JitterBug FMJ: USB noise filter with a shielding metal case
The JitterBug FMJ is a small passive filter that fits a USB port and lowers the radio-frequency noise that computers, cars and other devices inject into the connection. Compared with the first JitterBug it adds a defence against interference coming from the surroundings, to which the USB interface is especially exposed. RF noise cannot be heard as such, yet it strips detail and contrast from music.
Filter circuits and shielding
Inside, two separate Noise-Dissipation circuits are at work; they attenuate the noise produced by both the transmitting and the receiving device and limit jitter and packet errors. FMJ stands for Full Metal Jacket: the shell is metal throughout, and the hinged door over the socket, which looks like plain rubber, is loaded with carbon and absorbs radio frequency. The device meets every USB 2.0 specification.
How to use it
In series it goes between the source (computer, smartphone, NAS, streamer, car system) and the USB input of the DAC. With DragonFly Black and DragonFly Red the result is always positive; with DragonFly Cobalt, which already contains part of the same filtering, a trial is advisable, because the effect depends on the system. In parallel, a second JitterBug takes another free USB port, with its door closed, and removes further noise from the USB power line: this is why it is effective even on ports reserved for service or updates.
Main features
- Dual Noise-Dissipation circuit for RF noise generated by the connected devices
- Full Metal Jacket case against outside interference
- Hinged door in carbon-loaded material, proof against radio frequency
- Usable in series ahead of nearly every USB DAC, or in parallel on a free port
- Complies with USB 2.0 specifications
