# measure input max

**URL:** <https://forum.quantasylum.com/t/measure-input-max/969>\
**Category:** QA401\
**Created:** [August 9, 2023, 2:44am UTC](https://forum.quantasylum.com/t/measure-input-max/969 "2023-08-09T02:44:48Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jumpod](https://avatars.discourse-cdn.com/v4/letter/j/a88e57/32.png) [@jumpod](https://forum.quantasylum.com/u/jumpod)\
**Post date:** [August 9, 2023, 2:44am UTC](https://forum.quantasylum.com/t/measure-input-max/969/1 "2023-08-09T02:44:48Z")

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I want to measure input headroom at 1Khz how many dBUs does a measuring device such as an isolator have to do?

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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 10, 2023, 7:28pm UTC](https://forum.quantasylum.com/t/measure-input-max/969/2 "2023-08-10T19:28:45Z")

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Hi @jumpod, I’m not sure I understand the question. A good way to determine headroom of an amp is to plot distortion versus amplitude, and you’ll see the distortion increase suddenly at some point due to (usually) supply rail limitations. And knowing the limit, you can then back off from that limit depending on your source material demands.

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**Author:** ![jumpod](https://avatars.discourse-cdn.com/v4/letter/j/a88e57/32.png) [@jumpod](https://forum.quantasylum.com/u/jumpod)\
**Post date:** [August 11, 2023, 5:27am UTC](https://forum.quantasylum.com/t/measure-input-max/969/3 "2023-08-11T05:27:44Z")

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Thank you 😘

เมื่อ ศ. 11 ส.ค. 2566 เวลา 02:38 Matt via QuantAsylum Forum \<[notifications@quantasylum.discoursemail.com](mailto:notifications@quantasylum.discoursemail.com)\> เขียนว่า: