problems with a Polk Monitor 10B crossover.

transmaster

I just finished changing out the cap's and resistors on my Monitor 10B's. One of them worked ok before the recap job and, of course worked afterward. The other speaker had problems only the tweeter functioned, the 6 1/2 inch drivers did not. When i started removing the cap's for replacement I found the 34uf 50V electrolytic had over heated and split open. It was replaced with a 33uf 250V cap an Axon True Cap. When I button this speaker up and tested it the tweeter sounded better but the 6 1/2 inch driver still do not work. I tested them out individually and they work just fine. The only thing not changed out is, of course, it the inductors. I tested the inductors and they seem to be OK but I don't have any experience with inductors in crossovers. I my world of vacuum tube inductors either work or are fried, makes it rather easy to DX a problem. I am not a noob with electronics, but I am with crossovers. Where do you suggest I proceed from here.

bmbguy

When in doubt, I'd get the ohmmeter out and check the wiring continuity. Check from '+' binding post to the '+' terms on those drivers, and '-' post to '-' terms. Inductors should be near shorts to DC. Assuming the schematics here match yours, there's only the one series inductor.

Could have a bad wiring connection somewhere.

transmaster

Remember said I am not noob in electronics I have been going over it with my test equipment, which includes several very nice digital VOM's. I have been consulting with a couple of hamradio compadres we have determined it is the 1.55mH inductor. Now I have the fun of choosing a new inductors. I am sure some where on the net right now there is a flame war going on inductors in crossovers :razz:

bmbguy

Well, you did say that you had checked the inductors, which I assumed to mean that you have found they weren't open. That one must have been open to prevent the drivers from working.

transmaster

I did check the inductors but I discovered belatedly when the display faded away the battery was all but dead on the digital VOM is was using. So I unlimbered a vintage Simpson analog VOM and discovered what was really going on. The tweeter is capacitive coupled so it was somewhat cushioned, but there is nothing between the two 6.5 inch drivers and whatever evil comes their way. In this case it was a demon possessed Sony AV receiver which is now getting recycled.

bmbguy

transmaster wrote: »

I am sure some where on the net right now there is a flame war going on inductors in crossovers :razz:

You can count on it!

transmaster

I think I am going to get a pair of Alpha-Core Inductors. They are available in 12, 14, and 16 gauge ribbon wire. Sonicap actually has the cheapest price on them by a few cents anyway. All three of them will fit nicely in the space below the circuit boards. It is hard to find spec's on these inductors the way some people talk about these inductors it reminds me of Richard Simmons, stupendous. fabulous, throwing up there hands in hosannas and all I want to know is how many watts each gauge can handle I have a general idea 12 gauge about 700 watts, 14 around 500 watts, and 16 300 watts I think. When we realized how the circuit worked it was simple, and you suggested this up thread I plugged the leads from the Simpson into the working speaker 4.3 ohms resistance, did the same thing with the non-functional one and it was an open circuit. The 1.55mH inductor is the only thing in between the 6 1/2 inch drivers and the evil outside. It is actually a no brainer. The twin drivers are apparently sound. The only two parts not replaced are the two inductors, the tweeter works so that inductor is fine, that leaves only one thing.:cheesygrin: Here is yet another lesson in audio amp output. The 10B's power range is 20 - 250 watts. The demon Sony was 90 watts at best but whatever happened to the right front channel Nuc'ed the 10B.

bmbguy

Still, if you're checking the spkr resistance at the binding posts that doesn't rule out a wiring issue/broken wire/solder joint/connector problem etc. inside, rather than the inductor. If it were me, I'd still check for continuity inside the cabinet before ordering new inductors. If the inductor is indeed open, just jumpering it with a clip lead (for test purposes) would bring those drivers back to life.

You know, just to make sure. A coil of wire doesn't just open up that easily.

transmaster

I agree I am going to take the Crossover completely out. It puzzles me that whatever the Sony did that blasted the 34uf cap didn't destroy the speakers in passing. Over the years I have got into the habit of re soldering all of the solder points on a circuit board. The only thing I have not looked at is the connection point for the 1.5mH inductor at the binding post which is buried in some sort of sealant. I am going to bridge the inductor today, something I should have done yesterday. But I am going to bring in my audio signal generator to do the testing this time I need to understand what is going on here.

I was told in the beginning over at the Classic speaker forum when I learned that I had an old pair of speakers worth refurbishing that it would get expensive, they where not kidding. I am having a great deal of fun so I guess it is worth it.

bmbguy

Well, the inductor should be cheaper than two new drivers!

But I was kinda thinking the same thing -- I would think that the drivers' voice coils would be more fragile than that inductor. Though you said you checked the drivers and they were still good.

Here's to hoping that it's something simple, like a bad connection somewhere. I'm just of the opinion that an inductor made of any decent gauge of wire isn't real likely to just open up like a fuse does.

So did you have both a Sony and an Onkyo rcvr blow up on you? I thought you talked a bit ago about an Onkyo blowing up.. or am I getting things confused?

transmaster

First it was the Sony. It failed several years ago and It was put on a shelf. The Polk 10B's where up in the corners of the ham-shack out of the way so they stayed there. I had a very good Klipsch Pro-Media sound system with my PC. The Klipsch system gave up the ghost completely a couple of months ago. I decided I needed a modern home theater receiver and the Onkyo was on sale at Crutchfield. I have always liked Onkyo but before the internet they where very hard to find, so in was first Sansui, and then JVC.

The first Onkyo TX-NR709 let loose on the right channel, Why is it always the right channel, have I pissed off the Right channel music God, when it let loose destroyed the woofer in the right hand Warfedale W-35 I had hooked up, The Warfedale's are rebuilt with new woofers and and re-capped crossovers, and are sounding better everyday. I was turned on to the woofers I used by a person who restores speakers as a hobby and part time business over on the Classic Speaker forum, They where intended for a acoustic suspended speaker from NHT. http://www.apexjr.com/speakerstuff.html rubber surrounds, poly cones, for $10.95, as I pointed out to somebody else they are inexpensive but not cheap speakers.

I had the crossover out again this time isolated the 1.55mH inductor and it is open. So where down in the winding there is a break some place.

bmbguy

Well, now you can the 10Bs up and running again -- and hopefully stay on the good side of the left-channel gods. Seems like you've already sacrificed enough to the right-channel gods!