The JDI Mk3 from Radial Engineering is a professional, passive direct box that converts hi-impedance instrument signals to a balanced low-impedance output, allowing long cable runs without noise. The unit is ideally suited for all instruments including keyboards, bass guitar, and acoustic guitars for use in studio, broadcast, and live sound reinforcement.

Because of the transformer, the JDI provides 100% isolation between the instrument input side and the balanced output, eliminating hum and buzz caused by ground loops. Passive DIs that use inexpensive iron or steel core transformers can degrade sound through phase shift at various frequencies, a phenomenon known as group delay. This has the effect of making bass sound indistinct, causing the mid-range to smear and lack punch.

The JDI employs a Jensen transformer with a nickel-laminated core which does not retain a memory or polarity. This reduces phase distortion, improves linearity and lowers harmonic distortion. A 15 dB pad is provided for high-level instruments to avoid input distortion. A merge switch converts the thru output to a second input, allowing two signals, such as those from a stereo keyboard, to be summed to mono when input channel availability is limited.

The unit is built to withstand the abuse of the road. The book-cover design features an internal 14-gauge steel skeleton that is corner welded to ensure the internal electronics will never be subjected to outside stress. The military grade PC board is mounted on steel pem nuts and the whole is then enclosed in a second steel casing. The passive design requires no power source.