Wednesday, 24 June 2015

555 Resonator Build Notes - NLC (NonLinearCircuits)

This is one of my favourite NLC circuits.
It's very versatile. It can be used as a filter, a VCO, a voltage controlled noise source and a voltage controlled drone module.

The module will oscillate without input (depending on the pot settings).
I like inputting a signal from a VCO which will trigger each 555 IC to create pulses.
These pulses can be manipulated with CV to create complex waveforms.

Andrew's manual for the 555 can be found here:
http://www.sdiy.org/pinky/data/FILTER%20panel%20manual.pdf
And his official build notes are here:
http://www.sdiy.org/pinky/data/Its%20555%20build%20notes.pdf

I have a version of this module in Serge/Banana format.


This build however is for a Eurorack Format module.
First, some pics of the virgin panel & PCB before we begin.


The module takes it's name from the 555 timer IC. This integrated circuit is used in a variety of timer, pulse generation, and oscillator applications. It's a very common IC and is cheap as chips.
The standard 555 package includes 25 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8) .


There are plenty of great videos on this versitile chip:
https://www.youtube.com/watch?v=tn5-XiB8oJk
https://www.youtube.com/watch?v=stN-ZzHfiO4

Andrew's module uses 5 of these 555s.  If I understand Andrew's schemos correctly,
each is part of an individual one shot circuit (also known as a Monostable Multivibrator).

Pin 1 is grounded.
Pin 2 - The trigger input.(connected to C5 - 1nf cap)
Pin 3 - Output.
Pin 4 - usually connected to + VCC to avoid accidental reset.
Pin 5 - grounded through a capacitor (c3 - 10nF?) to avoid noise problems. (This is the decoupling cap?).
Pin 6 - (threshold) is shorted to pin 7 - both are connected to ground via C6 (10nF cap).
Pin 7 - connected to the pin 6 & the discharge capacitor (not shown in the above schemo) - C6 
           C6's discharge time determines the pulse width.
Pin 8 - connected to the supply VCC.

The output of the 555-Monostable Multivibrator/oneshot remains low until a trigger pulse is applied to pin 2. 

It's probably a good idea to install the headers for these ICs along with the other 3 ICs and power connector first.

The other integrated circuits used in this build are two TL072s & one TL074.
The TL07x series are pretty common Op Amps that you will often find in synthesizers.
The TL 072 is a low noise JFET input Op Amp .....commonly used in filters & audio preamps.
The TL074 is a quad Op Amp.
Each of these 4 operational amplifiers incorporates well matched, high-voltage JFET and bipolar transistors. Each op amp has 1 input & 2 outputs (inverting & non-inverting). Voltage is on pins 4 & 11.

But before I install all these, I'll install the resistors, then caps & trannies

The easy ones first.
10uF electro caps (x7), 1nF (x10) & 10nF polyesters (x5).

Now it's time to install the 'cp' caps & decoupling caps.
 The cp caps & trannies form VC resistors that control the pulse width of the signal from each 555. Andrew has suggested starting with 10nF caps and then experimenting with different values.

Next the decoupling capacitors. As their name implies, they decouple or separate one part of a circuit from another. 555 ICs can be very noisy and these caps absorb some of the noise, reducing the effect one part has on another. There are 15 of these caps.

Andrew has suggested values between 47nF & 100nf. He says that the exact value won't make any difference. Use whatever fits and you have a lot of. "The main point is the 555s have plenty of decoupling, hence the 10uF as they virtually short +V to gnd as they do their thing".

Next, the transistors. These include ten BC 547 & ten BC557.
The BC 547 is a NPN transistor.
The BC 557 is a PNP. The cp capacitors and the transistors form VC resistors that control the pulse width of the signal from each 555.

Install the pots:


And the jacks.
Initial jack connections: Blue = Ground, Black = Out, Brown = In.
Test to see how it sounds as a filter by plugging in a sound source (eg: your Dual VCO).

Now connect the rest of the jacks.

Wow ... looks and sounds great !!!
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     Useful Links:
1.  NLC filter panel
2. NLC notes (5 more)
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http://djjondent.blogspot.com.au/2015/03/non-linear-circuits-ncl-index.html

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