Modular Synthesizer Proposal

Dominik Martinez April 25, 2017

Introduction

Since the early production of analog circuit design, engineers have applied the principals of electronics to produce music. Some of the earliest synthesizers were developed in the late 18th century including the musical telegraph and the teleharmonium. In the early 19th century several music synthesis instruments were developed that used vacuum tubes, including the Audion piano, the Theremin, the ondes Martenot, and the Trautonium. A major development in synthesizer design was when Harald Bode, Don- ald Buchla, and Robert Moog separately helped to develop the modular synthesizer. The modular nature of the synthesizer made it much easier for musicians to create a wide variety of sounds as opposed to being locked into one timbre as with previous electronic instruments. Synthesizers are example of the intersection between engineering and art. Electrical engineers would become musicians while designing their instruments. I chose this project because I am a musician and have always wanted to build my own instrument. While many of the techniques involved in analog modular synth design has already been designed and perfected, there is still much value in designing a modular synth for a ﬁnal project in 6.101. First, analog music synthesis is a very complex electrical engineering endeavor with many complex parts. It involves the design of diﬀerent modules that uses analog circuit design principles that have been introduced in this class. Second, because of the modular nature of this synthesizer, even though many of the modules have already been implemented by engineers in the past, the design of this synth in particular will be unique and personal.

1 Power Supply

Keyboard Sound Processing Ampliﬁer

Figure 1: Very general block diagram

Block Diagram

Figure 1 shows a very general overview of how this synth works. The power supply and ampliﬁer are simple circuits that we have looked at in class, so I won’t spend that much time discussing them. In Figure 2, we go more in depth to see how the sound processing system works. In the next section, I will discuss what each of the modules do.

The Sound Processing Subsystem

First, a brief discussion on the diﬀerent acronyms that synth designers use.

• VCO - Voltage Controlled Oscillator

• VCF - Voltage Controlled Filter

• VCA - Voltage Controlled Ampliﬁer

• ADSR - Attack-Decay-Sustain-Response

I’ll give a brief explination on each module.

2 VCO1 VCF VCA

VCO2 ADSR ADSR

Keyboard

Figure 2: Detailed sound processing block diagram

3 Figure 3: ADSR example

VCO The voltage controlled oscillator is the heart of the analog modular synth. Without it, we would not be able to produce any musical notes rendering the rest of the sound processing chain useless. The purpose of the VCO is to convert the voltage input from the keyboard into a pitch. The trick of the module is to convert the linear input into an exponential output, as music is exponential in nature. This module also has to produce several types of output waves, including sine, square, triangle, and pulse.

VCF The voltage controlled ﬁlter is essentially a high, low, and band pass ﬁlter with the intensity being controlled by voltage.

VCA The voltage controlled ampliﬁer simple changes the intensity of the signal based oﬀ of the control voltage.

ADSR The ADSR is a envelope generator that is triggered by the keyboard. Each ADSR generates an envelope based oﬀ of four parameters, attack, decay, sustain, and release, as seen in Figure 3.