A buzz/hiss in the bottom range of the B string (open and fretted string) was bothering me for almost 4-5 years. The degree varied with the type of strings, tension, weather etc. etc. but never really diappeared. Nut/saddle modification/exchange showed no improvement and there was obviously no crack nor loose strut. So I had already accepted this fact, when I happend to make business trip to Reutlingen and decided to take this opporunity to consult luthier Armin Gropius, who I from earlier contacts considered to have some experiences with Kohno guitars.
The visit progressed as usual. Not easy to demonstrate the problem but this time I was more lucky, as Armin turned out to be a very nice and patient guy with a great deal of interest and commitment. After inspecting all typical aspects, nut, loos strut etc. he remained clueless at the end and we entered another string discussion. In that context I explained that really high tension trebles cause a sharp line below the trebles side of the soundboard running parallel to to the center line and extending from almost the lower edge of the bridge up to the upper bout (fingerboard). My idea was, that this was caused by a strut but he immediatelly opbjected, that there is no strut in that area usually. It was again not easy to show, but when viewed from a certain angle he could identify this line. He then inspected this area from inside with light and mirror and detected that there is no crack BUT this line looked from inside as if somebody has drawn a was a very fine pencil line. This immediatelly arouse his interest as this might indicate a partial crack which probably extends not completely through the soundboard as there was definitly no sign of crack from the outside. There was only one night at disposal for actions, as I had to return the next day, he offered me to close this potential partly crack with glue and an appropriate suspension. He was convinced that it was at least worth to try, whereas the risk for unexpected downsides was close to zero. I agreed to this action and when I returned the next day he handed over the guitar with the only comments that he in addition had replaced the Dogal HT with Hannabach Silver 200 MHT and he was curious about my comment.
In brief, the result was unbelievable. No hiss any more and the basses stood out so clear that I seemed having back the beautiful sounding guitar from when I bought it in 2006. Armin was happy to find his oppinion confirmed and explained that this somehow provisional sizing might be always stable but adding some small wooden support under the pretended crack line could be more secure. But I felt happy with the result the way it was and we kept this option for the case that the hiss might come back, which is luckily not the case and it is even quite the contrary as my Kohno keeps improving, is significantly louder with even better separation.
The intention to share this experience is to highlight this as a possibility for problems like this, in praticular as the diagnosis is everything else but obvious. Would be glad if this helps one or the other!
After that I was lucky being confronted with three finished double tops from Armin for testing prior to their shipment. One Spuce/Brasil w/h double sides, one Spruce/IR and on one Cedar/IR. No wood combination for the double tops. In the first place I was impressed by their playability and Armin's immaculate work. As it was the first time for me to play a double top I can only report my subjective impression. Very fundamental and intimate sounding, well balanced, more separation on the spruce guitar with moderate power. Albeit being double tops It didn't took long that the spruce/IR became my favorite but unfortunatelly I had only "small money" with me!