Troubleshooting Polk SDA-2

Scott99

This is my first time posting to this forum. I recently purchased a pair of Polk Audio SDA-2. These have two tweeters, three 5" drivers and a 12". The left speakers outboard tweeter is not making any sound. I believe this is the SDA system tweeter. The speakers can still create a stereo image but not great. I disconnected the interconnect cable for the SDA system and it seems to image a little better but the left speaker seems to have a slightly lower volume. I am going to start with the low volume issue first. Any suggestions on what to look at first? Something is probably adding resistance to the left speaker circuit or possibly a bad cap in the crossover? Is there any fuses or switches that should be looked at?
Any suggestions are greatly appreciated.
Thanks!
Scott

pitdogg2

They are 6.5" midwoofers and 12" passive radiator.
So you have the interconnect cable does it fit the socket pretty firm or is it real loose? There are no fuses i know of on those, if there was they would be next to the binding posts. Those should have polyswitches, which act like fuses somewhat but reset when you turn down the volume. Yes they do go bad and they usually trip very easy when they do go bad. Have you removed they tweeter and checked for continuity across the leads the wires attach to? If not remove the tweeter and remove the wires. Be sure to look to see which wire goes where. You can check ohms or continuity with a DVM to see if you have either. If not the tweeter is bad. For the low volume take the passive radiator out and look at the boards for loose wires or caps the may of puked innards?
Pictures will help as well if you like to post some. Just for reference most disable the sda tweeters any way.

FestYboy

Start with a leak down test (press on the PR, hold it in, and watch the MWs. They should stay pushed out for at least 3 seconds). You can then move on to the DCR comparison (L to R).

tonyb

I think first tell us what your driving them with. You need a common ground amp to drive them.

F1nut

In addition, make sure you have them set up correctly. 5 to 6 inches from the back wall, NO toe in, at least 3 feet from any side wall and 6 to 8 feet apart.

Scott99

I started with F1nut's advice. I re measured all my distances and all looked good but I have a railing to the left of the problem speaker. Its an open railing that protects the stairwell going down stairs. I repositioned speakers further away from this railing and it may have solved the lower volume issue in the left speaker. I need to do some more listening to confirm. Also went to audiocheck.net and did their stereo imaging tests before and after with a noticeable improvement.
I would like to continue to troubleshoot the SDA system and will check the tweeter resistance and remove the passive radiator and inspect the boards next.
To answer TonyB's question. I am currently driving them with a Primaluna Dialogue Premium Integrated tube amp. I think it produces 35 watts per at 8 ohms. Not sure what it produces at 4 ohms. I have a Arcam Delta 290 integrated amp that my brother in law will be bringing in two weeks. I plan on using it for these speakers. Produces 70 watts per at 8 ohms. Not sure if this amp doubles to 140 watts at 4 ohms. It is supposed to be a nice sounding amp. I also have a Mcintosh mc7270 amp with a Mcintosh C30 pre amp on another system that I could use for troubleshooting if needed.
Passive radiator test. Festyboy, can you explain in detail how to do this. I don't want to push to hard on the passive radiator and not sure what to look at "MV"? Also what does "DCR" stand for. Sorry to many acronyms in this world to keep track of.
Thank you all for that great advice!
It might take me a day or two to take apart the speakers and inspect and test. I will let you know what I find.

Scott99

TonyB, I forgot to ask about the common ground amp. I wasn't sure so I called the manufacturer of each of my amps. None of them seemed to be confident in their answer and the rep for Arcam said he didn't know. I emailed Arcam in the UK but have not heard back. Would you happen to know if these three amps have a common ground or how I can determine?
Thanks again for your help!

Scott

FestYboy

@Scott99 sorry for the acronyms, it's Mid Woofer, and Direct Current Resistance.

For the leak down test, the passive gets pressed in with just the weight of your hand ( ~1/4") and hold it there steady. The smaller drivers should push out and STAY out for at least 3 seconds before moving back to their resting position. If they don't pass that test, the enclosures need to be resealed.

DCR is just a resistance measurement with your multi meter.

To check to see if your amp is common ground, set your multi meter for continuity check or the lowest resistance value. Then put the meter leads into the negative terminals on the amp (one in each). The read value should be a dead short. If it reads open, the amp is NOT common ground, and the crossovers need to be checked for damage.

Scott99

After listening for a couple of hours the low volume issue gets worse. When I moved the speakers and noticed an improvement this morning. That was the first time I had turned on the system for the day. So it looks like the problem is electrical. Hope to be able to open them up tomorrow.

tonyb

Scott,

Do you have them hooked up to the 4 ohm taps ? Try the UL mode ?

I'm not sure if that amp is common ground or not. What I can tell you is your symptoms are exactly the same when I tried a non common ground amp on some SDA 2's.

Scott99

They are hooked up to the 4 ohm taps. I measure the resistance between the two speaker ground taps and got .1 ohm. When I was looking to buy these speakers the seller had them hooked up to one of his amps and produced the same symptoms. It is very possible that he had hooked them up to an amp that did not have a common ground at some point and caused some damage. He is a musician and had them hooked up to a guitar amp and an EQ for the demo.

Scott99

I did the leak down test and I did not see the 6.5" drivers leak down at all in 10 seconds. Measured the resistance of the dead tweeter and got 7.2 ohms.
I tried to remove the 12" passive radiator and it is not budging. Anyone have a trick for breaking it loose from its gasket without damaging anything? Do these gaskets usually tear and need to be replaced. If so, does Polk still sell them?

pitdogg2

Take the lowest 6.5" driver out push passive from rear.

F1nut

I did the leak down test and I did not see the 6.5" drivers leak down at all in 10 seconds.

If those drivers didn't start moving back for 10 seconds something is seriously wrong. 3 seconds is a minimum, 5 seconds is excellent and the most I've seen or heard of.

Scott99

Wow, even pushing from behind that passive radiator was in there. That 33 year old two sided tape is good stuff. Thanks for the tip pitdogg2. Visual inspection of the two cross overs in the left speaker didn't have any burnt components, corrosion or bulging or leaking caps that I noticed. I will have to do some checks with my meter. What do you guys use to replace the two sided tape? More two sided tape or other sealant? Is there a brand that works well?
In regards to the leak down test. Both speakers seem to hold the pressure for a long time. I didn't notice them leaking down. Maybe I wasn't looking close enough to notice a small movement but when I released the passive after 10 seconds the 6.5" drivers all moved back. They sill had quite a bit of travel after 10 seconds. Since both speakers are this way. I would guess it is not causing the low volume problem in the left speaker.
Does anyone have the acceptable resistance range for the tweeters and 6.5 drivers?
Does anyone have a schematic for the crossovers?
I am considering building new crossovers. I know someone has built upgraded crossovers for these. Any recommendations?

pitdogg2

well which MW drivers are in the speaker ? It is listed as MW6501, My SDA1 Signature used MW6600 and they have a thick felt type dustcap in the center. That dustcap does not let the air pressure flow through the cap as easily as newer MW 6503,6502, 6510 etc. The original MW6501 was a very similar dust cap. My speakers are tight but I get a slow 6-7 second fall nothing near 10 seconds and still up. Are you sure that is not a paper type gasket? it could be reused if it is not torn. Some back in the day used rope caulk or mortite caulk is the trade name, it that what you have?

Scott99

My 6.5" drivers are the MW6501 and have the thick felt dust caps. Manufacture date is Oct 18, 1985. on the magnet it has four check boxes and SDA II is checked. This driver measured 7.5 ohms. The driver came out easy and has a similar gasket as the passive but not sticky like the passive. The passive gasket came apart in several pieces.

pitdogg2

Home sells pipe insulation tape called armacell it works good.
Well that explains the slow drop time.

Scott99

Thanks for the gasket replacement ideas. I think either of those will work well.

pitdogg2

I would not use mortite !!

Scott99

Thanks!

Scott99

I finally found the time to complete the repairs and modifications on my SDA-2 Polks.
I built new crossovers that combined the two crossovers in each speaker. Updated with new caps and resistors. Removed poly switches and replaced them with .5 ohm resistors. I removed all spade connectors and other bolt on / crimp on connections in the speakers and replaced all wire with high quality 12 gauge silver plated wire with teflon insulation for everything. All connections in the speaker are now soldered. Installed hurricane nuts for all of the drivers. Replaced all four cable connections on the back of each speaker. I still have to make some new speaker cables and interconnect cables.
My first impression is that there is a huge improvement in imaging. The SDA function seems to work very well now. I am sensitive to speakers with overly bright tweeters. I was worried that removing the poly switches would reduce the resistance in the tweeter circuit dramatically and cause them to be over powering. All the drivers have come alive and seem to be balanced nicely. The speakers are a little light on the bass but fare pretty well for their size. It is amazing how many spade connectors are in these speakers. Not only are these made out of poor quality, they don't make great connections. Plus the crimped wire connection on the spade is another bad connection. Removing these is a low cost modification that can make a noticeable difference. This combined with replacing the wire. I used almost 90 feet of wire inside these speakers. Thats a lot of wire in the audio circuit. It didn't cost that much to buy higher quality wire. You will notice the previous owner had replaced the veneer with curly maple. Looking forward to running them for a while and see how they sound. Note the placement of the speakers in the photo was only for testing them with another amp. I realize they are not supposed to be that far apart and not toed in.
Thank you for your help!!!
Scott

FestYboy

Bring them closer to the back wall, that should improve the bass output. Also I would recommend you have the inductors at 90° angles to each other.