Active D.I. Box
Contents
1. A typical D I configuration has an instrument plugged into the input of the D I and a mixing desk into the XLR output A stage amplifier can be connected to either the direct or buffered output jacks If the stage amplifier is connected to the Buffered output jack the instrument will only see the 30 Megohm input impedance of the D I box This results in the best possible frequency response when using high impedance pickups such as piezos An extra octave of low end or part thereof can be obtained compared to a regular D I Box This may cause problems for the musician as his stage sound will be different If this increased low end is unacceptable connect the stage amplifier to the Direct output jack The instrument will now be loaded by the input of the stage amplifier Depending on the type of pickup used large amounts of bass roll off may occur The Direct output jack was provided so that the musician can retain their normal but degraded sound that they are used to Connect the stage amplifier to the Buffered output whenever possible Curve 2 30 20Hz 100Hz 1000Hz 10KHz Curve 1 Spirit Folio LF EQ at Max Curve 2 Piezo pickup into 1Meg ohm guitar amplifier Curve 1 2 EQ of curve 1 applied to pickup on curve 2 Low frequency roll off showing poor bass response even with 15dB of EQ 20KHz Power Source Power for2. I Boxes are usually very poor at providing good earth isolation because there is usually a direct electrical path between the instrument and the sound system even if its earth lift switch is lifted The Leon Audio Active D I Box uses a quality transformer to provide excellent earth isolation Earth Lift Switches D I boxes have an earth lift switch to allow the earth connection between its input and output connectors to be broken to prevent earth loops Disconnecting the signal audio earth is not a safety issue as the Protective Earths in all the mains cables are still connected and fully functional Pad Switches Pad switches are often provided to allow D I boxes to handle higher level signals which would otherwise overload the D I s electronics Description The Active Direct Inject D l Box is designed for optimum performance with any musical instrument signal source especially in electrically hostile environments such as live performance venues using light dimmers The input is buffered by a class A FET Field Effect Transistor amplifier which has a 33 Meg ohm 33 million ohms input impedance The XLR output is isolated via a custom made high performance audio transformer There are two unbalanced outputs for connection to a musician s stage amplifier The first is connected directly in parallel with the input The second provides a buffered output to prevent the musician s stage amplifier from over loa
3. Active DI Box ADIB Mk2b User manual Active DI Box ADIB Mk2b An Active Direct Box featuring the best of active and passive designs with none of their short comings e Genuine earth isolation e Buffered and direct outputs Class A FET input amplifier e No pad switch e Low noise and distortion e Transformer balanced output aC audio co What s in a D I Box D I Boxes are constructed using one of two common techniques e The first type uses electronic circuitry and are known as active D I Boxes They require either Phantom Power or a battery supply e The second variety uses an audio transformer and are known as either transformer or passive D I Boxes They require no power supply A D I box is required to perform three separate basic tasks 1 Impedance Conversion 2 Unbalanced to balanced conversion 3 Earth isolation 1 Impedance Conversion The medium or high impedance of a signal source is converted to a low impedance suitable for feeding down a long multicore to a mixing desk s microphone input A low impedance enables long cable runs with very little quality loss and also low susceptibility to external electrical interference which can cause hum and buzzes A D I box should provide a high input impedance for connection to a signal source and a low output impedance for connection to the microphone input of a mixing desk The input impedance of many D I boxes is too low resulting i
4. R Output Genuine Neutrik 3 pin male XLR Frequency Response 10K ohm source 1K ohm load 20Hz 20kHz 0 15dB 1 000 pF source 1K ohm load 20Hz 20kHz 0 45dB Power Supply 48V Phantom Power with indicating LED Supply Current 4 2mA at 48 volts Dimensions W 95mm H 120mm D 67mm Finish Powder coated die cast aluminium Weight 520 grams net 620 grams gross The Leon Audio Active DI Box is guaranteed for two years from date of original purchase against defects in workmanship and materials If such malfunction occurs the item will be repaired or replaced at our option without charge for materials or labour if delivered prepaid to THE LEON AUDIO COMPANY Unit will be returned prepaid Warranty does not cover finish or malfunction due to abuse or operation at other than specified conditions Repairs by other than THE LEON AUDIO COMPANY or authorized agents will void this guarantee 12 10
5. arrangement the piezo pickup is only loaded by the input impedance of the D I box resulting in a flat and wide frequency response The Leon Audio Active DI box is one such solution udio Active D I Guitar amplifi Typical active D I 15 20Hz 100Hz 1000Hz 1000pF transducer Load type Leon Audio Active D I Typical guitar amplifier Typical active D I Input impedance 6dB point 4 8Hz 160Hz 1600Hz 1 Meg ohm 33 Meg ohms 100K ohms Piezo pickup frequency response Vs various load impedances 10KHz 20KHz Attempts to recover the lost bass of an overloaded Piezo pickup using conventionaltone controls is usually less than successful The problem is that the bass rolls off at the rate of 6dB per octave and conventional one controls can not create an inverse of this roll off Curve 1 is atypical bass tone control set at full boost Curve 2 in the graph below shows the response of a Piezo pickup olling off at 6dB per octave The centre curve in red shows the bass boost applied to the signal acking in bass The result is still lacking in bass but more importantly it is far from flat It is much better to cure the disease than to treat the symptoms Using a DI box with a very high input impedance to prevent the loss of bassin the first place is much better than trying to patch it up later Two Output Jacks
6. ding the instrument s pickup and degrading performance The active FET input stage provides the benefits of low noise low distortion and high input impedance while the heavily screened output transformer provides very high isolation between the input and XLR sides of the D I Box The transformer provides maximum immunity to external electrical interference and also reduces earth noise to an absolute minimum The D I is designed to operate without compromise when the earth lift switch is lifted Many other active D I boxes will not operate correctly or at all when the earth switch is lifted as there is no return path for the Phantom Power A DC DC converter is used to power the active input stage via it s own isolation transformer This allows genuine earth isolation atalltimes The ability to handle high level inputs up to 15dBu means that a pad switch is not needed The D l s high input impedance minimises loading of the signal source This results in minimal loss of bass or treble when used with instruments with high source impedances Piezo pickups are one example of high source impedances A high input impedance is also suitable for connection to low output impedances such as keyboards or mixers Impedance matching is not required nor is it even desirable as we want to achieve the maximum possible signal transfer not the maximum possible power transfer that a matched impedance offers Matched impedances are generally u
7. n either the highs or lows being attenuated The very high input impedance of The Leon Audio Active D I Box preserves the full frequency response of the original signal 2 Unbalanced to balanced conversion The unbalanced 2 conductor wiring of a signal source is converted to the balanced 3 conductor wiring of a mixing desk s microphone input A balanced cable provides good rejection of electrical interference while an unbalanced cable does not Active D I Boxes are potentially capable of providing excellent unbalanced to balanced conversion but due to cost restrictions most are poor performers in this area The Leon Audio Active D I Box uses a quality transformer to provide excellent unbalanced to balanced conversion 3 Earthisolation A D I Box provides isolation between the earth wiring of a signal source e g musical instrument and the sound system to which it is being connected This prevents earth loops from occurring An earth loop occurs when a device such as a keyboard is connected to the mains earth via more than one path The first path is via the instrument s own power cable to the mains earth The second path is via the interconnecting audio cable to the sound system then via the sound system s power cable to the main s earth Any resultant circulating earth current is amplified and is heard as a hum or buzz These unwanted earth currents are usually induced from nearby power and lighting cables Active D
8. ndesirable and not normally used in audio systems 1000Hz 10KHz Source Z It 1000pF represents 1000pF DI Box Load Z iezo picku Input Output BEGGE eae 1K ohm Test circuit Active D I Box frequency response when fed from a piezo source 20KHz Piezo Pickups Q Why do many Piezo Pickups sound thin and bright A Because the bass is heavily attenuated The capacitive characteristic of piezo pickups results in their output evel decreasing as frequency decreases when connected to a typical instrument amplifier which has an input impedance ofabout 1 Megohm 1 Million ohms This loss of high frequencies is due to excessive oading of the pickup by the amplifier which was never designed to work with piezo pickups An extremely high load impedance typically greater han 20 Megohms is needed to provide negligible loss of bass requencies The above situation is further compounded by connecting he piezo pickup to a D I box The total load seen by the pickup is now hat of the DI box and the instrument amplifier in parallel The input impedance of a typical D I is 100K 200K ohms which results in avery heavy load on the piezo pickup and consequentially a heavy loss of low frequencies The solution is to use a D I box which provides an extremely high input impedance and a buffered output to drive to the instrument amplifier With this
9. the FET input amplifier needs to be returned to the XLR connector This can not be achieved when the Earth Lift switch is open There are 4 possible options 1 Use batteries This option was considered unacceptable in a professional D I box 2 Do what other act ve D boxes do and allow the Phantom Power to return via the instrument s mains earth connection A great way to pick up lots of electrical n 3 Do what other acti concept works well electrically noisy env oise ve D in the ronm boxes do and use a partial Earth Lift This showroom It fails in the real world when ents are encountered 4 Use a complex isolated DC DCinverter for the FET input amplifier Option 4 was chose nasi is the only one that offers genuine earth isolation between the input and the XLR output of the DI Box 100kHz DC DC inverter Amplifier Input Direct Out Buffered Out Isolation Transformer The drawing b elow shows that there is no direct electrical connection across the Earth Isolation Barrier A DC DC inverter is used to get the FET amplifier s power across Earth solation Barri DC AC conver he FET amplif operating ona ransformer T power transformer is rectified and filtered to provide 18 volts DC to run er Phantom Power is first extracted from the centre tap on the bifilar wound secondary of the audio transformer This drives a er running at 100kHz which in
10. turn drives a small power he resultant 100kHz AC voltage on the secondary of the ier As a result there is no interruption to the FET s power supply when the Earth Lift switch is operated As the FET amplifier is n 18 volt supply it is able to handle much higher signal evels than if i were operating from a 9 volt supply such as a battery This means that the DI Box can handle input signals up to 15dBu without the need for an input Pad switch OdBu 0 775Volts to mixer Block Earth Isolation Earth Lift Barrier switch diagram of the Active D I Box audio co 62 Edgeware Road Aldgate South Australia 5154 Phone 08 8339 3865 Fax 08 8370 8780 International Phone 61 8 8339 3865 Fax 61 8 8370 8780 www LeonAudio com au Specifications ovdBu 0 775volts Input Level 15dBu Maximum Input Impedance 33 000 000 ohms unbalanced Outputs 1 Direct out In parallel with the input 2 Buffered out 3 XLR Out Transformer balanced with earth Lift switch Output Level Buffered Output OBu when driven with OdBu input XLR Output 15dBu when driven with OdBu input Output Impedance Buffered Output nominal 5 000 ohms XLR Output nominal 75 ohms Recommended Load Impedance Buffered Output 50 000 ohms or greater XLR Output 600 ohms or greater Warranty Connectors Input 6 5mm 1 4 nylon jack socket Direct amp Buffered Outputs 6 5mm 1 4 nylon jack socket XL
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