VCF.SCI.2

Lesson Summary 

Define and describe atomic properties of transistors in relation to the Moog ladder filter. 

Skills 
Programming
Vocabulary 
Conductor - A material that allows electricity to flow freely though it. Metals are great conductors, with copper being a commonly used conductor in electronics. 
 
Insulator - A material that restricts the flow of electricity.  No material is a total insulator, common examples include glass and paper.  

Semiconductor - A material which has electrical properties between that of a conductor and that of an insulator. The electrical properties of a semiconductor change with increasing temperature.  Because the electrical properties of a semiconductor can be modified by controlled addition of other materials (impurities), devices made from semiconductors are very flexible.  Semiconductors are the foundation of modern electronics, including transistors, solar cells, light-emitting diodes (LEDs),  and analog integrated circuits (ICs). 

 

 

Atomic Bond - Atoms can bond together in amorphouspolycrystalline, or single-crystal forms

 

Silicon -  A chemical element with the symbol Si and atomic number 14.  When Silicon is single-crystal structure it is the most commonly used semiconductor material.  Monocrystalline Silicon (Mono-Si) is commercially created in disks known as wafers.  An interesting quality of the Werkstatt's  Moog ladder filter is that each transistor in the ladder is created from the same Mono-Si wafer. 

Transistor - A semiconductor device used to amplify and switch electronic signals and electrical power. Transistors are composed of a semiconductor material with at least three terminals for connection to an external circuit.  Prior to the development of transistors, vacuum tubes  were the main active components in electronic equipment.  It was the development of transistors that not only made the analog synthesizer possible, but sparked the technological age we live in today. 

Exercise 

Experiment with the VCF and VCF MOD of the Werkstatt.

Materials 

 

 

1 x Arduino Microcontroller

 

Jumper Cables

 

Hardware 

An interesting feature of the Werkstatt's ladder filter is that it can be voltage controlled. If we match the settings in Figure 1 we will be able to hear how the LFO can control the VCF.  

 

 Figure 1. VCF MOD LFO Settings. 

 

By turning the LFO RATE knob and VCF MOD AMOUNT knob we can hear the variation in VCF control.  Experiment with the CUTOFF and RES knobs as well to see the wide range of available timbre's by using the VCF.  This flexibility is all thanks to the ladder filter, which is made possible by transistors made of Mono-Si

Now, unplug your Werkstatt and unscrew the top four panel screws to remove the top plate.  Figure 2 highlights the are of the PCB that holds the ladder filter with Q3 - Q7 being our matched silicon transistors. 

 

  Figure 2. Highlighted ladder filter on the PCB. 

Software 

To see how the resonance filter sweep looks we will need to put the top plate back on our Werkstatt using the same four screws and then plug it back in.  We will then need to plug our Werkstatt's audio output into an audio input on whatever computer we are using.  On my laptop I am simply changing the headphone output settings to allow the port to act as an input.  

 

 

 

 

Once we are sending signal into our computer we need to check that it is the primary audio input source.  If the Werkstatt is plugged into the primary audio input source then we are ready to run our Frequency_visualizer.pde program. If we carry out the same CUTOFF filter sweep we should see a visual response similar to Figure 3.

 

 

 Figure 3. GIF screen capture of CUTOFF frequency sweep.

 

 

For more information regarding the specifics of Frequency_Visualizer.pde please refer to the comments in Figure 4. 

 

 

 Figure 4. Screen capture

Downloads 

Processing is an open source programming environment and community.

moog_werkstatt processing_files.zip

 

 

The Arduino is a micro controller and programming environment for interactive systems. 

Standard_Firmata.zip

Subject 
Unit