AM8069 VCF & VCA

NJM2069 chip

Overview  This module is replica of the filter used in many Korg synths and samplers around 1985/86, such as the DW6000, DSS-1, DSM-1 and Poly 800. The rich analog filter based on a NJM2069 chip counter balanced the digital waveforms in the DW/DS range. and output VCA’s.

EuroRack Module: 14HP wide
User Manual:           Download PDF

Description The AM8069 design has been kept simple and harnesses the VCF and final VCA in the NJM2069, but not the signal input VCA’s. This means it can fit into a 14HP EuroRack module. The NJM2069 chip is hard to locate, but they can be located NOS or salvaged from old Korg circuit boards.  The development of the module took many years (on and off) as I worked out the signal voltages. I eventually powered up a DW8000 voice PCB and tested the voltages and then replicated these in my design. Two audio signals are buffered and level corrected before going into the NJM2069, the filter cutoff frequency and resonance, as well as the VCA level are individually controlled by 3 buffered and level corrected CV signals.

The additional VCF signal input and Log VCA pins are not used. The filter response is switched between 2 and 4 pole by a front panel push button, that triggers a simple CMOS 4013 latch to drive a M5201 Op Amp on and off, and to switch the panel LED on and off. The wait was worth it, these are very nice sounding filters!

NJM2069 Measured Pin Out

  1. GND
  2. LEVEL 1 = 0 to +650mV
  3. LEVEL 2 = 0 to +650mV
  4. RESONANCE = 0 to +880mV
  5. 12dB Output
  6. 24dB Output
  7. VCA IN
  8. VCA LOG = GND
  9. VCA LIN = 0 to +29mV
  10.  VCA OUT
  11.  GND
  12. -5V
  13. VCF LIN = -18mV
  14. VCF LOG = +113mV (closed) to -130mV (open)
  15.  C4
  16.  C3
  17.  C2
  18.  C1
  19.  VCF IN
  20.  Signal 2 Input
  21.  Signal 1 Input
  22. +5V

AM8069 Module

Module Outcome & Availability  An initial prototype was made in 2014 and refined using the DW8000 voice card into a final production version in 2016. In 2019 I had sufficient time to complete a production run of 10x modules, with the first modules shipping to customers in June 2019. I have sufficient 2069 chips to ship another 10x. The schematics are here.


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