Our Passive Audio CW Filter Kit was inspired by our enthusiasm for non-powered – no batteries or power supplies required – electronics. The kit includes parts for a 250 Hertz bandwidth and one of the following center frequencies: 500, 600, 700 Hz. The circuit expects to see an 8 ohm source and an 8 ohm load, such as a pair of stereo headphones. A bypass switch allows for bypass and in-line reception comparison. The unit installs between your receiver's headphone jack and headphones or speaker. Assembly for experienced kit builders is less than an hour. The kit consists of eleven parts, including three high-mu ferrites, quality PCB and black plastic case. The kit can accommodate other center frequencies and bandwidths.