Panel rebuild guide?

[Jazzman53]

Hey Jazzman, Just found your webpage. Should have looked there first, lots of good information within. Will need to disassemble the Sequel II panels to understand if the copper foil covers the perimeter of the mylar. Its only visible at the single contact point so my one dimensional brain couldn't envision it along the entire edge.

By the way, nice pic with Mr. Carver. I live in WA state near Lynwood where he used to manufacture. Have an old M-500t amp and C1 preamp but it doesn't have long enough legs to drive electrostats. But his "new" Sunfire stuff definitely does. .

Cheers, Mark

Yeah I see Bob every year at CarverFest. He's a smart guy who thinks outside the box. We affectionately refer to him as the Bobfather.

Regardless of whether ML used a full periphery charge ring or a local contact only, I would add a full-periphery charge ring on any rebuild.

 

[Mark F]

The sketch shows how the diaphragm was coated in the Theater panel. I understand why ML did it this way, and I would guess most panels are configured this way. There's no real loss of output where the coating was omitted because the diaphragm is anchored and can't move at the spars. The omitted area also acts as a fire-break, preventing charge from reaching the spars and finding a leak path to a stator, which might otherwise happen if there were a dust buildup along the spar edges.

Yep. Sequel II panels (from 1995) have a continuous charge coating. SL3 panels (from 1999) have coating islands. Am assuming the charge rings extend along the entire perimeter of the panel making electrical connection with the islands but that won't be apparent until stators are separated exposing the mylar.

Have not disassembled my panels yet but inspected them and they are definitely not attached at edges or spars. Only held at top and bottom edges, likely with 2 sided tape. This is supported by a post on DIY Audio shown below. Makes chances of disassembly without tearing mylar higher assuming one goes slow with exacto knife and/or string saw.

Will order a can of Licron Crystal and continue to read up while awaiting delivery.

Its really too bad ML doesn't publish an exploded diagram of panels with a materials list and assembly tolerances.

Thx again for sharing all your wisdom and insight.

https://www.diyaudio.com/community/threads/help-me-fix-these-poor-ml-sequels.248926/page-4
"Yes the old MLs were just fixed by tape along the upper and lower rim.
That kept cost lower as for faster and easier mounting.
It also made repair and service easier.
A major drawback was that the panels tend to rattle like hell."

 

[Mark F]

Yeah I see Bob every year at CarverFest. He's a smart guy who thinks outside the box. We affectionately refer to him as the Bobfather.

Regardless of whether ML used a full periphery charge ring or a local contact only, I would add a full-periphery charge ring on any rebuild.

Do you have a source for adhesive copper tape? Pretty sure I'll roll the dice and move forward. In the worst case, I tear the film and end up with new replacement panels. .

Ya, Bob has made some pretty amazing products over the years. The M-500t + C1 preamp was my first big purchase after college. Still have both although the amp has bug in the power supply and needs recapped. His new tube amps and line source speakers are pretty sexy but my budget suggests rebuilt 29 year old MLs Sequels are a better fit.

 

[Jazzman53]

Do you have a source for adhesive copper tape? Pretty sure I'll roll the dice and move forward. In the worst case, I tear the film and end up with new replacement panels. .

Ya, Bob has made some pretty amazing products over the years. The M-500t + C1 preamp was my first big purchase after college. Still have both although the amp has bug in the power supply and needs recapped. His new tube amps and line source speakers are pretty sexy but my budget suggests rebuilt 29 year old MLs Sequels are a better fit.

Yes, I get the tapes from McMaster-Carr. At the end of my write-up for the Theater panel is a parts list for all of the materials.

Different speaker models may use different tape thicknesses but I'm guessing they would be the same. You would want to measure before ordering, to be sure.

Here's a link to my write-up with materials list:
https://jazzman-esl-page.blogspot.com/2011/11/compensating-diplole-phase-cancellation.html

 

[Jazzman53]

It will be interesting to see if the front spars are bonded to the diaphragm in your Sequel panels.

There is no compelling reason why the front spars would need to be bonded to the diaphragm, or for the stators be bonded together at all.

Functionally, the stators need only be constrained together in contact. The frame alone may be sufficient for that.

However, from an ease of handling during manufacturing standpoint, it makes sense to partially bond the stators together.

It's been a pet peeve of mine that manufacturers don't make the diaphragms easily accessible for servicing.

 

[Mark F]

It will be interesting to see if the front spars are bonded to the diaphragm in your Sequel panels.

There is no compelling reason why the front spars would need to be bonded to the diaphragm, or for the stators be bonded together at all.

Functionally, the stators need only be constrained together in contact. The frame alone may be sufficient for that.

However, from an ease of handling during manufacturing standpoint, it makes sense to partially bond the stators together.

It's been a pet peeve of mine that manufacturers don't make the diaphragms easily accessible for servicing.

Found another thread on the ML forum describing disassembly and repair of Sequel II panels with pix posted by Member Leethomas in 2008.
https://www.martinloganowners.com/threads/renovating-my-sequel-2-panels-part-1.7424/

Sounds like the only hard part is getting the front stators separated without damaging mylar film?

Waiting delivery of adhesive copper strip and Licron Crystal spray. Only real unknown is what thickness of tape to use for re-attaching front stators. Doesn't seem to be published anywhere. Will try to measure spacing before disassembly and use 1/16" foam VHB for reassembly in absence of other data.

Thx again for sharing all your wisdom and expertise!

 

[Jazzman53]

Found another thread on the ML forum describing disassembly and repair of Sequel II panels with pix posted by Member Leethomas in 2008.
https://www.martinloganowners.com/threads/renovating-my-sequel-2-panels-part-1.7424/

Sounds like the only hard part is getting the front stators separated without damaging mylar film?

Waiting delivery of adhesive copper strip and Licron Crystal spray. Only real unknown is what thickness of tape to use for re-attaching front stators. Doesn't seem to be published anywhere. Will try to measure spacing before disassembly and use 1/16" foam VHB for reassembly in absence of other data.

Thx again for sharing all your wisdom and expertise!

You may not need any tape at all.

If the stators were only bonded together at the top & bottom edge bands, then the only tape that would conceivably be needed would be the tape along the top & bottom edges of the front stator (only).

If that tape is intact and still tacky after separating the stators, you would not need to replace it--- just press the stators back together, after re-coating the diaphragm and replacing the charge ring.

If that tape is not tacky enough to re-bond the stators, then just add a layer of 4-mil double-sided adhesive tape. You can find 1/2" X 65" roll on Ebay for $20

One more thing: The foil tape used for the charge ring will have a thin adhesive on one side, and it's available with either non-conductive adhesive or conductive adhesive. You want the type with conductive adhesive, which is McMaster-Carr part number 76555A711 (per my parts list).

 

[Mark F]

You may not need any tape at all.

If the stators were only bonded together at the top & bottom edge bands, then the only tape that would conceivably be needed would be the tape along the top & bottom edges of the front stator (only).

If that tape is intact and still tacky after separating the stators, you would not need to replace it--- just press the stators back together, after re-coating the diaphragm and replacing the charge ring.

If that tape is not tacky enough to re-bond the stators, then just add a layer of 4-mil double-sided adhesive tape. You can find 1/2" X 65" roll on Ebay for $20

One more thing: The foil tape used for the charge ring will have a thin adhesive on one side, and it's available with either non-conductive adhesive or conductive adhesive. You want the type with conductive adhesive, which is McMaster-Carr part number 76555A711 (per my parts list).

Would be nice to assume 29 year old foam tape will release freely from the stator. If that happens, I owe you a beer and should probably buy a lottery ticket. It seems I have 1/2" x 0.004" VHB adhesive on wax film here. That's the same material used to attach detailing chrome to bumpers. Ask me how I know.

Cheaped out and bought the 1/4" copper tape from Amazon. It was specified to have conductive adhesive so hopefully is the right stuff.

Also bought Kapton tape to place over the copper charge ring if needed. Doesn't seem like anybody bothers since its not exposed on the finished unit. Handy to have either way.

What would be your best guess for mylar to front stator spacing should the foam tape holding the front panel not cooperate?

 

[Jazzman53]

Would be nice to assume 29 year old foam tape will release freely from the stator. If that happens, I owe you a beer and should probably buy a lottery ticket. It seems I have 1/2" x 0.004" VHB adhesive on wax film here. That's the same material used to attach detailing chrome to bumpers. Ask me how I know.

Cheaped out and bought the 1/4" copper tape from Amazon. It was specified to have conductive adhesive so hopefully is the right stuff.

Also bought Kapton tape to place over the copper charge ring if needed. Doesn't seem like anybody bothers since its not exposed on the finished unit. Handy to have either way.

What would be your best guess for mylar to front stator spacing should the foam tape holding the front panel not cooperate?

Actually, you want the tape on the front stator to remain bonded to the stator but you want it to release from the diaphragm.

When I did the Theater panel, I inserted a butter knife between the diaphragm and front stator tape.

Unlike your Sequel panel, the Theater panel's stators were bonded together around the entire periphery, and the front spars were bonded to the diaphragm, which is why I was unable to save the diaphragm on that panel.

Regarding the Kapton tape, you want to make the soldered connection between the wire and foil as thin as possible so that it doesn't prevent the stators from mating, and you want to wrap that connection with the Kapton tape so that you don't have any exposed bare wire near the stator edge where it could arc to a stator. There is no need or advantage in covering the charge ring with Kapton tape.

 

[Jazzman53]

Actually, you want the tape on the front stator to remain bonded to the stator but you want it to release from the diaphragm.

When I did the Theater panel, I inserted a butter knife between the diaphragm and front stator tape.

Unlike your Sequel panel, the Theater panel's stators were bonded together around the entire periphery, and the front spars were bonded to the diaphragm, which is why I was unable to save the diaphragm on that panel.

Regarding the Kapton tape, you want to make the soldered connection between the wire and foil as thin as possible so that it doesn't prevent the stators from mating, and you want to wrap that connection with the Kapton tape so that you don't have any exposed bare wire near the stator edge where it could arc to a stator. There is no need or advantage in covering the charge ring with Kapton tape.

I want to add to the above information:

The double-sided tape adhesive on the front stator forms two bond lines. One being stator-to-adhesive and the other being adhesive-to-diaphragm.

The separation method most likely to save the diaphragm is to cut thru the adhesive tape with a sharp blade where the tape contacts the stator. This way; the cutting implement will not contact the diaphragm. However; you then have to replace that spacer tape. ($58 + shipping for a 15ft roll). I suppose if you cut thru it cleanly, you could insert a layer of 4-mil double-sided tape and reuse it.

The separation method most likely to save the tape adhesive is to insert a butter knife between the front stator tape and diaphragm. Pyring the stators apart there offers the possibility of saving both the diaphragm and front stator tape.

You could pry a corner and see if it pops loose. And if not; cut thru the tape where it contacts the front stator.