Ljunggren Audio

Roll Your Own

Eurorack DIY


Altered States - Dual State Variable Voltage Controlled Filter


Altered States is a dual analog state variable filter in a 20hp module.


The filter cores are 12db/oct and based around the clean and reliable 2164 Quad VCA chipset and offers full voltage control over cutoff frequency and resonance as well as individual outputs for each filter response, including a variable state output with manual as well as voltage control.


The filters are identical in featureset, and featureset is as follows:




Frequency cutoff control knob

Resonance amount control knob

Frequency cutoff CV attenuverter knob

Input level attenuator with overdrive knob

Variable state control minishaft type

Resonance amount CV attenuverter minishaft type




Filter audio input

Frequency cutoff CV input

Frequency cutoff 1V/O scaled input

Resonance amount CV input

Variable state CV input

Variable state output (LP-Notch-HP)

Lowpass output

Bandpass output

Highpass output


Also available are a toggle switches for Combine (links the filter B frequency cutoff controls to filter A), and serial or parallel input routing.


Altered States is a highly versatile dual filter, the input and resonance controls have plenty of range to dial in anything from smooth and clean to harsh, overdriven and screaming resonant tones. The cores are very stable and will give you around 5 octaves of 1V/O tracking sine wave self-oscillation, the LP, BP and HP outputs each have a different phased sine. The state outputs offer seamless fading between lowpass and highpass filter response, with an all-pass/notch response around 50% of the knob setting. With voltage control available on frequency cutoff as well as on resonance and state outs, the Altered States is perfectly suited for the modular environment.




Kits comes supplied with PCBs, front panel (PCB material), component kit, power cable and mounting screws. Solder and tools are not supplied.



Download assembly instructions and BOM here (4.3MB).

Download schematics here.

Download Bills Of Material only here.


Basic specifications

Width: 20 hp

Depth: 45 mm.


















Aperture - Resonant vactrol VCF/VCA


The RYO Aperture is a vactrol lowpass filter and VCA module inspired by the much beloved 292 Lopass Gate from the Buchla 200 series modular system of the 1970s. However, rather than being a straight up clone, the Aperture is a newly developed and reworked design for eurorack modular synths.


Aperture can be used as a 12dB lowpass filter, a VCA or a combination of the two similar to the 292 but also adds a new switchable resonance circuit. This solution gives you no less than 6 different characteristics!


* Non resonant lowpass filter

* Resonant lowpass filter

* Both: Non resonant lowpass gate

* Both: Resonant lowpass gate


* 6dB variety of resonant lowpass gate in the VCA mode with resonance on.


The resonance goes from smooth and twangy to increasingly bubbly and acidic to wild and untamed howling towards the end of the pots range. The self-oscillation also lends itself well to creating kickdrums, toms and other percussive sounds.


The result is a very wide range of sound shaping possibilities, from the classic resonant filter sweeps of east coast to the plucky acoustic timbres of west coast synthesis and everything in between.


Also added is a unique "Klang" function. The Klang input generates a decay slope from a trigger, the shape is very steep in the beginning and quickly smooths out to a nice prolonged ring, resulting in a very natural acoustic sounding tone.The circuit was specifically tailored for this purpose and does not give the same result as just using a decay envelope with the regular CV input. Experimenting with different trigger voltage and length will affect the response of the decay and overall shape. It will also work with other control voltages but will add a falling slew to the signal. Trigger the CV as well as the Klang input at different intervals for simulating the impression of striking a drum or string instrument in different ways.


Finally, the input is AC coupled and has a dedicated attenuator with clipping overdrive towards the end of the pot range for adding a bit of extra bite to the incoming signal. The signal input is scaled for 10Vpp audio signals. The AC coupling comes after the overdrive circuit so you can add offsets to your audio with RYO Ampmix and many other modules to get an asymmetric clipping.



Kits comes supplied with PCBs, front panel (PCB material), component kit, power cable and mounting screws. Solder and tools are not supplied.



Download assembly instructions and BOM here (3.4MB).

Download schematics here.


Basic specifications

Width: 8 hp

Depth: 27 mm.

Max power: +12V 50 mA / -12V 70 mA (when self oscillating in max pitch)

Average power: +12V 25mA / -12V 45mA (with no self oscillation)



* Regarding our PCB/panel only offerings, please note that these are mainly offered due to popular demand from the experienced DIY community. Hence we are counting on that you know what you are doing and how to source parts. If you feel the least bit uncertain, please consider going for the kit.