6300: Mic input circuit, actual impedance?

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  • Updated 5 years ago
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When interfacing a mic that has an internal transformer for its (250 ohm) output, it's important to know the actual impedance that the transformer will "see" to assure that the transformer is properly terminated.  Anybody know what actual input impedance is presented by the 6300's mic pre-amp?

Another way of posing this question is:  what kind of load does the radio present to the mic? The specs say:  Microphone Impedance:  600 Ohms Nominal (200-10kΩ). This suggests that the input impedance is high, otherwise a 10K mic might be loaded down too much, but it's just a guess.

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Jim, KJ3P

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Posted 5 years ago

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Paul Christensen, W9AC, Elmer

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A quick check of the schematic diagram would provide the information we need.  Are schematics of the Flex 6000 series available?  I'm interested not just for this reason but to better understand the internal relationships of the Flex 6K hardware.

Paul, W9AC   

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W5XZ - dan

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me too!  w5xz, dan
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Gerald - K5SDR, Employee

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Official Response
The microphone inputs are high impedance.  The actual impedance varies by the gain setting of the DVGA in the CODEC.  The minimum impedance at maximum gain is about 5k on the front panel mic and about 3k on the balanced input.  The maximum impedance is over 80k at minimum gain settings.  
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Jim, KJ3P

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Just what I needed...thanks!