DI boxes are nothing new. So you would think everybody knows how to operate one and where it can be utilized. However, a specialist magazine went so far as to call a DI box a “hum killer” in a 19“ rack. We would therefore like to give you some brief details of the capabilities and uses of Palmer DI boxes.
The simplest way to give you a clear picture of how DI boxes work is to look at how they developed. In the “electronic Stone age”, only acoustic instruments were recorded using a microphone. When electronic instruments first appeared on the scene, you simply placed a microphone in front of the sound source, i.e. the loudspeaker. Then somebody hit on the idea of cutting out electric/acoustic signal conversion using a loudspeaker/microphone. This was achieved by feeding the electrical signal produced by the electronic instrument directly into the mixing console. However, as the electrical signal from a musical instrument is not necessarily compatible with a microphone output signal, a special signal converter box was required. This was where the DI box came in.

A DI box usually has three functions: 1. It reduces the line output level from electronic musical instruments to microphone level, so as not to cause overloading at the mixing console input. 2. Almost all musical instruments have an unbalanced output level. Microphones, on the other hand, have a balanced level. This means that an unbalanced signal must be converted into a balanced one. 3. Instrument output signal levels are in the mid to high impedance range, whereas microphone levels are in the low impedance range producing a nominal approx. 200 Ω. A DI box must therefore also be able to convert impedance levels. It basically consists of a transformer, which also isolates the electronic instrument from the mixing console. This in turn suppresses ground loops and any associated humming noise. It is obvious that a DI box cannot provide a 1:1 transfer ratio. However, in some cases, it may be possible to do this with an active DI box (PAD in 0 dB position), but only just within the DI box performance range. This is because the DI box output level is designed to operate within microphone level ranges and not at +22 dB line levels, e.g., required by radio stations.