90 degree baffle edges, large tweeter-mid CTC spacing (which gives rise to lobing). The crossover on the tweeter is only second order which probably does not provide optimal power handling (obviously!). Measurement may uncover further problems. For example, its not clear what the distortion numbers are. This is a critical consideration when starting a new design, and also cannot be cured in the crossover. Instead, you have to start with a low-distortion driver like this one:

http://www.parts-express.com/pe/show...number=296-602

This will sound more natural/correct in the critical midrange than the Polk MW6503. Moreover, I do not understand the SDA crossover well enough at the moment to improve it. With something like a monitor 5/7/10 it would be easier.

Anyhow, I now have them up and running with the RDO-194s I picked up directly from the Polk Warehouse in Vista (just north of me). They sound very good (I have other "vintage" speakers from the 90s that sound horrific) but I can tell right away that the FR is not flat. I want to do some measurements to verify this, but have to figure out how to manage that with the SDA effect.

[F1nut]

You see, when I look at (and in) the SDA2Bs, I see a very clever, innovative speaker, but with some problems that cannot be solved with the use of boutique capacitors, such as: inadequate bracing, poor inductor placement, 90 degree baffle edges, large tweeter-mid CTC spacing (which gives rise to lobing). The crossover on the tweeter is only second order which probably does not provide optimal power handling (obviously!). Measurement may uncover further problems. For example, its not clear what the distortion numbers are. This is a critical consideration when starting a new design, and also cannot be cured in the crossover. Instead, you have to start with a low-distortion driver like this one:

You couldn't be more wrong. TL'd 2B's with better crossover components sound absolutely nothing like what you are hearing now. Add Larry's rings and as Russman says, you'll **** your flat hat.

[jcandy]

As long as you are stuck in the show me the measurements state of mind, audio nirvana will never be obtained.

Anyway, this is a great read. http://www.humblehomemadehifi.com/Cap.html

Yes I've seen that. I won't tell my wife, though. She's Dutch and wouldn't tolerate such subjectivity from a fellow countryman :)

I honestly doubt there is any significant improvement to be had over an Erse or Dayton poly.

[jcandy]

You couldn't be more wrong. TL'd 2B's with better crossover components sound absolutely nothing like what you are hearing now. Add Larry's rings and as Russman says, you'll **** your flat hat.

Does somebody have a measurement of the original versus the modified 2B? Seriously guys

Here is a measurement of what I just A/B tested the SDA2Bs against to verify that they do not have a flat frequency response.

[TrashyTrucker]

...

Anyway, this is a great read. http://www.humblehomemadehifi.com/Cap.html

F1nut,
That was a very good read! Thanks for sharing that with us. BTW if this guy DOES NOT want to change his uncles stock sda's, (may have sentimental reasons) then thats on him. I know I have had my SDA SRS 3.1's since the 90's and by all of you guy's testimonies, I will doing the other upgrades real soon.(the RDO198's worked well after breakin) I almost cant wait to recieve my packages in the mail! After that I will get started and soon begin the tedious task of breaking in the Sonicaps by playing hours and hours of music. JK, LOL :D cant wait!

Matt