Schematic of Pleiades K117 pre preamplifier
Used to connect for example a Shure Unidyne iii (SM57) to iPad for extreme sensitivity and low noise. This is an attempt to play fair game with condenser microphones and dynamic or ribbon ones. Impedance of voice coil is stepped up. The high stepped up voltage drives a high imput impedance K117 JFet. The output of the JFet is low Z. Power for the jFet is provided by the mic input of the iPad, as it does for electrets. For load resistor the internal iPad resistor is used. The amplified voltage is developed across this load resistor (or the varying JFet music signal output current is converted to music varying voltage). iPad's further circuitry takes over then and compensates for proximity effect by its deep low cut filter etc. A 47pF shunt capacitor is used across the high Z input to simulate some cable capacitance, reducing high frequencies a little to compensate for voice effort and Fletcher Munson curves as well as the obstacle effect (of HF increasing at small mic distance due to the addition of the direct and reflected from the mic sound wave). The Shure Unidyne has an internal step up mic transformer with 2 secondaries, hence the 4 pin connector.. The high Z, high turn ratio high output is connected directly to the JFet. For connecting an ordinary SM57 or any other low impedance mic a step up transformer can be used, for example a Pleiades microphone transformer wound on a Magnetec nanocrystaline toroidal core.
general view inside Shure Amphenol MC4M plug
detailed view inside MC4M
public domain dedication
Used to connect for example a Shure Unidyne iii (SM57) to iPad for extreme sensitivity and low noise. This is an attempt to play fair game with condenser microphones and dynamic or ribbon ones. Impedance of voice coil is stepped up. The high stepped up voltage drives a high imput impedance K117 JFet. The output of the JFet is low Z. Power for the jFet is provided by the mic input of the iPad, as it does for electrets. For load resistor the internal iPad resistor is used. The amplified voltage is developed across this load resistor (or the varying JFet music signal output current is converted to music varying voltage). iPad's further circuitry takes over then and compensates for proximity effect by its deep low cut filter etc. A 47pF shunt capacitor is used across the high Z input to simulate some cable capacitance, reducing high frequencies a little to compensate for voice effort and Fletcher Munson curves as well as the obstacle effect (of HF increasing at small mic distance due to the addition of the direct and reflected from the mic sound wave). The Shure Unidyne has an internal step up mic transformer with 2 secondaries, hence the 4 pin connector.. The high Z, high turn ratio high output is connected directly to the JFet. For connecting an ordinary SM57 or any other low impedance mic a step up transformer can be used, for example a Pleiades microphone transformer wound on a Magnetec nanocrystaline toroidal core.
general view inside Shure Amphenol MC4M plug
detailed view inside MC4M
public domain dedication
No comments:
Post a Comment