Another Monitor 10A thread

jdjohn

I picked up another pair of M10As off CL for just under $100...literally bought them out of the back of a rental truck. I should have walked away when I noticed the mid drivers were frozen, but at that point I really just wanted to get out of there, so I took them.

The magnets had shifted on all four drivers, causing them to seize, but I pulled them apart, reset and glued them back together utilizing a jig, and later added epoxy around the edges so it won't happen again. They work fine now...those drivers, that is.

Upon testing the speakers, I then noticed that one of the Peerless tweeters wasn't producing sound. No worries, I had an extra NOS Peerless, but after unsoldering the 'bad' one, I tested it and it actually worked. That has led me here since I think that crossover is bad somewhere, so I might as well just upgrade them. I removed the crossover from the cabinet that has no highs, and sure enough, the big yellow capacitor in this pic did not have any continuity. The same cap in the other, working, speaker does have continuity.

I believe I need both 2.5 & 2.7ohm 5W resistors, two 12uF capacitors, and one 34uF cap. The wiring schematic I found here on the forum for the M10 'original' indicates that one of the 12uF caps should be mylar, and the others electrolytic. Is that correct? It looks like other folks are using film capacitors for replacements. It's a little confusing two since all three caps are different sizes, but two of them are apparently 12uF.

Thanks for clearing things up for me.

Faustin

I am sure others will chime in, but you want to use film caps for both of the 12uf's. Resistors available today will be more in the 10 or 12W range.

westmassguy

The yellow cap is Mylar. The two black caps are Non-Polarized Electrolytics. All should be replaced with Metalized Polypropylene Film caps. As Bruce mentioned, use 10 or 12 watt Mills MRA or Mundorf MOX resistors, especially with the Peerless Tweeters. The Film caps will be quite a bit larger than the NP Electrolytics, so creative placement will be required.

jdjohn

Thanks for the help. How critical is it for the component measurement specs to match-up exactly? For example, Dayton makes a 33uF capacitor (for sale at Parts Express), but not a 34. Sonic Craft doesn't sell a Mills 2.5 ohm resistor, although they do sell a 2.4, and they have the 2.7. Parts Express has a Mills 2.5, but not a 2.7. I guess I could get a 2.5 from PE, and a 2.7 from SC, but I think I read that the Mills resistors at PE were made in Mexico, and QC is suspect, whereas the Mills at SC are NOS made in the US. Madness!

Westmassguy, I read in another thread where you suggested mounting the resistors underneath, so I definitely plan on doing that to save real estate on the top side.

Thanks again guys!

westmassguy

The 33uf is fine for the shunt. Sonic Craft has the 2.5 and 2.7 ohm Vishay/Mills, 12 watt.

jdjohn

Many thanks! I think those Vishay Mills are what PE sells...just not the 2.7 ohm.
I thought about Sonicaps for the capacitors, but it would be about $200 of caps altogether...worth more than the speakers. Since I now have two pair of M10As, maybe someday I'll splurge on the other pair with Sonicaps.

CGTIII

@jdjohn - I believe others about the value of upgrading 10A crossovers, though I haven't myself yet. If you just want them working perhaps stock crossovers would do. I have two extra if you're interested. PM me.

M10A's < $100. M10A upgrades > $200. Upgraded M10A's = Priceless???    

jdjohn

Thanks for the offer, CGT. These 10As are for the bullpen and testing purposes, so I can take my time with them...and I have a second stock pair that still work very well. My main loudspeakers are SDA-2Bs. I spend my tinkering time switching between restoring old turntables, vintage amps, and the occasional speaker. This will be my first attempt at XOs.

lawdogg

Good luck and enjoy the learning curve! I believe you will be impressed with the improvements.

jdjohn

Getting back to this project now (I actually upgraded my SDA-2Bs first), and wow I am really surprised at the amount of solder the factory used under the board of these 10As. They also left the leads quite long on the caps and resistors, and then slopped tons of solder on them. I certainly don't plan on doing the same when I put them back together unless someone tells me there is a good reason for it.

Here's a pic. In the 10 o'clock position is where the bare wire from the big bottom coil came in (it has already been removed), and it is particularly heavily soldered.

westmassguy

Typical. They're all that way

jdjohn

Thanks for your reply, Dave. Do you mean typical for 10As...maybe M7s as well? I know my SDAs were not like that.

I guess the plus side is that I could just re-flow that solder when installing the new passives. I would like to remove all that flux, though. I've used isopropyl with a big foam swab in the past. Any better tips for that job?

westmassguy

All the Monitors, RTAs, and 1st through 3rd gen SDAs from that era look like that. I remove all the excess solder with a solder sucker, clean both sides of the boards with alcohol, and start fresh with Cardas Quad Eutectic Solder.

jdjohn

Sounds good. That's what I did on my SDAs, including braided wicking for the final step of solder removal. My new solder is not quite as fancy as the Cardas, but it does contain silver.

Thanks again!

P.S. I did get some extra-long zip-ties for this project to hold down these big new capacitors, so will be drilling a couple of holes in the PCB. Of course the copper pads on these boards are huge.

westmassguy

I try and line up any new holes with the gaps in the copper.

VSAT88

jdjohn wrote: »

Thanks for the offer, CGT. These 10As are for the bullpen and testing purposes, so I can take my time with them...and I have a second stock pair that still work very well. My main loudspeakers are SDA-2Bs. I spend my tinkering time switching between restoring old turntables, vintage amps, and the occasional speaker. This will be my first attempt at XOs.

If you need a stock (or two, three, four) 12uF Mylar that will work let me know. Price is shipping only. An attempt at paying it forward for all the help I receive here. Just PM.

Edit: I am sure I have the 34uF's as well..Same cost..Free.

jdjohn

Thanks for the offer, VSAT, but I have new Clarity caps and Mills resistors waiting in the wings

I actually have a second pair of Monitor 10s as well that are stock and in working order, so it will be interesting to do an A/B comparison of those to this upgraded pair.

motorhead43026

I pulled my 10's from storage a week ago, has been over a year since I listened to them. I had rebuilt the crossovers a couple years ago but bought my SDA-2B's so into storage they went. I had forgotten how good these sound.

westmassguy

I developed a little modification, that my help with image smearing between the two woofers: http://forum.polkaudio.com/discussion/173834/westmassguys-idea-employing-damping-to-mitigate-comb-filtering-and-lobing/p1

jdjohn

Ok, all done. Real estate was scarce top-side, so I moved the small inductor coil to the edge, and mounted the resistors underneath - wrapped the leads of the 2.5ohm resistor around the leads of the 12uF cap.


For finally assembly, I actually had to hold the crossover board from inside the cabinet (passive radiator removed), and then attach it to the clips of the big lower coil and binding post section from the outside, with the very short coil lead as my last soldering bit...pretty tight space! Had a bit of a scare when one tweeter wasn't working, but it was just the fuse holder needing some more cleaning. I did an A/B with my other pair of stock 10As, and although I can't say it is night-and-day, there is more clarity, separation, and air with the upgraded pair...of course. The stock still sound pretty darn good, but I am pleased with the upgrades.

I still need to Dynamat the PRs and get or build stands, and consider westmassguy's woofer box treatment. Thanks for all the help and encouragement!

StantonZ

Looks good...better than mine! Hope you enjoy the "new" sound as much as I have.