So, I've had the pleasure to build three different khbaur YH-100's now (ty
@Philimon for the opportunity). For ease I'll call the first pair KH-100.1 (short for khbaur, YH-100, revision 1), and the other two KH-100.2 and KH-100.3. The first pair that I built, KH-100.1, which I've spoken about many times in this thread, seems to be a slightly different tuning than the other two!
KH-100.1's have better sub-bass extension, slightly pronounced 2.5kHz peak, more tinny upper-mids and seemingly a lot more mid-treble (few dB's @7-10kHz). It was most noticeable with a pad swap. The Aliexpress lambskin MDR-ZX700 pads I was using with KH-100.1's were solid lambskin and never accentuated the harsh upper-mids and mid-treble for me, they always sounded very good and balanced, yet once swapping to a revision of the same earpads which were fenestrated lambskin it was extremely evident. That said, KH-100.2's and KH-100.3's both play very well with these same fenestrated lambskin pads.
@Takarajima says KH-100.2's (which are now his) have more bloated and muddy bass, yet better midrange and treble clarity/airiness which I agree with on most accounts. To my ears KH-100.2's bass didn't sound muddy, just a bit more pronounced which I considered beneficial as KH-100.1's were always bit more bass light than HP/YH-1's, yet I didn't spend much time with KH-100.2's before sending them off and
@Takarajima has much more discerning ears than me, so I will yield to his impressions.
From memory, KH-100.1's drivers were never as shiny as KH-100.2's and KH-100.3's. The metal flux plates on 100.2's and 100.3's drivers looked almost polished to me. Maybe it's just been a while since I built the KH-100.1's but as soon as I opened the YH-100 enclosure for KH-100.2 transplant purposes my mind went "Whoa... that's shiny..." KH-100.3 drivers were also similarly shiny. I might be completely off-base here, but this was the only way I visually made any distinction. So maybe in fact there was at least one revision of the YH-100. Interesting, because I've never heard of any talk regarding this topic (am I out of the loop?). I hear differences between isotropic HP-1's and YH-1's, too, I believe they are slightly different tunings per subjective and objective measurements, it's just hard to make out these differences in their stock enclosures with so much backwave reflection/distortion, imho.
So maybe there is still more to be discovered with these vintage gems.
Just some food for thought. There very well may be bass light and bass heavy versions of YH-100 with bass light revision eeking out a little more sub-bass extension and bass cleanliness at the sacrifice of midrange and treble clarity. My KH-100.3's have a bass channel imbalance, and also the left driver can buzz with certain bass textures, however aside from these downsides, I feel they are actually more engaging! So if you thought you heard everything the YH-100 has to offer maybe think again. Differences are not huge, yet still substantial enough to make me prefer one over the other.