The Threek 13700 filter is an OTA-based filter that consists of two serially linked multimode circuits. The first stage can be operated in a high pass, bandpass, low pass, or all pass mode with a slope of -12 dB per octave. The second filter is a high-pass or low-pass circuit. The slope here is -6 dB per octave. The combination of both stages makes all kinds of complex filter shapes possible. Thanks to the 2-pole output and 1-pole input, it is also possible to use the filters individually. As a result, the following operating modes are available:
- 3LP: Low pass characteristic with a slope of -18 dB per octave
- 2L-1H: Bandpass characteristic consisting of 2-pole low pass and 1-pole high pass
- 1L-2H: Bandpass characteristic, consisting of 2-pole high pass and 1-pole low pass
- 3HP: High pass characteristic with a slope of -18 dB per octave
- 1L-2A: Combination of 2-pole all-pass and 1-pole low-pass
- 1H-2A: Combination of 2-pole all-pass and 1-pole high pass
- High pass, bandpass, low pass or all pass characteristics with a slope of -12 dB per octave. (Depending on 3-pole mode selected)
- High-pass or low-pass characteristic with a slope of -6 dB per octave. (Depending on 3-pole mode selected)
By flipping the Mode toggle switch you can manually change between the two bandpass types and allpass combinations. Alternatively, this can also be controlled per CV.
A diode circuit allows continuous morphing between the different filter modes with the Mode potentiometer. It can also be modulated via control voltage far into the audio range. This opens up new unheard-of sounds. The signal is inverted at the transition of the center position. It behaves like a mixture of rectifier and filter.
The cutoff frequency is adjusted with the Frequency knob and the Freq CV attenuator is used for fine tuning if no cable is plugged into the Freq input. Control voltages at the 1V/Oct input set the filter frequency accordingly to 1V per octave. Ideal to play the filter tonal in self oscillation (resonance completely clockwise).
For the resonance behavior there are two additional variations which can be selected with the Type switch. You can choose between Classic, Vari 1 and Vari 2, which all sound very different. Thanks to the LP-Comp switch, a bass boost can be activated, so that you get a constant level even with increasing resonance.
The filter offers two assignable CV inputs, one with bipolar attenuator and the second with attenuator and switch for turning on/off and inverting. Each CV input is normalized and can therefore function without additional control voltage at the input. For example, it is possible that the filter mode or the resonance follows the frequency automatically, depending on the position and switch setting of CV1. Interesting is also the feedback of the output signal to the mode input via CV2, which leads to a crunchy and resonant behavior.
Audio input and output
1 Pole audio input and 2 Pole audio output
Two CV inputs with routing options
1v / octave input
Mode CV input
Cutoff CV input
3U Eurorack module, 14 HP wide, compatible with Skiff cases