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The CEM3340 and CEM3345 are a self contained VCO, originally produced by Curtis Electromusic Specialties. With both exponential and linear control inputs and up to four output waveforms: triangle, sawtooth, square, and pulse with voltage controllable pulse width. It has full temperature compensation making it extremely stable. Also included is provision for hard and soft synchronization of the frequency, and an output for easy adjustment of high frequency tracking.[1]

CEM3340/3345 differences

  • The square wave output on the CEM3345 (pin 7) requires a pull down resistor to any negative supply greater than -4 volts.
  • The frequency control is pin 15 on the CEM3340, pin 17 on the CEM3345.
  • The precision multiplier output is pin 14 on the 3340, pin 16 on the 3345.
  • The reference current input is pin 13 on the 3340, pin 15 on the 3345.
  • The hi-frequency track is pin 7 on the 3340, pin 8 on the 3345.
  • The threshold voltage pin is pin 9 on the 3340, pin 10 on the 3345.[1]

Clones and equivalents

In 2016 after twenty or more years of diminishing availabilty, in response to Coolaudio's V3340 re-design of the part to the same specifications, OnChip Systems remanufactured the 3340.[2][3][4]

Alfa parts

Alfa Rpar AS produces the AS3340 and AS3345. The 3340 is available in both 16 pin DIP and SOIC packages, the 3345 is available in 18 pin DIP and 24 pin QFN packages. Alfa recommend a 51K resistor on the pulse output instead of the 10K resistor that the CEM3340 uses. [5][6]

The AS3340-HYB is pin compatible with the CEM3340. It is a AS3345F with an additional PWM comparator in order to minimize frequency modulation by the PWM control circuit.[7][8]


To prevent the IC being put under too much stress if/when the outputs are shorted, all outputs should have a series 1K resistor. The triangle wave output is unbuffered and should never be used to drive an output directly, add a J201 FET follower to buffer it.[9] A better sine output can be achieved by using instead the Thomas Henry VCO-1 waveshaper.[10][11]


  1. ^ a b CEM3340/3345 data sheet
  2. ^ Curtis Electromusic Specialties, Facebook, 5 June 2016
  3. ^ Curtis Family Speaks Out Against Behringer Synth Clone Plans Using CEM3340 by Rounik Sethi, Ask.Audio, 21 Mar 2017
  4. ^ CEM3320/V3320, SDIY list, Sep 2017
  5. ^ AS3340 VCO, Electric Druid
  6. ^ AS3340 data sheet
  7. ^ AS3340-HYB New VCO chip, Mod Wiggler Forum, May 2019
  8. ^ AS3340-HYB data sheet
  9. ^ Does the A SOL MC-202 modular kit work on the SH-101?, Mod Wiggler forum, Nov 2010
  10. ^ The VCO-1 Project
  11. ^ VCO/LFO PCB for CEM3340 chips, Mod Wiggler forum, Aug 2015

External links