AM8005 Diode Multi Mode VCF

Overview This module is unique and very powerful diode ladder VCF which has three different modes selected by a front panel slide switch:

  • Low Pass
  • Band Pass
  • High Pass

All three modes have voltaged controlled frequency modulation. Frequency Cutoff and Resonance can be adjusted and there are 2x audio inputs and 2x CV inputs for frequency modulation. The module has a mixture of slide and rotary potentiometers, and it is a replica of the voltage controlled filter in the Roland SH-5 analog synthesizer.

EuroRack Module:   18HP wide
User Manual:          Download PDF

Description This 18 HP wide module has at its core a 4-pole low pass diode filter, along with a 1-pole High Pass Filter which can be used in conjunction with the diode LPF to create Band Pass and High Pass filter responses. In LP mode the signal is simply sent straight to the Low Pass VCF although the signal level is reduced down at higher Resonance levels, by use of a dual Resonance potentiometer. The filter will self oscillate and it sounds rather like a traditional EMS VCF.

In HP mode the  input signal is sent to the high pass filter, and a non inverted HP output goes onto the LPF. An inverted high pass signal output is mixed with the low pass-signal output. This adds back in the high harmonics that the LPF removes thus  approximating a resonant high pass filter. The inherent phase cancellation does most of the “high pass” filter work and creates a steeper cutoff and has the added bonus of resonance in a HPF. In BP mode the input signal goes via the HP filter and then the LP filter but with no HP signal mixed in at the last stage. This provides the traditional BP response. All three filter modes have voltage controlled frequency cutoff and variable Resonance with self oscillation. Quite a filter!

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