High-and low-level inputs (program sources) are selected by the Program Selector Pushswitches and applied in accordance with signal level. When low-level sources are selected (PHONO or MIC), the Program Selector Pushswitch applies the input signal to the Phono/Mic Amplifier circuit and selects the proper equalization, RIAA or Mie. The output of the Phono/IVlic Amplifier is then returned to the Program Selector Pushswitches where it is handled as another high-level input. High-level input signals TUNER, AUX, TAPE 1, TAPE 2 or the output of the Phono/Mic An plifier are applied to the Dolby encoder/decoder 1-1 through the buffer amplifier circuit, TAPE REC-EQand DOLBY Switches. The input level to the encoder/decoder is regulated by the RECORD LEVEL Controls. The output of the encoder/decoder is applied to the TAPE OUTPUT and DUBBING OUT Jacks. With the DOLBY Switch set to OFF, the encoder/decoder is bypassed and the high-level input signals are applied directly to the TAPE OUTPUT and DUBBING OUT Jacks. The encoder/decoder functions as a flat amplifier, an encoder, or a decoder depending on the position of the DOLBY Switch (Figures 1-1 and 3-9). The high-level input signals are concurrently applied to the SCOPE OUTPUT Jacks and to the Dolby decoder, through the TAPE MONITOR Switch and PLAY CAL Controls. The decoder functions as a flat amplifier, or a decoder, depending on the position of the DOLBY Switch, the TAPE MONITOR Switch, and the TAPE COPY Switches (Figure 1-1). The output signal ofthe decoder is monitored by the Dolby Level VU Meter and applied to the MODE Switch. The MODE Switch determines the manner in which the left- and right-channel signals of the program source are applied in the Model 3800: LEFT channel only, RIGHT channel only, twochannel STEREO, STEREO REVERSE, or L + R (left and right channels combined). The signal selected by the MODE Switch is then applied to the BALANCE Control. The BALANCE Control adjusts the relative signal level of the left and right channels by attenuating the level of one channel while maintaining the level of the other. From the BALANCE Control, the signal is applied to the VOLUME Control, which varies the level of the output signal available at the PREAMPLIFIER OUTPUT Jacks. The signal is also applied to the Loudness Contour Circuit which, when activated, boosts low and high frequencies at low listening levels so that all frequencies appear to have equal loudness. The Loudness Contour Circuit adjusts the frequency response of the Model 3800 to compare with the Fletcher-Munson loudness curves (Section 2). The signal from the VOLUME Control is then applied to the input of the Times-Ten (X10) Amplifier Circuit. The X10 Amplifier increases the signal level to that required to drive power amplifiers. The output of the X10 Amplifier is applied to an Active Filter Network comprised of three filter circuits (30Hz, 5KHz and 9KHz) and a Filter Amplifier. The Active Filter Network sharply reduces low- and/or high-frequency noise that may originate at the program source. The output ofthe Filter Amplifier is then applied to the Tone Control/Turnover Network (BASS, MID and TREBLE Tone Controls), the 250Hz and the 4KHz TURNOVER circuitry, and a Tone Amplifier stage (through the TAPE REC-EQ Switch). The output of the Filter Amplifier after TAPE REC-EQ is also applied to the TONE DEFEAT Switch. The Tone Control/Turnover Network performs a dual function: the tone control portion of the network boosts or attenuates low, middle and high frequencies; the turnover portion of the network, when activated, decreases the point at which low frequencies are affected by the BASS Control (250Hz) and increases the point at which high frequencies are affected by the TREBLE Control (4KHz). The TONE DEFEAT Switch selects either the flat output of the Filter Amplifier (bypassing the tone controls) or the tone-control-altered output of the Tone Amplifier. From the TONE· DEFEAT Switch, the signal is applied to the Time Delay Relay. The circuit associated with the Time Delay Relay holds.the relay contacts open for approximately five seconds after power is applied to the Model 3800. After the power supply circuits have stabilized, the relay contacts close. Audible “ pops" that may arise from power supply transients are thereby eliminated. From the relay contacts the signal is applied to the PREAMPLIFIER OUTPUT Jacks and connected to drive an external power amplifier. The power amplifier outputs are connected to the SPEAKER SWITCHING INPUTS Terminals and the signal is applied to the stereo PHONES