Usable as an add-on for last month’s Sound Card Mixer or as a stand-alone unit

This circuit was designed to be built into the Sound Card Mixer (Feb ’05). With it, the user may monitor the output using a pair of headphones and make accurate adjustments while recording is in progress. Some readers will not need this facility because their configuration already allows headphone monitoring. This is why the circuit was not included as part of the original design.

Equally useful to some readers is the ability to use the circuit as a self-contained unit. This will allow listening to the sound output from any Line level source, such as an electronic musical instrument, using headphones.

If the Sound Card Mixer has been constructed in the specified sloping-front case, there will be ample space inside to accommodate this new circuit and it may share its power supply.