R1 Dual Voltage Processor
From a 70's catalog: The DUAL PROCESSOR (PRC) is two independent circuits for adding and inverting control voltages. Full processing control of level and polarity of three input voltages is provided. A manual offset voltage is available as an additional voltage level which is summed to the other three inputs.
The Dual Processor served as the systems's control voltage mixer, while the R2 MIX mixer was for audio signals only, being AC coupled.
In this model, the only a positive offset was available. The earlier runs had additional clamping components to limit the output swing. These were not installed on later boards. My examples have LM741 used on the 1973 version, and LM307 used on the later. The choice of chip may have been due to whichever was more economical at the time of purchase.
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