The integrated circuit MM5837 from National Semiconductors was used in many synthesizers like Jen SX-1000, Crumar Spirit, Moog Memorymoog, The Rogue, Micromoog, Sequential Circuits Prophet 5, Prophet 10 and Oberheim OB-x. But this circuit had a design flaw and the noise will exhibit a cyclic heartbeat sound (about 0.8s).
This replacement module uses the MM5437, also from National Semiconductors. This chip had the cycle time increased to about one minute, it’s less likely to be noticed. The chips are not pin neither electrically compatible, so a circuit was made to adapt it for the task.
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