Filter Threek 13700 VC-Morphing Filter

Funkstill Filter Threek 13700

Filter Threek 13700 is a three-pole voltage-controlled morphing filter from the Swiss modular brand Funkstill, built on the LM13700 OTA its name refers to—three analog poles of it, with FET/Darlington buffering. The filter morphs continuously across four dialable positions, the middle two of which switch to a second pair via the Mode-Toggle for six distinct modes in total. Turn Resonance fully clockwise in Classic mode and the filter self-oscillates, tracking 1V/Oct accurately through the lower range up to around 1kHz. The control layout features Resonance and cutoff Frequency at the top, In gain, Mode, and Freq CV at the center, Mode CV below, as well as assignable CV1 attenuverter and CV2. A collection of switches right under define the CV assignments, Resonance type, LP-Comp level compensation, and the Mode-Toggle behavior.

A plethora of patch points ensure a variety of creative applications for the module. The main Input and Output are supplemented with 1 Pole Input and 2 Pole Output, bringing the total to twelve filter modes, and there are control inputs for Mode and Mode Toggle, two assignable CV inputs, and separate 1V/Oct and Freq CV inputs. Mode itself takes CV at audio rates, and that's where the module gets interesting: patch a VCO into the Mode input, or route the output back to Mode through CV1, and the diode-based morphing circuit turns rectifier, producing dynamic, resonant tones that a conventional filter has no route to. With such a versatile design, Filter Threek lends itself equally to classic subtractive patching and to more experimental waveshaping and sound design.

Filter Threek 13700 Features

• Analog three-pole voltage-controlled morphing filter, built on LM13700 OTAs with FET/Darlington buffering
• Six three-pole modes—lowpass, two bandpass configurations, two allpass configurations, and highpass—with stepless morphing between them
• Mode-Toggle swaps the two middle positions between the bandpass and allpass pairs, by switch or automatically when Mode reaches either extreme
• 1 Pole Input and 2 Pole Output add six further responses, for twelve across the three signal paths
• Voltage control of Mode, including at audio rates, with a dedicated attenuated CV input
• CV1 attenuverter and CV2 attenuator, each assignable to multiple destinations and normalled to internal modulation routings when unpatched
• Resonance with three variant characters, LP-Comp level compensation, and self-oscillation at full clockwise
• 1V/Oct and attenuated Freq CV inputs, the latter doubling as fine tune when unpatched