Converting a Stereo Signal to Mono

CHAPTER 9: Audio Hacks 217

Figure 9-4 Mixing stereo to mono

Converting a Stereo Signal to Mono

Stereo audio is made up of two slightly different audio signals that give the stereo effect when played through two separate speakers. Sometimes, you have a stereo output that you want to input to a single channel (mono) amplifier. You could use just one of the channels of the stereo signal (say, the left channel), but then you will lose whatever is on the right channel. So a better way of converting stereo to mono is to use a pair of resistors to mix the two channels into one (Figure 9-4).

Looking at the schematic of Figure 9-4, you could be forgiven for thinking all you need to do is connect the left and right channels to each other directly. This is not a good idea, because if the signals are very different, there is the potential for a damaging current to flow from one to the other.

As an example, we could use the mono 6.3mm jack we just soldered leads to, and combine it with a pair of resistors and a stereo 3.5mm jack plug so we could, for example, plug an MP3 player into a guitar practice amplifier.

Figure 9-5 shows the steps involved in this. To make it easier to photograph, the author’s lead is made very short. You will

Figure 9-5 Making a lead

(a) (b)

(c) (d)