X3 with K67 Capsule. The hand-tuned 34 mm K67 capsule is gold-sputtered and made from pure brass and Japanese Mylar at 3 microns (as opposed to the traditional 6-microns), which according to TZ (Tech Zone) makes the microphone more sensitive with an improved signal to noise ratio. The transformerless JFET circuit enables the. To handle transients (like drum overheads) with minimal distortion, or any unwanted compression effects – a max SPL of 135 dB with very low self-noise at.