Crossover upgrade on the SDA IA

dcmeigs

ajcutler53 wrote: »

dcmeigs:

Your documented process and experiences with the SDA-1A crossover mods has expired me to do the same. I have taken out the fuses to the dimentional tweeters, and have ordered the RDO-194 tweeters from Polk.

While not very experienced with electronics and circuit board work, I was able to successfully follow the SDA-1 to SDA-1A upgrade from Polk many years ago without any problems. So I am going to attempt the crossover mods. I have a few questions that would help me get started.

I am trying to put together the list of parts. You listed the following:



1. I assume 27uF Sonicaps are also needed which were in your photos?

2. What brand 3.5 ohm resistor did you get? and which brand 0.5 µF capacitor did you get that is in parallel with the 3.5 ohm resistor on the stereo array board?

3. Are the following the Dayton caps you used?

DMPC-25 25uF 250V Polypropylene Capacitor
DMPC-2.0 2.0uF 250V Polypropylene Capacitor

4. Where do the Dayton 25 and 2uF caps get attached?, I didn’t see them on the SDA-1A schematic? Do they replace the 750 silver mica caps?

5. I did not see a 12 watt resister on the schematic for the SDA-1A, where do the Mills resisters attach?, and where would they appear on the schematic?

6. I didn’t quite understand what you hooked up the extra wires to that you used to avoid the daisy-chain? Could you provide a little more detail?

Thanks in advance,

Alan

First, let me clear up the Dayton and Sonicap mystery. I had planned to use the Daytons but was persuaded in the end to use Sonicaps. I still have the Daytons and I can fix you up if you decide to go that way. Read F1nut's posts and Bens posts and perhaps you can follow the thinking. To summarize, the Sonicaps are the more expensive and it is generally agreed that they sound better. The Daytons would no doubt be a big improvement if cost is an issue. If you are trying to save money, use Sonicaps on the high pass (tweeter) and Daytons on the low pass. If the cost is not a big deal, then by all means go with the Sonicaps. I was over at my friend's "man cave" tonight listening and I am amazed at their continued improvement between the last listening at 300 hrs and tonights at 600. I think you will be happy with your decision.

I replaced all of the resistors with 12 watt rated resistors of the resistance called for in the drawing. I read Bens post above and will tell you that his advise was of great help to me and you should listen to him. Having said that, you should explore the resistor issue as I think there is not complete agreement here. Specifically, the 5 watt resistors have less inductance than the 12 watt and may therefore be better for the application, assuming of course you don't burn up the resistor. Perhaps Ben will reply to this or maybe F1nut will weigh in on this issue. I don't have the answer.

Don't worry about the extra wires and the daisy chaining. That's just me being obsessive. I would upgrade to at least 16 gauge wire internally. I used 14ga.

If you still have questions, I'll be glad to help.

ben62670

The Mill's are non-inductive;)

dcmeigs

ben62670 wrote: »

The Mill's are non-inductive;)

There you have it. Go with the 12 watt.

I missed one of your questions. Look at the first photo on page 4 posted 4/5/08. The group of parts on the right hand side is for the SDA 1As but two of the 27uf are not pictured. You will need 4.

4- 27uF Sonicap (Dayton or Solen if the cost is a burden)
2-12uF Sonicap (use the Sonicap here)
2-0.5uF Sonicap (use Sonicap here)
2-3.5 ohm 12 watt mills
2-2.7 ohm 12 watt mills
2-Polk RD0194 tweeter

The 3.5ohm resistor in the high pass was a judgement call but I would absolutely go with that value again. 3.5 seems to nail it for me.

Note that there is no need to replace parts in the dimensional array high pass because that tweeter is left unhooked.

Do one board at a time so yo have a go by. Clean one board off and sketch it out so you can understand the layout. The 12uF and the 0.5uF/3.5 ohm RC pair in series are actually reversed on the layout. This is just fine.

This crossover is among the least expensive because it uses relatively small and inexpensive caps. Look at the parts required for the SDA-2Bs on the left side of that photo. The improvement is a huge bang for the buck.

Good luck and post photos.

ajcutler53

dcmeigs, and ben62670:

Thank you so much for the help/answers.

I plan to break in the RDO-194 tweeters (they should be arriving in the next few days) for a while, and get used to them. I will then do the cap upgrade (and take photos along the way).

I clearly remember how much of a sound quality difference the SDA-1 to SDA-1A upgrade made (which included the tweeter upgrade from SL1000 to SL2000, along with a crossover mod). So I am looking forward to the improvements with the RDO194 tweeter and cap mods.

Alan

dcmeigs

ajcutler53 wrote: »

I plan to break in the RDO-194 tweeters (they should be arriving in the next few days) for a while, and get used to them. I will then do the cap upgrade (and take photos along the way).

How many 194s did you buy?

ajcutler53

dcmeigs wrote: »

How many 194s did you buy?

i bought two 194s for $102

dcmeigs

Before you install them, let me suggest that you listen with familiar material to the SDA effect with both tweeters in operation, then pull the fuse and listen again with just the two stereo tweeters. It is this test that made me sure I wanted to operate with just the stereo tweeter.

More to the point, I thought the improvement was minor but noticable until I reconnected the dimensional array tweeter and then it hit me over the head.

I'll be interested in reading about your experience. I'm sure mine is colored by years of listening to SDA-2Bs; perhaps I crave the familiar .

ajcutler53

dcmeigs:

Following your recommendation of pulling the fuse on the Dimentional tweeters several days ago, I did that and have been listening to all my well known/familiar material for several days and what I have noticed is a subtle but present clearness in the high-end that is easier to listen to. Vocals seem to be a little more well-defined.

I wanted to start getting used to just listening to the Stereo tweeters and get familiar listening to my well know material so when I drop the RDO-194's in I will be better able to notice the difference.

On anothet subject, back to the crossover upgrade; both F1nut and BEN62670 recommended getting rid of the 750 silver mica caps. My question is what did these caps do?, and what does removing them do?

dcmeigs

They are bypass caps and they are not necessary on polypropylene film caps.

ajcutler53

I've had the RDO-194s in for several days now and played all the familiar material I have listened to on my SDAs for years. Even out of the box I was able to tell a significant improvement, my ears don't hurt after listening for an hour, and I can turn up the volume to levels I wouldn't dare to with the Sl2000's. No I didn't do a "scientific" test, but when your ears no longer hurt on the high-end, no need to measure anything.

Unfortunately the plastic collar on one of the dimentional fuse holders busted when I was putting the fuse cap back on, and will no longer hold the fuse. So even though I'm not using the dimentional tweeters, I don't like anything not working, so next step is to replace the fuse holder.

dcmeigs

Why bother? I've never looked back after pulling the plug on the dimensionals.

altecman

Finially my 1A's are now sounding as they should, I removed the lead from the SDA tweeters as stated in this thread and boy what a difference. I don't seem to mind the sound of the SL2000's, I have noticed that they are bagged because of the 5dB peak in the 14-15K region but this isn't much of a concern as I use my spare Technics SH-8055 Graphic Equalizer to rempve this.
Has anyone tried to make an 1A into a 1C by blanking the existing tweeter cut-outs and put a tweeter in the middle between the old existing spots. I think the way the two tweeters are originally mounted on the outside edge of the enclosure must cause of reflections between the tweeter and grill frame. This has to be more apparent once you disactivated one tweeter.

ajcutler53

dcmeigs:

dcmeigs wrote: »

Why bother? I've never looked back after pulling the plug on the dimensionals.

Well in addition to liking things working, if I ever sell my SDA-1As (to upgrade to 1Cs, 2Bs or possibly SRS), I would want them in perfect working order. Since I'll have the insides open when I do the CAP upgrade might as well replace the fuse holder.

By the way what was the voltage(s) of the capacitors you used in your upgrade; 200v?

dcmeigs

altecman wrote: »

Has anyone tried to make an 1A into a 1C by blanking the existing tweeter cut-outs and put a tweeter in the middle between the old existing spots.

I certainly considered it. Problem is, there is a baffle in the center of the cabinet.

heiney9

altecman wrote: »

Has anyone tried to make an 1A into a 1C by blanking the existing tweeter cut-outs and put a tweeter in the middle between the old existing spots. I think the way the two tweeters are originally mounted on the outside edge of the enclosure must cause of reflections between the tweeter and grill frame. This has to be more apparent once you disactivated one tweeter.

The problem with doing this is in the 1C the tweeter array is arranged and crossed over as a progressive point source. The 1A uses the other tweeter for dimensional sound and therefore converting to a progressive point source like the 1B's and 1C's is impossible.

The ONLY reason the tweeters were mounted that way on the 1 and 1A were to utilize the second tweeter for dimensional sound only. If it were a full output tweeter they would NEVER have been side by side as that design is pretty much no good at all.

The only true way to solve the problem is to get a pair of 1B's or 1C's

H9

altecman

Why did Polk put the tweeters in the middle of the baffle when the SDA drivers are all facing straight ahead, is this why people say that the SDA loudspeakers series don't image as the tweeters are facing forward and not towards the listener. I now understand how the SDA system works but shouldn't the tweeters be facing towards the listener as they are independant to the SDA principle, to me it looks like facing the tweeters in the same plane as the rest of the drivers would cause a large hole in the tweeter frequency range. Any thoughts on this??
For the SDA-1A's would it make sense to mount the tweeter like what was done to the RTA 12C's and make this tweeter enclosure/baffle pivot so you can position the tweeter towards the listener and still enjoy the SDA midrange effect.

F1nut

I replaced all of the resistors with 12 watt rated resistors of the resistance called for in the drawing. I read Bens post above and will tell you that his advise was of great help to me and you should listen to him. Having said that, you should explore the resistor issue as I think there is not complete agreement here. Specifically, the 5 watt resistors have less inductance than the 12 watt and may therefore be better for the application, assuming of course you don't burn up the resistor. Perhaps Ben will reply to this or maybe F1nut will weigh in on this issue. I don't have the answer.

As the original resisitors are rated at 5 watts, you can safely use the Mills 5 watt and it's true that the 5 watt version has less inductance, although both are non-inductive.

F1nut

Why did Polk put the tweeters in the middle of the baffle when the SDA drivers are all facing straight ahead, is this why people say that the SDA loudspeakers series don't image as the tweeters are facing forward and not towards the listener.

Who says they don't image well??? That's one of the things they excell at.

ben62670

F1nut wrote: »

Who says they don't image well??? That's one of the things they excell at.

I found that kinda humorous myself. If they didn't image well I wouldn't be an SDA freak:D

DarqueKnight

altecman wrote: »

Why did Polk put the tweeters in the middle of the baffle when the SDA drivers are all facing straight ahead...

This arrangement provides the most coherent sound field and three dimensional imaging.

altecman wrote: »

...is this why people say that the SDA loudspeakers series don't image as the tweeters are facing forward and not towards the listener.

SDA imaging is affected by room acoustics and the quality of the signal provided by the associated electronics. Best imaging will be realized in a room of adequate size and with the use of low noise, high current amplification and low noise source components.

altecman wrote: »

I now understand how the SDA system works but shouldn't the tweeters be facing towards the listener as they are independant to the SDA principle, to me it looks like facing the tweeters in the same plane as the rest of the drivers would cause a large hole in the tweeter frequency range. Any thoughts on this??

For the SDA-1A's would it make sense to mount the tweeter like what was done to the RTA 12C's and make this tweeter enclosure/baffle pivot so you can position the tweeter towards the listener and still enjoy the SDA midrange effect.

Matthew Polk published a technical paper in the June 1984 issue of Audio magazine entitled "Polk's SDA Speakers-Designed -In Stereo". After you read that paper you will have a full understanding of why the tweeters shouldn't be aimed at the listener and why SDA's should not be "toed in".

As with all things relating to SDA's, the paper is obscure and takes a bit of effort to find. Polk's customer service department used to provide free copies of this paper, but I do not know if they still do. If they don't, your local library should have that issue of Audio on microfilm or microfiche. If neither of the above work, reprints of old Audio magazine articles can be purchased from Roger Russel for $6. His web site and email are http://www.roger-russell.com/magrevsr2.htm and rogerr4@earthlink.net.

dcmeigs

altecman wrote: »

the SDA loudspeakers series don't image

Now that's news.

altecman

Sorry for all the confusion, I think my medication was playing tricks on me!! The reason I spoke about the imaging was what some people said to me when mentioning SDA's, they must be non believers. What was funny is that I connected the SDA tweeters again and placed the loudspeakers closer together eg 8 foot apart and 12 foot from listening position. The phasing problems between the tweeters now seem to be very much reduced. You must have to be in a perfect position when listening to the earlier side by side version. I could almost live with this sound now but will upgrade tweeter as mentioned in previous threads.
Once again I wish to apologize for my ignorance!!!

heiney9

You are correct, later model SDA's are much less dependent on listening position. There still is no substitute for being in the sweet spot but the last and 2nd to last generations are much more forgiving.

H9

altecman

Over here in Australia the Polk distributor said that the RDO-198-1 was the replacement for the SL2000, while you guys have mentioned that the RDO-194-1 is the correct replacement. If I am going to use one tweeter only I need to find out which of the new tweeters has the highest sensitivity, I might even have to reduce the 3.5 ohm resistor to 2 ohms to match sensitivity to the rest of the system. And yes I am going to mount it in the middle by removing a small bit of the center baffle. This is no big deal as we are all qualified DIYers.

F1nut

Your distibutor is wrong.

jimreeves

dcmeigs wrote: »

4- 27uF Sonicap (Dayton or Solen if the cost is a burden)
2-12uF Sonicap (use the Sonicap here)
2-0.5uF Sonicap (use Sonicap here)
2-3.5 ohm 12 watt mills
2-2.7 ohm 12 watt mills
2-Polk RD0194 tweeter

The 3.5ohm resistor in the high pass was a judgement call but I would absolutely go with that value again. 3.5 seems to nail it for me.

Note that there is no need to replace parts in the dimensional array high pass because that tweeter is left unhooked.

Do one board at a time so yo have a go by. Clean one board off and sketch it out so you can understand the layout. The 12uF and the 0.5uF/3.5 ohm RC pair in series are actually reversed on the layout. This is just fine.

This crossover is among the least expensive because it uses relatively small and inexpensive caps. Look at the parts required for the SDA-2Bs on the left side of that photo. The improvement is a huge bang for the buck.

Good luck and post photos.

Dave, your project has inspired me to upgrade my SDA-1A XO's while I'm in the process of refurbing them. I've found one more fly in the ointment with mine however. Seems the previous owner may have been harder on these than originally thought, in that the tweeters have been changed to Peerless drivers (shown). No other mods done, short of the crude bi-wire job you helped me with. These are obviously 8 ohm nominal and I'm assuming the 194's are 4 ohm, do I have that right? If I do, the single tweeter won't mate with the HP filter unless I wire the stereo & dimensional tweets in series. This would be a stop-gap measure until I have funds for 194's.
Lastly, where did you find all the values of the Sonicaps you used? I'm seeing the 12's and the 27's at Sonicraft but no 0.5's? Did they produce them for you? Thanks again for your help with the re-wire.
Jim

dcmeigs

I really don't know about the impedance issues but I do understand your concern. Pick up the phone and call polk.

Sonic Cap makes a 0.47uf cap. That is how a 0.5uf is spec'd.

jimreeves

Thanks again, I'll give them a ring. Wasn't there a SDA conversion at some point in the past that involved Peerless tweeters? Or is this just a fluke?