Lesson Summary 

Define the role of the VCA in a synthesizer and describe the historical importance of specific song examples.

The earliest audio amplifier was created in 1909 by Lee De Forest.  This amplifier was made by using triode vacuum tubes.  This kind of vacuum amplifier was used to make the first AM radio.  For 50 years the vacuum tube amplifier was the industry standard to be found in radio's, television's, and musical equipment.  
After the transistor revolution of the 1960's most audio amplifiers were re-engineered to use transistors instead of vacuum tubes. This is because the transistor is a much more reliable and cost efficient component.  Vacuum tubes would go bad often and need to be replaced on a regular basis. 
It was the transistor that sparked the creation of the transistor radio in the 1950's.  The transistor radio is a small portable radio receiver that uses transistors instead of vacuum tubes, and still holds the record for the most popular electronic communication device in history.   It was also the transistor that made Bob Moog's VCA possible.
Vacuum tube amplifiers are still commonly used in boutique audio equipment and guitar amplifiers for their perceived "warmer" valve sound.  Realistically, a transistor amplifier represents the input signal much more truthfully than a tube one.  

Amplifier - An electronic device that increases the power of a signal by taking energy from a power supply and increasing an input signals amplitude.

VCA -  An amplifier whose gain is set by the voltage level of a control signal.

Tremolo - A musical effect made by varying an instruments amplitude. 


Experiment with the VCA.


1 x 10kΩ Potentiometer

Jumper Cables


First let's experiment with the EG section of our Werkstatt.  Match the settings shown in Figure 1. 


  Figure 1. EG VCA modulation



Figure 1 will let us play with the envelope of our sound.  The EG stands for envelope generator and allows us to modulate our VCA by pressing the keys.  Experiment with the DECAY knob to hear how the VCA can change in time. Now switch the SUSTAIN mode to ON and experiment with the ATTACK knob.  How do both of these controls effect the sound? 


Now lets use a jumper cable to modulate our VCA with the LFO not the EG control signal.  Both settings are sending a voltage to our VCA to control the amplitude of the output.  By connecting the LFO OUT to our VCA IN we can hear the variations in amplitude as voltage oscillations.  Experiment with the VCA MODE and LFO WAVE settings.   



  Figure 2. LFO modulation of VCA.