Nonlinearcircuits Null-A2, Build & Bom

Page: 10 / 26

Set-Up
VCOs: The 100k trimpots on the VCOs are used to set up the panel pots so they
have minimal dead zones at the start and ends of their travel.
The 20k trimpots are used to dial in 1V/oct tuning; you should be able to get
3 octaves of decent tracking from these VCOs. I use a guitar tuner and get the
VCO to some note, then stick in 1V to the CV input (make sure the CV pot is
turned to max) and adjust the 20 trimpot until the tuner shows the same note 1
octave up. Remove the 1V source and your VCO will not return to the original
frequency, tune the 20k trimpot again to a note, put in 1V…..and so on. It
takes a few goes until you dial it in to the correct tuning.
State VCF: The balance trimpot (TR5) can usually be left at its mid-point. If
you notice one of the outputs is much louder than the other, adjust this
trimpot to get the outputs balanced.
TR6, the Freq offset trimpot is used to ensure the Freq pot is functional
across its range, same idea as the 100k trimpots on the VCOs.
Ladder VCF: TR9 Ladder VCA trimpot at the top of the PCB is used to set up the
VCA. Plug in a signal and listen to the output. Now plug a lead into the VCA
CV input with the other end hanging free. Use this trimpot to turn off any
signal you may still hear. Set it to the point just where the signal can no
longer be heard. Remove the lead plugged into the VCA CV input; you should now
hear the signal again.
TR7 Freq this sets the useful operating region of the CV inputs and Freq
cutoff. Adjust it so you get good sounds coming out of the VCF when tweaking
the Freq pot, by good sounds I mean runny liquid acid.
TR8 Q sets the range for the Q or resonance, set it so you get the filter
screaming when the Q pot is turned up near max.