Frequency Central System X Filter
Roland System 100M 4-pole VCF clone with simultaneous 12dB and 24dB outputs
10 HP Eurorack module
The System X Filter is a Eurorack clone of the Roland System 100M VCF (model 121), built by UK DIY house Frequency Central as a kit module. The classic 24 dB/octave OTA-cascade lowpass — originally implemented in the System 100M with four CA3080 OTAs and FET buffers — is reproduced faithfully, with a 12 dB/octave tap added on the second pole that is 180° out of phase with the 24 dB output. Two audio inputs each have their own LEVEL attenuator and sum into the filter core; two CV inputs each have their own attenuator and sum into the cutoff control along with the FREQ knob. RES sweeps from clean lowpass through resonant peaks into self-oscillation at very high settings.
Features
- Roland System 100M VCF (model 121) topology in 10HP Eurorack
- Original revision uses 4x CA3080 OTAs with FET buffers (Roland-faithful); v2.0 uses 2x LM13700
- Simultaneous 12 dB/oct (2-pole) and 24 dB/oct (4-pole) lowpass outputs
- 12 dB output is 180° phase-inverted relative to 24 dB output
- Two audio inputs each with its own LEVEL attenuator and pre-filter sum
- Two cutoff CV inputs each with its own attenuator and pre-filter sum
- Self-oscillation at high RES — usable as a tracking sine source
- Build doc includes optional modifications for highpass / bandpass alternatives on the 12 dB tap
- DIY kit form factor (now discontinued — replaced by XVCF TWO)
- Available also as PCB+panel set or PCBs only for builders
- 10HP, 65mm depth, classic Roland-style sound
Controls & Jacks (12)
- Level 1
- Audio In 1
- Level 2
- Audio In 2
- 12 dB/Oct Out
- Freq
- 24 dB/Oct Out
- Res
- CV 1 In
- CV 1
- CV 2 In
- CV 2
How-To Guides
- Classic Roland 100M lowpass voice
- Self-oscillating sine source
- Stack two VCOs into one filter
- Phase-difference pad from both outputs
- LFO wobble with envelope keytracking
Explore the interactive System X Filter panel on BleepDex — tap any control to learn what it does.
