Zlob SVF (State Variable Filter) - build notes

 These are some build notes for the ZLOB filter.

It's just 4HP and sounds great

It love the small form factor.

Just 4HP. WE need more 4HP filters ... useful for compact performance rigs.

The official build notes are very good.

Comprehensive.

https://zlobmodular.com/product/svf/

 

These are just my personal build notes to help troubleshooting should I run into any problems.

The official build notes: 

https://zlobmodular.com/wp-content/uploads/2021/01/svf_6612_builddocs-compressed.pdf

 

It provides Low Pass, Band Pass, and High Pass outs inspired by WASP and Thomas Henry filter topologies. 

 

Resistors. caps, IC headers

Everything is through-hole

Quite easy to build.

That 2K resistor needs to be in contact with the two transistors

 2N3906 PNP transistor TO92D Q1, Q2 (tayda or mouser)

 

The power section ... 

2 1N4001 1N4004 DO41-10 D1, D2
3 1n4148 DIODED0-35 DO-35 D3, D4, D5 

This trimmer is used to set the lowest cutoff frequency. 

With resonance at 0(fully CCW) and with the frequency up the filter will self oscillate in some modes/situations. 

This is the control board. It sits at right angles to the main PCB

.They are connected with a header

ICs are finally in.

1 LM13700N LM13700N DIP16 IC3
1 TL072IP 8-DIP(has to be a low offset voltage dual opamp)
1 TL074 TL074_ DIP14 U1

The 2019 revision also adds improved cutoff and resonance response and attenuversion through the ACV IN using the above pot. CV IN provides another unattenuated voltage input to modulate the frequency.

 At the CV in, +10v will open the filter completely if the cutoff pot is CCW(counter clockwise). With the cutoff knob at noon the filter can be opened with +5v or closed with -5v. CV input at the ACV in is dependent on the CV attenuverter knob.

The filter has 2 audio inputs, but channel 2 is jumper selectable between standard audio in or Ping-able operation. 

There are 3 jumpers located at the bottom of the main PCB near the power section.

 

These allow you to select the modes for max resonance, self oscillation or no oscillation. 

This is all based on the setting of the resonance pot.

 

When set to self oscillation mode, the filter can produce a sine like wave with no input and a trapezoid like wave in the max resonance jumper setting.  

 

In max resonance mode, the filter output can exceed 10Vpp

 

At the CV in, +10v will open the filter completely if the cutoff pot is CCW(counter clockwise). With the cutoff knob at noon the filter can be opened with +5v or closed with -5v. CV input at the ACV in is dependent on the CV attenuverter knob.