The circuit of the SSP—2001-Surround-Sound-Decoder Besides the 30- pin Surround-Sound-processor (IC 1) needs only some external components to cinfigure. The audio signals of the left and right stereo channels are fed to the circuit on the two RCA sockets SK1 and SK2.
The LF-signals reach at the respective input of the operational amplifier lC2A and IC2B used as impedance converter through the electrolytic condensers C5 and C6 acting as galvanic decoupling.
While the gain at the stages is re- sulted by means of the resistance ratio R1 to R3 or R2 to R4, the in- put impedance of the circuit issimultaneously defined by R1 and R2 (47 kohms). The working point of the operational amplifier is the semi-operating voltage connected to the pin 24 of the Surround-Chip through R5.
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While the ceramic condensers C7 to C9 block the frequently occurring interference radiation, C10 and C11are used for the suppression of oscillations. Finally the stereo signals reach at the inputs (pin 25 and pin 26) of the Surround-sound-decoder (IC 1) via the two coupling electrolytic condensers C32 and C33. The decod- ing of Surround-information summed up at the right stereo channel with +90° phase position and also at the left stereo channel with -900 phase position takes place within this highly integrated chip.
At the time of normal stereo repro- duction through two loudspeakers these additional signals gets mutually blanked out. The selection of different operating modes of (IC 1) is made with the help of the regulated DC voltage, which is fed to the pins 7 and 8 of the module. Table 1 shows the logic positions on the mode—seIect-pins (pin 7 and pin 8) with respect to the relevant function.