Audio In direct to Balanced Modulator
This mod is for those using an external mic preamp with adjustable output
1. Remove the DSB board generator board (unplug cables and unscrew).
2. On the solder side, locate U1 pin 1 (Balanced Modulator - see below image)
3. Disconnect the existing cable going to Audio In jack on the rear panel and tape/insulate cable out of the way.
4, Solder one lead of a 1uF capacitor to U1-1. Run a new shielded cable from the Audio In jack on the rear panel to the other lead of the capacitor. Ground the shield on an adjacent trace (see below image - use Ohmmeter to locate).
5. Connect your level-adjustable external audio source via isolation transformer (e.g. Bourns LM-NP-1001-B1L); you may find that adding 1K-10K series resistor or other resistor divider network may help in bringing the level down