Rebuilding the Polk Monitor 10B crossovers

[transmaster]

Purchased a really nice set of 10B crossovers. Nice to have a clean undamaged pair. The originals I refurbished that are in my 10B now were damaged. The originals were rebuild with C1; Sonic Cap Gen 1’s, C2&3; Axon Truecaps, and Mills 2.7 Ohm 12-watt resistors. I like the sound of this setup but there is a problem my Yamaha is occasionally acting on in the left side 10B.

I know a whole lot more about the subject, plus I have much better equipment to do the job with.

I am looking at using a complete set of Mundorf MCap EVO 450VDC cap's and a set (4) 2.7 Ohm Vishay Mills MRA-5 resistors. Apparently, the MCap EVO is not made in a 250 VDC version. It isn't the voltage it is the physical size of the caps, smaller would be better. I used 12-watt resistors on the original set, I seem to recall that was all I could find at the time. The schematic calls for 5-watt resistors and that is what I am going use. Looking at the datasheet for Vishay Mills MRA-5 resistor it can handle up to 25-watts for brief periods that is good enough. The Polyfuse will be replaced by a 0.5 Ohm 5 watt Vishay Mills.

I know, I can spend fantastically more money but this parts list comes in at bit over $100 bucks at Sonic Craft. Any suggestions?

 

[F1nut]

Stick with Sonicap or Clarity CSA as they work very well with vintage Polk speakers. Mundorf caps have a tipped up top end, which you don't want, especially with the stock SL2000 tweeters.

The reason to use the 10 or 12 watt Mills is they have even less inductance than the 5 watt.

 

[Tim D]

I generally use Daytons and never use boutique caps. I'll defer to F1nut regarding his recommendations regarding Polks. He seems to specialize in Polks, but his recommendation is also not a boutique cap. Keep in mind too that manufacturers such as Polk had great results from off the shelf caps (often NPE's) - although you can always do better than the manufacturer since you aren't trying for lowest cost - just reasonable cost.

 

[bigaltx24]

Your problem is probably the poly switch. Replace on both crossovers with 1/2 ohm 10 or 12 watt Mills. Sounds like you have good caps in the crossovers already. While the Polk Monitors are decent speakers, putting a bunch of expensive caps in them is a waste of time and money.

 

[transmaster]

I purchased these Monitor 10B's new in 1988. The rebuild of the original crossover did improve the sound in a big way. The polyswitches on the crossovers in it now where removed, and bridged, when I did the rebuild what I didn't do was install a resistor to take it's place there is an interesting posting on the Audio DIY site about rebuilding 10B crossovers and that is where I learned about installing a 0.5 ohm resistor in its place. Unlike that posting, I am not going to spend $100+ dollars on each crossover. The 10B crossovers I just purchased were assembled in 1985. It is different from what came in the 1988 crossovers. In the originals C2, and 3 where both NP electrolytics. In this 1985 version, only C2 is. I have the instruments to test the capacitors for capacitance, leakage, ESR, and Power Factor.

I know about wirewound resistors. The schematic for the 10B crossover shows both R1 2.0 Ohms and R2 2.7 Ohms with 5-watt resistors. except for heating why use a 15-watt resistor in its place that seems like overkill, there is not much difference in price but its size makes it interesting to install on the board.

I was looking at the Dayton capacitors and cost wise.
Mudorf MCap EVO's 12uF 450 VDC: $10.81 each,
Dayton Audio PMPC-12 12uF 250V Precision Audio Capacitor: $8.87 each
The single 33uf capacitor C1 is a 33 uF cap.
Mudorf MCap EVO's 33uF 450 VDC: $23.69 each
Dayton does not list a 33uf capacitor in the Precision Audio series
They have a 30uf and that one sells for $18.72.
The Dayton Audio DMPC 33uf 250V Polypropylene capacitor sells for $10.98 each

I am not going to waste my money on magical capacitors that are assembled by naked Rhinemanidens during a full Moon, under the great oak tree Yggdrasil, and touched by Mjölnir. But I don't mind paying for something just a little better.

 

[kermit z]

I used Jantzen caps on my mild rebuild of me 10Bs'. Difference was noticeable from originals.
My problem was getting them back into the cabinets

 

[F1nut]

You can lead a horse to water.............

 

[transmaster]

There are people who have made up new circuit boards that they mounted above the original and used radial caps instead of axial they also replaced the L2 inductor with one such as you see from Parts Express. The Monitor 10B is a very good speaker but that is getting a little more trouble then I want to get into.

My 10B's are actually only 5 years old. I ended up replacing all of the drivers. What in my system was the right-hand speaker was blasted by a DC nuke job by an early Sony AVR I had. it blew open C-2 and 3, which were NPE's, but before they let loose the 2 midwoofers were fried. only the SL2000 tweeter survived. The polyswitch utterly failed, I wonder if the fused crossover the 10A used would have fared better. After an interlude with a Klipsch Pro Media 5.1 system on the PC, I purchased an Onkyo TX-NR709. I decided to fix the 10B's to get me by until I could afford to replace them. This is when I learned just what I had in the 10B's. One of the SL2000 had a damaged dome so I replaced both of them with the much better RDO-194. I rebuilt the crossovers with Axon True Caps C2 and 3 and a Sonicap Gen 1's for the C1 caps. Mills resistors for R1 and 2. I could not believe how good these 10B's sounded. Then the two 6503's on the left side 10B died, they also had been damaged by the Sony AVR. I ended up with a new set of 10B's. Polk had still supports their old speakers, Thank you Polk Audio!