Intercom preamp - Universal high quality preamp

The circuit is so simple that there is little to say about it, but it gives very good results. Tr1 is operated in grounded base mode with input to its emitter to give low impedance input. The values shown give correct operation from 9v. If operating from other voltages you may wish to alter the 1K8 resistor to give symmetrical clipping at high levels. The third circuit is one I was working on as I left the audio company but is seems to be potentially very useful. It should be simple to use it as a low impedance mic amp or as a high input impedance preamp for mic or, with a suitable RIAA equalization, for phono pickup or similar. It can even be used as a balanced input mic preamp.

Source:http://www.4qdtec.com/preamp.html