Thank you for buying 2CK by SYNTHFOX. 2CK is an intertwined dual clock generator with wide frequency range. In this manual, an overview of 2CK's features is given, as well as some additional information, such as a flowchart (logic diagram) of the module's insides and some patch ideas. Please, read the safety notice carefully!


  1. Installation / Safety Notice
  2. General Overview
  3. Controls
  4. Flowchart
  5. Calibration and settings
  6. Patch Ideas

Installation / Safety Notice

Thank you for buying 2CK! We at SYNTHFOX want people to have as much fun with and make as much good use out of our gear as possible. But firstly, we want users to be safe and their synthesizer systems to be fully functional. This device is not a consumer piece of electronics. This is a specific part (module) that is to be installed into Eurorack system and interfaced with other parts of it. The user handles the installation process - extra care should be taken!

2CK has a keyed connector. The included ribbon cable is tested to comply with standard Eurorack boards, and it cannot be inserted the wrong way into the module without brute force. However, the power distribution boards may vary, and it is up to the user to well understand which way to connect the ribbon to the distribution boards. The red line on the ribbon cable marks the -12 volts line. The module should be connected like in the picture below: on the left side is the bus board connector, and on the right side is the connector on 2CK.

image by David Haillant

When installing the module:

The module should now be ready to play. Have you any troubles, feel free to reach out to SYNTHFOX through synthfoxmodular@gmail.com.


Meet 2CK, an intertwined dual clock source. This module provides two identical low frequency squarewave generators.

The frequency of each generator is determined by a manual initial frequency control (big knob) and the CV input with the associated attenuverter (small knob). Controls for Clock A are yellow, and controls for Clock B are blue, for easier navigation.

Both clock generators have a nice frequency range of approximately from cycle per half a minute minimum up to 20 cycles per second maximum, or appr. 0.03 - 20 Hz. Clock A can also be internally preset to be an audio frequency oscillator (refer to the calibration section). Both halves track CV exponentially, and it's possible to tune it very close to a good 1 volt per octave with the built in attenuverter.

There is a pre-patched 'intertwine loop' set up for easy and instant generation of clock pulse patterns: Ck. A output is normaled to Ck. B CV input, and vice versa. This makes the two generators affect each other - sometimes more orderly and forming a pattern, sometimes more chaotically unpredictable.

The clock output is a bipolar squarewave swinging almost rail to rail - that is, a bit less than 12v to -12v. This is to ensure it successfully clocks any eurorack device. Please, attenuate the clock output if you want to use it as an audio source! It is also possible to use it as a classic squarewave VC LFO, for the output is bipolar.


Ⓐ Clock A initial frequency setting
Ⓑ Clock A activity monitor LED
Ⓒ Clock A CV attenuverter
Ⓓ Clock A CV input
Ⓔ Clock A output
Ⓕ Clock B initial frequency setting
Ⓖ Clock B activity monitor LED
Ⓗ Clock B CV attenuverter
Ⓘ Clock B CV input
Ⓙ Clock B output


Calibration and settings


There is one pin header on 2CK V1.0 - it selects the range of Clock A to either low (CLK) or audio (VCO) frequencies. Reposition the pin jumper to the desired position. If your V1.0 2CK has "1" in the BATCH field next to the power header, the selection is inverted! Set the header to CLK for VCO action and vice versa. We are sorry for this silkscreen mistake.

There is one calibration trimmer on 2CK V1.0 - it sets the duty cycle of both outputs. Since there is certain tolerance in parts etc., it's almost impossible to have both clocks perfectly symmetric, so from factory, it is calibrated so that Clock A is as close to 50% duty cycle as possible. and Clock B would usually have a slight error. Generally, this setting doesn't have to be changed.

Patch Ideas

While 2CK is more of a universal clocking utility module, and it already has a patch that yields a ton of fun patterns and unpredictable effects pre-made through CV cross-normalisation, here are a couple more ideas you may like to try out with your new 2CK.


Mult a control voltage (e.g. a triangle LFO) to both Clock A and Clock B CV inputs. Set the initial frequency knobs to noon for both clocks. Now, set the attenuverter for Clock A to about 3 o'clock, the attenuverter for Clock B to about 9 o'clock. Use both clock outputs to trigger similar, but different musical events (e.g. trigger the drums, clock two different sequences). A nice effect of one slowing down while other speeds up and vice versa will happen.

Quick'n'Dirty Krell

This feedback loop will easily start your krell ambient patch going! You will need a random source, such as a sample & hold with some noise at the input, for this patch to work. Set the Clock B initial frequency knob to about 10 o'clock, the CV attenuverter to about 3. Patch the Clock B output to a multiple (or use a stackable cable), and from there patch it to trigger the random generator module. and patch the result back to Clock B CV input. The clock will start bouncing around chaotically. Now you can adjust the CV level to taste with the attenuverter, and use the multed clock to drive your patch.

Duty Cycle Hack

Although you could permanently re-tune both clocks' duty cycle with the trimmer on the back (not recommended), you may use this little hack to temporarily alter it just for your patch. Patch either half's output to a mult, or use a stackable cable. From there, patch back to the same clock's CV input. Now the attenuverter will act like a hacky pulsewidth control while inbetween about 9 and 3 o'clock. This also affects the frequency, so add a VCA in this path to have a weirder way to voltage-control the clock. A summator can be used between the clock output and the CV input to blend in additional CV.


[20210709] 1.0: initial document

Happy patching!