The Radial J+4 (part R800 8015 00) is a stereo line driver that takes unbalanced, low-output (-10 dB) sources such as computers, phones, tablets, CD players, DJ mixers and keyboards and boosts them to a balanced +4 dB professional line level on XLR outputs. That lets consumer gear connect directly to mixing consoles, recording interfaces and installed AV systems and run over long cables without signal loss. It combines active signal buffering with transformer isolation, so it adds clean gain while eliminating hum and buzz from ground loops. Inputs are provided on stacked 1/4" jacks, RCA and a 3.5 mm mini-jack, with a level control, high-pass filter and ground lift. Radial specifies 20 Hz - 20 kHz (+/- 2 dB), 102 dB dynamic range and 0.004% THD. It is built in a 14-gauge steel chassis measuring 84 x 127 x 48 mm (0.70 kg) and powered by the included 15 V DC adapter.