Compact 6HP VCF for Eurorack Modular synthesizers

DIY - PCB AND PANEL ONLY

This is a state variable filter with a nice fat sounding low pass output. The two pole filter has simultaneous -12dB per octave roll-off for high pass and low pass and a -12 db wide (-6dB either side) bandpass output. It has voltage control of cutoff frequency (F) and voltage control of resonance (Q). F and Q are adjustable with panel controls and from external sources using three F CV inputs and two Q CV inputs.

There are many weird and wonderul things you can discover with this filter but the provision of the multiple F and Q control voltage inputs means you should plan on a separate attenuator (at least for your envelope output) if you plan to use it for more conventional music.

A demo of the filter

The videos, courtesy of Randy Piscione, supplement the main demo (also presented below):

2 pole to 4 pole Comparison

The frequency response is exponential at 1Volt/Octave. The Q response is also exponential.

The design uses a positive feedback resonance circuit that maintains a high input signal level as resonance is increased. This enables low noise output regardless of the resonance. The input level control can be used to provide a smooth or clipped high pass output during resonance, further increasing the opportunities for sound experimentation.

• Two pole 12dB filter
• Simultaneous high pass, low pass and band pass outputs
• Exponential 1V/octave response
• Exponential voltage control of resonance
• Self-resonance adjustable
• Three frequency CV inputs
• Two Q CV inputs. This frees up one Q input to be used to track the frequency input allowing constant bandwidth on the BP output
• Input level control for smooth or overdriven sounds
• 6HP Eurorack with our panel

This is a low component count project so you can have high quality VCFs in your rack with minimum expense.

Build it yourself - This is a set of one high quality PCB and front panel ONLY for users who want to purchase their own components and build their own module. Some product photos above show COMPLETED build.

This module will fit perfectly into a 6HP Eurorack space.

Comprehensive manuals, parts lists and component shopping carts are provided in the documentation link for building, testing and using the module. (use the Design Files link for version 1.0 of the board please and the Documentation link for the current version (V1.1))

You can select the option to add an Attenuator or Attenuverter to the order if you need to.