Fortitude
Fortitude is a sub-octave generator with multi-feedback path resonant low pass filter. The module works by first turning the input into a square wave and using that signal to generate the sub-octave, 2x sub-octave and 3x sub-octave square waves. Each of these goes through an attenuverting input mixer, before passing through a Sallen-Key filter. Voltage control over the filter cutoff is achieved by DIY dual vactrol. The filter has the standard 'Q' resonance and 2 additional strange feedback paths we're calling Strange Frequency and Strange Timbre. Both of these feedback paths provide data for their own shift register. Strange Timbre's shift register is used to create short pulses that are fed back into the pre-filter mixer, producing bright and biting overtones. Strange Frequency's shift register is used to interrupt the sub-octave generation and depending on the attenuverter positions can either produce interesting grumbling tones, crunchy growls, or entirely collapse the sub-octaves!
Fortitude is a sub-octave generator with multi-feedback path resonant low pass filter. The module works by first turning the input into a square wave and using that signal to generate the sub-octave, 2x sub-octave and 3x sub-octave square waves. Each of these goes through an attenuverting input mixer, before passing through a Sallen-Key filter. Voltage control over the filter cutoff is achieved by DIY dual vactrol. The filter has the standard 'Q' resonance and 2 additional strange feedback paths we're calling Strange Frequency and Strange Timbre. Both of these feedback paths provide data for their own shift register. Strange Timbre's shift register is used to create short pulses that are fed back into the pre-filter mixer, producing bright and biting overtones. Strange Frequency's shift register is used to interrupt the sub-octave generation and depending on the attenuverter positions can either produce interesting grumbling tones, crunchy growls, or entirely collapse the sub-octaves!
It's worthy of note that the module has both very high internal gain and output clipping at +/- 5v. If you find as you change the sub-octave attenuverters you aren't getting much change at the output, try bring them all closer to 0. If you find not much change even at high level of S Hz and S T, try bringing the attenuverters away from 0, or increase Q either of which will increase the signal being fed to the shift register data pins.
It's worthy of note that the module has both very high internal gain and output clipping at +/- 5v. If you find as you change the sub-octave attenuverters you aren't getting much change at the output, try bring them all closer to 0. If you find not much change even at high level of S Hz and S T, try bringing the attenuverters away from 0, or increase Q either of which will increase the signal being fed to the shift register data pins.
When building the module always start with the lowest and smallest components first. Resistors and capacitors, then ICs and diodes. When it comes to building the vactrol we have found it's pretty hard to screw up. All varieties of LDR we have tried have worked without much difference as long as off resistance is roundabout 1 meg. We have had success with both a nice tidy shrink wrap job (yes, you can get the LED and both LDRs positioned properly in some shrink wrap, take your time!) and a quick and dirty electrical tape job. Just make sure you get the LDRs looking at the LED and seal it up as best you can. Next install the board connecting pin headers and finally the pots and jacks. Have the faceplate installed while soldering them and always start with just one leg before checking alignment and then finish soldering.Â
When building the module always start with the lowest and smallest components first. Resistors and capacitors, then ICs and diodes. When it comes to building the vactrol we have found it's pretty hard to screw up. All varieties of LDR we have tried have worked without much difference as long as off resistance is roundabout 1 meg. We have had success with both a nice tidy shrink wrap job (yes, you can get the LED and both LDRs positioned properly in some shrink wrap, take your time!) and a quick and dirty electrical tape job. Just make sure you get the LDRs looking at the LED and seal it up as best you can. Next install the board connecting pin headers and finally the pots and jacks. Have the faceplate installed while soldering them and always start with just one leg before checking alignment and then finish soldering.Â
There are many components in this module that are well worth experimenting with to get your module to sound more unique. In particular the resistor between the Q pot and ground, the 1k that feeds back into the filter, the resistors and capacitors that make the pulses for S T, etc. If you come up with an interesting combo you want to share, let us know at sentientsynths@gmail.com and we'll list a link to it here!
There are many components in this module that are well worth experimenting with to get your module to sound more unique. In particular the resistor between the Q pot and ground, the 1k that feeds back into the filter, the resistors and capacitors that make the pulses for S T, etc. If you come up with an interesting combo you want to share, let us know at sentientsynths@gmail.com and we'll list a link to it here!
