Signal detecting, power on circuits

[Borg1n]

I was thinking of using the 12V output trigger from a pre-amp to power on some Hypex smps400/180, ucd180 and wonder if there is some recommended circuits (diagram or ready made) for doing this (the way I understand it the 12V trigger should be pulled down).

Then I also found this guide on a signal sensing circuit (Signal Detecting Auto Power-On Unit) and thought that could even be more neat, i.e. driving the power on. But would this be recommended or would I risk that this could add noise to the input signal? Anyone with experience or solid understanding of how/ if this could affect the SQ.

[elevator]

Originally Posted by Borg1n

...But would this be recommended or would I risk that this could add noise to the input signal? Anyone with experience or solid understanding of how/ if this could affect the SQ.

Hi, welcome.
As far as I can tell, the circuit should work as advertised, but:
- since it uses both L and R inputs, it may cause a blending of the two channels, depending on their output impedance. As an alternative, consider monitoring only one channel (omit either R1 or R2).
- The Opamp, while fit for the purpose, can be substituted with a more modern, lower power equivalent.
- Consider using a pot (or trimmer) at the input to tune the circuit sensitivity.
E

[firechief]

I dont understand your use of the word "trigger" The circut your identify is well thought out, and will take an audio output from a preamp and turn on most any AC powered device. Is that what your need to do?