# QA471 mic pre question

**URL:** <https://forum.quantasylum.com/t/qa471-mic-pre-question/954>\
**Category:** QA47x\
**Created:** [August 3, 2023, 4:43pm UTC](https://forum.quantasylum.com/t/qa471-mic-pre-question/954 "2023-08-03T16:43:08Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Chicago](https://avatars.discourse-cdn.com/v4/letter/c/ecae2f/32.png) [@Chicago](https://forum.quantasylum.com/u/Chicago)\
**Post date:** [August 3, 2023, 4:43pm UTC](https://forum.quantasylum.com/t/qa471-mic-pre-question/954/1 "2023-08-03T16:43:08Z")

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Hi Matt, can you share the input Z of the 2 independent gain blocks? I can’t seem to find that spec. Thanks!

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**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\
**Post date:** [August 3, 2023, 8:16pm UTC](https://forum.quantasylum.com/t/qa471-mic-pre-question/954/2 "2023-08-03T20:16:10Z")

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Hi @Chicago, the input from the BNC is as follows: Shunt 100K, series 22uF/100V, shunt 100K, series 49.9 ohm, into OP1612.

So, roughly, your looking at 50K input impedance.