Audio Engineering

Components 121

example given earlier, 0.9 kohm is less then 1 kohm (the smaller). For more than two
resistors connected in parallel (you can use as many resistors as you want), the rule is

111113/total resistance. resistor resistor2 resistor

Here’s another example. A 1-, 2-, and 3-ohm resistor are connected in parallel. The result is

1   11 12 13 1 05 ... 033 1833/total resistance ohms.

To check our math, since 1/total resistance is 1.833, the total resistance is
1/1.833  0.545 ohm, and this value is less than the smallest value (1 ohm). However,
adding two or more resistors in series (end to end) merely gives you the sum of all the
individual resistor values. A 1-kohm resistor and a 100-kohm resistor connected in series
thus yield 101 kohms. So by combining resistors in series and parallel you could make up
almost any value you want. Figure 4.2 shows the series, parallel combination. However,
it’s much easier to go out and buy a resistor with the value you want (and that one resistor
will take up less space).

Apart from the actual resistance value, there is a second parameter associated with
resistors, the tolerance rating, and it is designated by an extra color band. The most
commonly specifi ed tolerance is 5% (a gold band), followed by 10% tolerance (indicated
with a silver band). In case you encounter them, there are also resistors with no color
band that are equal to 20% tolerance, but it is inadvisable to use them because they tend
not to be accurate. The tolerance percentage refers to the spread of values on either side

10 ohm

10 ohm

10 ohm

10 ohm

5 ohm

20 ohm

Figure 4.2 : Resistors in series and resistors in parallel.