Series vs. Parallel Connections

Series connections are what most people are used to - simply chaining the output of one device into the input of another, and so on as shown below. This is how effects pedals are most commonly used. Chaining MIDI devices together via the MIDI Thru to the next module is another example of a series circuit.

If we send a signal into multiple devices simultaneously, and then add the various outputs together as in the lower half of Figure 1, we have a parallel network. Most multi-effects units are parallel at some level which allows you to mix different types of sounds together. For example, you may send a guitar's output into a delay, reverb, and chorus, and then mix those together with the dry input to get the total sound.

Basically, if there is only one path to get from the input to the output, then it is a series circuit. If there is more than one way to make it through (excluding any feedback), then the connection is parallel, at least at some point. (It's these multiple paths that reduce the impedance of speakers connected in parallel, while a series connection produces a longer path with twice the impedance.)

Diagram of a series and parallel network
Figure 1: (a) a series connection of four devices, and (b) a parallel network.