Tuesday, 6 December 2016

Sauce of Unce - NLC - Build notes

This is a Eurorack module based upon the Buchla 265 Source of Uncertanity module.
The 265 is the first in a long string of modules bearing the name "Source of Uncertainity" which I
think is poetic and apt for such a module.

The Buchla 265 is one of  the greatest modules Don ever built.
However, the original 265 uses lots of rare and expensive parts and needs +24V to operate so is out of reach of most people.

The Nonlinearcircuit module though not a complete clone is very close.
The noise source uses a TL074 (quad op-amp). The 265 used four uA741s (single Op-amp).
The 0.05-50 Hz VCO is op amp based (again TL074).
The Sample & Hold sections are changed to use the hi-Z input of TL074 op amps (ie not uA741s). 
The 265 used an uA741 at the S/H output.

I've often wondered where did the name "unce" come from?
Maybe as it's the written form of the sound heard in most club music, Andrew named it from there? You have probably heard the sound unce,unce,unce,unce, etc coming from a club.

Andrew's build notes are here:

NLC Blog descriptions:

I'll be building two versions: one for the Buchla system & one for the Euro.

First the Eurorack one.
This is what the virgin boards look like.
There are four surface mount TL074 op-amps and some passive resistors in SMD format.
The rest of the build is through the hole.

There are two sides to this PCB

I like to get the SMD op amps onto the board first. Be careful there are no shorts.
Then the rest of the passive SMD stuff. The spacing is for 1206 SMDs.
I'm using 0805 SMDs. 
The 47K resistor  next to the 4u7 cap (marked in yellow) should be added last.
It sets the level of the noise output and determines the behaviour of the entire circuit.
It's value can range from 47K to as low as 12K if you have noisy transistors.
read Andrew's build notes for more info.

T1, T2 & T3 are test points.
T1: should just be noise like the three noise outputs
T2: a noisy approx 100Hz tri wave
T3: turn up the random pot to max, depending on your vactrol you should hear approx 30Hz +/-10V signal .
T3 is the output of the VCO that controls the S&H on the 'random' output, 

The orange & blue circles mark resistors that should be left out or changed. These set the output voltages.
Euro require voltages in the 0-5V range.
Buchla require a 0-10V or 0-15V range.

The blue circle marks the 12K resistor which I'm changing to 6.8k to give a Euro voltage output (0-5V).
The Orange circle marks the 10K & 33K which I'm changing to just a link (on the 10K) to again give out Euro voltages.

I'm using a J112 for the FET.
 Caps next.
 I'm using 68uf ceramics for the decoupling caps.

I used a 10uf 50V non polarized electro here.
The remaining 10uf Electros were 35V
 Vactrol time.
Using a VTL 5C3/2 for the dual vactrol.
It's what I had on hand at the time.
Probably a VTL 5C2/2 would be better ??
The VTL 5C2/2 has slower attack and decay response times.

For the single vactrol I used a NSL 32.

Almost there.
Pots, LEDs & jacks now.
I used 510 Ohm SM resistors for the LEDs.
Before setting the noise levels with the resistor marked "47K" I had a listen with just headphones.
Yup !!! lovely noise.

I measured an average of 0.175V at pin 1 of the TL074.
It fluctuated  quite a bit.
So the resistor value was 62K
11000/0.175 = 62.857

I blew the 10 ohm resistor in the lower right corner of the pic. It's now replaced with a SMD 10Ohm.
The culprit was I think a short  between the dual vactrol and the resistor (now covered with plastic shrink).

For the Buchla module:
To get approx 0-10V, install the 10k and 33k resistors as described. To get it up to 15V, replace the 10k resistor. Use 0805 smd (which will fit nicely), so you can easily remove them, try 22k for starters.

Similarly, on the smooth output you can change the 10k resistor to increase the output voltage.  
The build guide I suggests using 6k8 to 8k2 instead of the 12k. "The output still gets pretty hot but very rarely clips, this depends a lot upon your dual vactrol, so some experimentation is needed. I (Andrew F) used a rare dual Silonex. "Best to use 0805 resistors which can be easily installed and removed".

Another way is to use 6k8-8k2 as suggested to keep signal levels at comfortable (for the op amp) levels and then adjust the '10k*' resistor at op amp C1 to get the range you want, higher resistance = higher voltage.


Muffs- 265sou

You can find more NLC builds here.

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