SDA SRS Mods - Ready to roll!

BlueMDPicker

I received my crossover components and binding posts from Parts Connexion today for modifications to my SDA SRS's. Solen PB series caps and Mills MRA-12 resistors. The posts are Vampire BP-1's and I'll be leaving the speakers bi-wire compatible.

Thanks again to DarqueKnight for the great pictorial layout and parts listing for this project. I can't wait to smell the solder melting!

trubluluc

Let us know of any gains in performance,
once the solder cools.

-Luc

jcmccorm

Cool!! I'm going to order the same stuff tomorrow for my SRSs as my replacement tweets should be in soon. I remember looking at the binding posts and being confused about which ones to get. BP-1 is all I need to know??

Let us know how the mod goes and what you think when it's done!

Cary

BlueMDPicker

Carey,

I selected the Vampire BP's for their price point and build quality. Any good quality BP should work. The SKU for these is VAMPIRE-55452.

I'm seriously considering removing the polyswitches during the parts upgrade as well. Driving the speakers with both 400wpc SS amplification and 75wpc tube amplification I've never "tripped" the switches.

What I'm hoping to gain from this project is something akin to Raife's post-mod critical listening observations:"bass had more articulation and definition. There was more “shimmer” and overtones on the drum kit’s cymbals." I'm sure you've read through his original post, but it deserves a link here.

His results were the inspiration for the project, but what finally drove me to do it was two hours of critical listening comparing the SRS's and Klipsch RF-3's. Notwithstanding the individual differences inherent in design of the two speakers, I'm left with an overall sense of "veiling" of total SQ with the stock SRS's.

Mike

reeltrouble1

Very nice Mike, looks like you are going to be busy this week.

RT1

jcmccorm

Thanks Mike!

I've read Raife's thread (and yes, it always bears repeating) and read the thread you linked to about your Klipch's.

I'm in a similar situation. I desire to upgrade the audio side of things. Although I have not yet auditioned any new speakers yet (in a long time), I can't help but wonder if technology of the last 15 years has brought something to the table that my trusty SRS's can't compete with.

On the other hand, the SRS's still sound great and I enjoy them a lot. I want to perform the mods that Raife detailed for us so that I can hear the absolute most and best they have to offer before considering a switch.

Thanks for the part number on the Vampires!

Cary

PS. I plan to go ahead and short out the poly's as well.

madmax

Let us know the results! I would like to take a new poly fuse, test to find out which value ceramic fuse blows at the same volume then just use the ceramic fuse. I'm just so lazy.
madmax

BlueMDPicker

MM,

Since the "polyswitch" (as I understand it, and as usual I will probably be told I'm FOS) is a thermal device - more commonly known as a thermistor in its non-resetting form - I guess there's no way, short of trial and error, to match it up with a fuse?

I'm going to try to research regular thermistors and see how they're rated (amps or temperature.) Why? Hmmm, it might be a reasonable compromise to put a one-shot-and-it's-done static thermistor in the circuit versus a polyswitch (which must have a "moving part" to enable resetting.) Any thoughts?

Mike

madmax

Poly fuses are tough to deal with. When cold they blow at one current and after they blow and reset (still hot) they blow at a lower value. They also start limiting somewhat as they get hot. They have about one ohm resistance when conducting which I would like to get rid of as well.

The ceramic fuses have gained an audio acceptance with some maggie fans as far as sounding better than standard glass fuses.

I personally wouldn't mind having to replace the fuse the few times I would blow it so long as I made it easy to get to.

My main concern is that possibly a much higher value fuse would have to be used to allow the peaks through with very dynamic music but then when you play music which is very constant the damage would be done before the fuse blows. (Or if you used a smaller fuse the dynamic peaks would blow it way too soon). Maybe a slow blow would be OK. Yep, a lot of testing...

madmax

jcmccorm

Just look up the part based on the part number printed on the side. There's only a couple of manufacturers of the Polys. They have datasheets that indicate what the trip current is for them. They'll withstand some maximum amount of current indefinitely and spec some level of current that they'll definitely open up in a short period of time for. There's many different trip levels for these. Also, they really are different from Thermistors (wouldn't say you're FOS though)

The way I understand it, there are many contact points in the device that allow current flow. Once it heats up, some of the contacts retreat and therefore more current has to flow through the remaining contacts, so they heat up faster and it avalanches until there are no contact points. The device has to cool down before it'll make contact again.

I have never tried to measure signal quality through one of these things (I've only used them in power supply rails) or ever read any data regarding that. I'm curious though. In the mean time, I'll probably leave them in but short them out.

Cary

hoosier21

Stole this off the net

A Polyswitch is a form of Positive temperature coefficient resistor which acts as a self repairing fuse.

A polyswitch has a current rating. When the current flowing through the polyswitch, (which acts as a resistor) exceeds the current limit of, (for example) 100mA, the polyswitch warms up above a threshold temperature and the resistance of the polyswitch suddenly increases from a few ohms to a few kilo ohms.

When the polyswitch cools down again the resistance drops to its former level.

madmax

Well here is a thought. Leave the poly fuse and put a small value fuse in parallel with it. When the fuse blows but the poly fuse doesn't blow then go to the next larger size. Just keep this up until you find out what size fuse blows and then the polyfuse trips. I guess there is still a little danger when you get to the correct range of fuse but since you are watching closely and moving up by small steps it would be fairly safe. At first I was thinking in series but you have that one ohm poly fuse resistance in there which means you may not have the proper fuse value when you are done. (Although the fuse value picked would be a little lower than the poly fuse at that point). Probably either way would work.

If the range jcmccorm is talking about is small enough maybe just pick a fuse and see? I wish I had done this before replacing all my tweets with new ones.

Just rambling at this point.

madmax

BlueMDPicker

Here is a very informative link on the polyswitch.

Tour2ma

From BMDP's link, I'd say pick the higher, "trip current" rating for a fuse and go with slo-blos...

Edit: After further review...
Whether you rounded up (normal blo) or down (slo blo) in selecting a fuse would come into play...

madmax

Originally posted by madmax
When the fuse blows but the poly fuse doesn't blow then go to the next larger size.

Well that was pretty stupid! If the polyfuse doesn't open up the fuse would never blow. Ha ha...

madmax

ardvark1

I don't own a pair of SRS' but I have a pair of SDA-2's which use a fuse system, two per speaker, one for each tweeter.

Polk calls for a 1 amp 3AG fast blow fuse for each tweeter.
I have driven this pair with a Hafler DH-500 which puts out approx 500 wpc at 4 ohms.
I have taken these speakers to hell and back since 1984 and have never blown a fuse (or speaker).

I don't know if this insight is of any help to you, just thought I would throw it out there.

BlueMDPicker

Originally posted by ardvark1
I don't know if this insight is of any help to you, just thought I would throw it out there.

Thanks for the info. I believe I'm going to short the polys out.

I asked, in another thread - but got no takers, why the interconnect cable and associated parts aren't looked upon as a something to be upgraded. I'm going to take a closer look at what might be done there when I do the BP upgrade. The original cable is nothing special and the blade/blade or pin/blade connector and socket are pretty sloppy on every SDA I have.

jcmccorm

Good point. I've always been curious as to whether or not I'm making good contact with my blade/blade since it fits so loosely. It *does* seem like a good spot for an upgrade.

Cary

DarqueKnight

Originally posted by BlueMDPicker
I asked, in another thread - but got no takers, why the interconnect cable and associated parts aren't looked upon as a something to be upgraded.

The interconnect cable carries a limited frequency range, out of phase signal to the other speaker. The overall effect of this cable is subtractive, rather than additive, and the effect of the cancellation signal, rather than the cancellation signal itself, is what is important. Therefore, a higher grade wire should not produce any audible benefits. However, everyone's ears are different, and you may discern some difference or improvement.

While we are discussing wire replacement, I replaced the internal wiring of my SDA 1B's with 10 guage, oxygen free copper and heard no difference or improvement. A Polk Audio engineer told me it would be a waste of time and money, but I wanted to see for myself.

BlueMDPicker

Thanks for the insights Raife, always appreciated!

I was up until 2 a.m. this morning re-reading the excellent article "Polk's SDA Speaker - Designed in Stereo" from your compendium. It was worth being a little tired this morning.

I have a few follow-up questions.

Is the 16 mH coil in the dimensional array crossover what limits the frequency range of the inverted signal being shared speaker to speaker? And, if the speakers are not bi-wired, what effect (if any) might that have on the inverted signal being shared (i.e. would it then make it full frequency inverted that is subsequently dealt with by the opposing speaker crossover networks?)

Mike

DarqueKnight

Originally posted by BlueMDPicker
Is the 16 mH coil in the dimensional array crossover what limits the frequency range of the inverted signal being shared speaker to speaker?

Yes. The 16mH coil presents an impedance of 200 ohms at 2000 Hz.

Originally posted by BlueMDPicker
...if the speakers are not bi-wired, what effect (if any) might that have on the inverted signal being shared (i.e. would it then make it full frequency inverted that is subsequently dealt with by the opposing speaker crossover networks?)Mike

If the speakers are run in a "strapped" configuration (i.e., high frequency and low frequency circuits connected), the other speaker would still see a restricted range phase inverted signal because of the filtering effect of the low frequency crossover circuit.

If you are interested in removing the 16mH coil in order to extend the operation of the SDA effect, you would also need to construct a phase inversion circuit, with tweeters, for the high frequency range.

BlueMDPicker

Originally posted by DarqueKnight
Yes. The 16mH coil presents an impedance of 200 ohms at 2000 Hz.

If the speakers are run in a "strapped" configuration (i.e., high frequency and low frequency circuits connected), the other speaker would still see a restricted range phase inverted signal because of the filtering effect of the low frequency crossover circuit.

Thanks!

If you are interested in removing the 16mH coil in order to extend the operation of the SDA effect, you would also need to construct a phase inversion circuit, with tweeters, for the high frequency range.

No thanks!

F1nut and I are preparing to dive in as I write. I have your mod photos printed as a reference. Thanks for doing all the hard part.

Mike

BlueMDPicker

Mission accomplished!!!!

It took F1nut and I about 8 hours, counting breaks and dinner, to turn the SRS's into entirely different speakers. Tight, punchy bass is what leapt out at you when we first fired them up with the cossover mods completed. Well worth the time and expense.

I can't thank Jesse enough. He's top shelf and a real craftsman!

We didn't take any pictures - they would have looked just like DarqueKnight's. Jesse talked me into hot glueing everything and I'm glad he did - the board and components are rock solid. The Vampire BP's really let me cinch down the spades on my PS Audio bi-wires and look fantastic (thanks again, Jesse!)

DAMN, I'm tired.... but, I think I'll keep these for awhile.

F1nut

Hey, it was fun and besides you did the hard stuff. End result.......they sound great! Now, I've really got to get mine done.

jcmccorm

Thanks for the update!

My parts from Parts Connexion should come in mid-week and I'll tackle this next weekend.

Great idea on the hot melt glue. A couple of those caps are whoppers (have mass!).

Nice to hear that there's some audible improvement to be gained here.

Cary

BlueMDPicker

Cary,

If I had it to do again, I might look at pulling all the drivers and tweeters and bringing the wiring harness out intact (if possible.) The most tedious part of the upgrade is the hard wired connections that must be removed and made at the cabinet. Check the color coding of the wires to the binding posts/SDA jack and note any differences from what's documented. My left cabinet had two black spade terminated leads versus a black and a blue.

Test fit your PC board (PCB) to the treelocks as you mount the caps and use Raife's photos as a reference. The radius of the first 130 mF cap can't be too far past the edge of the PCB due to the large air coil spool on that end. It also needs a tight knee bend to match the PCB holes, but not symetrically - let the end on the PCB closest to you in the side view run slightly off the edge of the PCB towards you. This keeps the other end away from the spade lugs that feed the binding posts and SDA interconnect wires. The other 130 needs jumpers due to lead length. The second 20 mF cap barely has enough lead length, but will fit without jumpers.

As Raife indicated, the four resistors sitting side by side should be mounted to the PCB bottom (due to extra length of the Mills.) If you don't, re-wiring the solder connections to the wiring harness feeding the drivers and tweeters is impossible. All resistors need tight knee bends to fit the PCB (again, due to length.) Look carefully at Raife's side view photo, last resistor on the bottom right. It needs to be rolled slightly to miss the treelock hole in the PCB. If any of the treelocks don't seem to be positively "latching" when the board is re-affixed, put hot glue over the tip.

Another pair of hands makes the reinstallation much easier. I sat the Xover assembly on a box of the right height - but, Jesse's help with a pair of needle nose inserting the wires as I soldered saved a lot of cussing and frustration.

Okay, I'm off to give them a listen. Good luck with your mods!

Mike

DarqueKnight

Mike,

I'm glad everything went well! You should hear more improvements in resolution over the next couple of weeks as the capacitors burn in.:)

BlueMDPicker

Raife,

Thank you for the detailed photos. They were right in front of me during the first board mod and saved me a great amount of grief through trial and error. The second board took less than 90 minutes. I'm sure Jesse thought I was deranged as I de-soldered and tossed parts in the middle of the table at a mile a minute clip!

One observation this morning after I got them back into the position I had them: with better overall definition, placement becomes more critical. I spaced them a bit farther last week when I got a new audio rack - purely to allow better separation of my Klipsch to the inside of the SRS's. I pulled the RF-3's out of the way and used a tape measure to set the outside edge of both SRS's at exactly 3' from the side walls. This placed them 5'-2" inside to inside (approx. 7' c to c.) The result was a HUGE expansion of the SDA soundstage. I know that placement has always been stressed by Polk and reiterated in your observations, but it never was a factor that I could fully appreciate until now.

Matt Polk is at "audio genius" level in my book.

Mike

DarqueKnight

Originally posted by BlueMDPicker
Matt Polk is at "audio genius" level in my book.

Matt agrees.:D

madmax

You guys suck... I wish I had time to do this stuff.
madmax

BlueMDPicker

Isn't wireless networking great?! I'm in the SDA sweetspot typing away with Sekou Bunch spinning his bass magic through the "new" SRS's.

The modifications to the crossovers have produced a totally engaging tightness to the music. Open, airy, pinpoint imaging in the soundstage (with realistic depth to boot), breathtaking clarity across the frequency spectrum - yes, all of that. But, now it's TIGHT in the sense that a group of musicians would look at each other and nod wordlessly after absolutely nailing it.

This is the best bang-for-the-buck I've yet experienced in audio. If you've been contemplating the upgrade/mod, just do it. :cool: