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Dual Q Filters - $1600 USD
Notice that on the Dual VCAs, the bottom one is AC coupled w/ black Signal I/O jacks & the top one is DC coupled with all blue jacks.
Serge Mayhem

Features and Notes

Audio Mixer w/ phase switch (3x1) (AMX)

The Audio Mixer is a three-in/one-out manual mixer with a phase switch on input 3.

Variable Q VCF (VCFQ)

The VARIABLE Q VCF (VCFQ) is an excellent general-purpose VCF offering simultaneous low-pass, high-pass, band-pass and notch (band-reject) outputs. The resonance (Q) of this filter is dynamically variable by manual or voltage control. The VCFQ has two signal inputs. One incorporates an automatic gain control to prevent the filter from overloading at high Q settings. The second input has a level control so that the percussive effects of overloading the filter can be exploited. When a pulse is applied to the Trigger input, the filter will ring, producing a damped waveform similar to that produced by striking a resonant object. The nature of this ringing is controlled by the Q and the filter frequency. Percussive effects ranging from clicks to the sound of wood blocks and bell tones can be produced and controlled. This ringing effect can be used in conjunction with signals applied to either of the audio inputs to achieve highly controlled complex tonal qualities.

Other comments:
A nice bit of flexibility is the "LO" setting that turns it into a CV processor! ... Recent updates to the filter's circuitry are noticeable as well - Its much easier to get tube-type harmonic warmth just by nudging the gain control. The feedback and overdrive characteristics have also been tweaked to be more musically useful... This filter will not oscillate unless you patch it up for feedback... Hi-Lo range switch for fantastic and unique audio/cv applications - hit it with a pulse, get an unbelievably slow damped sine wave. Calibrated 1 v/oct and attenuated cv inputs, just like the oscillators... Since it's a multimode filter, it's 12 dB/oct rolloff. You may want a LPF with more 'bite' in some applications. I think the bandpass and allpass sections of this filter have 6 dB/oct rolloff.

Wizardry: Must be patch-programmed to oscillate. Feed an output back into an input, then turn the Q up to get a nice sinewave. The various outputs will then be 90 degrees phase-shifted from one another.

Dual VCA (2VCA)

The DUAL VCA (2VCA) employs two high-quality VCA's. This module is an excellent inter-patch VCA, featuring very low noise and exponential response. It was designed as a small VCA function for use at various places within a system for internal VCA functions (as opposed to the VCA's for output mixing). Like the new Universal Audio Processor and the Cross-Fader this VCA has an audio taper that is an exponential curve with a 12 db per volt sensitivity throughout the range except below about .5 volts. Below this threshold, the output of the VCA will decrease rapidly to completely attenuate the signal. This response is perfect for our envelope voltage range. and is responsible for exceptionally quiet operation. Control voltage rejection is very high, and the unit cannot be overdriven beyond a gain factor of two.

Thanks to Ty Hodson for pulling M-Class module information together from various sources. Other references include "Introduction of the Serge Modular Music System" by Rich Gold, Darrel Johansen, and Marina LaPalma
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 Dual 'Q' Filters  Dual Oscillator
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