The Sonic XV Eurorack module is a four-pole Diode Ladder Filter, featuring the circuitry and sound of the Musonics Sonic V synthesizer, which has a quite different character from transistor ladder filters. In addition to the regular 24dB Low Pass output, we have added a 6dB Low Pass output and a Bandpass output, along with full voltage control of the resonance.

Two waveshapers have been added to greatly increase the sonic versatility of this module. There is a breakpoint-based wavefolder on the input, with a drive level that can be manually adjusted or voltage controlled. A bias control switch allows extra waveshape variations.

A second waveshaper is connected to the resonance circuit, which adds distortion and waveshaping to the resonance loop signal; again, the drive can be adjusted manually or under full voltage control. A wet/dry mix control allows resonance waveshaping to be added from 0 to 100%.

These additions take the diode ladder filter core far beyond its original function; it becomes a harmonic filter module that can add harmonics and shape waveforms rather than simply filtering them. With four independent CV inputs, very complex filtering and waveshaping sounds become possible.

The AJH Synth Sonic XV filter core is based on the diode ladder filter from the original Musonics Sonic V synthesizer dating back to the early 1970s. This particular diode ladder filter was originally developed by Eugene Zumchak (a former Moog employee) as a "workaround" of the original patent (held by Dr. Bob Moog) for the transistor ladder filter – the diode ladder was considered sufficiently different that it did not infringe the patent at the time. The diode ladder filter has quite a different character from its transistor ladder parent, largely because the individual filter poles are not fully buffered as they are in the transistor ladder variant.

The diode ladder filter topology used in the Sonic V is rather different from the better-known diode filters from EMS and Roland, as the frequency cutoff control voltage is actually summed with the audio signal before being added to the top of the diode ladder string. The early Roland and EMS diode ladder designs followed the more usual practice of feeding the frequency control voltage into the bottom of the diode ladder string.

It has a different character from the AJH MiniMod transistor ladder filter; sonically it is closer to the Roland 303 and EMS Synthi A, but with its own take on the diode ladder sound.

We have added many features that make the Sonic XV one of the most versatile Eurorack Modular filters currently available, and with the waveshaping features, it can go far beyond traditional subtractive filtering.

More information can be found here: MiniMod Sonic XV