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Move 1 VCO to top in the VCF mixer and try to close the Filter, the signal must stop at 10-20hz Initial Frequency settings., not by 100hz or more, just turn the Trimmer as shown on bottom picture. (read the TTSH calibration guide too, to understand what you do)
VCF Modification
ModdedVCF with 1% LCR caps in the 4012 and matched 2.5% to 1% tolerance in the 4072 VCF
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