Before getting into building analog synthesizer modules, let’s look at some basic electronic components, and some of the basic circuits that use these components. These articles will be short introductions to the components. They will not be a thorough introduction to electronics. Hopefully it will be just enough to get started. If you would like a GREAT, easy introduction to electronics get Forrest Mimms’ book Getting Started in Electronics. For now, let’s get started with . . . . Resistors.
Resistors are probably the most common component used in synth circuits. They are easy to spot, they usually look like a small brown tube with stripes. Resistors are used to limit current. The stripes on the resistor indicate the resistor’s value. If you do not know how to read these color codes, you can find out here. Also, this site has an easy to use resistor calculator. You select the resistor color codes, and it tells you the resistor’s value.
If you are new to resistors, analog synthesizer circuits will primarily use 5%, 1/4 watt, carbon film resistors. These can be easily purchased from Mouser Electronics or Digi-Key Corporation. Digi-Key has a kit containing 5 each of the most common resistor values from 1 ohm to 1 Meg Ohm. If you would like to have a selection of resistors on hand, it’s a great deal.
On a schematic diagram, a resistor is indicated with a wavy line like this:
This Voltage out of this circuit is determined by a ratio of R1 and R2. The formula is
Vout = Vin x (R2/(R1 + R2))
So if R1 and R2 are both the same value the voltage out will be half the voltage in.
You can see a voltage divider circuit working in these photos of a small test I did.
First I measured the voltage of a 9 volt battery I would use to power this test. The voltage was 8.8v.
I then configured two 10k resistors as a voltage divider in a solderless breadboard. I connected the voltage divider In to the + terminal of the battery and I connected the voltage divider ground (the downward arrow on the drawing) to the – terminal of the battery. I measured the voltage at the out point (where the 2 resistors meet). It was 4.4 volts – exactly as you would expect (8.8 volts x (10k / (10k + 10k)) = 4.4 volts).
I then replaced R1 with a 20k resistor. You can see, the output was now 2.94 volts Considering we are using resistors with a 5% tolerance, this is well within the expected 2.9333 volt output (8.8 volts x (10k / (10k + 20k)0 = 2.9333 volts).
I will end here on this introduction to resistors. Next time we will look at a very simple design for an audio mixer using only resistors. In the meantime, let me know if you have any questions or would like more details.