Standby Amplification

The passive loop described can be used for listening to audio from any source. However some users might wish to be able to listen to very low power "Line Level" audio signals that are very low current sources and are not meant to drive earphones (or loops).

To do this it might be useful to add a second jack to the loop's housing and add a stand-by amplifier for such uses. Normal cell phone use probably wouldn't ever make use of this jack and the battery would never be drained. Accordingly lithium batteries that can sit idle for 5 years without self-discharge would probably be chosen.

Battery power needed for low level "Line-Out" use would be about 1.5ma at 1.2 volts. An EverReady 1.5V lithium “Photo” AA primary cell (2900 mah) would be suitable and would probably last about 2.5 years even with daily use. There are some new 1V amplifier IC's with very low quiescent current that should do the job

A switch has been provided in the prototype below to mute the mic.