Forbidden Planet User Manual
The Tiptop Audio Forbidden Planet is a voltage controlled resonant multi mode lter in Eurorack
format. There are 3 modes: High Pass (HP), Band Pass (BP) and Low Pass (LP). Each mode has its
own audio input that can be used simultaneously. The lter frequency cuto has two voltage
control inputs, one attenuated and one full scaled. The lter also has a resonance control knob
and an output master volume knob.
Lets get started:
Begin with the RESO all the way OFF (counterclockwise).
Plug a saw wave into the LP IN jack, set the RESO knob all the way down counter
clockwise, set the Volume knob to about 3 o’clock and plug the OUT jack to your audio
system.
Rotate the FREQUENCY knob full scale, you are now hearing the lter in Low Pass mode.
Connect the output of an envelope generator into the un-attenuated CV input, turn the
frequency knob to around 9 o'clock and trigger the envelope now you can hear the
envelope modulating the cuto frequency of the lter. Adjust the envelope attenuator to
vary the modulation amount.
Plug an LFO into the attenuated CV input, adjust the attenuator to increase and decrease
the amount of LFO modulation. Now you can hear the lter being modulated by an
envelope and an LFO at the same time with full control over modulation amounts.
Manually play with the lter frequency and slowly turn the RESO knob clockwise, listen to
how it starts emphasizing the cuto harmonics and as it increases the lter starts to self
oscillate creating a sine wave tone whose pitch is controlled by the lter cuto frequency,
essentially turning the lter into a sine wave oscillator. As the resonance knob reaches its
maximum position the circuit starts to saturate and becomes unstable and confused,
making it sounding aggressive and scattered. Forbidden Planet can go from smooth and
crisp all the way up to aggressive and chaotic plus anything in between. The resonance is
impacted by the gain of the input signal, a lower gain will make the resonance appear
strongly.
Turn o the RESO knob, unplug the LP in jack and plug the audio signal into the HP IN.
Follow the steps above to get a feeling of the beautiful quality of Forbidden Planet's
highpass mode. Note that the frequency control and and CV inputs will now work in
reversedirection to the low pass mode, set them opposite to what described above.
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