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  1. Many of you recall from my post titled "AR-9 / AR-90 Crossover Re-capping Adventure" that I had a heck of time trying to find the proper combination of the attenuation resistor switches to achieve acceptable results. People probably thought I was crazy or losing my hearing. The culprit was the 24uF Solen MKP 400V capacitor installed inline with the Upper Mid Range (UMR.) It was all over the place depending on program material. It sounded anywhere from great to shrill and exhibited the uncanny ability to drill down into a recording, extract whatever grain is there and put it front and center. This cap seems to be incompatible in this particular circuit with this driver. Stimpy suggested adding a Dayton 0.1uF F&F bypass cap as a fix. Doing so decreased the shrillness of the Solen, but also increased the grain to the point of rendering many recordings unlistenable. My goal is not simply to obtain the best sound from the best source material, but also to get acceptable results from average recordings. So this very unforgiving capacitor had to go. I decided to try one other poly cap before going to an NPE as Carl, RoyC and others had suggested. I had read that the Jantzen Cross Caps are considered comparatively smooth sounding, so I installed them in place of the Solen. Although the improvement was a step change, I still wasn't quite where I wanted to be. A 16 hour burn-in period using high volume pink noise made no difference. So I installed Mundorf E-Caps (Plain) in matched pairs purchased from Sonic Craft: http://www.soniccraft.com/index.php/mundorf-ecap-ac-c-23_318_358 Like magic, everything was now where I wanted it to be and has remained so after several days...no "it sounds different on Tuesday afternoon than it did Monday night;" no waiting for burn-in; no endless effing around with the attenuation switches. Great recordings still sound great, average material is very listenable, and I perceive no loss of detail in going from the poly cap to the Mundorf. Remarkably, the Mundorf sounds like it has more "air" and "depth." I surmise that this perception is related to how the E-Cap integrates into the entire speaker system rather how it directly compares to the poly caps. Notes: 1) I confirmed with Carl that the E-Caps with their 70VDC/50VAC rating is a suitable replacement for the stock 100VAC Callins NPE. 2) The 24uF Solens were still installed in the AR9 surround speakers and got the 16 hours of pink noise burn in. It still isn't acceptable but for some unknown reason has always sounded more tame in the AR9 than the AR90. 3) I use -4.5dB (estimated) attenuation with the E-Caps in the UMR. I've always used -3dB going back to 1980. The attenuation network is now set up so that I can go back to -3dB if desired. The AR9's are next. I may try the Cross Caps first just as an experiment before going to the E-Caps.
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