most of the way to these speakers’ potential once I replace the resistors.
Super cool that you have Lexington boards and upgraded the coax feeds to ESAs. I am confident you’re getting better SQ than the SE version (FST boards plus SAs on the coax feeds).
My SEs had the FST boards with CYC MKT caps (other than the Clarity SAs on the coax), air core coils but with less than optimal winding integrity, and sandcast resistors (manufacturer unknown but similar construction to sandcasts from Xicon or Erse). Additionally, the printed circuit boards looked to have been somewhat burned underneath a couple of the resistors, so perhaps these were damaged by a previous owner playing very loudly.
During my upgrade, I did not listen to each single change I made so am unable to pinpoint everything. But I did pause at several stages and compared modified and reference channels in mono (using Roon to produce a mono mix). Comparisons I made were: 1) FST boards with sandcasts v Mills; 2) FST with Mills v “Tom Thiel boards” (CSAs though out, including on coax shunts, Lex-equivalent coils including Erse FoilQ in feed positions, and Mills resistors); 3) Tom’s boards with and without RTX Multicap bypasses on the coax feeds; 4) 160 v 250 V woofer shunt caps; 5) OEM binding posts and hookup wire v Cardas binding posts and hook up wire; 6) single v biwiring from the amp.
I heard at least some difference from each of these changes. In significance, I rank them: 1) CSAs + Lex/FoilQ coils (better resolution/textures/microdynamics; more open, clear, and transparent); 2) Mills MRAs (mitigated “glassy” midrange, improved bass impact/soundstage/“ease”): 3) Cardas wire and binding posts (more open/clear/holographic/“immediate”); 4) tie among biwiring (more relaxed/liquid/dimensional), coax Multicap bypasses (better “jump factor”, smidge more resolution), and higher voltage woofer shunt caps (bass “heft”, ease of presentation).
So,
@sdecker I strongly recommend you upgrade the resistors. That’s a nice upgrade for short money. Several sources indicate the CSA improves on the ESA but is it worth your time and effort? I recall you kept the 1 uF bypass caps, so maybe “yes” (ie, get full capacitance in a single cap or, if forced to run parallel, have the smaller cap represent a larger portion of the total capacitance). In your shoes, I would upgrade the *feed* coils to FoilQ or Jantzen wax foil (one coil on each board). I did not directly compare the foil to air core but I think it’s worth trying this given that you can get all four foil coils for <$100. I would replace the 100uF coax shunts if only because electrolytics drift with age. The best solution is to go with film caps as they sound better and will last far longer but those are also far more expensive and larger. Sticking to electrolytics, I would pick the Jantzens.
The other changes I made fall in the category of diminishing returns (although I had a big smile on my face with the Cardas, it seemed to snap everything into focus). You might try a small bypass on the coax feed caps. Something like a 0.1 uF Audyn True Copper Max, Clarity CMR, or Jupiter copper foil. I don’t know that these are better than the more affordable Multicap but am curious. I have each coax feed, including the 43 uF subfeed, bypassed at ~1% but you might try a single 0.1 uF on the 28 uF cap.