This was from Tom 5/25/2018
"The 2.7 midrange is fed through a 400uF electrolytic cap, albeit with a PP and styrene bypass in parallel. The 3.7 uses a bank of 75uF polypropylene caps with a styrene bypass. Multiple smaller PP caps provide faster reactions and less distortion than a large electrolytic. " "I believe this could be the main reason for the improvement in detail and smoothness in the sound " Rob
From me 7/3/2022
A few months ago I had finished upgrading the woofer board and heard some improvement but nothing earth shattering , I am almost finished with the coaxial and the improvement is way beyond anything I would have thought possible .
I kept things simple , replaced the resistors with Mills , upgraded the capacitors , bringing the electrolytic capacitors within and/or lower tolerance specs , making only one change suggested by Tom , replacing the 400uf capacitor with 4 100uf caps .
What I discovered was that the electrolytic capacitors used on the shunt or negative side were out of tolerance , the 68uf cap used on both the tweeter and woofer were up to 20% over while the 330 and 220uf used on the mid was about 7% over . The 68uf caps were replaced by Mundorf caps that were about 3% over but replacing the 330 and 220uf caps was a bit of a problem . First I replaced them with ERSE " 5% " tolerance caps that turned out to be over 11% over ! I didn't even try to listen to them . Then I tried Jantzen " 5% ' caps , they were about 6% over . I listened to them for a while and was happy with hearing the improvement that the other upgrades made but it bugged me that Tom was telling me that Thiel's tolerance max was 5% and mostly within 3% , so after asking Tom's advise I went with a 300uf Jantzen cap that together with the 220 I was able to achieve a 2% over tolerance .
Since I replaced/upgraded the resistors and capacitors ( except the 1uf's ) on coaxial boards at the same time I can't say how much the replacing of a 400uf cap is improved by using 4 X 100uf caps would be , I used Jim Thiels philosophy and Tom Thiels suggestion , if I had the room I would have replaced the 330 and 220 caps with 100uf max caps . Also I can't say how much better the 100uf Mundorf caps are than Solen or Jantzen caps would have been , the same for the Jantzen used on the negative side . I will say that the 1uf Purity cap on the tweeter made a large improvement in the sound stage and definition so I'm hoping/exception that replacing the 1uf " Made For Thiel " cap on the mid with the new 800v Purity cap will take the sound to a whole new level .
