From the early eighties until the early nineties the transparency of audiophile-quality gear improved enormously. This is almost certainly the improvement in passive part quality (mainly capacitors, but also to a degree in resistors.) My observation is that J. Peter Moncrieffe in his publications and promotion of WonderCaps made believers out of many who had heretofore scoffed at the notion that these passive devices had a "sound". Electrical engineering courses, of course, had not even considered these subjects. I know for a fact that the folks that developed the HK Citations found part swapping a critical part of their development, at a time when virtually no one else was doing it.