Tuesday, 15 August 2017

Feague - NLC - Build notes

These are my build notes for the Nonlinearcircuits Feague module.

Feague is defined as:
"To decorate or improve in appearance through artificial means.. To increase the liveliness of a horse by inserting an irritant, such as a piece of peeled raw ginger or a live eel...."
This module is a 4 pole filter and Quadrature oscillator in Eurorack format.
It has 4 outputs, each 90°phase shifted, two CV inputs, a signal input, sync input and a hi/lo range switch.

It looks very similar to a module Andrew built into his Serge format Drum Panel.
Andrew described this as:
Quadrature Oscillator (QUO) / Low Pass Filter (LPF) with chaotic feedback.
It can be switched to perform as a very low freq QUO, quadrature VCO, LPF with Q and a pot
allows non-linear resonant feedback to obtain richer and irregular harmonics.

Below is a panel and bare PCB for the Eurorack version.
Andrew's build notes are here:

A Quadrature oscillator is a phase shift oscillator.
 It uses an op amp integrator to obtain a full 90° phase shift.

 Here is a simplified circuit to demonstrate the principle.

 In this video Andrew is demonstrating two Feagues. The one on the left is used as a VCF and the right as a oscillator (QUO). QUO mode is obtained by cranking the Q pot up to 9-10

Back to the build. The virgin PCB:

Get those ICs on first.
We have three TL074 (Op-amp), two LM3700 (op-amp) and a DG411
The DG411 is a multiplexer
Trannies on next:

Some NLC words of wisdom:
Monday Morning Gunk.

The BOM requires:
a S1JL rectifier
Mouser No: 821-S1JL.
There is a long waiting list for this.
A replacement is  Mouser Part No: 583-FM4005-T.
The rectifier is polarized. The cathode end is marked with a band. 

This replacement is slightly too big for the PCB. so i had to solder it on its side.

Rest of the Thruhole and passives.

Resistor RL - for LEDs. I'm using 470R.
Resistors marked with a "C" = 100K
 Don't forget the Tempco  resistor. The LEDs colour isn't imporant.

 Headers next. Install the heareds before you install pots and jacks

Time for the Jacks & pots

Time for the last 4 LEDS.

You can use this module as either a VCF or Quad Oscillator.

"To use as a VCF keep the Q pot at zero.
Patch in an audio signal and adjust the Coarse freq pot and Q pot to use as a filter.
Keep the switch on Hi, add CV as you like. Once sounding good, try tweaking the nonlin Q pot and see what you get. "

To use as a Quadrature Oscillator
"Keep the nonlin Q pot at zero then turn up the Q pot until the module starts to self-oscillate
(around 8-9).
Adjust the frequency with the freq pots.
When the switch is Hi the range is at audio rates, set the switch to Low for LFO rates.
When using the module as an oscillator, the nonlin Q pot can be used to adjust the amplitude of the output signals.
Don’t forget to play with the sync input; it is more like a freeze function."

+ NLC Build notes
+ NLC Blog
You can find more NLC builds here.

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