Tech Tips

Balancing An iPod Output

By Pro AV Staff

It’s tempting to want to use an iPod as a program source for driving powered loudspeakers for room testing. But since the output level of 1Vrms (0 dBV) may be well below what’s usually required, here’s a little trick for creating an interconnect cable and getting the extra level you need.

1. Make a cable using this diagram.

2. Create a stereo file from mono, and invert polarity of channel 2.

The source file is most easily generated in a wave editor. It consists of two identical channels that are reversed in polarity. This provides an identical signal to pin 2 and pin 3 of the balanced output (one of which is inverted). Balanced inputs like this type of signal, because they accept the voltage difference between pins 2 and 3 as the signal, and reject the common mode voltage between pins 2 and 3. What we are doing is giving up stereo in favor of a balanced source and 2x the voltage (+6dB).

3. Connect iPod to powered loudspeaker.

The level control can be advanced until clip/limit is indicated.

A few caveats