SEM design with modern improvements.
The Boomstar SEM is known as a 'Voltage Controlled State Variable Filter' because it provides simultaneous high pass, low pass, and band pass outputs, all with a 12 dB/oct slope. The notch is the inverse of the bandpass, achieved by summing the low pass and high pass outputs. This version is a combination of the original SEM filter and the newer design from the OBX, along with improvements by SE. It has a modest current draw, which it pulls evenly from the plus and minus rails.
This filter is a 'State Variable' circuit, which is an analog computer model of a pendulum. When the resonance is increased, the "damping" or stabilizing of the circuit is actually decreased. This makes the pendulum swing more wildly. If it is hit hard enough, it will swing all the way to one side and 'stick' there, what we call 'bonk out'.
Many sound designers like the sounds that can be gotten as it goes into and out of 'bonk out', so Boomstar has not made the filter 'idiot proof' by limiting the input level and resonance amount. If you don't like it, limit your input level and/or resonance amount. Otherwise, go wild! It won't hurt the circuit.
Three attenuverter and four attenuation pots control the FREQUENCY, RESONANCE, FREQ CV 1, RESO CV, LP HP, INPUT and OUTPUT, delivering smooth, detailed, and complex expression.
Switch it Up
FULL and HALF strength filter frequency keyboard/voltage tracking, and BP / LP-HP modes.
Patch it Up
Seven patch points: 1 V/O, FREQ CV 1, FREQ CV 2, RESO CV, INPUT, BP LP-HP, and OUTPUT direct the deepest manipulation.
- FREQUENCY – Adjusts the frequency, or cut-off of the filter.
- RESONANCE – Adjusts the resonance of the filter.
- FULL HALF TRACK – Switch between full and half keyboard/voltage tracking.
- FREQ CV 1 – Frequency control voltage 1 input attenuverter.
- RESO CV – Resonance control voltage input attenuverter.
- LP HP – Low Pass / High Pass attenuverter.
- INPUT – Adjusts the audio input.
- OUTPUT – Adjusts the audio output.
- 1 V/O – One volt per octave control voltage input.
- FREQ CV 1 – Frequency control voltage 1 input.
- BP OUT – Band Pass Output. No cable patched, BP passes through the mains.
- RESO CV – Resonance control voltage input.
- INPUT – Audio input.
- BP LP-HP – Switch between Band Pass and Low Pass - High Pass modes.
- OUTPUT – Audio output.
- Size - 12hp
- Depth - 39.7mm with ribbon cable attached
- Power Usage - 32mA (+12 / -12)
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