Infinity Quantum Series Midrange Dome Repair, Complete Tinsel Replacement

Here's a 'how-to' I wrote up a little while back in a past forum life. Since I determined the process through experimentation and hard earned experience and since I wrote this up, I'm bringing it with me.

Advanced Infinity Quantum Midrange Dome Repair -- Complete Replacement of Broken Tinsels.

The tools you’ll need are as follows: a low wattage iron with a fine point tip – I use a cheap 15 watt Radio Shack special with the fine point that I’ve filed to be finer and cut a small groove in like a fountain pen to hold a solder drop where
I want it, a good pair of sharp, fine dikes/side cutters/ or whatever you call them, a pair of locking hemostats (sometimes called clamps or roach clips if you’re a child of the ‘60s/’70s), a magnifier lamp on a swing arm (its hard to make do with just a regular swing arm lamp and uncorrected vision as I do), and a sharp knife with a good handle and a short blade – keep a decent whetstone on hand as its easier if you keep sharpening the tip as it dulls in use during the repair. For materials, I use regular magnet wire that’s ~36 gauge I believe, 240 grit sandpaper to sand the enamel off the ends of the wire before soldering, solder tip cleaner (just makes it easier to keep the solder drop on the tip where you need it), flux and silver solder.

For preparation of the driver for repair, take some tape and place a piece on the back of the face plate and a piece on the magnet to mark alignment. Then remove the four screws holding the face plate to the magnet and gently pull the dome straight out to keep from buggering the voice coil. Leave the foam plug in the hole in the center of the magnet and put the whole thing in a new sandwich bag and seal to keep from accidentally getting filings into the VC gap. Put the screws and washers someplace where you won’t lose them and watch out for the silver washers, they’ll want to stay in place at first, but may fall out during repairs and roll off the face of the Earth. Fortunately, the VC on these midranges are shorter than the plastic ring on the back of the face plate that helps align the magnet during assembly (I think). So, if you’ll bed the connection tabs back, you can set the whole front plate right on your workbench without messing up the VC.

Now that you have the face plate with the dome before you, swing your lamp down for good light, sharpen your knife, and dig in. The channel where the wire leads from where it’s soldered to the connector tabs (the round depression on the front) is square bottomed and should have the resin dug out of for future replacement by something. Typically, the tinsel wire is wedged into one of these corners and just for the heck of it I like to remove it with all the rest of the old resin (mostly hard and will come up in shavings, but in the round depression is typically a little rubbery for some reason). Be careful to pull the knife tip out from the dome rather than push lest you slip and slice the dome in half. Where the channel ends, the resin is typically piled up a little bit to support where the tinsel goes out into free air to meet the dome. You can use the side cutters to cut this down relatively flat to easier tackle with the knife. Sharpen the tip as needed, for it dulls quickly (at least with my cheap Swiss Army knife, but not as fast as the scalpel dulled that I used initially) and sharper makes it easier.

When done, get the knife tip back ¼” as sharp as you can. Pick up the top plate and place your finger tip inside the dome supporting the fabric where the tinsel enters – try not to press too hard lest you deform the VC nearby or break it’s lead underneath. Very carefully bring the blade tip up along the fabric and pry/cut the resin off while approaching from several angles. This isn’t difficult or time consuming, but you do want a steady hand lest you slide the dome (fairly resilient and the resin will go before the fabric, but just in case …). I’ve considered using some solvent to make better work of this, but nothing seems to work. I’ve found that tetrahydrofuran (read the warnings and be careful) softens it up enough to be scraped away easily, unlike all the other solvents I’ve tried, but not to the degree to allow dabbing removal with a cotton swab. When that’s all cleaned up, take a sewing needle or a pin and prick a small hole in the dome near where the old tinsel entered. The needle is easier as you can roll it in your finger tips to drill a hole through the coating that stiffens the fabric without risking deforming the dome by pushing too hard.

Now, turn the front plate over and figure some way to secure it so that while pressing down or rough handling the dome you won’t smash it in too badly or break the other tinsel. For simplicity’s sake, I electrical taped a roll of masking tape around the dome to provide a firm surface while protecting the rest. Now, on the inside of the dome, you’ll see the tinsel wire glued to the fabric with more of that resin in a little loop before it heads up to the VC wires and joins up with them. Here you’ll prepare a little section of the loop for soldering using the process mentioned in the “Quantum 5 midrange help” thread I linked to earlier. Tin the bare metal and be sure to scrape away enough of the resin that it won’t flow over the tinned spot preventing soldering, but not so much that the wire comes free – it’ll break far, far too easily that way.

Take a ~6” length of magnet wire, long enough you have plenty to compensate for any mistakes, but not so long as to get tangled on everything. Take a little square of your sandpaper, fold it in half, and sand the enamel off 1/16” of the end by pinching the paper over it and pulling off the end, repeat. Add a hair of rosin to the bare copper here and tin it. When ready, take one of the ends and feed it through the needle/pin hole so that the tinned end remains inside the dome. Bend it just slightly so that the end will lay flat against the tinned portion of the dome VC. Use the linked to trick to wave a droplet of solder over the two to solder them wires together without melting the resin and forcing the need to scrape clean the tinned area. If need be, use the hemostats here to hold the wire in place, but do not lock them! If you do, it’s likely you’ll tear the connection apart or break the VC wire while trying to carefully unlock them (sliding teeth catch). Measure from the outside end of your replacement tinsel wire the resistance of the VC to the other tinsel’s connection tab. Make sure you’re measuring around 8 ohms so that you know your solder connection has good continuity and isn’t just pretending to be soldered while trapped in melted resin.

Before moving anything, very carefully apply something over the solder joint and the wire inside the dome so that it’s secured firmly to the fabric. Elsewise the loose wire could very well break when first playing music through your repaired dome or at the very least you’ll hear unpleasant rattling as the wire strikes the inside of the dome. The goop I’ve found to work fairly well is that little vial of clear liquid vinyl that comes with vinyl patch kits (for air mattresses and the like), it’s gooey enough to hold the wire well, but soft enough to flex with the dome. Be sparing, a little goes a long ways, but too much might add too much mass to the dome (you do have a little play room as the new tinsels are less massy than the old).

When the glue is set, flip the face plate back over and remove the tape roll or whatever else you used. Now, arc the magnet wire where it comes out of the dome into a similar shape and size as the original tinsel, lay the rest into the trough out to the solder tab spot to figure length and cut off the excess. Take your hemostats, lock them onto the wire to firmly secure it (to prevent stressing the solder connection inside the dome), and sand ~1/4” of the end of the wire free of enamel. Take your soldering iron and while holding the wire end down into that circular depression where I earlier mentioned the tinsel is secured to the connection tabs and solder it into place. Carefully lay the tinsel into the trough and figure out some way to secure it to prevent rattling. If you can find similar resin, great, pour that in there and coat the rest of the magnet wire to match the original. If not, take a short piece of electrical tape, fold it and press it into the channel securely over the wire using a flat bladed screwdriver of the back of you knife blade.

Carefully place the front plate over the magnet so that the VC goes into the magnet gap without and lateral torsion or scraping while eye-balling the screw holes so that they’re aligned with those in the front plate. Line up the previous markers so the same screw holes are lined up as before since nothing’s perfect and you may have VC rub if you don’t. When in place, loosely replace the screws and gently press with fingers on the surround roll of the dome nearest where the VC former is glued, press just a little bit in (<1/4”) and listen/feel for rub (slight hashing sound). If everything seems to be alright with no rub and the dome moves freely, tighten the screws, and recheck for rub.

Take your multimeter and in the resistance setting scrape the leads across the connection tabs. If the repairs worked, the driver will make a crackling sound. If it does, reinstall it while observing that the positive side of the driver marked by the orange dot is reconnected to the positive lead that was formerly removed from it, and enjoy the music.

If you have any further questions about the process, just ask. The whole process should take under 1.5 hours to 2 and only about an hour after you’ve had a little practice.

For final protection of the new tinsel and to prevent any rattling of the wire against the face plate channel, I’ve found “Liquid Tape” to be a good option. It flows to smoothly fill the channel and cover the wire while holding everything in place and damping vibrations. Cut some strips of masking tape to place along the edges of the channel and connection hole, then use the brush applicator that cones with the jar to dab in the liquid tape. Using your knife again, drag its edge lightly across the channel to level it with the face place so that when you remove the masking tape you don’t have a ledge sticking up. Again using the brush, carefully add a coating to the tinsel wire with a little dab at the dome to help hold the tinsel in place. I say be careful here as if you take too long or hurry too much, then you’ll end up with little hairs of solidified liquid tape sticking up and not looking so great. When done, remeasure your drivers to make sure nothing was damaged in the process and put on a good track to test for voice coil rub – George C. Scott’s voice in Patton makes for an excellent test in my experience.

- JP

Just heard from a big QLS-1 fan about a possible replacement option for broken tinsel midranges:

- JP

I recommend the above diaphragm replacement for any broken midranges. The re-doming diaphragm can be found for ~$10 per kit online and any competent speaker repair place should be able to install it.

For those who would like to attempt a DIY tinsel repair, which is perfectly alright as I have found my patches to be very reliable and more resilient than the aged originals, here are some pictures to go with the instructions in the first post. This is a partial repair as the tinsel stub on the dome was still pretty secure and offered a good soldier point. I had patched this driver before, but a friend of mine walked into the speaker and managed to break the repaired tinsel where the original segment was still bridging the gap -- the repair didn't suffer damage.

Here's your typical Belgian built Quantum 2 2" midrange dome, damaged tinsel on the right.

- JP

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This was the first dome I ever attempted to repair, hence the sloppy tinsel patch on the right. The break is at the kink of the original resin covered section.

- JP

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The driver disassembled via the removal of the four face screws. The pole piece is hollow, as per usual with better built domes (cheaper variants use a solid pole piece with a cotton wad glued to the front), and packed with a piece of foam held in place with the perforated cover. Be sure to keep track of how the faceplate is oriented to the magnet as you'll want to realign the same screw holes as before to prevent rub as they aren't perfectly centered. A piece of tape on the magnet corresponding to the side that matches the red sticker indicating the positive terminal should be sufficient.

Place the magnet in a sandwich bag to keep any foreign metallic shavings from being pulled into the gap while the driver is apart. If shavings or the like get in there, the driver may not work due to severe VC rub, may suffer damage with use, or exhibit a 'hash' sound. The connection tabs for the diaphragm may be gently bent out so the faceplate will set flat on a table surface. The raised plastic ring around the voice coil will prevent damaging the VC when done this way and provide a stable support for any work on the front.

- JP

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The backside of the faceplate. A roll of masking tape makes for a good support to hold the faceplate so while preventing crushing the dome or damaging the tinsels. Be sure to tape it into place if you're seeking to do a complete tinsel replacement, requiring the connection of the new tinsel to the voice coil just inside of the dome so the roll won't slide and undo your hard work. You can see the bent tabs and the rim that was mentioned in the prior post. The red sticker indicates the positive terminal, if this is loose, be sure to secure it to ensure proper phase when returned to the speaker.

- JP

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Close up of the voice coil and underside of the dome. Inside the voice coil former on the left can be seen the magnet wire tail secured to the dome cloth with glue. If a complete tinsel replacement is desired, this is where the glue will be scraped away to solder on the new magnet wire and the new tinsel glued back down. This is a good time to check to see if the magnet wire of the voice coil is still securely glued without any loose loops indicating melted glue or dark corroded spots indicated VC burn through before proceeding with the repairs.

- JP

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Close up of a tinsel channel after the old resin and tinsel has been removed using the point of a knife blade. This once soft coating has turned brittle after thirty years and so is easy to chip out in the square bottomed channel. At the solder connection on the right, the resin is usually still a bit soft and so may seem a bit rubbery to cut out.

The sticky coating originally applied to the dome and surround can be seen to have attracted a great deal of foreign matter. This doesn't affect the sound to a perceptibly degree and can be left.

- JP

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What the new magnet wire will look like when soldered to the connection on the right and to the old tinsel stub on the dome to the left. This piece is actually a bit too long and was later cut to approach the dome from the same angle as the original. Care has been taken to shape it to fit the channel and arch to the dome to make for a cleaner install and likely longer lasting fix. The tail on the right is temporarily left in place just in case the solder connection to the dome breaks necessitating re-replacement.

- JP

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The faceplate taped off around the tinsel channel to make for a clean application of the new tinsel coating. Masking tape works well enough for this purpose. The replacement tinsel tail was cut off shortly afterwards when the connections proved secure.

- JP

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Liquid Tape ™ is brushed into the channel and connection hole until filled to the top. This is done to strengthen the tinsel, prevent rattle, and make a slightly cleaner looking repair. The excess is carefully removed by running a knife blade across the top to level the surface and scrape off the excess. This liquid vinyl substance cures to a rubbery coating such as the original resin was when new. If desired, it can be and probably should be added to the arched tinsel section for damping purposes just as the dome was originally. When cured, carefully pull the masking tape off, check to verify continuity one last time, and reinstall.

- JP

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