via this auction
"AS NEW IMMACULATE Synthesizers.com Portable 22 Customized System Synthesizer. In place of the ring modulator and blank space, I had this built with the Q150 Ladder Filter...'The Portable-22 is a powerful three-oscillator analog machine complete with envelope generators, amplifiers, a mixer, state-variable filter, ring modulator and more in rugged vinyl-covered portable cabinet. Patch cables included.
Add a controller bundle or drive the system with MIDI.
Expansion is easy by adding more cabinets. This system has a QPS1 power supply which is capable of powering up to 66-spaces of modules.
The Q150 Transistor Ladder Filter is based on Bob Moog's famous design and provides incredible-sounding -24dB lowpass filtering which has become the standard of subtractive analog synthesis.
The cutoff frequency can be controlled manually and by control voltages from an envelope generator, oscillator, keyboard, etc. Frequency control signals can be attenuated and inverted without the need for utility modules. Resonance (Q) of the filter can be adjusted with the front panel control. The filter will self-oscillate and track a 1V/Octave keyboard control voltage. Both -12dB and -24dB slopes are available offering a wide range of sounds. One pole and three pole responses are jumper-selectable for even more possibilities. A convenient two-channel mixer is provided for incoming audio signals.
A special feature of the Q150 is output leveling. In most ladder filters the output signal level is greatly reduced as the resonance is increased. This usually requires resetting input levels (sometimes many) when changing resonance settings and can become quite annoying. Special circuitry in the Q150 maintains constant output level at various resonance settings while keeping the harmonic content unchanged. This feature is jumper-selectable and can be deselected if identical behaviour to the Moog ladder filter is desired.'"
