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Old Martin Logan Aerius Crossover rebuild

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I recently picked up a nice old pair of Martin Logan Aerius speakers (built May 93) which I’m looking to do a complete rebuild of when I find the courage to do so. I’m looking for some advice as to the best way of tackling the crossovers since the majority of the existing caps are 25 year old electrolytics.


Martin Logan sent me the crossover schematic which I’ve included below. Reading this I’m looking at 2 of each of the following caps:

For the top end: 10uF, 15uF & 22uF

For the woofer: 80uF, 100uF, 470uF


The inductors are air core so I’m not going to worry about those or the resistors.


I don’t have a small fortune to invest in super high end caps so am considering some bypass options as well as some premium ELKO caps for the bottom end - I may need to combine a few to get the 470uF.


I’ve looked into this a little and there is a lot of talk about using the Vishay MKP1837 0.01uF (readily available at Speakerbug) as a tiny bypass cap. At this stage, for the ESL panel capacitors, I’m *thinking* about using a combination of Jantzen Standard Z-caps and Premium Z-caps where my budget will allow and add a bypass to each using the Vishay.


I haven’t had any experience with bypassing though so I’m unsure if this is the best approach or even a good one. The speakers which I’ve recapped have always just been like for like values.


I would appreciate any suggestions & advice

ML Crossover.JPG

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I’ve used the Vishay MKP1837 0.01uf as a bypass on a 47uf and 25uf MKP on/off....beat me if I can tell the difference.   Not sure if you are going to notice the difference in a XO network for speakers.  I’ve used them for psu bypass too on electrolytic 100uf....

However utilising these instead of ceramic smooth the SQ up in a input fet stage.    The ceramic that was replaced were for RF suppression.

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Not capacitor related, but the main problem with all ML speakers of that vintage is that the conductive coating on the Mylar membranes degrades over time. I have heard that the conductive particles float off the membrane as they get attracted to the charged stator panels, eventually leading to a dull lifeless sound in the speaker. Some call it a fatal flaw, but my suspicious nature tells me it was a bit of planned obsolescence by ML as they did a roaring trade with replacement panels @ $1-2K a pop!


Also, ML panels are difficult to take apart being glued tightly in place (with risks of bending and crumpling the metal stators) making refurbishment difficult. If you do manage to remove the stators successfully, then it is just a matter of recoating the Mylar membrane with a specific conductive liquid solution. A repair kit for all electrostatic speakers can be purchased cheaply from Rob MacKinlay at ER Audio.com in Western Australia.


Once repaired in this manner the MLs should go for another 10yrs+. Btw, I don’t think the newer ML speakers are prone to this problem.



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Posted (edited)

Maggie’s have a different kettle of problems ...aluminium strips attached to a moving plastic sheet of mylar/kapton, the glue denaturing over time and causing the sheet to resonate, flap and rattle. 

Edited by Steve M

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Thanks guys, I'm tackling the panels separately and have already spoken to Rob and a few others :)


I've also read that aside from the Vishay's using corresponding values ~1% of the main capacitor is an effective bypass. I.e. Running a cheaper 10uF Janzten Z-cap in parallel with a 0.1uf Superior/Silver Z-cap. Not sure how effective that is? 


Given that the panels are so revealing (when working 100%) I'm keen to get the most out of the crossover within my budget of a couple of hundred dollars.

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