Polk Monitor 10 Capacitor Replacement

[FireGuruMN]

I got this pair of of Polk Monitor 10's on CL for $50.00 plus a rather long drive. But it was Fall and long drives are nice along the river in the Minnesota Fall. I was sort of just after the stands.

But I got them home and thought the drivers looked a whole lot like the drivers in my SDA-1's Sure enough these are pretty much SDA-1's with out the SDA option. And they sounded pretty nice.

Now don't everyone scream REPLACE THE TWEETER at once. It will break the internet. I'll get to that.
If anyone cares: the back:

Big round speaker terminal plate. That's curious. Must have the crossover built into it. Well, actually it's more cool than that:

They built one of the inductors right into the plastic molding. Awesome. Reminds me of a book I read in my younger days, The Mote in Gods Eye or something like that. Aliens visit earth sorta thing but the aliens were all into making things server more than one purpose when they designed things. Like a structural column in a building would hold up the building but then it would be made out of bi-metal and also act as a thermostat. but I digress. . .

A couple of electrolytic caps and a big film cap. Just replace them all:
Parts total for both speakers (parts express numbers):
Qty 4 of 027-572 Solen 12uF 400V Polypropylene Capacitor (yes, one of the originals was electrolytic but if you go with film it will never need replacing and there is room.) I think both 12uf caps are in the audio path but it could be argued.
Qty 2 of 027-350 33uF 100V Electrolytic Non-Polarized Crossover Capacitor (shunt capacitor so I went with electrolytic. There is not much room for a big film cap in this case.) The original was 34uf but who is counting.

I personally pulled the PS1 safety guard out of my circuit and put in a jumper. Really it should be replace with a 0.5 ohm 5 watt resistor because the safety guard has some internal resistance. I ordered one but I am not a patient person. Jumper or resistor it's a personal choice but get that thing out somehow.
If you unsolder the L1 inductor lead you can open the assembly up like a clam shell:

I bought this really cool wire bending tool on Etsy.

There is a variety of similar tools:

The end looks like this:

 

[FireGuruMN]

It makes nifty loops in wire like this:

Which is great when you have to extend the leads on your capacitors because they are not long enough:

This is how you have to bend the wires on one of the film capacitors so it fits into the holes where the electrolytic was located.
There is a lovely example of this work hidden under this blue heat shrink. Yep, lost a photo there I think. But this is what you have to do to convert an axial capacitor into a radial one or the other way around, I keep getting those words confused.

The other film capacitor that replace the existing film capacitor works best if you bend the leads like this:

This is what mine looked like in the end. Notice the yellow and blue heat shrink. Heat shrink is cheap. Use it wherever you can when doing crossovers. If a component comes loose that is bad but if it comes loose and shorts on another component and blows your amplifier that is worse.

Another view:

Lots of hot glue everywhere to hold things down. I put some under the 33uf cap as I was sitting it in place as well as under the film caps when they were set in place. Then lock everything together from the top again also. Hot glue is cheap. Notice all the labels are facing up and easy to read. Be nice to the next guy. I also label the backs of my speakers with the dates they were recapped. It keeps me from duplicating work and might help the next owner.
When hot gluing the 33uf cap, TRY TO NOT PLUG UP THE L1 HOLE. I plugged mine both times. Face Palm. Also when replacing the L1 wire. Hold a lighter to it to burn off some of the lacquer insulation. On one of my speakers either the lacquer or hot glue prevent a good connection. I didn't find out until I reassembled and checked the resistance across the input terminal. It should be 5 ohms or so but I was just seeing a capacitor. Oh well. It's all better now.
Continued. . .

 

[FireGuruMN]

I mostly bought the wire bending tool for reaching into point-to-point wired tube amplifiers when I am replacing capacitors in there. Instead of trying to pull the capacitors off the terminal strips, I cut the leads, put loops in the cut off end and in the new capacitor and solder them that way. It is far less frustrating and destructive than trying to get wires off the terminal strips. I used to use a needle nose pliers to twist the ends but that made for rather big loops and big solder blobs. This work much better. I've also seen similar tools for working in spring wound clocks. Something about unwinding main springs. I'd can't say for sure what the use is.
But I finished one speaker and hooked them up to do a before and after comparison. There was a huge difference in high end response. Now some of that is due to removing the safety thingy and replacing it with a jumper instead of a resistor but this was a huge difference. So I had about half an hour of happiness while I recapped the other speaker thinking I had done a great thing. Then I plugged that speaker in and it still sounded dull. The tweeter was putting out some high end but noting like the first speaker. So I am assuming there are issues with the tweeter. So off to the interweb.

SL2000 tweeter. The interweb says replace it with a polk RDO-194. It is supposedly a drop in replacement that sounds super good. It gets ordered directly from Polk. If you are a member of the Polk forum you get a bit of a discount. But probably about $50 each in the end. I don't know if I am going to do it yet. My thoughts are to order a pair of RDO-194's and put them in my SDA-1's as the main tweeters (leaving the other two as SDA tweeters--don't hate me, I cannot use the SDA crossover cable because some of my amps do not have a common negative and will blow up) then move one of the SL2000's into replace my bad one. If that all balances out I can sell the good SL2000 or heck, I could sell both of them for that matter if I could still sleep at night. There seems to be a flood of SL2000's on E-pray. Probably from people doing just this sort of swap out.

Either way, the speakers sound very nice just as they are and most people would just stop right there. But I am not most people. It is amazing the bass that comes out of the speakers with the passive radiator and two 5"(?) drivers. Good design wins over bigger drivers I guess. I still like big drivers.

I'm a programmer so here's my Easter egg for you:

TTFN.

 

[Justgotohm]

Thanks FireGuruMN, this thread made it clear what to expect before I pulled any screws. I’ll post a few pics of mine given the slightly different arrangement. I used what caps I had in my stash so one 12uf is a 10 and a 2 together.

 

[F1nut]

While the drivers look the same in the vintage Polk speakers there are 6 or 7 different models with very specific parameters, therefore they are not interchangeable.

Solen caps should never be used for anything other than the shunt circuit and even then there are better choices and yes, the proper 34uF value does matter.

Don't forget to upgrade the resistors.

 

[Justgotohm]

I am guilty of using a 33 in place of a 34 as well. I figured the difference is less than the 10 percent tolerance, I checked the old caps as I removed them. The shunt caps were the only ones way out at 37 and 39uf, the four 12’s were within tolerance. The new caps going in are all spot on.