6_interconnection

6_interconnection - Lines and Interconnections Juan P Bello...

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Lines and Interconnections Juan P Bello
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Transformers (1) Laminated core + primary and secondary windings If AC is passed through the primary winding a magnetic flux flows in the core Flux changes cause a current to be induced in the secondary winding Only AC induces the magnetic flux. A transformer does not pass DC signals
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Transformers (2) The difference in voltage across the windings is proportional to the ration of turns between the coils Equal power exists in both coils, thus the current is in inverse proportion to the turns ratio The transformer also works in reverse
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Transformers (3) Impedances are proportional to the square of the turns ratio E.g. the square of the turns ratio below is 1:16, thus the impedance across the secondary = 1k ohm x 16 = 16k ohms The used turns ratio need to be suitable for the task at hand, e.g.: – Microphones like to work into impedances 5x or more their own impedance, – Electronic inputs (e.g. mixers, pre-amplifiers) need to be driven by low impedances.
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Transformers (4) An audio transformers should be able to work well on the complete audio range. In reality, average transformers introduce more distortion at very low and very high frequencies. The frequency response falls away at the extremes (BW = 20kHz) Transformers are designed to work within a specific voltage and current range. When used outside its intended application, the frequency response and distortion of transformers is likely to be affected. They are sensitive to electromagnetic fields, thus they should be protected against interference (e.g. radio frequency, mains hum, etc). Therefore their placement and encasing are of great importance.
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Unbalanced lines (1) They consist of a signal send and a return paths The return path is an outer screening braid that encloses the send wire to attenuate the effect of electromagnetic interference. Over long distances the cumulative effect of interference may be unacceptable. Unbalanced lines are common to domestic audio equipment and (to a lesser extent) to professional audio equipment Common terminations include the phono and 1/4 inch jack plugs.
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Unbalanced lines (2) Connecting the screening braid to earth at both ends can result in earth loops (if there is a small differential potential between the earths) A better unbalanced connection uses a dedicated return wire and the screening braid connected to earth in only one end
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This note was uploaded on 03/03/2012 for the course FMT E85 taught by Professor Juanpablobello during the Fall '09 term at NYU.

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6_interconnection - Lines and Interconnections Juan P Bello...

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