Palmer Audionomix Active DI Box
Standard active DI box. Can be operated with 9 V batteries or 48 V phantom power. High-impedance input; higher output level than with a passive DI box. Active circuitry allows for high input impedance ( 1 meg. ohm) and higher input sensitivity (typical difference between in and out -4 dB). Maximum output impedance with phantom power operation +10 dB. Output: transformer balanced. The special "floating ground" circuitry enables ground lift even during phantom power operation. Metal case 110 x 73 x 42 mm.
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.
Passive or Active?
People often claim that “Active DI boxes are always better than passive DI boxes”. It is true that you can use cheap electronic components to tweak up a “doorbell” transformer and so reduce its ear-piercing frequency response. The question is whether such an active DI box actually produces a better sound than a passive one. We believe that even inexpensive electronic musical instruments have adequate output level ranges to produce satisfactory, if not excellent, results using a passive DI box. A passive DI box is therefore the right choice for most purposes. However, some instruments without electronics, such as passive bass guitars and acoustic guitars fitted with a pick up but no preamp, require very high input impedances which can only be supplied by an active DI box. Experienced professionals also use active DI boxes when transmission routes are severely distorted. The DI box produces higher levels, which can be reduced at the microphone input on the console by pressing the PAD key. This improves the signal-to-noise ratio. If possible, active DI boxes should be connected to a +48 V phantom power supply. This produces a better dynamic range compared to using a 9 V battery power supply.