Infrared emissions detected by Ql are fed through Ula to Ulb, which amplifies the signal by a factor of 100. The amplified output ofUlb is fed to Ulc through R9, C2, and R6. Potentiometer R9 serves as a volume control. With R9 set to pass the maximum signal, Ulc provides a gain of 100, for a total system gain oflO,OOO dB.
The output ofUlcis connected to voltage follower circuit Uld to better match and drive headphones that can be plugged into J1.