I decided to rebuild the components in my Monitor 5 Jrs a few weeks ago. There was talk about doing it by a couple members, but to my knowledge, it hadn't been done lately. The benefits of replacing stock components with higher quality ones had be proven in the past to me, but the benefit of replacing old, leaky capacitor with new ones is a sound investment, both sonically and electrically. So I decided to order some parts and put some heat in the old iron.
My Monitor 5 Jrs were not stock to begin with. A few months ago I swapped RDO194s into them and have highly enjoyed the upgrade. When I started looking at parts, I realized that I didn't need too many. The Monitor 5 Jr only has 5 components in its crossover (the simpler the better, right?). It uses two inductors at .56mH and .19mH which I just left. It's debatable whether changing the inductor is an improvement, so I just decided to leave it. Plus the fact that the bind post cup and .56mH inductor are the same unit, so that is just more work than I wanted. There is also a polyswitch which luckily had never acted up, but I decide to replace them with a jumper just for good measure (the simpler the better, right?).
The two components that I did replace were the 1 Ohm, 5w resistor and the 12uF, 100v capacitor. Because there was only two components, I knew I could keep the price of this rebuild low. On my SDAs, I used Mills and Sonicaps with great success, but wanted to try something different (and cheaper) for my little guys. I decided to buy from Parts Express because of my great history with them and their good selection. For the resistors, PE offers Mills 12w for $3.25 and Dayton Audio 10w for $1.25. I thought both were good selections, being that they have similar power ratings and both have reviewed well. I was actually going to use the Dayton to try something different, but the part was back ordered and I can be impatient. So Mills resistors were chosen even though they were a little more money.
For the capacitors, there were many options available, and it took me awhile to make my selection. PE offers a "12uF 100V Non-Polarized Capacitor" for $0.60, but I was going to be audiophile snob and use a name brand. Dayton Audio offers two 12uF caps, both at 250v. However, one has a 1% tolerance and sells of $8.08, and the other has a 5% tolerance and sells for $4.34. The three other options were a Jantzen 400v at $5.63, a Solen 400v at $7.03, and the most expensive Kimber Kap 200v at $27.66. I have heard many mixed reviews of Solen, so they have never been my first choice. The Kimber was out because I was trying to stay "budget" as was the Dayton 1%. This left the Dayton 5% and the Jantzen for my choosing, and here was the breakdown:
Dimensions: 22.5mm x 56mm
Construction: Metallized Polypropylene
Dimensions: 27mm x 44mm
Construction: Metallized Polypropylene
As is obvious, the caps are similar and the only real difference is the voltage. I'm not sure that the voltage of the cap has an effect on the sound as long as the stock voltage is meet, but being a tube guy, I like high voltage. One point for Jantzen. The price of the Dayton is lower, so one point for them. After reading many reviews, both the Dayton and Jantzen tested well for "budget" caps, which makes the score tied 2-2. The last thing I am looking at is the size. Since the Monitor 5 Jr has a compact crossover, size was a concern. I didn't feel that diameter was a huge concern because they are both mid size and similar sizes. However, the Dayton was longer than the Jantzen by 12mm, so that makes the winner Jantzen at a score of 3-2. Plus, I just wanted to try them, so call me biased.
My bag of parts (four total to be exact) took about a week to arrive and I only paid $1.50 for shipping! The total came to about $20, which I thought was a great deal and well worth it for a little crossover work (and hopefully a sound improvement). When they arrived, I inspected the contents of the package and received everything that I had ordered (which is my experience with PE). Even though I had the dimensions of the components, I never really know the size of something until I see it and hold it. The components were a little larger than I expected, but still medium size as far as hifi components go.
The Monitor 5 Jr rebuild started with opening up the speakers cab by removing the binding post/crossover cup from the back. The speaker leads are soldered directly to the crossover, so I had to disconnect them from the drivers themselves. This proved easy as the mid parallels the crossover, but I actually had to remove the tweeter to disconnect its leads because of the cramped quarters. I then pulled out the cup to look at what I had. The board is actually screwed to the cup face down so that the components are inside the .56mH inductor. I removed the screws that held down the board, and the board didn't come up. After a few "polks" around I realized that the leads from the .56mH inductor, as well as the leads from the binding posts were soldered on in a fashion that provided very little wiggle room for the board.
My first task was desoldering these joints to allow me to remove the board for further work. Be sure to mark where components and leads were removed so that you replace them in the right location when you are putting the board back together. I started desoldering all the components on the board and cleaning up the holes and pads. The only tricky piece to remove was the capacitor since one side of it was glued to the .19mH inductor. This was successfully removed my desoldering one end, prying the cap off the board and inductor by pulling from that end, then desoldering the other end. Once everything was removed, I started by soldering in a jumper where the old polyswitches had been. I bent the jumpers over on their sides since this would allow the new caps to sit lower on the board. Next was the resistor. Since it was somewhat tall and skinny, it went in standing up, with the top lead having to be extended and run back down to the other hold. Both of those pieces went back onto the board like stock.
Installing the new Jantzen caps however changed the board on my little Jrs. Soldering them into the original holes was not an issue as they were just about as wide as the caps. A little fitting was required, but no where near that of my SDAs. The problem came when I soldered the caps on, and then turned the now completed board over to reinstall it in the inductor/cup. There was no way that it was going to fit. After considering my options, I figured out that I was going to sandwich the board against the inductor/cup. I straightened the solid inductor wires and the binding post wires and placed the board and components against the inductor/cup. Then, soldered the four wires to keep them and the board in place. The physical strength of the unit is not as good as if it was screwed or glued to the inductor/cup, but it does hold pretty well because of the solid core wire. I don't know if I would trust this set-up if I was shipping the speakers or something violent like that, but for normal wear and tear, it will work well.
Now that the rebuild was complete on the board, all that was left was reconnecting the leads to the drivers and reinstalling the tweeters and binding post cups. Luckily, the new, larger capacitors don't change the clearance of the cups in the speaker cabs. With all the screws back in place, I connected the speakers to my amp to make sure that everything was working and operating properly. With all the drivers checked and working properly, I turned the amp back off as I didn't want to get an impression of the sound before they were burned in at least a little. My little Monitor 5 Jrs are now being burned in using a combination of music and pink noise. I will do initial listening tests at around 10 hours of operation.
If I were to do this over again, I would probably solder the cap upside down on the board so that I could screw down the board back onto the cup in the original fashion. This would probably provide a little more stability to the crossover, as well look a little better. This was an easy project and once I figured out how I was arranging the components, the second board took me only about 15 minutes. I would highly recommend this for anyone wanting to get into electronics work but not wanting to get over your head for a first project.