Monitor 10 Crossover Rebuild

nspindel

I'm helping my nephew put together a decent little 2-channel system, he's caught the audio bug and I'm going to get him off the ground. I've got my re-capped and modded NAD 2200 that I'm going to give him, and we tracked down a pair of Monitor 10's on CraigsList quite close by that we're going to check out tomorrow.

I've been looking at the schematics, and it looks like there were two revisions, one with 6501's and then they moved to 6503's. Then I see a third schematic for switching to the SL3000. When I'm looking at the SL3000 mods, what I see is that there is a 0.4mH coil that needs to be switched to a 0.27mH, in addition to a few resistor changes. However, the schematic doesn't give any other values for the coils, e.g. what gauge they need to be. Wondering if anyone has any details here that they could share?

Also, I'm seeing on the schematic that there are places specifically calling for mylar caps, and some places specifically calling for electrolytics. I can replace both the molars and the electrolytics with film caps, e.g. Sonicaps, correct?

teekay0007

nspindel - check with westmassguy. I'm pretty sure he did these exact mods to a pair of Monitor 10s, with great results. He put in new RD-0198 tweeters.

nspindel

Why do I have a feeling he'll find his way into this thread?

Schurkey

nspindel wrote: »

I'm seeing on the schematic that there are places specifically calling for mylar caps, and some places specifically calling for electrolytics. I can replace both the molars and the electrolytics with film caps, e.g. Sonicaps, correct?

Yes. Mylar is a type of film cap. Polk specified Mylar caps in the most-crucial location(s); but replacing all the electrolytics and the original Mylar with fresh Mylar or other film caps is perfectly acceptable, the only down-side is increased cost.

I can't help you with molars, except to say that if you install those, the treble will have more bite, and the bass will be kind of long-in-the-tooth.

nspindel

Thought so. Thanks.

nspindel

Ah just noticing now that the schematic specifies that the new .27mH inductor needs to be .5ohm. Nice.

nspindel

Another question. I notice when they went from the first revision of the Monitor 10 to the second revision, they switched from a 1A fuse to a polyswitch. Wondering if the fuse holder is visible from the outside of the speaker? That would be an easy way to tell which revision these are.

westmassguy

The early 10s with Peerless had fuse blocks above the binding posts, after that they went with Polyswitches. For the SL3000 Mod, you can unwind the .4mh which is 22 gauge, or buy a new 20 gauge .3mh Jantzen, and up the value of the downstream resistor to 3 ohm. I prefer the Jantzen over the old Polk Bobbin Inductors. If you use Sonicaps for the Hi and Lo-pass, you'll need a riser board to fit everything, and relocate the resistors to the bottom of the board. If you go Sonicaps for the Hi-Pass, and Dayton for the Lo-Pass, you can squeeze everything on the board, but the resistor will still have to be mounted on the bottom.

nspindel

Awesome. Thanks for the advice! I'll update one way or the other tomorrow after we see the speakers. Hopefully updating that we bought them!

DracoAmericanus

i have a early version and on mine there are 2 external fuses, i would almost always scrap the poly fuse for a normal fuse or a resistor, you risk burning the tweeter is the resistor is the wrong value so that's why i prefer fuses, on units with a peerless tweeter the little hole in the middle is normal.
the poly fuses from that era had some problems, they where slow to respond and there resistance was not that consistent from one device to the next

westmassguy

nspindel wrote: »

Awesome. Thanks for the advice! I'll update one way or the other tomorrow after we see the speakers. Hopefully updating that we bought them!

Forgot to add, if you do go with Jantzens, you'll still have to unwind it. If they're Peerless, you're better off keeping them, or updating them to the Midwest Peerless Clones.

nspindel

Tonight worked out well, textbook case of things working out for the better in the end. We had found a pair of Monitor 10's with stands on CL last week for $100, but they were way out on Long Island. Would have been a 1:45 hour drive in each direction. We emailed the guy, but never heard back from him. Just when we were getting pissed off that we weren't getting a reply, up pops a pair 20 minutes away! The guy was selling a complete 80's vintage system, not much that I was interested in other than the speakers, so I asked if he'd sell the speakers separately. He said sure, for $250. I replied that he was pretty off on the price, showed him two ebay auctions for 10's that sold for $100 and $120, and told him that I paid $250 for SDA-1C's. I told him that if they were in perfect shape I'd pay $150 for them, but that I'd be giving them a good look over and if they had any issues I'd offer $100-$125. He agreed, so we drove to the guy's house and checked them out.

They are the earlier version, with the peerless tweeters, the fuse, and (presumably) the 6501's. The guy even had the original boxes and foam. Glad they have the peerless, good to know my nephew doesn't need to buy tweeters. So we will just leave the stock inductors, and then do the caps and the resistors. The grill cloth had some obvious cat damage, so we offered $125 and he accepted. Nice score 20 minutes away!!!

Brought them to my house and just tested them out with the modded NAD 2200 amp of mine that never sold, and they sound great right out of the gate. I'm giving the NAD to my nephew, it pairs up great with the M10's.

Couple more questions - just testing these things out we blew the fuses, and my preamp wasn't even past the 9:00 position. Good opportunity to teach my nephew how to tin foil a blown fuse! The NAD puts out plenty of clean power, am I safe to jump out the fuse just as we usually jump out the polyswitches? Replace with just a jumper or put a resistor in line?

Speaking of the resistors - on my 4.1TL's I used Duelands, I haven't used Mills in quite a long time. I read somewhere that Mills moved it's production to Mexico, and they're not sounding as good as they once were. Anyone know that to be the case? What's a good alternative? Mundorf?

Also, you can see in the pictures that there is residue from the foam that's stuck to the vinyl. Suggestions for a good solvent to clean off the styrofoam residue that won't hurt the laminate?

Also, there's some corrosion on some of the screws, I'll see if I can clean that up. Probably will go with hurricane nuts and threaded screws.

Here are some pics:

Nightfall

How old is your nephew? That is what would determine to me if I'd want to ditch the fuses or not. Just remember besides the clones, there is no replacing a Peerless tweeter.

Why not make a day, or few, (you and your nephew) of re-veneering them?

Schurkey

The last thing I'd recommend is eliminating a fuse that's recently blown.

Get some time on these things without blowing fuses BEFORE disabling the protection.

Popping a fuse with the volume that low seems suspicious to me.

nspindel

My nephew is 21. I'm just thinking if it was a polyswitch we would undoubtedly pull them, so what's different about a fuse? I was not impressed with how easily the fuses blew, we weren't anywhere close to close to this amp clipping. With the amp I'm giving him, I don't think I'm too worried about him blowing the fuses. If it was some 60W Technics receiver I'd be worried, but this NAD has loads of power.

As for re-veneering, he might do that some day. But for now, there's other fish to fry and the laminate is actually in excellent condition, no dings or scratches at all from what I can see, so it's really the least of our concerns if we can get the foam residue cleaned off.

Nightfall

That is odd that it blew so easily... I wonder if the previous owner replaced it with the wrong fuse or does that not make a difference?

nspindel

Correct me if I'm wrong, but isn't that one of the advantages of the polyswitches over fuses? Don't the polyswitches blow when the amp is clipping, whereas the fuse will blow at 1A whether the amp is clipping or not?

I need to check if the fuses are even the correct value, good call.

nspindel

Schurkey wrote: »

Popping a fuse with the volume that low seems suspicious to me.

Don't get me wrong. It was pretty loud. This amp has plenty of power, we had the preamp at 9:00 for a reason!

nspindel

Just checked the fuses, they are the correct value - 1A, 200V.


Now that I think about it though, the reason we like to remove the polyswitches is that they degrade the audio signal. Is there such a thing as audio-grade fuses that wouldn't have a sonic impact? In which case, as you say, better to have the protection in place.

nspindel

Stupid question. Of course there are audio grade fuses :exclaim:

nspindel

Jeez. 16 page thread on head-fi about audio grade fuses, running for 5 years:

http://www.head-fi.org/t/419939/audio-grade-fuses

embrown057

Look's like you question about the Mills resistors got lost in the fuse discussion. Call Elliot at Sonicraft they stock Mills and may have the value in stock. They are NOT purchasing the newer production parts.

westmassguy

nspindel wrote: »

Tonight worked out well, textbook case of things working out for the better in the end. We had found a pair of Monitor 10's with stands on CL last week for $100, but they were way out on Long Island. Would have been a 1:45 hour drive in each direction. We emailed the guy, but never heard back from him. Just when we were getting pissed off that we weren't getting a reply, up pops a pair 20 minutes away! The guy was selling a complete 80's vintage system, not much that I was interested in other than the speakers, so I asked if he'd sell the speakers separately. He said sure, for $250. I replied that he was pretty off on the price, showed him two ebay auctions for 10's that sold for $100 and $120, and told him that I paid $250 for SDA-1C's. I told him that if they were in perfect shape I'd pay $150 for them, but that I'd be giving them a good look over and if they had any issues I'd offer $100-$125. He agreed, so we drove to the guy's house and checked them out.

They are the earlier version, with the peerless tweeters, the fuse, and (presumably) the 6501's. The guy even had the original boxes and foam. Glad they have the peerless, good to know my nephew doesn't need to buy tweeters. So we will just leave the stock inductors, and then do the caps and the resistors. The grill cloth had some obvious cat damage, so we offered $125 and he accepted. Nice score 20 minutes away!!!

Brought them to my house and just tested them out with the modded NAD 2200 amp of mine that never sold, and they sound great right out of the gate. I'm giving the NAD to my nephew, it pairs up great with the M10's.

Couple more questions - just testing these things out we blew the fuses, and my preamp wasn't even past the 9:00 position. Good opportunity to teach my nephew how to tin foil a blown fuse! The NAD puts out plenty of clean power, am I safe to jump out the fuse just as we usually jump out the polyswitches? Replace with just a jumper or put a resistor in line?

Speaking of the resistors - on my 4.1TL's I used Duelands, I haven't used Mills in quite a long time. I read somewhere that Mills moved it's production to Mexico, and they're not sounding as good as they once were. Anyone know that to be the case? What's a good alternative? Mundorf?

Also, you can see in the pictures that there is residue from the foam that's stuck to the vinyl. Suggestions for a good solvent to clean off the styrofoam residue that won't hurt the laminate?

Also, there's some corrosion on some of the screws, I'll see if I can clean that up. Probably will go with hurricane nuts and threaded screws.

Here are some pics:

Very nice pair. I use Denatured Alcohol to clean the wood grain vinyl. It's a mild solvent, and should remove any residue, old wax buildup and any dirt embedded in the wax. Once that's dry, I go over the whole cabinet with Fantastic or 409. Hurricane nuts, great idea of course. I use either black oxide, Phillips Head SS machine screws, or even better, black oxide Torx cap screws. The Torx are much easier to torque down, and very little risk of slippage. The Peerless tweeters can be cleaned and painted. I use a Q-Tip dipped in Fantastic or 409 to GENTLY clean the dome. The face plate may require careful, light sanding with a fine sanding sponge. I use a bottle cap from a pill bottle to cover the dome for painting. You should be able to find one that fits right in the groove where the dome attaches to the face plate. Hold the bottle cap in place with a pencil or similar, and spray the face plate with Krylon Satin or Flat Black Enamel. As for the fuses, I would not eliminate them, or use Audio Grade at this point. For whatever reason, the Peerless Tweeters draw a lot of current compared to later SL2000s. Clean and polish the fuse holder, and apply some DeoxIT to the prongs and the fuse. A supply of 1 amp AGC Fast Blow Buss fuses would be a good idea. When you pull the crossovers, don't be surprised if you find heat damage around the resistor that's in series with the tweeter. Polk used 5 watt Sand-Cast resistors. The Mills MRA-12 will handle the Peerless just fine. As I mentioned earlier, mount the new resistors to the bottom of the circuit board, to clear some room. If using Sonicaps, the two 12ufs will fit on the board, but the 34uf is big, and will need a riser board. I can make up a little kit for you with the board and new nylon standoffs if you need.

nspindel

I didn't see a 34uF Sonicap, looks like they only go as high as 33uF. Did they make a 34 for you? I was thinking of just using two 17's. But at this point you've got me thinking about using the Daytons. I'm wondering how much difference it would make? I've always used Sonicaps all the way, but a 21-year old looks at the budget a bit differently. The price of a Dayton polypropylene 33uF is about $10, where the Sonicap Gen I is pushing $50. So for two of them, he's looking at about an $80 price difference. If the difference is marginal, I think he'd probably opt for the Daytons.

westmassguy

nspindel wrote: »

I didn't see a 34uF Sonicap, looks like they only go as high as 33uF. Did they make a 34 for you? I was thinking of just using two 17's. But at this point you've got me thinking about using the Daytons. I'm wondering how much difference it would make? I've always used Sonicaps all the way, but a 21-year old looks at the budget a bit differently. The price of a Dayton polypropylene 33uF is about $10, where the Sonicap Gen I is pushing $50. So for two of them, he's looking at about an $80 price difference. If the difference is marginal, I think he'd probably opt for the Daytons.

The 34ufs are hand picked, and cost about 5 or 10% more than the 33ufs. Use the best he can afford in the Hi-Pass. I've never had a problem using the Dayton 33uf 5% MPs in the Lo-Pass, while others may disagree, I've never heard a difference. You'll also be able to squeeze everything on the top of board if you use the Daytons, and still relocate the resistors to the underside of the circuit board.

nspindel

Ok, I think we'll probably go for the Daytons on the low pass, to keep the budget under control. I'll measure them when they arrive, hopefully they're within 5% of 34uF so we're still within spec. Then we'll go with Sonicaps for the 12's. Should end up with something that looks rather similar to your photos! Thanks for posting those.

nspindel

Any experience with Dayton binding posts? I've always used Cardas, but again I'm thinking budget here. Thinking about going with these:

http://www.parts-express.com/dayton-audio-bpp-g-premium-binding-post-pair-gold--091-620

nspindel

Actually I have a question about your photos - I only see one coil. The schematic shows a 1.55mH and a 0.4mH. Where is the second coil? Undermounted with the resistors?

westmassguy

nspindel wrote: »

Actually I have a question about your photos - I only see one coil. The schematic shows a 1.55mH and a 0.4mH. Where is the second coil? Undermounted with the resistors?

The small coil is mounted on the top of the circuit board. The Large 1.55mh is wrapped around the spool, that's part of the binding post cup. Can't miss it.

westmassguy

nspindel wrote: »

Any experience with Dayton binding posts? I've always used Cardas, but again I'm thinking budget here. Thinking about going with these:

http://www.parts-express.com/dayton-audio-bpp-g-premium-binding-post-pair-gold--091-620

Those are fine, but I believe they're brass, not copper.

nspindel

On the hurricane nuts - #8-32? For the screws, I'm guessing button heads for the tweeters and socket caps for the drivers and the pr? I'll probably look for hex heads rather than torx, so I can just use allen wrenches.

I've never worked with hurricane nuts before, I've always used Larry's rings. What's the best way to install them? Drill out the holes and then tap in with a hammer?