“Most of the capacitors on the main board have been replaced with low ESR 105C Panasonic, and I replaced the 1uf electrolytes with much improved film to further reduce noise in the overall circuit. I replaced the NJM4556D headphone opamp with JRC2068DD which has faster slew rate and higher bandwidth. All these updates added more clarity on the high end (while still keeping the 16 bit K4 character) and with the mods it sounds better than the original K4 when I did a direct comparison against the unmodified one.
I replaced the LCD display with a much better one and installed a 10k trimmer resister. To adjust the display brightness simply insert a screwdriver in the + slot of the trimmer resister and gently turn however I already adjusted it to the best luminosity. I have also performed this modification to my other K4s since it’s a great improvement over the original display.
I installed a new volume slider potentiometer. It is now much smoother sliding than the original. And I also installed the latest Version 1.4 OS chip, purchased new.
I have found much (but certainly not all!) of what the K4 is capable and will keep the patches I designed after the circuit upgrade.
There are individual buttons to select or mute each layer which means that parameter access/sound design is relatively quick. Immediate muting lets you quickly hear the layer you are working on which is important for sound design. The K4 excels at resonant transcendent beautiful digital crystalline pads and the resonance is so high and fizzy that it can devolve into sizzling distortion so I never use maximum but it makes for a very interesting unique sound. Click here to visit listing on eBay