Adding an LFO to the Techwillsaveus Synth kit.

Add movement to your Atari Punk by adding an LFO!! 

An LFO is a low frequency oscillator which basically means that you can add movement to your sound by outputting a sound wave/pulse at a slower(or faster) rate. This can effect either the pitch or timing(or other parameters) of your Synth depending on the connection to it.

You probably have already noticed this with the Dub Siren as that has an LFO controlling an oscillator which is what gives you the ‘siren’ type sound.

 

With this tutorial I’ll show you how to add an LFO to the APC using the parts from another synth kit. You can of course use similar components if you have them to hand.

 

The IC chip that is used in the kits is a 556 timer which is basically two 555 IC’s in one.

The audio output of the chip is a square wave oscillator and by adding a few resistors, electrolytic capacitors and potentiometers you can adjust the speed(timing) and frequency of the output.

By adding an LFO to the Atari Punk Console you can do some interesting things.

 

Here is a schematic to show what each pin does:-

  

  • 1 A Discharge
  • 2A Threshold
  • 3A Control Voltage
  • 4A Reset
  • 5A Output
  • 6A Trigger
  • 7 Ground
  • 8B Trigger
  • 9B Output
  • 10B Reset
  • 11B Control Voltage
  • 12B Threshold
  • 13B Discharge
  • 14 V+

I’ll be using just the ‘A’ pins(plus positive and negative) for this but after you can of course transfer what I’ve done and turn the other part of the 556 IC into another LFO outputting at a different rate if you wish.

  

What you will need :-

 

  • 1 X Synth Kit built as an APC

 

From another Synth kit:-

  • 1 X 556 timer IC
  • 1 X 4.7k resistor
  • 1 X 100uf Electrolytic Capacitor
  • 2.2k Potentiometer
  • Jumper leads
  • Breadboard

 

 

You will not need to use another battery for this as we will take power from your APC.

 

First connect the power jumpers from the kits as shown from one breadboard to the other. On the bare breadboard connect the top and bottom rails with a positive and negative jumper cables. 

Now insert your 556 IC as shown and follow the diagram above.

Connect a red jumper from the Positive rail to row 14(pin 14)

Then a black jumper from the ground rail to row 20(pin 7)

Pin 14-pin 4

Pin 2-pin 6

Pin 14-VCC(positive)

Pin 7 to ground(negative)

4.7k Resistor Pin 1-positive

100uf Electro pin 2 to ground.

Pin 2 of the potentiometer pin 5

Pin 1 of the potentiometer pin 3


 

You should now have a completed LFO but you won’t hear anything until you connect it to your APC.

 

For this you will need to send the LFO to the APC circuit.

 

Connect a jumper lead to pin 5 on your LFO circuit(Output) and put the other end on pin 11(Control Voltage) of the APC circuit.

 

Attach jumper to pin 5 on the LFO as shown Attach other end of jumper to APC pin 11 as shown

 

You should now be hearing the pitch of the APC going up and down. 

Now try adjusting the potentiometer on the LFO circuit it should speed up/down as you turn it.   

 

By placing the jumper cable on different pins you can get different and sometimes cool results. Try moving the cable to pin 3 of the APC circuit and you’ll effect the other oscillator of the APC.

Also try replacing the electrolytic capacitor for the 10uf one from the kit and you’ll notice the speed of the LFO changes. You can also change the resistor or potentiometer too to get even slower/faster pulses(I’ve just used whats available in the kits. 

 

More things you can try

 

Another interesting thing to try is if you output the trigger(Pin 6) from the LFO circuit to the APC it’ll feed back on itself and give you some even more cool fx. Give it a go and see what results you get.

 

Experiment and have fun!!

  

By Richard Hider 2017.
 

 

 

 

 

 

 

 

 

 

 

 

 

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