SDA 2B - Crossover Help

gstein

I have a set of SDA 2B’s, one speaker works perfect, the other one emits no sound. After inspecting the crossover, I noticed the yellow capacitor has a few black burn marks on top, one directly under the wire the other one next to the black component in the P1 location. See pictures.

Should I replace the yellow and black components, and if so, what are the recommended replacements to use?

pitdogg2

Looks like that 750pf silver mica got rocket hot.

How's your soldering skills?

F1nut

Try posting a clear picture taken looking straight down at the entire crossover.

gstein

Update - looked at good the speaker crossover and noticed blue (transistor?) is there so it must have completely fried and disintegrated on the bad crossover. Obviously will need to replace that as well.

pitdogg2

That should be the poly switch. It was used to protect the tweeters. We remove them when we rebuild XO's. They go bad and get easier to trip the more they trip.

Need better pics of both XO's

F1nut

Ok, the small blue device is a polyswitch, which is a thermal reset device designed to cut the signal when it gets too hot from you overdriving your power source. In short, you turned the volume level up way too high and fried it so badly that it also cooked the 12uF mylar cap as well as the 750pF silver mica bypass cap.

While you are repairing the damaged crossover you might as well upgrade the components on both boards. A search here on 2B crossovers will bring up lots of info.

F1nut

I should also mention that in case this wasn't caused by cranking the volume it would be caused by your power source passing DC in which case you'll need to have it repaired before using it again.

gstein

Thanks all for the quick replies. Got the speakers at an estate sale the other day, previous owner must have cranked Ozzy a little to high!

I'll search PA forum for crossover repair for the SDA 2B's. Just for my own identification, is the 12uF mylar cap the yellow cylinder, and the 750pF silver mylar bypass cap the smaller black/brownish component directly to the side in the "P1" location?

Soldering skills are good, just not familiar with this crossover.

gstein

Ok, I've spend the last hour or so reviewing prior threads on rebuilding the crossover for the SDA 2Bs. I'm not sure I'm more educated or less clear on the direction to complete the job.

My goal is to simply get my one speaker working again. I realize I could upgrade to Gimpods boards or using expensive parts, but at this point I'm not currently interested at doing additional work as part of the repair.

That said, is there a post/thread that simply:

1. provides the parts to buy, and
2. provides pictures of the existing parts to be replaced, and
3. provides pictures of the new parts installed on the existing board?

F1nut

The answers are on the good crossover.

agfrost

Even without the gimpod boards, his site has nice resources (which parts are on the crossovers). If you're just getting them running again, capacitors and resistors (and perhaps the polyswitch if you want the protection) are listed here: http://gimpod.com/parts2b.html
Note that the 5.8 caps are only if you're planning on "TL-ing" them and replacing the SL2000 with the RD0198 tweeters.

Most of us are *upgrading* as we do crossover work, so we're buying considerably better components (Mills resistors and film caps of varying cost). The most common way is "Mills and Sonicaps" as suggested on Gimpod's site, but you can use capacitors of lesser cost. I very much hope you update both crossovers and not just the damaged one--it's impossible to imagine that you'd get pleasing sound out of mismatched speakers.

There are a host of threads of people's planning and work on 2B's (and CRS+, which have identical crossovers) but many are old with outdated links and dead photo links. Many refer to TL-ing them; you must decide if that's in your plans. (easy enough to do later on, but nice to do while crossovers are out and your iron is hot) This thread has some nice pictures of rebuilt original boards on page 2.

this thread has a very nice original board photo. You'll notice that in most of the rebuilt board threads that the 40uF capacitor adjacent to the inductors is replaced with a 20uF + 20uF (or 30 +10) in parallel--this is due to availability, size, and/or cost issues with using a 40uF film cap.

The 750pF bypass cap is simply deleted by people upgrading to higher-quality film caps. No longer needed. The polyswitch can be replaced (do both speakers), or replaced by a jumper or a resistor--I'd ask the board for their opinions on this matter.

Keep posting as you have thoughts and questions. It's not a race to get done and you'll be more sane if you plan it well and don't have to reorder or resolder.

agfrost

I realize that the original crossover picture I linked wasn't definitely an original 2B crossover --I doctored up this one I found with some labels, hope it helps. Someone yell at me if I've mislabelled anything important!

gstein

agfrost - thanks for all the info and labeled picture. Just want to make sure I purchase the correct parts, and more importantly, solder them into their correct location! As the old adage goes, “measure twice, cut once”😊

pitdogg2

Well do one piece at a time and they're no worries as to where they go. The 750pf silver mica location I'm sure you could just jump with a piece of wire to test and see if it all works.
When we delete the 750pf we jump the location.

Gardenstater

I'm pretty sure you mean to say jumper the polyswitch position. Also, I believe I have heard it said that the polyswitch is around 500mOhms, so in the long term if you were to do away with it you might want to raise the value of the resistor by that amount or purchase a 0.5 Ohm resistor to go in the polyswitch's place.

pitdogg2

I'm positive i meant what I stated.

Yes you could also jump the poly switch location as well just to see what is working.

pitdogg2

pitdogg2 wrote: »

Well do one piece at a time and they're no worries as to where they go. The 750pf silver mica location I'm sure you could just jump with a piece of wire to test and see if it all works.
When we delete the 750pf we jump the location.

This is bad advise I'm sorry. I was thinking you needed to jump this connection to complete the circuit for the 12uf cap. In looking again and someone pointing out IF you jumped this you will completely bypass the 12uf WHICH IS NOT GOOD
I apologize for my mistake. If you just remove(750pf) the 12uf will still be active IF that cap is even still good of course if you replace with another 12uf just remove the 750pf if the cap is a better poly cap. The older mylar caps needed it to sound better from my understanding. We completely remove the 750pf silver mica with current better poly caps as they are no longer needed like @agfrost touched on.

gstein

So the Sonic Craft seem to be highly regarded. Is there a manufacturer that has good, cheaper capacitors that would be recommended? I highly doubt I will be keeping these speakers (have several sets already) and would just like to get both speakers working.

Gardenstater

Clarity Cap CSA is much cheaper and highly regarded here. I have no first hand experience with. Soniccaps are awesome.

gstein

The Clarity Cap CSA 12uF appears to be 38mm length and 39mm diameter. At that size, it could be a little challenging to get it installed on the board. However, if I can remove the 750pF, I believe there should be enough room for the 12uF capacitor.

Anyone else ever replaced the 12uF cap with a Clarity capacitor?

The issue will be if the 20uF capacitor has to be replaced as well, then I don't believe there will be enough room to install it along with the 12uF capacitor.

Any way to use a DMM to test the 20uF to see if it still good?

Gardenstater

Well rest assured you can definitely remove the 750pf bypass capacitor. If you go with a high quality audio grade Polypropylene metalized film capacitor such as Clarity Cap or Sonicap you won't need it.

Some DMM's can measure capacitance. Depends upon the unit. Mine measures only up to 20uF. There are other ways they can break down though I believe, so if one reads good doesn't necessarily mean it is up to peak performance. Meters only measure capacitance at one frequency. When you get into audio grade you are talking about all sorts of nuances besides a raw capacitance reading. Read more here:

http://www.humblehomemadehifi.com/Cap.html

cwelk87gn

Good afternoon folks. I have these old SDA2b's with weak polyswitches. Going to the electronics store to buy what I need to replace the polyswitches and anything else that will improve
the sound quality. I'm doing both speakers, BTW. An other tweaks I can make while I
am in there?

F1nut

Search the forum, tons of info.

gstein

Received my parts and have one question. After reading the gimpod information I purchased a .51 Ohm 10W resistor and a 1.35A polyswitch (as well as new capacitors). I now notice on the gimpod parts list table that the resistor is used to replace the polyswitch.

Apparently over my skis here...which part on the board does the resistor replace? If it is indeed the polyswitch then why does the ginpod page show that the (optional) polyswitch can be purchased to replace the polyswitch?

[Deleted User]

The polyswitch can be left in the circuit to offer protection for the tweeter. If you tend to be an "enthusiastic" listener with a moderate power amp and high tolerance for distortion then leave it in place.
If you decide to replace it then you would substitute the small value resistor to maintain the tweeter's output level when the polyswitch was in place.

gstein

Well I received all the following parts — capacitor, resistor and polyswitch — and have installed them. Unfortunately it did not fix the speaker, still no sound coming out of any of the drivers. I switched the speaker cables to make sure there was a good connection, no issues with the speaker wire.

Back to square one. Any other suggestions on diagnosing the issue (with DMM or other method)?

Gardenstater

I'd have the amp checked out by a service tech. Do this before anything else!

Are you sure both channels on your amplifier are working? Swap the speakers channel for channel and see what happens. Check the drivers for DC resistance with the meter. If that is good check the tweeters with a AA battery momentarily to see if the dome moves and check the midwoofs with a 9V battery momentarily as well. If you still haven't found a problem you have to start checking all that you can in the circuit for conductivity and good connections.

gstein

No issues with amplifier as it has been tested on numerous other speakers without any left/right channel issues. For the DMM resistance test, is there a specific range of ohms that I should see for each driver?

Gardenstater

It's all searchable here but I'm trying to help ya out.

SL2000 7.31 Ohms
MW6503 6.540 Ohms
MW6511 3.130 Ohms.

I think it is more likely to be a cold solder joint or joints or bad connections somewhere. I would check continuity from the binding posts to the PC board first I think.

gstein

I may have fried drivers all around as I am unable to get an ohm reading on the MW6511 or the SL2000. I connect the speaker wire to each of these drivers directly from the amplifier and had no sound from either. Is it possible all drivers could have been damaged when the PC board overheated? Anyone heard of this possibly happening?

gstein

Well believe I have identified the issue. I had an extra tweeter laying around that I connected to the SDA speaker that was emitting no sound. The extra tweeter works when connected, leading me to believe all drivers were “fried” by previous owner. Also, as mentioned before, I could not get an ohm reading from any of the drivers.

I picked these up from an estate sale, I guess it’s a good thing I didn’t pay too much for them. Not sure I want to buy a new tweeter and two mids to fix these up, so I may see if someone locally wants them cheap (for repair or parts).

Thanks all for feedback!