NLC Plague of Demons

Wednesday, 12 July 2017

NLC Plague of Demons

Plague of Diamonds Eurorack module build notes.

Checkout electronotes EN #75.

It's a thru zero VCO that uses analogue switches (DG202) rather than FW rectifiers.
Should be easy to use; LEDs indicate when it crosses zero.

My understanding of the through-zero concept is that with a regular VCO, if the frequency modulation reaches or goes below 0, you won't hear anything. With a thru zero VCO, you'll hear "negative" frequencies.

"The negative-frequency version of a waveform is simply a time-reversed replica of the original waveform". (Ian Fritz. 2009)
Check out Dave Brown's scope shots on his site (Modularsynthesis.com)
of the Ian Fritz "teezer" Thru-Zero VCO
They explain the concept so well.

The BOM requires:
a S1JL rectifier
Mouser No: 821-S1JL

and a JFET
Mouser No: 512-MMBFJ108

Both have a long backorder wait at mouser.
So possible replacements are:
mouser no: 771-PMBFJ108-T/R for the JFET
and
Mouser Part No: 583-FM4005-T for the recitfier.
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.

On the PCB, I think Andrew has marked the cathode with a dot.

NLC words of wisdom

I like to get the ICs on first.

I'm using PCB version 2, so some mods are needed.
Had to cut one trace and add two resistors (10k & 2.2M).
Be careful not to short anything ... its a bit tricky

Q1. Its a PNP/PNP matched double trannie.
I used a microscope to find the dot that helps orientate it. But if your eyes are better than mine you could do without the scope.