Editing DI unit (section)

==History==
[[Image:WolfBox2.jpg|thumb|200px|right|A vintage Wolfbox custom-made by audio engineer Ed Wolfrum in the 1960s.]]
[[Passivity (engineering)|Passive]] direct boxes first appeared in the United States in the middle 1960s, most notably in Detroit at radio stations and recording studios like [[Motown]], [[United Sound Systems]], [[Golden World Records]], Tera Shirma Studios and the Metro-Audio Capstan Roller remote recording truck. These DIs were custom made by engineers like Ed Wolfrum with his "[[Wolfbox]]" and by concert sound companies to help amplify electric musical instruments.

These boxes typically contained an [[audio transformer]] with a turns ratio from approximately 8:1 to 12:1 to help with [[impedance bridging]] from the high [[output impedance]] of an instrument's [[Pickup (music technology)|pickup]] to the relatively lower [[input impedance]] of a typical [[mixing console]]'s [[microphone preamp]]. For example, the Triad A-11J used in the Wolfbox has a turns ratio of 10:1<ref>{{Cite web |title=Item # A-11J, 50 Ohm Primary DC Resistance J Series Audio Transformer On Triad Magnetics |url=https://catalog.triadmagnetics.com/item/audio-transformers/j-series-audio-transformers/a-11j |archive-url=https://web.archive.org/web/20220523210502/https://catalog.triadmagnetics.com/item/audio-transformers/j-series-audio-transformers/a-11j |archive-date=2022-05-23 |access-date=2022-05-23 |website=Triad Magnetics}}</ref> and thus an [[Electrical impedance|impedance]] ratio of 100:1. The typical console preamp input impedance of 1,500 ohms would appear to the electronic instrument as a high input impedance of 150,000 ohms.<ref>{{cite book |chapter=Audio Transformers |last=Whitlock |first=Bill |editor=Glen Ballou |title=Handbook for Sound Engineers |edition=3 |year=2001 }} Section 2.2.3: Line to Microphone Input or 'Direct Box'.</ref> 

The passive direct box was suitable for most electronic musical instruments but it negatively colored the sound of instruments with weaker output signals, such as Fender [[Rhodes piano]]s and [[Fender Precision Bass]]es with single-coil pickups. To accommodate these instruments, active direct boxes were designed containing powered electronic circuitry which increased the input impedance to above 1,000,000 ohms. In 1975, a 48-volt [[phantom power]]ed active direct box was designed for [[Leon Russell]]'s recording studio, its circuitry published in the April 1975 edition of ''dB'', the sound engineering magazine.<ref>{{cite journal |journal=DB |volume=9 |title=A Remote Powered Direct Box }}</ref> The sound company [[Tycobrahe]], known for supporting large rock festivals such as [[California Jam]], offered an active direct box for sale in 1977 capable of +9&nbsp;dBm line level output with a built-in attenuator to compensate for various input levels.<ref>{{cite journal |journal=DB: The Sound Engineering Magazine |volume=111 |year=1977 |title=Advertisement}}</ref><ref>{{cite journal |page=117 |journal=High Fidelity |title=Equipment Reports |volume=27 |year=1977 }}</ref>