NLC build notes 2 for a LPG

These are some build notes for a Nonlinear circuits LPG version 1.

Its actually a really old NLC design with through hole components.

The old silver panel version too. I first built one back in 2015. 

I bought 4 panels/ Pcbs with the intention of building a quad Low Pass Gate (LPG).

like a 292 and only got around to building one module.

These are the original notes:

Low Pass Gate - Filter/VCA - Buchla Style - Build Notes

And these are Andrews blog notes:

http://www.sdiy.org/pinky/data/WAMOD4%20lpg.pdf

I decided to finally finish off the remaining 3 PCBs

This came about when a friend recently asked me what was the best sounding 

LPG module in Eurorack.

He was particularly interested in DIY.

There are many low pass gates out there.... eg:

Makenoise QMMG (ridiculously expensive)

                    ... might as well buy a real Buchla 292e and be done with it.

MakeNoise MMG

MakeNoise LxD MakeNoise Optomix

NLC Dual & single LPG

Meng Qi - LPG (passive)

Erica Pico LPG

Synthrotek LPG

Endorphin.es Grand Terminal Pittsburgh Modular Lifeforms Dynamic Impulse Filter.

Ken Stone's LPG Mystic Circuits LPG

Malekko/Wiard Boogie & Borg filter RYO Aperture Takaab 2LPG Pittsburgh Modular LPG

The synthrotek, Ken stone & NLC ones are DIY.

Below is the rear of a NLC single LPG... half built.

Notice the headers for the vactrol ... hopefully will make it easier to swap vactrols.

All LPGs are based on the Buchla 292 which is expensive and hard to find... esp a original vintage one.

Part of the problem in attempting rebuilding from the original schematics are hard to find components.

Esp the vactrols.

Anyway, I think it's pointless trying to rebuild the past.

Like a dog chasing its tail. 

Better (in my humble opinion) to use the past as inspiration and build something that

is of this time and place.

Andrew also did a later version of a Dual LPG

which is well worth checking out.

66. Dual LPG - build notes

This version used headers to make the dual vactrol.

The pic below is of the single NLC LPG.

I'm adding headers for the pots & vactrol to allow some experimentation

Both versions are designed for a dual vactrol. 

Some of my earlier 4U builds (eg of a "cloned" 208) use dual vactrols like the VTL5C3/2, 

If you have a few spare use them. 

Dual vactrols are actually two photo-resistors and a LED in the one package ....

The VTL5C3/2 are hard to find and expensive

You could buy cheap Chinese copies but another way around this is to build your own. 

I kinda like this as DIY is fun, I don't want to make a 292 and DIY lets you experiment and 

find your own unique sound.

My friend wants the module to be flexible ... with the ability to swap components to adapt the sound.

The LPG version 1 is best for this as the vactrol is standard.

Version 2 uses a box to make the vactrol.

The other mod I'm making is with the pots.

Do I use log, linear, anti-log?

The BOM indicated 100k linear .. but it will be fun to experiment with this.

With the first build, I liked the sound of the module with a log 100K pot for the frequency.

So I'm adding some trimmed IC headers for the pots and vactrol.

The 33k can be varied up to 51K .... It sets the Cv level.
I left it at 33k.

The 10K sets the gain of the output signal.

I started with this at 10K

Decided to use surface mounted resistors to make changing them easier.

After playing around with the module I deciced to up the 10K resistor to 22K

Better !!

upped it again ... this time to 51K

Yes !!!

Who wants to die for art?

Divine as Dawn Davenport in John Waters' Female Trouble, 1974. ..... ???

DIY Vactrol time.

(Dual vactrol)

This was my first attempt ... not very successful

You can find a bit more info on vactrols here:

+ Vactrols - Optocoupliers

I started with a 5mm green LED and 

 two GL5549 LDRs

It was really hard to encase this in shrinkwrap.

so opted to try making two separate  vactrols

I used two GL5549 & two 3mm Red LEDs.

I joined the two LDR in series ......there are 3 connections on the LDR side.

The LEDs were connected in parallel ... just 2 connections on the LED side.

In the pic below, the LED side is on the left.

The LEDs are sitting on top of each other .... sharing the same anode & cathode sides.

Pretty messy I know.

The pic below is the vactrol looking at the   LDR side (3 terminals).

I'll make the next one cleaner. however, the vactrol works.

The buchla 292 I think used a VTL5c3/2 which had a dark resistance of 10M ohms

and a slow response time.

which is pretty similar to the GL5549 LDRs which has a dark resistance of 10M and a response time of about 20ms

... probably best to just experiment.

Second vactrol.

I used two GL5549 & two white 3mm LEDs

Sounds great. I think better than the red LED.

In this test I used B100K pots for both Freq & res.